Дисертації: "Magnesium alloys Surfaces"

1

Wong, Hoi-man, and 黃凱文. "Surface modification of biodegradable metallic material." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B41290689.

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Tang, Caixian. "Soldering in magnesium high pressure die casting and its preservation by surface engineering." Swinburne Research Bank, 2007. http://hdl.handle.net/1959.3/22747.

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Thesis (PhD) - Swinburne University of Technology, Industrial Research Institute Swinburne - 2007.
[A thesis submitted] for the degree of Doctor of Philosophy, Industrial Research Institute, Swinburne University of Technology - 2007. Typescript. Includes bibliographical references (p. 154-167).

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3

Baliga, Chaitanya B. "Bulk and surface studies of rapidly solidified Mg Al alloys." Thesis, University of Surrey, 1990. http://epubs.surrey.ac.uk/843174/.

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The effect of aluminium additions on the structure and morphology of the corrosion products formed on the surfaces of rapidly solidified Mg-Al alloy splats immersed at room temperature in a solution of 3%NaCl saturated with Mg(OH)2; has been studied under different analytical techniques. The adverse effect of contamination from copper particles during processing on the corrosion behaviour of the alloys is also highlighted. Aluminium additions were beneficial to the corrosive behaviour of the alloys with a marked improvement in their anti-corrosion resistance occurring in alloys containing more than 10 wt.% Al. This is attributed to the presence of aluminium ions in the prior oxide/hydroxide in the surface of the alloy. The thickness of the latter decreased with enrichment of aluminium ions and was 10-50nm for the Mg-16Al alloy splats as compared with 200nm for the Mg-3.5Al alloy splats. Hydromagnesite (3MgCO3. Mg(OH)2. 3H2O) formed as an overlayer on the surface of the alloy splats depending on the handling conditions. For the Mg-10Al and Mg-16Al alloy splats an admixture of a high temperature spinel (MgA12O4) in perlclase (MgO) and/or brucite (Mg(OH)2) was detected by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). It Is proposed that in the corrosive environment the Al3+ ions on the surface compete successfully with the chlorine ions for the anodic sites on the surface and anchor the growth of the layered brucite structure by the formation of a compound belonging to the pyroaurite-sjogrenite group of compounds. Hydroxyl ions, water, chlorine ions and carbonate ions are incorporated in The interlayers of the layered brucite structure. The formation of a double hydroxide with an acicular morphology and a structure close to that of hydrotalcite-manasseite (Mg6A12(OH)16. CO3. 4H2O) has been supported by scanning transmission electron microscopy (STEM), XPS, XRD, multi-element mapping by electron probe microanalysis (EPMA) and Rutherford backscattering spectrometry (RBS) analyses on the corroded splats. A growth mechanism is proposed on the basis of the structural chemistry, surface morphology and crystal structure of the corrosion products. The implications of this work for the design of Mg base alloys with improved corrosion properties are also discussed. The selected alloying elements are in excellent agreement with those selected from other studies on the development of corrosion resistant Mg alloys.

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Wong, Hoi-man. "Surface modification of biodegradable metallic material." Click to view the E-thesis via HKUTO, 2008. http://sunzi.lib.hku.hk/hkuto/record/B41290689.

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5

Xin, Yunchang. "Degradation mechanism and surface modification of biomedical magnesium alloy /." access full-text access abstract and table of contents, 2010. http://libweb.cityu.edu.hk/cgi-bin/ezdb/thesis.pl?phd-ap-b30011723f.pdf.

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Thesis (Ph.D.)--City University of Hong Kong, 2010.
"Submitted to Department of Physics and Materials Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy." Includes bibliographical references.

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6

KUPFER, JOHN CARLTON. "A SEARCH FOR CHANGES IN THE BAND STRUCTURE OF EXTREMELY STRAIN-FREE MAGNESIUM-CADMIUM CRYSTALS AS A FUNCTION OF ALLOYING, IN THE DILUTE LIMIT (DE HAAS-VAN ALPHEN, FERMI SURFACE)." Diss., The University of Arizona, 1985. http://hdl.handle.net/10150/187953.

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We report here a study of a specific doublet of de Haas-van Alphen frequencies in pure Mg and very dilute Mg(Cd) alloys with the magnetic field aligned with the c-axis. The work involved three stages. First, the use of extremely strain-free crystals, temperatures down to 40 millidegree Kelvin, large amplitude modulation, and the fast Fourier transform allowed the components of this doublet to be well resolved. This resolution allowed measurement of the changes in the cross-sectional area as a function of magnetic field orientation to verify the assignment of this doublet to the cap and monster arm junction at the top of the Brillouin zone. Third, with the magnetic field aligned with the c-axis, the splitting of this doublet offered a direct and sensitive indication of any symmetry breaking changes in the 0001 Fourier component of the ionic lattice potential in Mg upon the introduction of Cd. C. B. Friedberg's analysis of his electron interference lineshape data from the quantum interferometer in Mg had indicated that the energy of this band gap should increase by 40% with the introduction of 15 ppm Cd. Our data indicate that any change in the energy of the band gap must be at least three orders of magnitude smaller than that indicated by Friedberg. Our data are, in fact, consistent with there being no changes in the electronic band structure or the Fermi surface of Mg(Cd) alloys (with up to 0.02% (At) Cd), from that of pure Mg.

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Diplas, Spyridonas. "Bulk surface studies of vapour deposited Mg-V and Mg-Zr alloys." Thesis, University of Surrey, 1998. http://epubs.surrey.ac.uk/844498/.

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Mg-V and Mg-Zr alloys with nominal compositions 1, 6, 17.5, 27 wt% V and 2, 8.6 and 10.6 wt% Zr respectively were produced by PVD. All deposits exhibited compositional inhomogeneity, columnar microstructures and a strong basal texture. The solid solubilities of V and Zr in Mg were extended approximately to 17 wt% V and 10 wt% respectively. Grain refinement occurred with increasing solute content. The solid solution break up temperature decreased as the V and Zr content in the alloys increased. Pure V precipitated when the extended solid solubility of was exceeded. Both c and a lattice parameters, as well as the c/a ratio decreased with increasing V content in the Mg-V alloys. The slight increase of the a-lattice parameter and the decrease of the c one led to a decrease of the c/a ratio with increasing Zr additions in the Mg-Zr alloys. The air-formed oxide on the surfaces of the Mg-V alloys consisted predominantly of hydromagnesite at the outermost surface with Mg(OH)2 in excess of MgO underneath. No evidence of V oxide in the surface film was found. Magnesium oxide was also found between the grains of the deposits. The air-formed oxide on the surfaces of the Mg-Zr alloys consisted of ZrO2, MgO and possibly Zr sub-oxide. The presence of the oxides beween the columnar grains gave rise to graded metal/oxide interfaces. The outermost surfaces of the Mg-Zr alloys were similar to the Mg-V ones. Analysis of changes of the Auger parameters of the Mg-V and Mg-Zr alloys was also undertaken in order to investigate the electronic changes that take place upon alloying Mg with V and Zr. Charge transfer between 0.09 and 0.11 electrons/atom from Mg to V as well as changes in the V d charge were calculated by measuring the Mg and V Auger parameters and using the charge transfer model of Thomas and Weightman. Electron transfer between 0.02 and 0.03 electrons/atom from Mg to Zr was also found to occur upon alloying Mg with Zr. The electron transfer has been related to changes in crystal structure. The Mg-V and Mg-Zr alloys were examined after immersion in 3 wt% NaCl solution for 5 and 15 minutes, 9 hours and 7 days. The dramatic increase in the corrosion rate of the Mg-V alloys was attributed to the precipitation of pure V. The unsatisfactory corrosion performance of the Mg-V alloys was attributed to the absence of compositional uniformity through the thickness of the Mg-V deposits and the low thermodynamic stability of the corrosion products in the saline environment. Hydromagnesite at the outermost surface and Mg(OH)2, MgO and V2O4 in the bulk of the corrosion layer were the corrosion products. MgH2 and areas enriched in metallic V within the bulk of the corrosion products were also detected. The low corrosion rates of the Mg-Zr alloys, the lowest ever reported for Mg alloys, were attributed to the nature of the corrosion products and particularly the Zr contribution. The corrosion products were enriched in Zr, and were non-porous and in many cases well adherent. X-ray and electron diffraction suggested the existence of only Mg(OH)2 and MgO in the corrosion products, indirectly implying the participation of zirconium oxide/hydroxide in an amorphous/nanocrystalline state. Surface analysis indicated that a Zr oxide coexisted with Mg(OH)2 and MgO below a magnesium carbonate overlayer and also suggested the existence of Zr hydrous oxide (hydroxide). The repetition of the substrate pattern, as well as the fact that Zr hydroxide was replaced with ZrO2 and Zr sub-oxide as the metal-oxide interface was approached, implied a corrosion mechanism involving inwards diffusion of the anionic species.

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8

Bhat, Panemangalore Devadas. "Development of magnesium-based alloys for biomedical applications." Thesis, Lille, 2019. http://www.theses.fr/2019LIL1R002.

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Étant donné leur capacité à se dégrader à l'intérieur du corps, les implants biodégradables ont fait l'objet de nombreuses recherches médicales. Parmi tous les matériaux, c'est le magnésium, un élément indispensable du corps humain, qui conduit aux résultats les plus favorables car son module d'Young est similaire à celui de l'os. De ce fait, les méthodes adoptées afin d'améliorer le comportement du magnésium pur vis-à-vis de la corrosion sont les suivantes: a)Ajout d'éléments d'alliage comme le zinc, le calcium et l'erbium (Mg-2Zn-2Er, Mg-2Zn-0.6Ca-1Er, etc.) pour contrôler le comportement de dégradation b) Procédés secondaires tels que l'extrusion pour modifier sa microstructure c)Revêtements de surface à base de fluorure pour mieux protéger la surface. La première partie de cette thèse porte sur la caractérisation microstructurale d'alliages. La caractérisation microstructurale révèle la présence de MgZn2, de phases W (Mg3Zn3Er2) et i (Mg3Zn6Er) dans différents alliages. L'évaluation des propriétés mécaniques a révélé une augmentation des propriétés de traction et de compression des alliages ternaires et quaternaires par rapport aux alliages de Mg et de Mg-2Zn. Ces propriétés mécaniques améliorées sont attribuées à une réduction de la taille des grains, à la présence d'atomes de soluté et à des phases secondaires. Mg-2Zn-2Er et Mg-3Zn-0.5Er présentaient une résistance à la corrosion améliorée en raison de la microstructure à granulométrie fine et d'une répartition uniforme des phases secondaires. La viabilité cellulaire a été améliorée avec l'épaisseur du temps de revêtement et ces alliages pourraient servir de candidats potentiels pour d'autres tests in vivo
With the ability to bio-degrade and thereby reducing the stress-shielding effect, biodegradable implants are of great importance in medical research. Among all the materials, magnesium is the one which shows promising results being bio-degradable and with the properties comparable with its young's modulus to that of bones. In the present study, the approaches adopted to improve the mechanical and corrosion behaviors of pure magnesium using carefully chosen: (a) Alloying elements like zinc, calcium and erbium (Mg-2Zn-2Er, Mg-2Zn-0.6Ca-1Er, etc.) to control the degradation behavior (b) Secondary processes like extrusion to alter and improve the microstructure (c) Surface treatments like fluoride coatings to further protect the surface to resist the rapid dissolution. The first part of this thesis focuses on the microstructural characterization of as-DMDed and as-extruded alloys. The microstructural characterization (XRD and TEM) reveals the presence of MgZn2, W-phase (Mg3Zn3Er2) and i-phases (Mg3Zn6Er) in different alloys. The mechanical property assessment revealed an increment in the tensile and compressive properties of ternary and quaternary alloys as compared to pure Mg and Mg-2Zn binary alloy. These values are attributed to a reduction in grain size, presence of solute atoms and secondary phases. Mg-2Zn-2Er and Mg-3Zn-0.5Er showed enhanced corrosion resistance due to the fine grain sized microstructure and a uniform distribution of secondary phases. The cell viability values were enhanced with increased coating time and it was found that these alloys could serve as potential candidates for further in-vivo tests to establish their applicability

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Reis, Bárbara Araújo dos. "Avaliação das propriedades de superfície de ligas de titânio anodizadas com elementos bioativos /." Araraquara, 2018. http://hdl.handle.net/11449/153482.

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Orientador: Luis Geraldo Vaz
Resumo: O titânio comercialmente puro e suas ligas vêm sendo amplamente utilizados para confecção de implantes dentários e ortopédicos devido à adequada resistência mecânica, resistência à corrosão e biocompatibilidade. Entretanto, para aprimorar o tratamento com o uso de implantes, novas ligas e novos tratamentos de superfície vêm sendo pesquisados. A técnica de funcionalização de superfície, baseada em processos úmidos, é amplamente utilizada para desenvolver superfícies a base de óxido de titânio que induza e aumente a osseocondução. Assim, o objetivo deste estudo foi caracterizar a superfície de discos de Ti-6Al-4V e Ti-35Nb-7Zr-Ta após anodização para funcionalização com íons cálcio (Ca) e fósforo (P) ou fluoreto e dopagem com magnésio (Mg++) em diferentes condições experimentais, sendo a liga Ti-6Al-4V utilizada como controle. As ligas foram analisadas antes e após a realização dos tratamentos (anodização e dopagem), para avaliação das propriedades de superfície- composição química, energia livre de superfície (ELS), morfologia/ topografia e rugosidade média (Ra). Para interpretação dos resultados referentes a ELS e Ra foi aplicado teste estatístico por um operador cego, de acordo com o tipo de distribuição e nível de significância de 5%. As micrografias obtidas demonstraram que a anodização com Ca e P propiciou a formação de superfícies com poros interconectados e a anodização com ácido fluorídrico (HF) resultou em superfícies com formação de nanotubos. Todos íons adicionados ... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: Commercially pure titanium and its alloys have been widely used in the manufacture of dental and orthopedic implants due to adequate mechanical strength, corrosion resistance and biocompatibility. However, to improve the treatment with the use of implants to optimize osseointegration, new alloys and new surface treatments have been researched. The surface functionalization technique, based on wet processes, is widely used to develop titanium oxide based surfaces that induce and increase osseoconduction. The aim of this study was to characterize the surface of Ti-6Al-4V and Ti-35Nb-7Zr-Ta discs after anodization for functionalization with calcium ions (Ca) and phosphorus (P) or fluoride and doping with magnesium (Mg ++) in different experimental conditions. The Ti-6Al-4V alloy was used as a control. The alloys were analyzed before and after the treatments (anodization and doping), to evaluate the surface properties - chemical composition, surface free energy (ELS), morphology / topography and medium roughness (Ra). For the interpretation of the ELS and Ra results, a statistical test was applied according to the type of distribution and level of significance of 5%. The obtained micrographs showed that the anodization with Ca and P allowed the formation of surfaces with interconnected pores and the anodization with hydrofluoric acid resulted in surfaces with formation of nanotubes. All ions added to the electrolytes were incorporated into the samples, detected by ELS. The roughn... (Complete abstract click electronic access below)
Mestre

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Kecik, Deniz. "Ab Initio Design Of Novel Magnesium Alloys For Hydrogen Storage." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609722/index.pdf.

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A candidate hydrogen storing material should have high storage capacity and fast dehydrogenation kinetics. On this basis, magnesium hydride (MgH2) is an outstanding compound with 7.66 wt % storage capacity, despite its slow dehydriding kinetics and high desorption temperature. Therefore in this study, bulk and surface alloys of Mg with improved hydrogen desorption characteristics were investigated. In this respect, formation energies of alloyed bulk MgH2 as well as the adsorption energies on alloyed magnesium (Mg) and MgH2 surface structures were calculated by total energy pseudopotential methods. Furthermore, the effect of substitutionally placed dopants on the dissociation of hydrogen molecule (H2) at the surface of Mg was studied via Molecular Dynamics (MD). The results displayed that 31 out of 32 selected dopants contributed to the decrease in formation energy of MgH2 within a range of ~ 37 kJ/mol-H2 where only Sr did not exhibit any such effect. The most favorable elements in this respect came out to be
P, K, Tl, Si, Sn, Ag, Pb, Au, Na, v Mo, Ge and In. Afterwards, a systematical study within adsorption characteristics of hydrogen on alloyed Mg surfaces (via dynamic calculations) as well as calculations regarding adsorption energies of the impurity elements were performed. Accordingly, Mo and Ni yielded lower adsorption energies
-9.2626 and -5.2995 eV for substitutionally alloyed surfaces, respectively. MD simulations presented that Co is found to have a splitting effect on H2 in 50 fs, where the first hydrogen atom is immediately adsorbed on Mg substrate. Finally, charge density distributions were realized to verify the distinguished effects of most 3d and 4d transition metals in terms of their catalyzer effects.

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Wu, Tso-chang. "Laser Surface Modification of AZ31B Mg Alloy Bio-Implant Material." Thesis, University of North Texas, 2018. https://digital.library.unt.edu/ark:/67531/metadc1248459/.

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Magnesium and its alloys are considered as the potential biomaterials due to their biocompatibility and biodegradable characteristics but suffer from poor corrosion performance. Various surface modification techniques are employed to improve their corrosion resistance. In present case, laser surface melting was carried out on AZ31B Mg alloy with various laser energy densities using a continuous wave ytterbium laser. Effect of laser treatment on phase and microstructure evolution was evaluated by X ray diffraction and scanning electron microscopy. Multi-physics thermal model predicted time temperature evolution along the depth of the laser treatment zone. Additionally, electrochemical method and bio-immersion test were employed to evaluate the corrosion behavior in simulated body fluid medium. Microstructure revealed grain refinement and even distribution of Mg17Al12 phase along the grain boundary for laser treated samples leading to substantial enhancement in the corrosion resistance of the laser treated samples compared to the untreated alloy. The laser processed samples also possessed a superior wettability in SBF solution than the untreated sample. This was further reflected in enhanced bio-integration behavior of laser processed samples. By changing the parameters of laser processing such as power, scanning speed, and fill spacing, a controllable corrosion resistance and bioactivity/biocompatibility of the implant material was achieved.

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Córdoba, Román Laura Catalina. "Magnesium-based biodegradable materials : from surface functionalization to cellular evaluation." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066237/document.

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Les alliages de Magnésium (Mg) sont une nouvelle génération de matériaux biodégradables ayant une bonne ostéointégration et un module d'élasticité similaire à celle de l'os humain. Ces propriétés rendent ces matériaux attrayant pour produire des implants temporaires pour la réparation osseuse. Toutefois, les alliages Mg se dégradent rapidement in vivo, rendant nécessaire de contrôler leur vitesse de corrosion pour accompagner la régénération tissulaire. Parmi les approches proposées pour réduire la corrosion et la biocompatibilité des alliages Mg, les plus utilisées sont les couches de conversion et les revêtements de surface. Dans ce travail une approche synergique qui combine une réduction du taux de corrosion avec l'amélioration de la biocompatibilité des alliages Mg est proposée. De nouveaux revêtements bicouches ont été déposés sur la surface d'alliages AZ31 et ZE41 : (i) un revêtement de silane-TiO2 déposé par dip-coating et (ii) des couches supérieures de collagène de type I et/ou de chitosane. Le revêtement inférieur a été efficace pour réduire la corrosion des alliages dans un fluide corporel simulé et en milieu de culture. La culture cellulaire in vitro de fibroblastes et ostéoblastes, a révélé que le dépôt additionnel de biopolymères a amélioré la réponse biologique du revêtement de silane-TiO2. Ces résultats montrent qu'il existe un effet combiné des revêtements bicouches et de la composition des alliages sur la réponse à la corrosion et sur le comportement cellulaire. Ce travail apporte donc une nouvelle contribution à la compréhension de l'évolution de la corrosion des alliages Mg dans des environnements biologiques
Magnesium (Mg) alloys are a new generation of biodegradable materials with good osseointegration and elastic modulus similar to that of human bone. These properties make them attractive materials to produce biodegradable implants for bone repairing applications that require temporary support. However, Mg alloys degrade rapidly in the in vivo environment making necessary to control their corrosion rate to accompany the tissue healing processes. Several approaches have been proposed for reducing corrosion rate and improving biocompatibility of Mg alloys. The most used ones are conversion films and surface coatings. This project proposes a synergistic approach that combines both decreased corrosion rate and improved biocompatibility of Mg alloys: we developed novel bi-layered coatings to functionalize the surface of AZ31 and ZE41 Mg alloys for bone repair applications. First, a bottom silane-TiO2 coating was formulated and deposited on both alloys by the dip-coating technique. The silane-based coating was effective in slowing down the corrosion rate of the substrates in simulated body fluid (SBF) and in Dulbecco’s Modified Eagle’s Medium (DMEM). Secondly, top layers of type I collagen and/or chitosan were developed. Cell in vitro tests, with fibroblasts and osteoblasts, revealed that the biopolymers enhanced the biological response of the silane-TiO2 coating. Furthermore, the findings showed that there is a combined effect of the bi-layered coatings and the nature of the alloys on their final corrosion response and on the fate of the cells. In the same way, this work contributes to elucidating corrosion processes of Mg alloys in organic solutions in the long-term

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Amruthaluri, Sushma. "An Investigation on Biocompatibility of Bio-Absorbable Polymer Coated Magnesium Alloys." FIU Digital Commons, 2014. http://digitalcommons.fiu.edu/etd/1742.

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Advances in biomaterials have enabled medical practitioners to replace diseased body parts or to assist in the healing process. In situations where a permanent biomaterial implant is used for a temporary application, additional surgeries are required to remove these implants once the healing process is complete, which increases medical costs and patient morbidity. Bio-absorbable materials dissolve and are metabolized by the body after the healing process is complete thereby negating additional surgeries for removal of implants. Magnesium alloys as novel bio-absorbable biomaterials, have attracted great attention recently because of their good mechanical properties, biocompatibility and corrosion rate in physiological environments. However, usage of Mg as biodegradable implant has been limited by its poor corrosion resistance in the physiological solutions. An optimal biodegradable implant must initially have slow degradation to ensure total mechanical integrity then degrade over time as the tissue heals. The current research focuses on surface modification of Mg alloy (MZC) by surface treatment and polymer coating in an effort to enhance the corrosion rate and biocompatibility. It is envisaged that the results obtained from this investigation would provide the academic community with insights for the utilization of bio-absorbable implants particularly for patients suffering from atherosclerosis. The alloying elements used in this study are zinc and calcium both of which are essential minerals in the human metabolic and healing processes. A hydrophobic biodegradable co-polymer, polyglycolic-co-caprolactone (PGCL), was used to coat the surface treated MZC to retard the initial degradation rate. Two surface treatments were selected: (a) acid etching and (b) anodization to produce different surface morphologies, roughness, surface energy, chemistry and hydrophobicity that are pivotal for PGCL adhesion onto the MZC. Additionally, analyses of biodegradation, biocompatibility, and mechanical integrity were performed in order to investigate the optimum surface modification process, suitable for biomaterial implants. The study concluded that anodization created better adhesion between the MZC and PGCL coating. Furthermore, PGCL coated anodized MZC exhibited lower corrosion rate, good mechanical integrity, and better biocompatibility as compared with acid etched.

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Al, Rais Masood. "Effects of hydrogen in an aluminium-magnesium-silicon alloy during the production of extrusion ingots." Thesis, Brunel University, 1995. http://bura.brunel.ac.uk/handle/2438/5020.

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Hydrogen causes defects, for which aluminiurn alloy products are rejected. The behaviour of hydrogen in aluminium-magnesium-silicon alloy extrusion ingots, has been studied throughout the course of manufacture from freshly reduced aluminium. It is shown that hydrogen in the liquid metal is produced by temperature-dependent reaction between the metal and water vapour in the atmosphere. As the metal is received from the reduction cells, its temperature is -850 'C and its hydrogen content, >0.4 cm3/100 g, is too high for casting sound ingots. The metal is transferred first to a so-called melting furnace, where it is alloyed and stirred, thence to a holding furnace, where the composition is adjusted, the metal is degassed by gas sparging and allowed to settle before casting. The metal cools throughout these operations and as the temperature falls, the calculated value for the hydrogen content in equilibrium with the atmosphere falls in response to the reduced hydrogen solubility. The actual hydrogen content of the metal exhibited marked hysteresis in following the equilibrium value. Significant reduction of the hydrogen content occurred only when the metal was agitated. The hydrogen content never fell below the equilibrium value even during the nominal degassing operation, leading to the conclusion that gas sparging in a furnace does not positively remove hydrogen but only assists the equilibration. The hot-top DC casting process yielded a 8 m x 0.18 m diameter ingot with a virtually uniform hydrogen content. When this ingot was homogenised by heating it to 590˚C in a 7h cycle, a significant proportion of the hydrogen content was lost from the surface zone. By matching the loss to a theoretical model assuming diffusion control, it was shown that the loss of hydrogen is attenuated by trapping in micropores. The effects of simulated industrial atmospheres on the loss or absorption of hydrogen by the solid alloy were investigated in an extended series of laboratory heat-treatments. The interaction of the metal with these atmospheres was found to be determined by the nature of the oxide films formed and therefore the films were investigated by XPS and SIMS surface analysis techniques. In clean atmospheres the absorption or loss of hydrogen was determined by the balance between inward migration of protons and outward diffusion of hydrogen atoms through the oxide. Pollution of the air by chlorine or especially sulphur stimulated hydrogen absorption to a degree which seriously damaged the metal by pore growth. These effects are explained by modified compositions and structures in the surface oxide.

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15

Rampton, Travis Michael. "Deformation Twin Nucleation and Growth Characterization in Magnesium Alloys Using Novel EBSD Pattern Analysis and Machine Learning Tools." BYU ScholarsArchive, 2015. https://scholarsarchive.byu.edu/etd/4451.

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Deformation twinning in Magnesium alloys both facilitates slip and forms sites for failure. Currently, basic studies of twinning in Mg are facilitated by electron backscatter diffraction (EBSD) which is able to extract a myriad of information relating to crystalline microstructures. Although much information is available via EBSD, various problems relating to deformation twinning have not been solved. This dissertation provides new insights into deformation twinning in Mg alloys, with particular focus on AZ31. These insights were gained through the development of new EBSD and related machine learning tools that extract more information beyond what is currently accessed.The first tool relating to characterization of deformed and twinned materials focuses on surface topography crack detection. The intensity map across EBSD images contains vital information that can be used to detect evolution of surface roughness and crack formation, which typically occurs at twin boundaries. The method of topography recovery resulted in reconstruction errors as low as 2% over a 500 Î¼m length. The method was then applied to a 3 Î¼m x 3 Î¼m area of twinned Tantalum which experienced topographic alterations. The topography of Ta correlated with other measured changes in the microstructure. Additionally, EBSD images were used to identify the presence of cracks in Nickel microstructures. Several cracks were identified on the Ni specimen, demonstrating that cracks as thin as 34 nm could be measured.A further EBSD based tool developed for this study was used to identify thin compression twins in Mg; these are often missed in a traditional EBSD scan due to their size relative to the electron probe. This tool takes advantage of crystallographic relationships that exist between parent and twinned grains; common planes that exist in both grains lead to bands of consistent intensity as a scan crosses a twin. Hence, twin boundaries in a microstructure can be recognized, even when they are associated with thin twins. Proof of concept was performed on known twins in Inconel 600, Tantalum, and Magnesium AZ31. This method was then used to search for undetected twins in a Mg AZ31 structure, revealing nearly double the number of twins compared with those initially measured by standard procedures.To uncover the driving forces behind deformation twinning in Mg, a machine learning framework was developed to leverage all of the data available from EBSD and use that to create a physics based models of twin nucleation and growth. The resultant models for nucleation and growth were measured to be up to 86.5% and 96.1% accurate respectively. Each model revealed a unique combination of crystallographic attributes that affected twinning in the AZ31.

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16

Pu, Zhengwen. "CRYOGENIC MACHINING AND BURNISHING OF AZ31B MAGNESIUM ALLOY FOR ENHANCED SURFACE INTEGRITY AND FUNCTIONAL PERFORMANCE." UKnowledge, 2012. http://uknowledge.uky.edu/me_etds/5.

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Surface integrity of manufactured components has a critical impact on their functional performance. Magnesium alloys are lightweight materials used in the transportation industry and are also emerging as a potential material for biodegradable medical implants. However, the unsatisfactory corrosion performance of Mg alloys limits their application to a great extent. Surface integrity factors, such as grain size, crystallographic orientation and residual stress, have been proved to remarkably influence the functional performance of magnesium alloys, including corrosion resistance, wear resistance and fatigue life. In this dissertation, the influence of machining conditions, including dry and cryogenic cooling (liquid nitrogen was sprayed to the machined surface during machining), cutting edge radius, cutting speed and feed rate, on the surface integrity of AZ31B Mg alloy was investigated. Cryogenic machining led to the formation of a "featureless layer" on the machined surface where significant grain refinement from 12 μm to 31 nm occurred due to dynamic recrystallization (DRX), as well as increased intensity of basal plane on the surface and more compressive residual stresses. Dry and cryogenic burnishing experiments of the same material were conducted using a fixed roller setup. The thickness of the processed-influenced layer, where remarkable microstructural changes occurred, was dramatically increased from the maximum value of 20 μm during machining to 3.4 mm during burnishing. The burnishing process also produced a stronger basal texture on the surface than the machining process. Preliminary corrosion tests were conducted to evaluate the corrosion performance of selected machined and burnished AZ31B Mg samples in 5% NaCl solution and simulated body fluid (SBF). Cryogenic cooling and large edge radius tools were found to significantly improve the corrosion performance of machined samples in both solutions. The largest improvement in the material's corrosion performance was achieved by burnishing. A finite element study was conducted for machining of AZ31B Mg alloy and calibrated using the experimental data. A user subroutine was developed and incorporated to predict the grain size changes induced by machining. Good agreements between the predicted and measured grain size as well as thickness of featureless layers were achieved. Numerical studies were extended to include the influence of rake angle, feed rate and cutting speed on the featureless layer formation.

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17

Alias, Juliawati. "The influence of Hot Forming-Quenching (HFQ) on the microstructure and corrosion performance of AZ31 magnesium alloys." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/the-influence-of-hot-formingquenching-hfq-on-the-microstructure-and-corrosion-performance-of-az31-magnesium-alloys(01193b94-bcbd-452a-a4cb-2d2e93cd1afd).html.

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The hot forming-quenching (HFQ) process has introduced grains and subgrain growth, accompanied with modification of the intermetallic particle distribution in AZ31 magnesium alloys. Each region of the HFQ component represents significant grain structure variation and surface conditions that contributed to the corrosion susceptibility. The homogeneous grain structure significantly ruled the corrosion propagation features by filiform-like corrosion. Immersion of AZ31 alloys in 3.5 wt.% NaCl indicated higher corrosion rate of HFQ TRC (corrosion rate: 10.129 mm/year), a factor of 10 times, higher than the rolled alloy (corrosion rate: 0.853 mm/year) and a factor of 2 times, higher than the corrosion rate of MCTRC alloy (corrosion rate: 5.956 mm/year). Much lower corrosion rate was indicated in the as-cast TRC and MCTRC alloys, compared to the alloys after HFQ process that revealed the contribution of network or continuous distribution of β-Mg17Al12 phase particles to reduce the corrosion driven in chloride solution. In contrast, discontinuous distribution of cathodic β-Mg17Al12 phase particles increases the corrosion rate of HFQ TRC alloy by promoting the cathodic reaction and intense filament propagation resembling the coarse interdendritic and grain boundaries attack. The presence of high population densities of cathodic Al8Mn5 particles in HFQ rolled AZ31B-H24 alloy significantly reduced the corrosion driven for intense corrosion attack on the rolled alloy. The surface preparation by mechanical grinding process induced MgO and Zn-enrichment layer, accompanied with near surface deformed layer that consisted of nanograins in the range size of 40 to 250 nm. The grinding process refined the surface by removing the cutting damage and marks that formed during the thermomechanical process and led to stable potential of the HFQ AZ31 alloys, in the range of -1.59 to -1.57 V, during open circuit potential (OCP) measurement. The surface regularity with grinding path causing the filament to propagate following the grinding direction. The as-received surface contained many cutting damages and deep scratch marks from the rolling and casting processes that could introduce many corrosion initiation sites. The absence of the grinding direction on the as-received surface could control intense corrosion susceptibility, due to the non-linear filament propagation. The surface irregularity on chromic acid cleaned surface of HFQ rolled AZ31B-H24 alloy also contributed to low corrosion potential of the rolled alloy during OCP and potentiodynamic polarization measurement.

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18

Jay, Olivier. "Magnesium for biomedical applications as degradable implants : thermomechanical processing and surface functionalization of a Mg-Ca alloy." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAI104/document.

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Depuis la dernière décennie, les implants dégradables pour fixation de fracture connaissent un intérêt grandissant. Parmi tous les matériaux, le magnésium apparait comme un candidat prometteur dû à une combinaison unique de propriétés. Le magnésium est très bien toléré par le corps, il a une tendance naturelle à la dégradation et son faible module élastique peut aider à réduire le stress-shielding durant la reconstitution de l'os. Cependant, une combinaison optimale entre les propriétés mécaniques et la vitesse de dégradation doit être obtenue. Le calcium étant biocompatible et procurant différents effets bénéfiques, l'alliage sélectionné pour ce projet est le Mg-2wt.%Ca. Afin d'optimiser cet alliage, nous proposons une stratégie volume/surface : modifier la microstructure interne par des traitements thermomécaniques et fonctionnaliser la surface à l'aide d'une technique additive.Du laminage et de l'extrusion à chaud ainsi que de l'extrusion coudée à aires égales (ECAE), ont été utilisé afin de modifier la microstructure. La déformation plastique sévère induite par l'ECAE produit la plus fine microstructure (taille de grain et particules de seconde phase). Alors que différentes caractéristiques microstructurales (dislocations, macles, taille de grain) peuvent justifier l'augmentation de la résistance mécanique, l'évolution de la résistance à la corrosion semble principalement affectée par la microstructure de la seconde phase et la taille de grain. Cette influence résulte de la combinaison d'un effet micro-galvanique et de la dispersion des particules de Mg2Ca et possiblement d'une couche d'oxide plus stable. L'ECAP apparait comme le traitement le plus efficace pour augmenter les propriétés mécaniques et le comportement à la corrosion.La fonctionnalisation de surface a été réalisée par un dépôt à motif réguliers à l'aide d'une technique de microdéposition de nanoparticules d'argent afin d'apporter un effet antibactérien à la surface. La déposition est suivie d'un procédé de frittage par laser. Une série de déposition a été conduite afin d'optimiser les conditions du dépôt de nanoparticules d'argent. La topographie de la couche déposée, la qualité du frittage ainsi que l'impact thermique du traitement laser sur la microstructure du substrat a été caractérisée par profilommétrie, SEM et TEM. Une modélisation par éléments finis a été réalisé afin de décrire l'impact thermique du traitement laser. Cette simulation pourra être utilisée à des fins d'optimisation du procédé de dépôt.Combiner une approche sur la microstructure interne et la surface du matériau a permis d'obtenir un alliage de magnésium fonctionnalisé ayant des propriétés améliorées qui peut être considéré dans de futurs tests biomédicaux
Since the last decade, degradable implants for bone fixation have attracted special attention. Among different materials, magnesium appears as a promising candidate due to its unique combination of properties. Magnesium is very well tolerated by the body, it has a natural tendency for degradation and its low elastic modulus helps to reduce stress-shielding effect during bone healing. However, an optimal compromise between mechanical resistance and degradability kinetics has to be achieved. Since calcium is biocompatible and has several beneficial effects on magnesium, the alloy selected for this project is: Mg-2wt.%Ca alloy. To optimize this alloy for implant application, we propose a bulk/surface approach: i.e. tailoring the bulk microstructure by thermomechanical treatments and surface functionalization by additive manufacturing.Hot rolling and extrusion, and equal channel angular pressing (ECAP) have been used to tailor the microstructure. Severe plastic deformation induced by the ECAP process produces the finest grain and second particle phase microstructure. While different microstructural features (dislocations, twins, grain size) can account for the increase of the mechanical strength, the evolution of the corrosion resistance appears as primarily affected by grain size and second phase microstructure. This influence results from the combination of a micro galvanic effect, the dispersion of the second phase Mg2Ca and possibly a more stable oxide layer. Finally ECAP appears as the most efficient processing to improve both mechanical and corrosion behavior.Surface functionalization is achieved by designing a surface pattern using microdeposition with silver nanoparticles to add an antibacterial effect. The deposition is followed by a laser sintering process. A series of deposition were performed to optimize the deposition conditions for silver nanoparticles. The layer topography, the sintering, and the thermal impact of the laser treatment on the substrate microstructure have been characterized by profilommetry, SEM, TEM. A finite element simulation has been realized to describe the thermal effect of the laser treatment. This simulation can be further used for optimizing the patterning deposition process.Combining the bulk and surface approach have permitted to obtain a functionalized magnesium alloy with enhanced properties that can be considered for further biomedical tests

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19

Gawlik, Marcjanna Maria [Verfasser]. "The influence of surface defects on the degradation behaviour of magnesium alloys for medical applications / Marcjanna Maria Gawlik." Kiel : Universitätsbibliothek Kiel, 2019. http://d-nb.info/119008662X/34.

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20

Bergstedt, Edwin. "A Study in How Welding Parameters Affect the Porosity in Laser Welded High Pressure Die Cast AM50 Magnesium Alloy." Thesis, KTH, Materialvetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-291119.

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There are a need for reducing the weight of vehicles, one solution is to implement cast lightweight materials such as the high pressure die cast AM50 magnesium alloy. The weldability of this cast alloy is poor and to implement the use of the alloy commercially a welding process is needed that limits the porosity of the weld. The aim of this thesis is to study the effect of the welding parameters on the porosity in the weld, for three laser welding methods. The welding methods examined are single spot and twin spot laser using either a beam splitter or separate optics. The microstructure of the base material are also examined in order to evaluate relations between the components of the microstructure and the porosity in the weld. It was concluded that the hydrogen in the base material was the main reason for the observed porosity in the weld and that the material contains high pressure gas. The welding parameters did not influence the porosity for the single beam laser process, however, for the dual beam processes the welding parameters could affect the amount of pores. It was found that a double weld reduced the amount of pores and that the size and distribution of the secondary phase particles would benefit from the treatment. The cleaning of the samples prior to welding increased the porosity, however, non-cleaned samples contained more oxide inclusions. The results indicate that a twin beam process could reduce the porosity in the weld of the AM50 alloy.
Det finns ett behov av att reducera vikten på fordon, en lösning är att implementera gjutna lätta material såsom formsprutad AM50-magnesiumlegering. Svetsbarheten hos denna gjutna legering är dålig och för att kommersiellt kunna använda legeringen krävs en svetsprocess som begränsar svetsens porositet. Syftet med detta examensarbete är att studera svetsparametrarnas effekt på svetsens porositet för tre lasersvetsmetoder. De svetsmetoder som undersöks är enkelpunkts och dubbelpunktslaser där antingen en stråldelare eller separat optik använts. Basmaterialets mikrostruktur undersöks också för att utvärdera sambandet mellan mikrostrukturen och porositeten i svetsen. Man drog slutsatsen att väte i basmaterialet var huvudorsaken till den observerade porositeten i svetsen och att materialet innehåller gas under högt tryck. De undersökta svetsparametrarna påverkade inte porositeten för processen med en laserstråle, men för dubbelstråleprocesserna kan svetsparametrarna påverka mängden porer. Det visade sig att en svets utförd med två strålar minskade mängden porer och att storleken och fördelningen av sekundärfaspartiklarna gynnas av behandlingen. Prover som rengjordes före svetsning hade ökad porositet, men icke-rengjorda prover innehöll mer oxidinneslutningar. Resultaten indikerar att en dubbelstråleprocess kan minska porositeten då AM50-legeringen lasersvetsas.

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21

Ho, Yee Hsien. "In Vitro Behavior of AZ31B Mg-Hydroxyapatite Metallic Matrix Composite Surface Fabricated via Friction Stir Processing." Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc862762/.

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Magnesium and its alloys have been considered for load-bearing implant materials due to their similar mechanical properties to the natural bone, excellent biocompatibility, good bioactivity, and biodegradation. Nevertheless, the uncontrollable corrosion rate in biological environment restrains their application. Hydroxyapatite (HA, Ca10(PO4)6(OH)2) is a widely used bio-ceramic which has bone-like mineral structure for bone fixation. Poor fracture toughness of HA makes it not suitable for load-bearing application as a bulk. Thus, HA is introduced into metallic surface in various forms for improving biocompatibility. Recently friction stir processing (FSP) has emerged as a surface modification tool for surface/substrate grain refinement and homogenization of microstructure in biomaterial. In the pressent efforts, Mg-nHA composite surface on with 5-20 wt% HA on Mg substrate were fabricated by FSP for biodegradation and bioactivity study. The results of electrochemical measurement indicated that lower amount (~5% wt%) of Ca in Mg matrix can enhance surface localized corrosion resistance. The effects of microstructure,the presence of HA particle and Mg-Ca intermetallic phase precipitates on in vitro behavior of Mg alloy were investigated by TEM, SEM, EDX,XRD ,and XPS. The detailed observations will be discussed during presentation.

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22

Wahman, Clarence. "Corrosion of additively manufactured magnesium alloy WE43 : An investigation in microstructure and corrosion properties of as built samples manufactured with Powder Bed Fusion-Laser Beam." Thesis, Uppsala universitet, Tillämpad materialvetenskap, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-448525.

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The work presented in this thesis was conducted at Uppsala University and at Swerim AB. The study aims to broaden the knowledge about the corrosion of additively manufactured bioresorbable alloy WE43 in humanlike conditions for future applications. Biodegradable metal implants are implants meant to stay in the body and support the wounded bone for a certain time period, and then degrade as new, healthy bone forms in its place. Magnesium alloys have properties that are desired for these kind of implants as it is biodegradable, non-toxic and matches the mechanical properties of bone. Furthermore, magnesium alloy WE43, containing yttrium, neodymium and zirconium, already exist on the market as a powder extruded screw that treats Hallux valgus, thus proves the alloys compatibility as a bioresorbable implant. However, in order to optimize implants for specific situations, additive manufacturing can be a powerful tool. By utilizing the advantages of additive manufacturing, patient specific, complex designs implant can be manufactured rapidly in order to be used in a patient. On the other hand, additive manufacturing is a complex method with many aspects affecting the outcome. Therefore it is important to study the influence that different parameters have on the material's properties, especially the corrosion properties. This thesis aims to study different power settings on the laser in the manufacturing process and what effect it has on the microstructure as well as the corrosion properties of as built WE43 samples. Samples of three different parameters settings were manufactured with a Powder Bed Fusion-Laser Beam 3Dprinter. These samples were analyzed regarding surface roughness and microstructure with Light Optical Microscope, Scanning Electron Microscope, Energy Dispersive Spectroscopy, Electron Backscatter Diffraction and Alicona InfiniteFocus. Furthermore, the corrosion properties of the samples were investigated by collecting and measuring hydrogen gas that is released during the corrosion process. In addition, the electrolyte were examined regarding the change in ion concentration and electrochemical tests were performed. It was found that the samples did not differ substantially in microstructure as all three parameter settings exhibited a matrix of magnesium and precipitates of alloying elements. However, the sample manufactured at the lowest energy density had pores incorporated in the bulk. Despite the porous bulk this sample performed best in the immersion tests and exhibited the lowest corrosion rate over 28 days. The reason for this behavior is not determined, however possible causes are discussed and further studies are recommended.

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23

Albo, Zieme Louise, and Pontus Bergstedt. "A pre-study for functional coatings evaluated on light metals to be applied on a new HPDC Mg-alloy : Investigating tribological and thermophysical properties, as-cast and coated." Thesis, Jönköping University, JTH, Industriell produktutveckling, produktion och design, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-53096.

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Magnesium with two-thirds of the density compared to aluminium and one-quarter of steel, intrigues product developers and material scientists due to the light metal’s excellent combination of strength to weight ratio as well as their capability of being produced as a High Pressure Die Cast component compared to other ferrous or light metal alloys. However, a magnesium alloy inherits some concerning drawbacks, limiting the exploitation in structural applications and mechanical design such as automotive, heavy machinery and aerospace components. The need for a magnesium alloy that could withstand a sufficient amount of wear, temperature and corrosive environment, leads towards the investigation and evaluation of a suitable, functional coating as a solution to exploit the evident advantages a magnesium alloy exhibits. A substantial amount of research is required in order to reduce an existing knowledge gap that is the ongoing development in the search for a sufficient functional coating and adherence capability to the highly reactive substrate that is a magnesium alloy. This industrial master thesis is an early stage investigation to evaluate how the currently used aluminium substrate with an electrodeposited coating relate and compares to a heat-treated electroless deposited coating through tribological and thermophysical induced stresses. These properties are tested with proven industrial standard methods resulted in a comprehensive conclusion and discussion regarding the feasibility of applying the coating onto a commercial magnesium alloy closely related to the Mg-alloy developed by Husqvarna and thereby contributing to technological advances to the highly relevant topic within product development in materials engineering.

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24

Ghaffari, Tari Dariush. "Room and Elevated Temperature Constitutive Response of Polycrystalline Materials Exhibiting Tension-Compression Asymmetry under Monotonic Loading." Thesis, 2014. http://hdl.handle.net/10012/8432.

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A continuum plasticity yield function is developed that captures tension/compression asymmetry and its evolution as exhibited by HCP materials such as magnesium alloy sheet. The model, referred to herein as “CPB06ex3ev”, is based upon the CPB06 [1] yield surface which is extended in this research to consider evolution of asymmetry and anisotropy under monotonic loading. The model is further modified to incorporate thermal softening and strain rate effects. Mechanical characterization experiments are performed to acquire uniaxial tensile and compressive stress-strain data along a range of in-plane and through-thickness loading orientations. Experiments are performed for a range of strain rates (0.001-1s-1) and temperatures (23-250°C). A strong, evolving asymmetry is observed at room temperature when comparing tensile and compressive flow stresses and r-values, while asymmetry and anisotropy are reduced dramatically as temperature is increased. AZ31B exhibits moderate strain rate sensitivity at room temperature, however, the rate sensitivity increases with temperature. The CPB06ex3ev model is applied to simulate AZ31B magnesium alloy sheet. An error minimization scheme is used to fit the yield function and evolution coefficients over the entire data set. The calibrated model is shown to capture the evolving asymmetric/anisotropic response of both flow stresses and r-values in tension and compression, while also fitting the flow stress at the biaxial tension and pure shear locations on the yield locus. The model, which uses three stress transformations, is implemented within a user defined material model (UMAT) and linked to the commercial finite element software LS-DYNA. In order to assess the finite element implementation of the CPB06ex3ev model, a series of validation experiments were performed and corresponding finite element models were developed: (i) room temperature three-point bending; (ii) elevated temperature (250°C) limiting dome height experiments; and, (iii) warm cup drawing experiments. The three point bend simulations demonstrated the importance of capturing material asymmetry and the associated shift in neutral axis. Comparison between the warm forming experiments and models revealed qualitative agreement between the predicted punch load-displacement and strain distributions. The CPB06ex3ev formulation was able to capture the anisotropy trends in terms of the differences in strains measured along the sheet rolling versus transverse directions. Beyond the constitutive characterization and modeling effort, the cup draw formability experiments have provided interesting insight into the effect of temperature and temperature distribution within the AZ31B sheet. The current work has served to show the existence of a process window in which the blank center temperature must lie below the die temperature but above the temperature for activation of non-basal slip systems (to avoid low temperature fracture). Two modes of failure have been identified at the process window boundaries in which the cup either fractures due to low temperature (brittle) failure or a high temperature (necking) failure.

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25

Chen, Yuan-Ming, and 陳遠銘. "Electrochemical Surface Treatment of Magnesium Alloys." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/91594123739413034244.

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碩士
明志科技大學
化工與材料工程研究所
97
Effects of electrolyte composition, pH, potential and reaction time applied during anodizing, corrosion of anodic films formed on AZ91D magnesium alloy were investigated in this study. Corrosion potential of Mg alloy was examined by current-potential relationship. Microstructures of Mg alloy and anodic film were examined by optical microscopy; the gloss of anodic film was determined by gloss meter; the surface roughness of anodic film was determined by surface roughness tester and atomic force microscope (AFM). Protection of anodized film was evaluated by electrochemical impedance spectroscopy (EIS). The results showed that the concentration of hydrogen ion of electrolyte and temperature increased with increasing corrosion current. Addition alcohol was decreasing corrosion current. Change in the ratio of phosphoric-alcohol and application of ultrasonic vibration increasing corrosion current. In alkaline solutions containing 1 M NaOH, the gloss of Mg alloy could increase. In alkaline system, effects of grinding by sandpaper, anodizing potential and reaction duration on surface roughness of Mg alloy were investigated. The results showed the surface roughness of the specimens treated by grinding and 2 V anodizing was best. The surface roughness of specimens without grinding also improved with increased reaction duration. The corrosion resistance of the anodized AZ91D Mg alloy in 3.5 wt.% NaCl solution was evaluated by electrochemical impedance spectroscopy (EIS). Anodized AZ91D Mg alloy at 1 V for 60 min exhibited better corrosion resistance than that at 1 V for 10 min. Higher corrosion resistance was also found for Mg alloy anodized at 2 V than that at 1 V. Even a better result could be obtained after sealing with hot water. The optimal parameter of electrochemical treatment was obtained via the Taguchi orthogonal design. Using optimal parameters could improve gloss by 19.40% and surface roughness by 23.7%. Furthermore, the design proved that applied potential was the key parameter.

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26

Rapheal, George. "Corrosion And Wear Behaviour of Plasma Electrolytic Oxidation And Laser Surface Alloy Coatings Produced on Mg Alloys." Thesis, 2016. http://etd.iisc.ernet.in/handle/2005/2716.

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In the present investigation, surface coatings employing laser surface alloying (LSA) and plasma electrolytic oxidation (PEO) processes have been prepared on Mg alloys. The coatings have been investigated for corrosion and wear behaviour. Two important Mg alloys based on Mg–Al system were selected namely, MRI 230D and AM50 as substrates. LSA coatings have been prepared employing Al and Al2O3 as precursors using different laser scan speeds. PEO coatings were prepared in standard silicate and phosphate based electrolytes employing unipolar, pulsed DC. Hybrid coatings using a combination of the two processes were also produced and investigated for corrosion and wear behaviour. Hybrid coatings of LSA followed by PEO (LSA+PEO) were investigated for effectiveness of sealing the cracks in the LSA coatings by subsequent PEO process and consequent improvement in the corrosion resistance. Hybrid coatings of PEO followed by LSA (PEO+LSA) were prepared with an objective of sealing the pores in the PEO coating LSA treatment. In an attempt to produce more compact PEO coatings, electrolyte containing montmorillonite clay additives was employed for the PEO process of AM50 Mg alloy. The coatings were produced employing different current densities and the effect of current density on the microstructure and corrosion behaviour of coating was investigated. Electrochemical corrosion tests of uncoated and coated alloys were carried out in 3.5 wt.% (0.6M)NaCl, neutral pH, solution with an exposed area of 0.5 cm2 for a time duration of 18.5 h. For the PEO coatings with clay additives, corrosion tests were conducted additionally in 0.5 wt.% (0.08 M) NaCl, neutral pH, solution for a time duration of 226.1 h. Wear behaviour of LSA coatings was analyzed by employing a pin on disc tribo–tester conforming to ASTM G–99 standard at ambient conditions with ground EN32 steel disc of hardness Rc 58 as the counterface. Tests were conducted under dry sliding conditions for a sliding distance of 1.0 km at a sliding velocity of 0.837 m/s employing normal loads of 10, 20, 30 and 40 N. Friction and wear behavior of PEO and PEO+LSA coatings were analyzed at ambient conditions by employing a ball−on−flat linearly oscillating tribometer conforming to ASTM G–133 standard. AISI 52100 steel ball of diameter 6 mm was employed as the friction partner. Wear tests were conducted under dry sliding conditions for a total sliding distance of 100 m at normal loads of 2 N and 5 N with oscillating amplitude of 10 mm and mean sliding speed of 5 mm/s. LSA coatings could not improve the corrosion resistance of MRI 230D Mg alloy. This was attributed to the presence of cracks in the LSA coating, which resulted in the accelerated galvanic corrosion of the substrate. LSA coatings improved the wear resistance at all loads. The improved wear resistance was attributed to β (Mg17Al12) phase and Al2O3 particles in the coating which increased the hardness of the LSA layer. No trend in corrosion and wear resistance with laser scan speed was observed for LSA coatings. PEO coatings improved the corrosion resistance of the MRI 230D Mg alloy significantly. The improved corrosion resistance was attributed to the enhanced barrier protection provided by dense barrier layer formed at the substrate/coating interface and to the insoluble phase constituents in the coatings. PEO coating was effective in improving the wear resistance at low loads/contact pressures. At higher loads, the coating underwent micro–fracture as a result of the porosity in the coatings. Hybrid coatings of LSA followed by PEO (LSA+PEO) in silicate based electrolyte improved the corrosion resistance of LSA coatings. However, the corrosion resistance was not improved to the extent of PEO coatings on as–cast alloy as a result of cracks in the primary coatings, which were not fully sealed by the plasma conversion products. No trend in corrosion resistance with laser scan speed was observed for LSA+PEOcoatings. In hybrid coatings of PEO followed by LSA (PEO+LSA), primary PEO coating was completely melted and mixed with applied precursor to form a single composite LSA layer. The corrosion resistance of the hybrid coatings was observed to be lower than that of the as–cast alloy. The presence of solidification cracks reduced the barrier properties and resulted in the accelerated galvanic corrosion of the substrate similar to LSA coatings. Hybrid (PEO+LSA) coatings exhibited improved wear resistance as compared to as–cast alloy at lower loads as a result of increase in the hardness due to β (Mg17Al12) phase and oxide/ceramic particles in the hybrid layer. At higher loads, hybrid coatings exhibited higher wear rate as compared to as–cast alloy and PEO coatings. This was attributed to three–body abrasive wear as a result of dislodged hard oxide/ceramic particles in the wear tracks. No trend in corrosion and wear resistance with laser scan speed was observed for PEO+LSA coatings. PEO coatings on AM50 Mg alloy by employing clay additives in the electrolyte resulted in the reactive uptake of clay particles producing a predominantly amorphous coating at low current density. Clay additives were effective in improving the compactness of the coating at lower current density. At higher current densities, the porosity of the coatings increased. The clay particles got re–constituted producing increasing amount of crystalline phases with increase in current density. Long term impedance measurements showed that clay addition as well as increased current density employed for the PEO process was not effective in improving the corrosion resistance of the coatings. At low current density, even though the coating with clay additives was more compact, it was deficient in MgO and consisted predominantly of an amorphous phase, which underwent fast dissolution in electrolyte thereby resulting in an early loss of barrier properties. At higher current densities, even though the coatings consisted of increased amount of MgO and crystalline phases, which resist dissolution in the electrolyte, the increased porosity and defective barrier layer resulted in easy permeation of the electrolyte into the substrate/coating interface, which resulted in much earlier loss of barrier properties and inferior corrosion resistance.

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27

Garcia, Mónica Pereira. "Biological response to surface modified magnesium alloys-based biodegradable implants." Doctoral thesis, 2016. https://repositorio-aberto.up.pt/handle/10216/83539.

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28

Garcia, Mónica Pereira. "Biological response to surface modified magnesium alloys-based biodegradable implants." Tese, 2016. https://repositorio-aberto.up.pt/handle/10216/83539.

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29

張景翔, Ching-Hsiang Chang, and 張景翔. "Surface Processing of Magnesium Alloy in Organic Acid Solutions." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/92086828605214117579.

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Анотація:

碩士
淡江大學
化學工程與材料工程學系碩士班
98
In the trend of lightweight and energy-saving demands, magnesium alloys become important materials. However, magnesium alloys are susceptible to corrosion and this has limited the wide-spread application. Then a number of coating or surface processing for magnesium and its alloy are studied. This work used A and B to remove impurities and to level surface of magnesium alloys, AZ31; immersion, ultrasonic treatment or chemical mechanical polishing were conducted. The experimental results show that the removal amount of magnesium alloys was more in B than that in A, but high gloss improvement, 495%, and low surface roughness, 0.889 μm, were obtained after chemical mechanical polishing in A. In the processing with B, precipitates containing magnesium, aluminum and zinc were found, resulting in serious local corrosion on alloy surface. In addition, the application of ethanol in organic acids reduced the removal amount and changed surface topography of magnesium alloys, especially in B. The reaction mechanisms of magnesium alloys in B and A, and the corrosion behaviors in 3.5 wt% NaCl solutions were investigated using electrochemical polarization techniques. Our present study shows that A can be an alternative while B is not suitable for cleaning magnesium alloys, AZ31, and the better performance was conducted by chemical mechanical polishing than other processing.

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30

Chen, Kung-Liung, and 陳光亮. "An investigation of copper electroplating on surface of magnesium and its alloys." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/45128813147978998961.

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31

Tsai, Hao-Jan, and 蔡浩然. "The Heat Treatment & Surface Treatment of AZ91D Magnesium Alloy." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/spjz4t.

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Анотація:

碩士
國立東華大學
材料科學與工程學系
95
AZ91D has higher content of aluminums, it can precipitate the β phase(Al12Mg17) of BCC structure in the magnesium base of HCP with the proper heat treatment. Because of this precipitates are located slip plane（0001）under the room temperature, this kind of precipitates can not resisted the dislocation to slide very effective and it caused the purpose of precipitation hardening are very limited. In consequence, this study will use the different heat treatment ways which like T6 treatment（solid solution＋aging hardening）、T8 treatment（solid solution＋TMT＋aging hardening）and T9 treatment（solid solution＋aging hardening ＋TMT）on AZ91D magnesium alloy（As－Extruded）and survey the morphological distribution of samples after solid solution treatment、aging hardening treatment、TMT； and then, comprehend the effect of hardness and tensile strength for AZ91D magnesium alloy. The experimental result shows, the magnesium alloy of AZ91D is in the rising that after T6, T8 and T9 treatment are achieved with its hardness value will be obvious, especially T8, T9 treatment, It can make Al12Mg17 produced the discontinuous particle precipitates directly by the TMT, make its distributed evenly in the magnesium base, and then improve the effect of precipitation hardening. Can know by the result of tensile test, after T6 treatment, 200 degrees Centigrade of aging hardening temperature makes tensile strength value that can be obviously higher than the extruded magnesium alloy；and then, the T8、T9 treatment can also find the tensile strength of the two is higher than the extruded magnesium alloy, superior to the tensile strength value that T6 treatment. In consequence, after comprehensive hardness and result of tensile test, AZ91D extruded magnesium alloy can change morphological distribution ofβ phase(Al12Mg17) by the TMT to reach higher strength. The corrosion resistance of magnesium alloys was, however, very poor. Without proper corrosion-prevention treatment, their applications can be severely restricted, In this study, DC magnetron sputtering was used to deposit a thin film of photo-catalytic TiO2 on AZ91D Mg-alloy to enhance the corrosion-resistance and photo-catalytic properties of the AZ91D substrate. Experimental results showed that the contact angles of AZ91D surface, when coated with a thin film of TiO2 , decreased substantially down to 5° after exposure to UV light, From the experimental of photo-catalytic activity via methyllene blue, can knows that the methylene blue were catalyzed by TiO2 film，thus exhibiting photo‐induced hydrophilicity effect. On the other hand, the potentiodynamic polarization curves indicated that the corrosion potential of TiO2-deposited AZ91D was higher than that of the uncoated AZ91D Mg-alloy. While for TiO2-deposited samples this data suggested an increase in the intrinsic corrosion resistance, the current density of the TiO2-deposited samples was much higher than that for the uncoated samples. The overall corrosion resistance of TiO2-deposited samples deteriorated as compared with that of the uncoated samples. FE-SEM observation of the TiO2 thin film showed polycrystalline structure characteristics of anatase phase, as well as the presence of pinholes on the TiO2 thin film. EDS analysis revealed the pinholes to be locales of incomplete deposition, which caused accelerated corrosion by Galvanic corrosion effect, on the other hand, AZ91D substrate which coated TiO2 film to use voltage and which coated TiO2 film after conversion coating both can advanced the corrosion resistance of magnesium alloys.

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32

Chen, Bo-you, and 陳柏佑. "Surface Hardness Improvement in Magnesium Alloy byMetallic-Glass Sputtered Film." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/06128961540532745719.

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Анотація:

碩士
國立中山大學
材料與光電科學學系研究所
99
The Pd77Cu6Si17 (PCS) thin film metallic glasses (TFMGs) with high glass forming ability and hardness are selected as a hard coating for improving the surface hardness of the AZ31 magnesium alloy. Both micro- and nano-indentation tests are conducted on the specimens with various PCS film thicknesses from 30 to 2000 nm. The apparent hardness and the relative indentation depth (β) are integrated by a quantitative model. The involved interaction parameters and relative hardness values are extracted from iterative calculations. According to the results, surface hardness can be enhanced greatly by PCS TFMGs in the shallow region, followed by gradual decrease with increasing β ratio. In addition, the specimens with thinner coating (for example, 200 nm) show greater substrate-film interaction and those with thick coating (for example, 2000 nm) become prone to film cracking. The optimum TFMG coating thickness in this study is estimated to be around 200 nm. Keywords: Magnesium alloys, hardness, sputtering, thin film metallic glass, nanoindentation

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33

Chen, Jie-Ming, and 陳介銘. "Preparation of Magnesium-Substituted Hydroxyapatite Powder and Coating on Magnesium Alloy AZ91 Surface by the Hydrothermal Method." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/49qq8c.

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Анотація:

碩士
國立虎尾科技大學
材料科學與綠色能源工程研究所
100
This study is divided into two parts. First, using dicalcium phosphate dehydrate (CaHPO4‧2H2O, DCPD) and Calcium Hydroxide (Ca(OH)2) as starting material, mixed with DI water. The Ca/P ratios in the starting slurry was 1.67. This study intends to optimize the synthesis parameters of hydroxyapatite (HAp) powders by hydrothermal method. All conditions of HAp powder prepared by this method is composed of sheet particle with size about 20 to 70μm. The optimized synthesized of HAp powder without magnesium doping at 175℃ for 20 hours has best crystallinity and eliminates DCPA impurity phase. Referring to the IOC% analysis results, the crystallinity increases while increasing process temperatures and process time. Adding 1 wt% Magnesium hydroxide (Mg(OH)2) in starting material to synthesize magnesium-substituted hydroxyapatite powder (Mg-HAp) by hydrothermal method. Doping magnesium reduces the best condition of HAp powder crystallinity and improve the dicalcium phosphate anhydrous (CaHPO4 ,DCPA)impurity phase. The XPS analysis results showrd magnesium doping reduces the HAp crystal binding energy. Second, growth of hydrothermal coating on magnesium alloy AZ91 surface by hydrothermal method. Pre-treatment of Mg alloy sample was sand blast or Mg-Al hydrotalcite process to compare with surface effect. The hydrothermal process conditions are 150℃ for 6 hours. Mixed coating thickness is approximate 50μm. The mixed coating is composed of magnesium hydroxide, calcium carbonate and calcium hydroxide. From the analysis of Weibull distribution function, mixed hydrothermal coating are generally reliable materials with a wear-out failure model. Weibull modulus and reliability are reduced with pre-treatment of Mg-Al hydrotalcite process. Coating samples are immersed in Hank’s solution at 37.5℃ of various durations for 2 days to 32 days. The content of calcium and phosphorus for Hank’s solution are reduced, but for mixed coating surface are increased, with immersed from 2days to 32days. The mixed film is intend to make Calcium-deficient Hydroxyapatite deposition and improve Mg alloy corrosion in solution which contain chloride ion for great biocompatibility.

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34

Liu, Gang-Wei, and 劉剛瑋. "A study of connecting surface-treated aluminum-magnesium alloy 5052 with plastics." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/v74tjf.

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Анотація:

碩士
國立臺北科技大學
資源工程研究所
100
A study of fixing plastics to an aluminum-magnesium alloy 5052. First, the aluminum-magnesium alloy 5052 was surface-treated via electropolishing reaction. While the surface roughness of the aluminum-magnesium alloy 5052 was 16.3 mm before electropolishing, the roughness of the electropolished surface was 3.1 nm. We find that the surface morphology was uniform. The aluminum-magnesium alloy 5052 was further surface-treated via anodic treatment. After that, we observed self-organized formation of nanopores arrays in aluminum-magnesium alloy 5052, and the diameters of nanopores were measured 31.8 ± 3.6 nm. The connection between surface-treated aluminum-magnesium alloy 5052 and polyphenylene sulfide (PPS) was via injection molding. The mechanical properties of bonding plastic on aluminum-magnesium alloy 5052 were studied through both normal tension test and horizontal strength test. The testing result of normal tension test and horizontal strength test are respectively 95.7 ± 3.2 nm and 389.8 ± 7.4 nm. And in order to ensure the practical application in environmental temperature and humidity, the environment test of bonding plastic on aluminum-magnesium alloy 5052 was operated in the temperature between -10 ℃ ~ 70 ℃ and relative humidity remained at 75%. The result shows a slightly reduction mechanical properties after the environmental test.

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35

Bing-Ci, Shih, and 施並奇. "Micro-Arc Oxidation Surface Treatment of AZ31 Magnesium Alloy for Enhancing Osseointegration." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/57325062510574467094.

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Анотація:

碩士
國立高雄應用科技大學
機械與精密工程研究所
102
This study aims to utilize surface modified technology to manufacture medical magnesium alloy implant with uniform biodegradation and bone healing advantages which break through the current medical magnesium alloy technical obstacles: biodegradation rate unbalance and biodegradation speed problems. Furthermore, it can promote bone healing and also making a progress for medical material research of magnesium alloy. Research paper is divided into two parts: the first part is research micro-arc oxidation technologycan control and uniform degradable magnesium alloy which attempt to develop a composite electrolyte and select appropriate chelating agent and dispersant agent. We promote the anodic film properties of corrosion resistance and wear resistance which formed on magnesium alloy surface perfectly and effectively slow down the biodegradation of inequality and excessive biodegradation problems effectively with pulse power output and effective control of ion near the anode area ratio properly. The second part is talking about a surface modified formula that can increase the biological activity of magnesium alloy implant. We combine calcium and phosphorus ions electrolyte with promoting bone integrating capability and with non-toxic for human using chelating agent, in order to chelate calcium and phosphorus ions and make calcium and phosphorus ions from positive to negative potential shift which can go into the anode oxide film through micro-arc oxidation process. Magnesium alloy formed in this way will promote bone healing response after implanting the bone nail into human body. This study collocates the Taguchi method with validation experiments to attain optimal parameters of power supply pulse are current density of 200 mA/cm2, times of 30 minutes, frequency of 4000 Hz, duty cycle 20%, the corrosion current density for this parameter is 8.05×10-7 A/cm2. Further, the corrosion current was reduced into the optimum concentration 2.81×10-7A/cm2 when adds EDTA and Tricalcium phosphate which are kind of medicine with biological activity. After doing the cell toxicity test, the micro-arc oxidation film does not possess cytotoxicity. Via the XPS test, it indicates that EDTA can effectively put calcium ion chelating which making calcium ion deposit over the micro-arc oxidation film which can beneficial to increase of bone healing effect after implantation.

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36

Lee, Ya-Ju, and 李雅茹. "Effect of Cold-Spray Treatment on Surface Properties of AZ80 Magnesium Alloy." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/32726028278919498101.

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Анотація:

碩士
國立臺灣大學
材料科學與工程學研究所
100
It is commonly recognized that magnesium possesses poor corrosion resistance because of its high oxidation potential and porous oxide structure. The corrosion resistance is the most important topic for magnesium alloys application. The thesis aims to investigate how cold spray influences the properties of magnesium alloy, including microstructure, mechanical and corrosion property. The sprayed substrate is AZ80 magnesium alloy. IN625, 301 stainless steel and aluminum powder is used to spraying on the surface. In the study, the coating formed by cold spray treatment has some holes, and is a non-dense film. AZ80 substrate occurred grain refinement after spray IN625 and 301 stainless steel process. For the aluminum coating, it was observed that after coating process, substrate surface is obviously harder than after coating IN625 process. As to the corrosion behavior, the result of the potential-dynamic polarization curve tests reveals that, whether in the IN625 or the Al coating, the corrosion resistance are better than magnesium substrate. In the wear and erosion test, the cold spray coating are to improve the wear and erosion resistance of AZ80 magnesium alloy. After annealing, the AZ80 alloy interacts with Al coating to form Mg17Al12 and Al3Mg2 compound at the interface. After anodizing, on the aluminum coating surface formed a high hardness alumina layer that has excellent corrosion resistance than aluminum coating.

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37

Wang, Tsung-Hsing, and 王宗薪. "Development and study of copper electrodeposition on the surface of the magnesium alloy." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/23979991401152526351.

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Анотація:

博士
長庚大學
機械工程研究所
96
Owing to high specific strength and low density, magnesium alloys have been widely applied as the construction materials in 3C products, automobile and leisure products. However, surface treatments and coatings are needed for the magnesium alloys, because of their low corrosion resistance. In this study, an environmental-friendly alkaline copper-sulfate electroplating bath was proposed for obtaining a well adherent copper deposit on pure magnesium and its alloys (AZ31, AZ61 and AZ91). The copper-deposited magnesium specimens would be further electroplated in acidic copper and nickel plating baths to achieve protective coatings. Electroplating magnesium and its alloys was conducted in an electrochemical three-electrode cell, in which a rotating cylinder electrode was used as the working electrode. The parameters, such as plating current density, bath temperature, stirring velocity of plating solution etc., of copper electroplating on pure magnesium and its alloys were investigated. The surface morphologies of deposited magnesium specimens were examined with optical microscope and scanning electron microscope. The microstructures of the deposited magnesium specimens were studied with transmission electron microscope integrated with an energy-dispersive x-ray spectrometer for chemical composition analysis. The bonding strength between the coating and the magnesium substrate was evaluated with adhesion test (ASTM D3359-02) as well as with thermal cycle test. The corrosion resistance of a deposited magnesium specimen was determined with its anodic polarization behavior in the 3.5 wt.% NaCl solution. Based on the experimental results, the Cu-deposited magnesium specimens can be further electroplated with a protective nickel deposit in an acid plating bath. Furthermore, the proposed alkaline Cu-sulfate bath is environmental-friendly and convenient for operation.

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38

Chu, Chi-Hua, and 朱紀華. "The Improvement of Surface Roughness and Corrosion Resistance for Biodegradable AZ61 Magnesium Alloy." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/15380113027554326577.

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Анотація:

碩士
國立成功大學
製造資訊與系統研究所
102
In biomaterials , the mechanical properties of magnesium alloy is closest to human bone. In addition, its excellent of biodegradablility tends to be more appropriate than Titanium and Cobalt-chromium. Besides, it could decrease the damage to the human body through its degradation to motivate osteoclasts activity and it is decomposable to digestive system. Nevertheless, magnesium is susceptible to corrosion as revealed by experiments using simulation liquid immersing or clinic. Meanwhile, it could reflect resistance reaction from human body. The fast degradation of this material could led surface of objective releases hydrogen and pH value. In this study, sandblasting is applied to create rough surface on magnesium resulting in increased total surface area. Afterwards, flouride conversion coating are utilized in the following steps. In this stage, the intention is to raise its resistance ability to fluorinated by creating a homogenized MgF2 layer on magnesium. Finally, elevate the biodegradablility would be reached through immersing in Ca-P solution by hydrothermal. Following material analysis, SEM, EDS, pH value experience result, we confirm that sandblasting improves corrosion resistance.In vitro test, the factors of hydrophilic or hydrophobic of material, electric charge, and porosity of surface would be affected to the problem of cell adhering. In vivo test-rabbit experiment, after implantation through four weeks, also observed obvious growth of soft tissue and bone healing effect. In addition, the corrosion behavior of magnesium alloys appears quite ease. The result of this report based on cell morphology and cell proliferation illustrates magnesium alloys with rough surface and coating with Ca-P compound tend to have a similar outcome on the first period. The Proliferation of cell tends to be evidently in equal. Nonetheless, on the following stage the objective coating with Ca-P compound continuously has proliferation activity, which indicates it could achieve greater views.

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39

Li, Wei-Cheng, and 李偉誠. "The Influence of Different Cobalt Electrolyte on Magnesium Alloy Coating Surfaces by Micro-Arc Oxidation." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/5za3tx.

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Анотація:

碩士
龍華科技大學
化工與材料工程系碩士班
107
Magnesium alloys have been widely used in 3C products, automotive industry and leisure products due to their low density, heat resistance and heat dissipation. Most of the AZ series of magnesium alloys are favored on the market, but magnesium alloys have high chemical activity and are prone to corrosion in the atmosphere, which makes magnesium alloys extremely limited in application. Surface treatment is one of the methods to effectively improve the corrosion resistance of magnesium alloys. Therefore, this study used micro-arc oxidation technology to prepare high-strength ceramic oxide layer on the surface of AZ61 magnesium alloy, and compared the effects of three cobalt compound electrolytes on hardness, corrosion resistance and surface morphology of AZ61 micro-arc oxidation coating The results of the study are as follows: 1.AZ61 micro-arc oxidation coatings prepared by three cobalt compound electrolytes can obtain cobalt-containing components. 2.The average hardness of the micro-arc oxidation coating of different cobalt electrolytes is as follows: cobalt phosphateelectrolyte >cobalt nitrateelectrolyte>no cobalt in electrolyte >cobalt chlorideelectrolyte. 3.Comparison of corrosion resistance of micro-arc oxidation film layers of different cobalt electrolytes: cobalt phosphateelectrolyte>cobalt nitrateelectrolyte >cobalt chlorideelectrolyte >no cobalt in electrolyte >substrate 4.The corrosion resistance of the micro-arc oxidation film prepared by the cobalt phosphate electrolyte under the bipolar pulse power supply BP300V is the best (Icorr=5.77×10-8), which is about 2500 times higher than that of the substrate (Icorr=1.44×10-4).

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40

Lai, Yen-Tze, and 賴延則. "The Study of Corrosion Resistance on the Surface of ZK60 Magnesium Alloy Formed by MAO." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/33803835571763218133.

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Анотація:

碩士
龍華科技大學
化工與材料工程系碩士班
104
In all metal materials, magnesium is the most chemically active. Oxidation can occur at room temperature. But magnesium oxide film is porous and corrosion resistance is poor. Poor corrosion resistance limits the development of magnesium alloy.; therefore, the magnesium alloy surface treated to enhance corrosion resistance is significant. This study attempts to use micro arc oxidation method to fabricate the micro-arc oxidation coating to improve the corrosion resistance of magnesium alloy. This study was proceeded by changing the different power modes (DC, UPL, BPL) and voltage rise mode (Direct, Stage). And then the corrosion resistance and hydrogen evolution rate were analyzed. The results showed that the bipolar pulse mode can obtain the best corrosion resistance result. The corrosion resistance of the coating formed by mode F has is better than that of mode E. At the mode F, the positive voltage and negative voltage are 400V and 40V respectively, can obtain the corrosion current density, 3.334×10-7A/cm2, that is superior to the substrate up to three orders or more. Furthermore, the hydrogen evolution rate is 9.51×10-3mL/24hr．cm2, which is decreased to 300 times than that of the substrate.

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41

Ho, Jen-Chih, and 何仁智. "Study on the Corrosion Resistance of AZ31 Magnesium Alloy with Micro-Arc Oxidation Surface Treatment." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/50289834341633344088.

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Анотація:

碩士
國立高雄應用科技大學
機械與精密工程研究所
101
This study uses micro-arc oxidation process to improve the corrosion quality of magnesium alloy AZ 31, the solution for this process consists of 60 g/L of silicate, 80 g/L of citrate, 70 g/L of NaOH and 20 g/L of phosphate. In order to find the optimal treatment condition for improving the impedance resistance of the oxide film , the oxide films formed on the substrate under different solution temperature, working voltage, and treatment time are investigated, the results indicate that 30℃, 90V, and 15 min is the optimum operation parameter. The oxide film has two-layer structure consisting of a dense inner layer and an outer layer with porous structure. They were identified as MgO by electron diffraction pattern. The anodic film is mainly composed of two oxide phases, namely, MgO and Mg2SiO4 by X-ray powder diffraction.

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42

Lee, Hsien-Hsueh, and 李咸學. "Application of the Solders with Magnesium Alloy to Joining and to Surface Metallization of Alumina." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/92433261447935595541.

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Анотація:

碩士
國立雲林科技大學
機械工程系碩士班
97
In this study, Sn3Ag0.5Cu lead-free solder with the addition of magnesium alloy was developed and used to join ceramics. The active solders can wet the ceramics at low temperature (<250℃) in air. Thus, the soldering process can be applied to metallize the ceramics for electric and heat conduction and electroplating. The addition of magnesium from 1wt% to 2.6wt% into the Sn3Ag0.5Cu alloy caused decreasing the liquidus from 220.2℃ to 207.8℃. An addition of AZ31 magnesium alloy into the Sn3Ag0.5Cu alloy would form (Ag,Mg)3Sn and Mg2Sn intermetallic compounds. The average shear bonding strengths for Al2O3/Al2O3 and Al2O3/Cu using the AZ31 magnesium containing Sn3Ag0.5Cu solders were between 5 and 8 MPa. It is somewhat difficult to identify the interfacial reaction phases between alumina and solder even after thermal aging. There is also no apparent influence of aging for the bonding strengths of alumina joints. Magnesium addition into the solder can slow down the reaction of solder with copper to form Cu6Sn5 intermetallic compound. After long period aging, the bonding shear strengths of Al2O3/Cu joints using the solders containing 2.2wt% magnesium alloy were obviously higher than of 1wt% magnesium alloy solders. In the study, the active soldering technique was successfully developed for ceramic metallization and electroplating copper on ceramics at low temperature.

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43

Da-JunLin and 林大鈞. "The effect of surface treatment on the biocompatibility and corrosion resistance of biodegradable AZ61 magnesium alloy." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/81433935362164024805.

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Анотація:

碩士
國立成功大學
生物醫學工程學系
100
Magnesium (Mg) and its alloys are new biomaterials which have been studied recently for hard-tissue replacement. The advantages of magnesium alloy compared to other metal traditionally used in implant, such as stainless and titanium alloy. Magnesium alloy have good mechanical properties and biodegradable. In addition, magnesium is an essential component in human metabolism, and magnesium is known to play an important role in the bone formation. However, owing to high electrochemical corrosion, the poor corrosion resistance of magnesium alloy hinders their use in clinical application. Thus, surface treatment is indispensable to improve their corrosion resistance and biocompatibility. Compared to Ca/P deposition and anodic treatment, hydrothermal treatment could form a uniform, adhesive and protective oxide film on the surface of magnesium. The oxide film could protect magnesium alloys from the aggressive attack in human body. By T-BAG method, the hydrothermal oxide film can be modified with hydrophobic monolayers. The designed tail groups and molecules can be selected to form T-BAG for specific applications, such as corrosion resistance and biocompatibility. In this investigation, attempt will be devoted to apply hydrothermal treatment to grow protective oxide films of magnesium alloy. After hydrothermal treatment, biocompatibility and protective hydrophobicity could be achieved by grafted functional groups on oxide film by T-BAG method. The electrochemical and immersion test(in R-SBF) results indicated that anti-corrosion behavior can be enhanced by hydrophobic tail groups (-CH3) on hydrothermal coating surface of plate-like architecture. All the results suggest that the hydrothermal / T-BAG coating can effectively protect the magnesium alloy. And the biocompatibility of magnesium alloy and coatings was studied by using human osteoblast-like MG-63 cells. It was found that the MG-63 cells could grow well on the surface of hydrothermal/T-BAG coated AZ61 and the evidently cell proliferation rate were provoked by protein adsorption in culture medium. It was concluded that the hydrothermal/T-BAG coated magnesium alloy had good biocompatibility.

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44

Szu-JungPan and 潘思蓉. "Co-electrodeposition Behavior and Material Characterization of AlZn Coatings Formed in Ionic Liquid on AZ91D Magnesium Alloy Surface." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/68220355549141159647.

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45

Da-JunLin and 林大鈞. "Effects of Microstructure Modification and Surface Treatment on the Biodegradable Characteristics and Biocompatibility of Bio-Magnesium-Zinc alloy." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/hx59pd.

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46

Chen, Jeng-Hung, and 陳政宏. "Resistance Spot Welding of Die-cast AZ91D Magnesium Alloy Plates－the Residual Copper on Welding Surface and its Effects on Corrosion Properties." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/40182463153090807842.

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Анотація:

碩士
國立中興大學
材料工程學研究所
92
Automotive weight reduction contributes to the reduction of CO2 discharging. Magnesium alloys are attractive for structural components in transportation applications due to their light weight and high specific strength. 　　The spot welding skill is one of the important procedures to assemble automobile, by adding the loading of electrodes and producing resistance heat. However, the spot welding research about the magnesium alloy are limited. In this study, two kinds with different head morphology are used for the welding. The plane-electrode will cause the residual copper on welding surface. The spherical-electrode will cause the residual copper at the central region of weld surface, but left copper-magnesium alloy at periphery of weld surface. 　　After welding, nugget size is not related to the electrodes loading, but related to welding current and electrode form. The nugget size of the welded specimen by plane-electrode will increase with welding current apparently, but the nugget size of the welded specimen by spherical-electrode has no apparently variation following welding current. The microstructure changes of HAZ and fusion zone after welding are also related to welding current and electrode form, but not related to electrode loading. The corrosion behavior of welding surface was investigated in 3.5wt% NaCl(aq) at room temperature. Electrochemical testing results confirm the combined effects of the residual copper on the welding surface. The Icorr value of welding surface increases with welding current. The copper remains on the welding surface will reduce the corrosive resistance of welding surface. But when after welding machining the welding surface with the #400 sandpaper can increase the corrosive resistance of welding surface effectively.

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47

Jiun-WeiHuang and 黃君威. "Effects of Stabilization Heat Treatment on the Tensile Mechanical Properties and Blanking Surface of Friction Stir Processed Mg-9Li-2Al-1Zn Magnesium Alloy." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/33959645492695077156.

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48

Hsieh, Cheng-Han, and 謝承翰. "Hydrothermal growth of hydroxyapatite film on the surface of magnesium alloy (AZ31) based metal matrix compsite containing hydroxyapatite powder produced by friction stir processing." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/77292092080724628084.

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Анотація:

碩士
國立中山大學
材料與光電科學學系研究所
104
The friction stir process was employed to make a composite magnesium alloy AZ31B containing hydroxyapatite. Followed by hydrothermal method, hydroxyapatite (HA) film was deposited onto the sample surface. Hydrothermal reagents are composed of 0.25mol / M of Ca-EDTA and KH2PO4, and sodium hydroxide as a buffer to maintain the pH of the solution at 8.9 and the temperature controlled at 90 ° C. Magnesium in the surface would have replacement reaction with the solution in the system with the time of 3,6,12 hours. A Scanning Electron Microscope (SEM) was used to examine the specimen surface morphology and composition variations X-ray Energy Dispersive Spectrometer (EDS) and back-scattered electron imaging (BEI). Experimental results showed a bonding layer with thickness about 100 nm exists between the substrate and the coating. The bonding layer would become joining surface for substrate and Hap. The earlier forming of coating is probably calcium deficient hydroxyapatite (CDHA) , and the top of coating is probably hydroxyapatite (HA). The chemical solution also brings demineralization to form some vertical cracks. Keywords: hydroxyapatite , calcium deficient hydroxyapatite, friction stir process, coating technology , cracks, hydrothermal method , bonding layer.

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