Добірка наукової літератури з теми "Micro-Arc anodizing"

Oxide films have been produced on the AM60B magnesium alloy using micro-arc oxidation process in an environmentally friendly alkaline solution with and without addition of titania nanoparticles. The surface morphology and cross-section of anodized samples were analyzed by Scanning Electron Microscopy (SEM) coupled with EDS and the phase composition was investigated by X-ray Diffraction (XRD). Hardness tests were performed by means of a micro-hardness tester and the corrosion resistance was evaluated in 3.5% NaCl solution using potentiodynamic polarization tests. Addition of titania nanoparticles doesn’t affect corrosion resistance significantly, but the oxide films produced in titania-containing solution are denser, thicker and have more uniform morphology. In the oxides produced at 130V-140V in presence of titania (4g dm-3) a spinel (MgAl2O4) was observed. Spinel phase increases the hardness up to 550 HV (10mN, 10 s). The addition of titania nanoparticles in the solution could be an interesting way to synthesize hard coatings on magnesium alloy AM60B by micro-arc oxidation in a short process time (10 minutes).

Anodic titania film was synthesized by electrochemical micro plasma oxidation method in H2SO4/NH4NO3 electrolyte, and electrochemical anodizing was carried out at various electrolyte temperatures. The photocatalytic properties and surface characteristics of anodic titania film were investigated. For anodic titania film synthesized at higher electrolyte temperature, the specific surface area of anodic film and the anatase crystalline phase gradually increased. The anodic titania film fabricated in high temperature electrolyte showed not only a slight red shift related to increasing the anatase phase ratio but also a high efficiency of dye degradation.

The article deals with the theoretical aspects of the formation of oxide films on piston aluminum alloys at micro-arc oxidation. Possible schemes of formation of barrier and outer layers of surface coating in aqueous electrolytes are also considered. The mechanism of formation of the interface and possible deposition schemes of non-metallic inclusions on the surface are shown. The stage-by-stage formation of oxide layers on the surface of the piston, which has a fundamental difference from conventional films obtained during anodizing, is described.

Micro-arc discharge events and dielectric breakdown of oxide films play an important role in the formation process of plasma electrolytic oxidation coating. Single pulse anodization of micro-electrodes was employed to study the discharge behavior and dielectric breakdown of oxide films deposited on aluminum in an alkaline silicate electrolyte. Voltage and current waveforms of applied pulses were measured and surface morphology of micro-electrodes was characterized from images obtained using scanning electron microscope (SEM). A feasible identification method for the critical breakdown voltage of oxide film was introduced. Different current transients of voltage pulses were obtained, depending on applied pulse voltage and duration. In addition, the active capacitive effect and complex non-linear nature of plasma electrolytic oxidation process is confirmed using dynamic electrical characteristic curves. A good correlation between the pulse parameters and shape of discharge channels was observed. Circular opened pores were found to close with increasing potential and pulse width. Finally, the characteristic parameters of a single discharge event were estimated.

In this paper a protection process against corrosion and wear for AM60B magnesium alloys, by multilayer approach, is related. The coating consists of a porous oxide layer, obtained in micro-arc anodizing regime, and two or three layers deposited by sol-gel technique. The anodic oxidation pre-treatment improves the adhesion of the sol-gel layers, which are responsible for the sealing of the anodic oxide pores and for the corrosion protection effect. In addition the multilayer system significantly improves AM60B alloy wear resistance. Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) were employed to assess morphology and crystallographic structure. Electrochemical polarization and wear tests were performed in order to evaluate the corrosion resistance behaviour and the wear resistance of the coated magnesium alloys.

Oxide films have been produced on AM60B magnesium alloy using micro-arc oxidation process in an environmentally friendly alkaline solution with and without addition of different oxides nanoparticles (TiO2, ZrO2 and Al2O3). In order to seal the oxides porosity generated in the sparking process, a silane-based top coat has been applied. The surface morphology of samples was analyzed by Scanning Electron Microscopy (SEM). Scratch tests were performed for evaluating the adhesion strength of the anodic oxides. The corrosion resistance of the oxide- silane- based topcoat composite coatings was evaluated in 3.5% NaCl solution using anodic polarization tests. The anodizing in oxides nanoparticles rich solutions (ZrO2 or Al2O3), followed by a silane top coat treatment performed using OSi as precursor, is an interesting way to synthesize adherent corrosion resistant coatings on magnesium alloy AM60B.

ABSTRACTIn this work, surfaces of Al 6061 alloy were coated using anodizing and micro–arc oxidation ( MAO) duplex processes. MAO electrolyte was modified using ( 2-6 g/l )Al2O3 additives . X-ray diffraction (XRD), scanning electron microscopy (SEM), Vickers indenter, atomic force microscopy (AFM), and Microprocessor coating thickness meter ,were employed for characterization of the deposited coatings .Results showed that the coatings contained porous oxide ?-alumina with morphologies characterized by different levels of porosity non-uniform distribution, and their thickness and hardness increased by the increasing of Al2O3 additives. The research demonstrates that a relatively hard (421-490Hv), thick (43-65?m) and uniform coatings, can successfully be deposited on preanodized Al alloy (12-15 ?m with hardness of 190Hv) using Al2O3 additives containing MAO electrolytes as a new method for more future research on surface improvements of Al alloys.

Le présent travail de thèse a pour but le développement du procédé de traitement de surface d’anodisation micro-arc (MAO), appliqué au titane et alliage de titane. L’objectif est de déterminer l’influence des paramètres tels que la nature du substrat (éléments d’alliage), la chimie de la solution électrolytique et les paramètres électriques, sur le comportement électrochimique in-situ des couches en formation, ainsi que sur les caractéristiques microstructurales et chimiques des revêtements. Des méthodes de caractérisations notamment morphologiques (imagerie MEB et MET), chimiques (EDS, DRX, diffraction des électrons, EELS) et électrochimiques ex-situ (potentiel libre, courbes de polarisation, SIE) sont utilisées afin d’étudier les revêtements formés. L’étude systématique réalisée par voltampérométrie et chronopotentiométrie a permis de différencier trois stades ou régimes d’anodisation (I/ classique, II/ micro-arc, et III/ d’arcs), caractérisés par une réponse électrochimique particulière de l’interface métal/électrolyte, et qui impacte les propriétés de revêtement finalement obtenues. Des modèles phénoménologiques sont proposés aux différents stades d’anodisation et en lien avec les paramètres du traitement MAO. Le titane commercialement pur de Grade 2 et l’alliage de titane Ti-6Al-4V (ou TA6V) ont été étudiés comparativement ; l’influence des éléments d’alliage (aluminium et vanadium) a été discutée sur la conduite du procédé. L’élaboration d’une solution électrolytique a été étudiée dans le but d’obtenir un revêtement épais, compact et composé majoritairement de titanate d’aluminium. L’incorporation dans les revêtements des éléments provenant de l’électrolyte a été discutée en lien avec la réponse électrochimique ; cette étude conduit à une proposition de mécanisme de croissance de couche où interviennent les éléments du substrat et les éléments d’alliage aux différents stades d’anodisation. L’étude des régimes pulsés unipolaires et bipolaires a permis de discuter l’effet des temps de pause et des pulsations cathodiques sur la réponse électrochimique du matériau et sur les propriétés des revêtements. L’étude du ratio des charges anodiques / cathodiques a montré qu’il s’agissait d’un paramètre essentiel pour garantir la croissance d’un revêtement à la fois épais, homogène et compact
This thesis manuscript relates to the study of process set up of an electrochemical surface treatment, called micro-arc oxidation (MAO), and applied to titanium and its alloys. The aim is to determine the influence of parameters such as nature of the substrate (alloying elements), chemistry of the electrolytic solution and electrical parameters, on the process. In-situ electrochemical behaviour of forming oxide layers is studied, as well as microstructural and chemical characteristics of formed coatings. Many methods mostly to characterize morphology (SEM, TEM imagery), chemistry (EDS, XRD, electron diffraction, EELS) and ex- situ electrochemical behaviour (OCP, polarizing, EIS) are used. Systematic study realised by voltamperometry and chronopotentiometry allowed to differentiate three anodizing stages (I/ conventional, II/ micro-arc, III/ of arcs), characterized by a particular electrochemical response of the metal/electrolyte interface, and which impacts obtained coating properties. Phenomenological models are proposed for each stage of anodizing and linked to MAO process parameters. Grade 2 commercially pure titanium and alloy Ti-6Al-4V (or TA6V) are comparatively studied; the influence of alloying elements (aluminium and vanadium) was discussed in relation with running of the process. Development of an electrolytic solution was carried out to obtain a thick and compact coating, mostly composed of aluminium titanate. Incorporation into the coating of elements from the electrolyte was discussed, and linked to in-situ electrochemical response; this study leaded to a proposed coating growth mechanism which involves elements from the substrate and from the electrolyte. Study of unipolar and bipolar pulsed regimes allowed discussing the effect of pause time and cathodic pulses on electrochemical response of the material and on coating properties. Study of the anodic / cathodic charge ratio showed it was an essential parameter to ensure growth of a thick, homogeneous and compact coating

Les alliages aluminium-silicium de fonderie sont fréquemment utilisés pour la fabrication de pièces pouvant avoir des géométries complexes ayant des applications diverses (automobiles/ pistons/ électroménager). Suite à la préparation des échantillons par polissage mécanique, une couche d’oxyde poreuse de quinze microns est déposée à la surface de l’AS12 par anodisation en milieu acide ou basique. Après anodisation, un colmatage avec des acides carboxylique et phosphonique est effectué dans le but d’augmenter les performances mécaniques et anti-corrosion des échantillons anodisés. Afin d’évaluer les performances des couches élaborées plusieurs techniques de caractérisation ont été employées : la microscopie (MEB/ MET) pour l’analyse morphologique, les analyses EDS pour la composition, les mesures électrochimiques (SIE) et non électrochimiques au bouillard salin pour l’évaluation de la tenue à la corrosion et les tests tribologiques pour la caractérisation de la tenue à l’usure. À cause des fissures dues au silicium traversant la couche d’oxyde, les échantillons anodisés en milieu acide sulfurique ont montré une tenue à la corrosion réduite par rapport à ceux oxydés en milieu alcalin où le silicium est totalement oxydé en surface. Par contre, la taille nanométrique des pores issues de l’anodisation sulfurique offre une meilleure tenue à l’usure. Le colmatage des échantillons anodisés en milieu sulfurique mène au bouchage des fissures engendrées par le silicium métallique et par la suite à l’amélioration de la tenue à la corrosion. Néanmoins, vue la large taille des pores issus de l’anodisation en milieu alcalin, aucune amélioration significative au niveau de la tenue à la corrosion n’a été constatée. De point de vue tenue à l’usure, le colmatage n’apporte pas de valeur ajoutée remarquable aux échantillons anodisés
Aluminum-silicon alloys are widely used for the manufacture of parts with complex geometries for various applications (automotive / pistons / household appliances). Following the preparation of the samples by mechanical polishing, a porous oxide layer of fifteen microns is grown on the surface of the AS12 by anodization in acid or basic medium. After the anodization, a process known as sealing with long-chain carboxylic or phosphonic acids is carried out in order to increase the mechanical and anti-corrosion performances of the anodized samples. In order to evaluate the samples, several techniques were used: microscopy (SEM/ TEM) for morphological characterization, EDS analysis for composition, electrochemical (EIS) and non-electrochemical salt spray measurements for corrosion resistance evaluation and tribological tests for wear resistance characterization. Because of the cracks due to the silicon crossing the oxide layer, the samples anodized in sulfuric acid medium are characterized by a reduced corrosion resistance compared to those oxidized in alkaline medium where the silicon is completely oxidized on the surface. On the other hand, the nanometric size of the pores resulting from the sulfuric anodization offers a better resistance to wear. The sealing of the anodized samples in sulfuric medium leads to the plugging of the cracks generated by the metallic silicon and subsequently to the improvement of the corrosion resistance. However, due to the large size of the pores resulting from the anodization in alkaline medium, no significant improvement in the corrosion resistance is obtained. From the wear resistance point of view, the sealing does not bring any remarkable added value to the anodized samples

碩士
國立中央大學
機械工程研究所
96
This research tries to improve corrosion resistance of LAZ1110, LAZ1110 +Be, LAZ1110 +Sc, LAZ1110 +Be +Sc magnesium alloys by means of micro-arc anodizing. In the experiment, the electrolytic solution is composed of 40gl-1 Na2SiO3, 100gl-1 NaOH, 20gl-1 NaPO2and 80gl-1(COOH)2.2H2O in distilled water. After the micro-arc anodizing treatment, it will discuss to various parameters. The results indicated that the anodic oxidation film has better corrosion performance under the pulse current condition. In four materials of LAZ1110, LAZ1110 +Be, LAZ1110 +Sc, LAZ1110 +Be +Sc magnesium alloys, LAZ1110 +Be have the worst of corrosion resistance, and LAZ1110 +Sc have the best of corrosion resistance, in the basic extrapolate, add the Be element have decrease the oxidation on the magnesium alloys surface, this phenomenon destroy the anodic oxidation film of LAZ1110 +Be during micro-arc anodizing treatment, add the Sc element have increase the effect of corrosion resistance. Temperature, frequency, time, current density, duty cycle and electrolytic concentration have an influence on micro-structure and corrosion performance of anodic films. In our research, it fixed current density and another parameter, and it used various of time parameter to find out the best operate condition, the results indicated that at 8min of operate condition of micro-arc anodizing treatment have the best of anodic oxidation film.

碩士
龍華科技大學
機械工程系碩士班
102
Taiwan’s bicycle industry has been renowned as a leading role around the world. However, the bicycle industry in Taiwan has to progress in the research and design ability in order to face the global competition. Among the bicycle parts, shock absorbers are the main components. They are made of aluminum alloys under the treatment of anodizing oxidation. Unfortunately, the surface characteristics of the treatment are unable to match the demands from bicycle industry. As a consequence, we prepare anodized composite and micro-arc composite films on Aluminum alloy by means of adding various solid lubricant particles (PTFE and MoS2) and surfactant in the electrolyte. The results indicate that the composite oxide films added with solid lubricant particles have lower average roughness and friction coefficient. In particular, the micro-arc composite film added with MoS2 has the best result of roughness, 1.10μm and friction coefficient, 0.496. Along the same lines, adding surfactant SDS and 1g/L PTFE added in the electrolyte for the micro-arc oxidation film is also effective to reduce the friction coefficient and wear loss of the films to 0.451 and 2.4mg/3000 rpm.

This article presents the brief overview of fairly recent and eco-friendly micro arc oxidation (MAO) coating technology. The weight-cost-performance benefits in general raised the interest to utilize lightweight materials, especially the aluminum and its alloys. Despite numerous engineering advantages, the aluminum alloys themselves do not possess suitable tribology and corrosion resistance. Therefore, improvements in surface properties are essential to enable developing potential industrial applications. For improving wear and corrosion resistance of Al alloys, the most demanding surface properties are high hardness and chemical inertness. The technical and technological limitations associated with traditional anodizing and hard anodizing processes have been the strongest driving force behind the development of new MAO technology. While presenting the key technological elements associated with the MAO process, the basic mechanism of coating formation and its phase gradient nature is presented. Influence of various process parameters including the electrolyte composition has been discussed. The typical microstructural features and distribution of α- and γ-Al2O3 phases across the coating thickness as a key strategy to form dense coatings with required mechanical, tribological, and corrosion properties which are vital to meet potential application demands are briefly illustrated.