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Dissertations / Theses on the topic 'Aluminum alloys – Cracking'

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Published: 4 June 2021

Last updated: 29 January 2023

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1

Paramatmuni, Rohit K. "Solidification cracking resistance of high strength aluminum alloys." Morgantown, W. Va. : [West Virginia University Libraries], 2003. http://etd.wvu.edu/templates/showETD.cfm?recnum=2775.

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Thesis (M.S.)--West Virginia University, 2003.
Title from document title page. Document formatted into pages; contains xi, 71 p. : ill. Vita. Includes abstract. Includes bibliographical references (p. 53-56).

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2

Xiao, Ming. "Mechanism of stress corrosion cracking of aluminum alloy 7079." Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/19174.

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3

Yamada, Kazuo. "Stress corrosion cracking behavior of aluminum alloy 7079 in region II." Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/19078.

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4

Scott, Brian E.-S. "THE ROLE OF STRESS IN THE CORROSION CRACKING OF ALUMINUM ALLOYS." Monterey, California. Naval Postgraduate School, 2013. http://hdl.handle.net/10945/32897.

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This work examines the effect of stress on the rate of sensitization, the rate of pitting corrosion and the rate of crack nucleation of aluminum alloy 5083-H116 aluminum. Stress corrosion cracking in aluminum superstructures of Naval vessels is a multibillion-dollar maintenance problem, which requires more scientific understanding to better predict and mitigate. To investigate the role of applied stress on these corrosion-related processes, rolled plate of AA5083 was placed under tensile stress through bending while being subject to elevated temperature and salt spray. Nitric acid mass loss tests quantified the amount of sensitization as a function of stress level. Optical micrographs were used to determine the rate of pitting corrosion and crack nucleation while under applied tensile stress. The effect of applied, elastic stress on the degree of sensitization was inconclusive. Applied stress did increase the rate of localized corrosion, in terms of both pitting and intergranular corrosion. Moreover, the orientation of the plate with respect to the applied tensile stress, strongly affected the type and amount of localized corrosion observed. When the tensile stress was applied across the rolling direction, more localized corrosion occurred and intergranular corrosion dominant over pitting.

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5

Palmer, Benjamin. "Environmentally-Assisted Cracking Response in Field-Retrieved 5XXX Alloys." Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case1585061712231734.

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6

Harris, James Joel. "Particle cracking damage evolution in 7075 wrought aluminum alloy under monotonic and cyclic loading conditions." Thesis, Available online, Georgia Institute of Technology, 2005, 2005. http://etd.gatech.edu/theses/available/etd-11222005-144800/.

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7

Rechberger, Johann. "The transition from stress corrosion cracking to corrosion fatigue in AA-7075 and AA-8090." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/30779.

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The effect of crack tip strain rate (CTSR) on environmentally assisted cracking was studied for alloys AA-7075 (Al-Zn-Mg-Cu) and AA-8090 (Al-Li-Cu-Mg) in the artificially aged condition. Fatigue pre-cracked double cantilever beam (DCB) specimen were employed with the crack plane parallel to the rolling plane. The cracking behaviour under monotonic and cyclic loading conditions was investigated in aqueous sodium chloride solutions with and without additions of sodium chromate as a corrosion mhibitor. CTSR values were described in terms of K-rate ∆K/∆t (ie. dK/dt) as a measured average over the loading period of a fatigue cycle. This allowed a comparison with CTSR's of monotonically increasing load or constant load tests. At frequencies ≤1 Hz, the load was applied with a triangular wave form. A high frequency of 30 Hz was obtained by sinusoidal loading. Expressed as K-rate, CTSR values were varied over 7 orders of magnitude from 10⁵MPa√m/s to 10² MPa√m/s. Stress intensities investigated were mainly around region II values with respect to SCC K-log(da/dt) behaviour. At low K-rates, real time crack velocities (da/dt) measured under monotonic slow loading or constant load conditions were comparable to crack velocities obtained with cyclic loading experiments. As the K-rate was increased from low values, typical of constant load experiments, the real time crack velocities decreased. This was caused by plasticity induced crack growth retardation effects and a decrease in crack tip film rupture events during the unloading part of a cycle. The crack propagation rate decreased until minimal crack advance increments per cycle were dictated by mechanical parameters acting on a hydrogen embrittled crack tip region. Under monotonic loading conditions region II crack velocities were not influenced by an increase in K-rate which was explained with a mass transport controlled cracking process. Tests with alloy 7075 at intermediate K-rates and a high R-ratio of 0.78 allowed a crack tunnelling mechanism to operate. This overcame the plasticity induced crack growth retardation and, therefore, cracks propagated at the same rates as during low K-rate tests where no retardation phenomena were encountered. Scanning electron microscope investigations revealed a striated intergranular fracture surface of alloy 7075 if tested at K-rates above the transition value to K-rate independent crack propagation rates. Individual striations could be matched on opposing fracture surfaces and the striation spacing corresponded to the average crack propagation increment per cycle. The striations, therefore, were formed as part of the crack advance during every fatigue cycle. At the lower K-rates no striations were present but micro tear ridges could be found on the intergranular fracture facets indicating that dissolution processes alone did not cause the intergranular crack advance. Alloy 8090 did not reveal significant changes in fractography over the entire K-rate range investigated, except at the highest K-rates where small interlocking steps could be detected on some opposing transgranular fracture surfaces. In general, however, the crack path at all K-rates was mainly intergranular with dimpled fracture facets. Alloy 8090 exhibited a high resistance to SCC with fatigue pre-cracked DCB specimen. Therefore, to obtain crack velocity values with low K-rate monotonic loading tests very long test durations would have been necessary. It is concluded that the transition from intergranular SCC to intergranular CF occurs at a critical K-rate. Below the critical K-rate crack velocities are not increased by cyclic loading. Instead crack growth retardation effects can result in lower real time crack velocities than those typical for constant load tests at comparable stress intensities but much lower K-rates.
Applied Science, Faculty of
Materials Engineering, Department of
Graduate

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8

Borchers, Tyler Edward. "Weldability and Corrosion of 7xxx Series Aluminum Alloys." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1471362806.

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9

Balasundaram, Arunkumar. "Effect of stress state and strain on particle cracking damage evolution in 5086 wrought al-alloy." Thesis, Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/14809.

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10

Tirkes, Suha. "Hot Cracking Susceptibility Of Twin Roll Cast Al-mg Alloys." Phd thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/2/12611202/index.pdf.

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Increasing use of aluminum alloys in the automotive industry increases the importance of the production of sheet aluminum. To provide cost effective sheet aluminum to the industry, twin-roll casting (TRC) is becoming more important compared to DC casting. Demand for usage of different aluminum alloys in sheet form introduces some difficulties that should be considered during their applications. The main problem encountered during the welding of aluminum alloys is hot cracking. The aim of this study is to understand the difference in hot cracking susceptibility of two twin roll cast (TRC) aluminum-magnesium alloys (5754 and 5049 alloys) during welding. Varestraint test method was used to evaluate the effect of welding parameters, strain levels, filler alloys and mid-plane segregation on hot cracking susceptibilities. Hot cracking susceptibility of both 5049(Al-2wt%Mg) and 5754(Al-3wt%Mg) alloys increased with increasing strain level. Also, it was observed that hot cracking susceptibility was higher for the alloy having higher magnesium content. Thermal analysis results verified that hot cracking susceptibility indeed can be related to the v solidification range. As is suggested in the solidification range approach, the results of the present study confirm that the extent of solidification and liquation cracking depend on the magnitude of solidification range and the strain imposed during welding. Hot cracking susceptibility of 5754(Al-3wt%Mg) alloy has shown slightly decreasing behavior with addition of 5356 filler alloy. On the other hand, addition of 5183 filler alloy has increased solidification cracking susceptibility of two base alloys. The fracture surfaces of liquation and solidification cracks were investigated by scanning electron microscope with EDS. Liquation crack surfaces of the 5754(Al-3wt%Mg) alloy were found to have high Mg and Si content. For the 5754(Al-3wt%Mg) alloy, a quench test was designed to observe the effect of mid-plane segregation zone. It was observed that there was a eutectic reaction resulting in formation of liquid phase below solidus temperature of 5754(Al-3wt%Mg) alloy. Moreover, internal cracks have formed at the mid-plane segregation zone after Varestraint test. Results show that 5049(Al-2wt%Mg) alloy should be chosen compared to 5754(Al-3wt%Mg) alloy for welding. Moreover, low line energy should be applied and filler alloys with high magnesium content should be used during welding to decrease hot cracking tendency of welds.

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11

Legait, Pierre-Alexandre. "Formation and distribution of porosity in Al-Si welds." Link to electronic thesis, 2006. http://www.wpi.edu/Pubs/ETD/Available/etd-050806-132406/.

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12

Wong, Yat Khin. "A phenomenological and mechanistic study of fatigue under complex loading histories." University of Western Australia. School of Mechanical Engineering, 2003. http://theses.library.uwa.edu.au/adt-WU2003.0017.

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[Truncated abstract. Please see pdf format for complete text.] Over the years much work has been done on studying sequence effects under multilevel loading. Yet, the underlying fatigue mechanisms responsible for such interactions are not fully understood. The study of fatigue under complex loading histories begins by investigating strain interaction effects arising from simple 2-step loading sequences. Fatigue for all investigations were conducted under uniaxial push-pull mode in strain-control. Fatigue is traditionally classified as either low or high cycle fatigue (LCF and HCF respectively). The boundary for LCF and HCF is not well-defined even though the fatigue life of LCF is typically dominated by crack “initiation”, while for HCF, fatigue life is usually dominated by stable crack growth. The terms LCF and HCF, apart from referring to the low and high number of fatigue cycles required for failure, also bear little physical meaning in terms of describing the state of fatigue imposed. As a result, conventional definitions of the two distinct regimes of fatigue are challenged and a new method of classifying the boundary between the two regimes of fatigue is proposed. New definitions are proposed and the terms plastically dominant fatigue (PDF) and elastically dominant fatigue (EDF) are introduced as suitable replacements for LCF and HCF respectively. PDF refers to the condition of a material undergoing significant reverse plasticity during cyclic loading, while for EDF, minimal reverse plasticity is experienced. Systematic testing of three materials, 316 L stainless steel, 6061-T6 aluminium alloy and 4340 high strength steel, was performed to fully investigate the cycle ratio trends and “damage” accumulation behaviour which resulted from a variety of loading conditions. Results from this study were carried over to investigate more complex multilevel loading sequences and possible mechanisms for interaction effects observed both under 2-step and multi-step sequences were proposed. Results showed that atypical cycle ratio trends could result from loading sequences which involve combinations of strain amplitudes from different fatigue regimes (i.e. PDF or EDF). Mean strain effects on fatigue life were also studied. The objective of this study was to identify regimes of fatigue which are significantly influenced by mean strains. Results indicated that mean strains affected EDF but not PDF. 2-step tests, similar to those performed in earlier studies were conducted to investigate the effects of mean strain on variable amplitude loading. Again, atypical cycle ratio trends were observed for loading sequences involving combinations of PDF and EDF. It is understood that fatigue crack growth interaction behaviour and mean stress effects are two dominant mechanisms which can be used to explain cycle ratio trends observed. The significance and importance of proper PDF/EDF definition and specification are also stressed. The study of fracture mechanics is an important component of any fatigue research. Fatigue crack growth in 4140 high strength steel CT specimens, under conditions of plane stress and plane strain were studied. In this investigation, the effects of R and overload ratios were also studied for both plane stress and plane strain conditions. Results indicate that differences in the point of crack “initiation” under both plane stress and plane strain conditions decrease with increasing load range, while the extent of crack retardation as a result of overloading, is greater under plane stress than plane strain conditions. The extent of crack growth retardation increases with decreasing R ratios and increasing overload ratios. The final phase of this project involves the proposal of two practical models used to predict cumulative “damage” and fatigue crack propagation in metals. The cumulative “damage” model proposed takes the form of a power law and the exponent which governs “damage” accumulation can easily be calculated by knowing the failure life, Nf, for a given strain or load level. Predictions for the “damage” model performed better when compared to other popular cumulative “damage” models. The second model proposed predicts fatigue crack growth behaviour from known monotonic and smooth specimen fatigue data. There are several benefits of having a model that can predict fatigue crack growth from monotonic and smooth specimen fatigue data: a) traditionally, engineers had to rely on expensive and time-consuming crack propagation tests to evaluate and select materials for maximum fatigue resistance, and b) monotonic and smooth specimen fatigue data are readily available. The crack propagation model is proposed to alleviate the material selection process by providing engineers a means to rapidly eliminate and narrow down selections for possible material candidates.

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13

Padgett, Barbara Nicole. "Investigation into the stress corrosion cracking properties of AA2099, an Al-Li-Cu alloy." Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1204515486.

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14

Haase, Jake D. "Microbeam diffraction mapping of microtexture in Al-Li 2090 T8E41." Thesis, Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/19586.

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15

Palmer, Benjamin Clive. "Sensitization Effects on Environmentally Enhanced Cracking of 5XXX Series Alloys: Macro and Mesoscale Observations." Case Western Reserve University School of Graduate Studies / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=case1496232162170832.

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16

Lewis, Jeffrey Keith. "An investigation of stress corrosion cracking in high-strength aluminum alloys, the development of a new test method." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape7/PQDD_0002/MQ44916.pdf.

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17

Chen, Chih-Chang. "Evaluation of weld solidification cracking in aluminum alloys A1- 2219 and A1-2090 using the Gleeble 1500 system /." The Ohio State University, 1991. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487687115924536.

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18

Lozano-Perez, Sergio. "TEM crack tip investigations of SCC." Thesis, University of Oxford, 2002. http://ora.ox.ac.uk/objects/uuid:7e503ff9-782a-4f74-b184-dddaa96e03e2.

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Over the last few years, TEM has become a powerful technique to study cracks and specially crack tips. However, the number of publications including TEM results has not grown as it was expected. The main reason for this might be difficulties in the sample preparation. In this work we present a novel FIB sample preparation technique which has proved to be an ideal tool for preparing cross sectional samples containing crack tips. The morphology of intergranular stress corrosion cracking (IGSCC) has been investigated in Alloy 600 subjected to constant load and slow strain rate tests in simulated primary circuit pressurized water reactor conditions. Cracks were observed to nucleate at high-angle grain boundaries and propagate to depths of a few tens of micrometer along such boundaries, still in the initiation stage. Electron diffraction, energy dispersive x-ray (EDX) and electron energy loss spectroscopy (EELS) have been used to identify the different corrosion products and precipitates. Elemental mapping was employed to reveal changes in composition in the crack tip area. Major observations at cracks and grain boundaries include: the presence of different oxides in different locations, differences in grain boundary oxides and open crack/free surface oxides. These observations suggest that IGSCC involves oxygen diffusion through a porous oxide region along grain boundaries to the bare metal. This is a novel concept that offers an alternative to previous mechanisms proposed in the literature e.g. H embrittlement, slip-dissolution, etc., for which no supporting evidence has been found.

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19

Liu, Xiaodong. "Effects of stress on intergranular corrosion and intergranular stress corrosion cracking in AA2024-T3." Columbus, Ohio : Ohio State University, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1133313637.

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20

Lados, Diana Aida. "Fatigue crack growth mechanisms in Al-Si-Mg alloys." Link to electronic thesis, 2004. http://www.wpi.edu/Pubs/ETD/Available/etd-0204104-125758.

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Thesis (Ph. D.)--Worcester Polytechnic Institute.
Keywords: Microstructure; Elastic-Plastic Fracture Mechanics; Crack closure; A356; J-integral; Conventionally cast and SSM Al-Si-Mg alloys; Residual stress; Heat treatment; Fatigue crack growth mechanisms; Threshold stress intensity factor; Plastic zone; Paris law; Fracture toughness; Roughness. Includes bibliographical references.

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21

Hu, Chao. "Locally enhanced voronoi cell finite element model (LE-VCFEM) for ductile fracture in heterogeneous cast aluminum alloys." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1199209208.

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22

Morano, Robert Natale. "Effect of R-ratio on crack closure in Al-Li 2090 T8E41, investigated non-destructively with x-ray microtomography." Thesis, Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/19903.

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23

Cevik, Gul. "Investigation Of The Effect Of Orientation And Heat Treatment On The Stress Corrosion Cracking Susceptibility Of 7050 Aluminum Alloy." Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/3/12605220/index.pdf.

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In the present work, the effect of variation in specimen orientation and heat treatment on the Stress Corrosion Cracking (SCC) susceptibility of 7050 aluminum alloy was investigated in 3,5% NaCl solution and under freely corroding conditions. For this purpose, Constant Extension Rate Tests (CERT) was performed on precracked Compact Tension (CT) specimens and the Direct Current Potential Drop technique was applied to measure the crack lengths. In addition to crack length versus time curves, the relationship between the crack growth rate and the stress intensity factor was determined. Fractographic analysis was utilized extensively to support the findings related with basic mechanisms of cracking. The alloy was found to be in the most susceptible state in the SL orientation, in which the crack propagation direction is parallel to the rolling direction. The resistance to SCC is higher in the TS but at maximum in LT orientation where the loading direction is parallel to the rolling direction. In the peak aging treatment, T651, alloy is susceptible to SCC in SL orientation. When the over aging treatment, T7651, is applied the resistance is increased and the two step over aging treatment, T73651, has resulted in an additional improvement in this orientation. On the other hand, the alloy showed higher resistance to SCC in TS and LT orientations in T651 condition compared to the T7651 and T73651 treatments. In these orientations, the alloy is less susceptible in T73651 condition than in T7651 treatment.

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24

Schrock, David J. "The Effects of Loading Frequency, Sensitization Level, and Electrochemical Potential on Corrosion Fatigue Kinetics of Aluminum-Magnesium Alloys." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu158793003383275.

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25

Young, Paul S. "Modeling and Analysis for Atmospheric Galvanic Corrosion of Fasteners in Aluminum." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1430416832.

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26

Li, Yizhuo. "Experimental Study of Fatigue Properties under Different Loadings of an AA7075 Alloy Treated by SMAT." Thesis, Troyes, 2021. http://www.theses.fr/2021TROY0006.

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Les effets du SMAT sur les propriétés en fatigue uniaxiale et en torsion ont été étudiés pour un alliage d'aluminium 7075. Des éprouvettes de fatigue ont été traitées thermiquement pour augmenter la sensibilité du matériau au SMAT. Certaines propriétés de cet alliage traité par SMAT ont été caractérisées par des essais de traction et de microdureté. Par rapport à l'état brut d'usinage (AM), les durées de vie en fatigue uniaxiale des éprouvettes SMATées (AM-SMAT) sont augmentées pour des amplitudes de contrainte élevées, mais diminuées pour de faibles amplitudes. Cependant, pour les éprouvettes traitées thermiquement (HT), leurs durées de vie après SMAT (HT-SMAT) sont augmentées pour toute la gamme de contraintes étudiée. Des phénomènes similaires ont été observés pour les éprouvettes testées en fatigue sous sollicitations en torsion. D'autres analyses ont été effectuées pour étudier la dispersion des données de fatigue avec une approche statistique. Les mécanismes de fissuration ont été analysés à l’aide d’observations des éprouvettes rompues. Il a été mis en évidence que les mécanismes sont différents pour les éprouvettes présentant différents états et qu'ils dépendent également du niveau de contrainte imposée. En se basant sur ces résultats, les effets bénéfiques et néfastes du traitement SMAT ont été analysés. Le rôle joué par différents facteurs comme les contraintes résiduelles, le raffinement des grains et la rugosité de surface, a été examiné pour la fatigue sous sollicitations uniaxiales et en torsion
The effects of SMAT on uniaxial and torsional fatigue properties were investigated for a 7075 aluminium alloy. A part of fatigue specimens was heat treated to increase the sensitivity of the material to SMAT represented by its ductility. Basic properties of the alloy in different states treated by SMAT were characterized through tensile tests and microhardness measurements. Compared to as-machined (AM) state, the fatigue lives of SMATed specimens (AM-SMAT) tested under uniaxial loading were increased under high stress amplitudes, but decreased under low amplitudes. However, the fatigue lives of SMATed specimens (HT-SMAT) were increased under all the studied stress amplitudes, with respect to heat treated (HT) state. Similar phenomena were observed for the specimens tested under torsional fatigue. Further analyses were performed to investigate the scatter of fatigue data using a statistical approach. The cracking mechanisms of specimens in different states were analysed through observations of failed specimens. It was revealed that the mechanisms are different for specimens in different states and that they are dependent on the imposed stress levels. Based on these results, both beneficial and detrimental effects exhibited by SMAT were analysed. For this purpose, the role played by various factors including residual stresses, grain refinement and surface roughness, were discussed for both uniaxial and torsional fatigue

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27

Hepples, W. "Environment-sensitive cracking of 7000 series aluminium alloys." Thesis, University of Newcastle Upon Tyne, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375141.

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28

Yuan, Yudie. "Localised corrosion and stress cracking of aluminium-magnesium alloys." Thesis, University of Birmingham, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.433422.

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29

Warrington, David. "Studies on the hot cracking behaviour of aluminium alloys." Thesis, University of Liverpool, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316958.

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30

Green, P. D. "Sacrificial corrosion behaviour of thermally sprayed aluminium alloys." Thesis, University of Nottingham, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239875.

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31

Williams, J. R. "Corrosion of aluminium-copper-magnesium metal matrix composites." Thesis, University of Nottingham, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239852.

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32

Cano-Castillo, U. "Environment-assisted cracking of spray-formed Al-alloy and Al-alloy-based composite." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260730.

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33

Kelly, D. J. "Exfoliation and stress corrosion cracking of the aluminium-lithium alloy 8090." Thesis, Cranfield University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302803.

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34

Cormack, Emily C. "The Effect of Sensitization on the Stress Corrosion Cracking of Aluminum Alloy 5456." Thesis, Monterey, California. Naval Postgraduate School, 2012. http://hdl.handle.net/10945/7325.

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This work examines the effect of sensitization on the stress corrosion cracking behavior of marine grade aluminum alloys (Al-Mg). These alloys can be sensitized during operation, promoting their susceptibility to intergranular stress corrosion cracking (IGSCC). Aluminum alloy 5456-H116 (also identified as Al-Mg5.1) samples were sensitized at 175C for varying durations of time and then mechanically tested in salt water. Mass loss tests quantified the degree of sensitization (DOS) as a function of sensitization time. Dual cantilever beam tests were used to measure the SCC growth rate and cyclic fatigue tests were conducted to determine the corrosion fatigue behavior. DOS increased as sensitization time increased with little difference in mass losses above 336 hours. Stress corrosion crack growth rate increased as sensitization time increased. Although the sensitization rates for AA5456-H116 were higher than for AA5083, the stress corrosion crack growth rates were significantly lower. The stress corrosion fracture surfaces showed clear showed a clearly intergranular fracture path with extensive crack branching and delamination in the transverse direction.

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35

Akkus, Mert. "Effect Of Welding Parameters On The Hot Cracking Behavior Of 7039 Aluminum - Zinc Alloy." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612548/index.pdf.

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7039 aluminum alloys are widely being used in the aerospace, automotive and defense industries in which welding technique is used for their joining. The main problem encountered during the welding of 7039 aluminum alloy is hot cracking. The aim of this study is to understand the effect of welding parameters on the hot cracking behavior of 7039 aluminum alloy by using Modified Varestraint Test (MVT) with Gas Tunsgten Arc Welding (GTAW) technique. During tests, welding speed was selected as varying parameter, welding current was kept constant and to understand the effect of filler materials 5183 and 5356 aluminum alloy filler materials were used. It has been observed that with the change in welding speed hot cracking susceptibility of 7039 aluminum alloy changes. The effect of filler materials is found to be favorable by decreasing the hot cracking susceptibility of 7039 aluminum alloy. Filler material additions also improved the hardness of the weld metal. Based on the cracking mechanism hot cracks were investigated as solidification cracks and liquation cracks. It has been experienced that liquation cracking susceptibility of the filler material added samples has been affected from the magnesium and manganese contents of the weld seams. Effect of solidification range on liquation cracking was also justified with differential thermal analyses. With the micro examinations the intergranular structure of hot cracking is revealed. In addition, the characterization and growth properties of the hot cracks under cyclic load were tried to be understood and the fractography of these cracks were taken.

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36

Amurwabumi, Kreshna. "A study of ultrasound backscatter techniques for monitoring stresses and simulated crack mouth opening in aluminium alloys and steel used for offshore oil platforms." Thesis, Brunel University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235896.

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37

Eksi, Murat. "Optimization Of Mechanical And Microstructural Properties Of Weld Joints Between Aluminium-magnesium And Aluminium-magnesium-silicon Alloys With Different Thicknesses." Master's thesis, METU, 2013. http://etd.lib.metu.edu.tr/upload/12615649/index.pdf.

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For the last decades usage of aluminium alloys have been increasing tremendously. They have been used in aerospace industry widely and now aluminium alloys are becoming more and more popular in automotive and defense industries. Consequently
successful welding of aluminium alloys gains importance. In this study a research is carried out on eldability of plates having different thicknesses of composition 5754 aluminium and 6063 aluminium in T-fillet geometry using Gas-metal Arc Welding technique. It was aimed to have a successful joint without using pre-weld and post-weld heat treatments. During tests welding current and voltage were the varying parameters as welding speed was held constant. Macro-examinations were performed to see the penetration of the weld metal. It was seen that the type of filler wire greatly effects weld penetration. Hardness tests, tensile tests were done to compare the mechanical properties of the welded joints with different filler wires. Despite having better penetration in 4043 filler wire used weld joints, 5356 filler wire used weld joints had higher tensile strength and ductility. In the second part of the study, a dynamic loading machine was designed and manufactured to see the behavior of the fillet welds under dynamic loading. The amount of stress and strain given to the specimen on this machine was adjustable but can&rsquo
t be measured. The tests that were made with this machine aimed only to compare the number of cycles of specimens before fracture. For dynamic loading tests two groups of specimens were prepared with filler wire 4043
each group having been welded with different heat inputs. It was aimed to see the effect of welding heat input on service lifes but no significant difference between cycle numbers of specimen groups having been welded with different heat inputs was observed. Microstructure examinations of these specimens revealed that coarsening the grains, grain boundaries, particles in PMZ and HAZ regions between Al 6063 base metal and weld zone made these areas more susceptible and favorable for crack propogation than Al 6063 base metal.

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38

Goetz, John M. "Investigation of coating cracking and fatigue strength of 7050-T74 aluminum alloy with different anodize coating thicknesses." Connect to this title online, 2005. http://hdl.handle.net/1811/327.

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Thesis (Honors)--Ohio State University, 2005.
Title from first page of PDF file. Document formattted into pages: contains v, 40 p.; also includes graphics. Includes bibliographical references (p. 39-40). Available online via Ohio State University's Knowledge Bank.

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39

Seong, Jinwook. "Inhibition of Corrosion and Stress Corrosion Cracking of Sensitized AA5083." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1429701294.

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40

Waters, S. "The effect of heat treatment and microstructure on HAZ cracking in a 7XXX series aluminium alloy." Thesis, Swansea University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.639355.

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The effect of heat treatment and microstructure on liquation cracking in a 7XXX series aluminium alloy has been investigated using microstructural simulations in a Gleeble 1500 Thermomechanical testing machine. The work included analysis of instrumented 7017 aluminium alloy welds to assess their microstructural, mechanical and defect characteristics. Critical features of the crack sensitive white zone (WZ) were measured as a means of validating the microstructures simulated in the Gleeble facility. Four-point-bend fatigue testing was used to open the cracked welds and expose the surface of liquation cracks thereby allowing analysis of the localised chemical composition. Concentrations of zinc sufficient to cause liquation were identified in these regions. Simulations were executed on the basis of measured weld parameters. The validity of the generated microstructures were confirmed through grain size and microhardness measurements. The effect of time at peak temperature was also assessed and revealed typical solid state grain growth of recrystallised grains. Variation in peak temperature led to simulations of regions adjacent to the WZ, which have lower microhardness but no significant microstructural change. Such characteristics are typical of the over-aged zone seen in 7017 welds. Mechanical testing of the simulated WZ microstructure confirmed its reduced strength and hence, enhanced crack sensitivity. From this work recommendations concerning heat treatment and welding conditions have been made in order to help reduce the possibility of liquation cracking.

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41

Aravamudhan, Boopa Nandhini. "Study of the Effect of Laser Shock Peening on Corrosion Behavior of Aluminum Alloy 7075." University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1535374351540327.

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42

Albannai, Abdulaziz I. Mr. "Innovative Tandem GTAW with Alternating Side-by-Side Spot-Like Welds to Minimize Centerline Solidification Cracking." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1500528823020898.

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43

Batigun, Caner. "Determination Of Welding Parameter Dependent Hot Cracking Susceptibility Of 5086-h32 Aluminium Alloy With The Use Of Mvt Method." Phd thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/3/12605721/index.pdf.

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Hot cracking is a serious problem that encounters during welding of aluminium-magnesium alloys. In the present study, solidification and liquation type of hot cracks in weld metal and the heat-affected zones of 5086-H32 aluminium alloy were investigated by using Modified Varestraint Test (MVT) with TIG-AC and TIG-DC welding. With determining the size, type and number of cracks, a relation was established between welding line energy and strain on the hot crack formation. This information was used to determine the hot crack safe parameter ranges. The hot cracking tendency as a function of applied parameters were discussed in the frame of temperature fields around the moving heat source. Moreover, the characteristic hot crack locations on the 5086-H32 MVT specimens were generalized. The results of the study indicated that the increase in line energy and strain increased the hot cracking tendency of the specified aluminium alloy. In the low line energy range, the main hot cracking mechanism is the solidification cracking which could be overcome by the use of a suitable filler material. At high line energy range, due to the increased amount of interdendritic liquid, the amount of solidification cracking decreases by healing mechanism. However, because of the enlarged-temperature-field around the weld zone, fraction of HAZ cracking increases. The comparison between the hot cracking tendencies in low and high line energies indicates that the low line energy ranges with low augmented strains resulted in hot crack safer parameters.

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44

Coniglio, Nicolas [Verfasser], Andreas [Gutachter] Bertram, Thomas [Gutachter] Böllinghaus, Carroll E. [Gutachter] Cross, and S. [Gutachter] Marya. "Aluminum Alloy Weldability: Identification of Weld Solidification Cracking Mechanisms through Novel Experimental Technique and Model Development / Nicolas Coniglio ; Gutachter: Andreas Bertram, Thomas Böllinghaus, Carroll E. Cross, S. Marya." Berlin : Bundesanstalt für Materialforschung und -prüfung (BAM), 2008. http://d-nb.info/1122835884/34.

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45

Allo, Justine. "Mécanismes fondamentaux et cinétiques d'oxydation d'alliages réfractaires de nouvelle génération pour la prétrochimie." Thesis, Normandie, 2021. http://www.theses.fr/2021NORMR005.

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46

Dhondt, Matthieu. "Corrosion sous contrainte intergranulaire du noyau de soudure par FSW de l'alliage Al-Li 2050." Thesis, Bordeaux 1, 2012. http://www.theses.fr/2012BOR14738/document.

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Pour réduire le poids des structures aéronautiques, plusieurs voies ont été explorées. Parmi elles, l'utilisation des alliages d'aluminium légers et le remplacement des structures rivetées par des structures soudées par Friction Stir Welding (FSW) sont envisagées. La question de la durée de vie de ces structures préoccupe les industriels. Dans ce cadre, cette étude porte sur la sensibilité à la corrosion sous contrainte intergranulaire (CSC-IG) du noyau de soudure par FSW de l'alliage Al-Cu-Li 2050. Ce matériau est composé de grains équiaxes dont la taille diminue de 17 à 4 µm à mesure que l'on s'éloigne de la surface de soudage. Une variation de texture est révélée grâce à des cartographies EBSD formant la microstructure des « onion rings ». La périodicité de ces « onions rings » est égale à l'avancée du pion FSW sur un tour (500 µm pour notre matériau). Ces hétérogénéités microstructurales entraînent des gradients de champs mécaniques locaux quantifiés par corrélation d'images lors des essais mécaniques. Ces hétérogénéités microstructurales et mécaniques favorisent les phénomènes de corrosion localisée lorsque le matériau est soumis à un environnement agressif. Les effets des contraintes et de la microstructure sur la CSC-IG sont mis en évidence par des essais de corrosion et des essais de corrosion sous contrainte (CSC). Les essais de corrosion montrent une sensibilité du matériau à la piqûration alors que les essais de CSC révèlent l'amorçage de fissures intergranulaires. Les plus grosses fissures s'amorcent préférentiellement à la frontière des « onion rings ». Un modèle par éléments finis a été développé dans le but de simuler la propagation des fissures intergranulaires sur des agrégats réels générés par des cartographies EBSD
To reduce the aircraft components weight, several solutions were explored. Among them, the using of light aluminum alloys and the substitution of riveting by friction stir welding (FSW) are investigated. Industry is concerned by the question of the life of such structures. For this, this study is focused on intergranular stress corrosion cracking (IGSCC) sensitivity of the 2050 Al-Li-Cu alloy friction stir weld nugget. This material consists of equiaxed grains whose size is decreasing with the distance from the weld surface between 17 µm at the top and 4 µm at the bottom. The “onion rings” microstructure is revealed by EBSD cartographies as a texture variation. They appear with a periodicity of 500 µm corresponding to the advance per revolution of the tool. Those microstructural heterogeneities cause local mechanical field gradients quantified by digital image correlation measurements during mechanical tests. Those microstructural and mechanical heterogeneities promote localized corrosion when the material is submitted to an aggressive environnement. Microstructure and stress effects on IGSCC are shown by corrosion tests and stress corrosion tests. The first ones show a sensitivity to pitting corrosion and a stress application reveal initiation of intergranular cracks. The biggest ones preferentially initiate at “onion rings” boundaries. A finite element model was developed in order to simulate intergranular cracks propagation on real aggregates obtained by EBSD cartographies

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Chen, Jie. "Modelling of Laser Welding of Aluminium using COMSOL Multiphysics." Thesis, KTH, Materialvetenskap, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-284448.

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This thesis presents a modelling approach of laser welding process of aluminium alloy from the thermo-mechanical point of view to evaluate the occurrence of hot cracking based on simulation results and relevant criteria. The model was created stepwise in COMSOL Multiphysics, starting with the thermal model where heat conduction of solid and liquid phase was computed. Then the CFD model was created by involving the driving forces of liquid motion in the weld pool, i.e. natural convection and Marangoni effect. Lastly, the temperature profile calculated by the CFD model was loaded into the mechanical model for computation of thermal stress and strain. The mechanical results were required in criteria for measuring the susceptibility of hot cracking. The main findings include that Marangoni effect plays a dominant role in generating the fluid flow and convective heat flux in the weld pool, thus enhancing the heat dissipation and lowering temperature in the workpiece. By contrast, such temperature reduction caused by the air convection, radiation and natural convection is negligible. The welding track further from the clamped side experiences smaller transversal residual stress, but it does not necessarily suggest higher susceptibility to hot cracking according to the applied criteria. It can be concluded judging from current results that these first models of laser welding process work satisfactorily. There is still a work to do to obtain the full maturity of this model due to its limitation and some assumptions made for simplicity.
Denna avhandling presenterar en modelleringsmetod för lasersvetsningsprocessen av aluminiumlegering ur termomekanisk synvinkel för att utvärdera förekomsten av het sprickbildning baserat på simuleringsresultat och relevanta kriterier. Modellen skapades stegvis i COMSOL Multiphysics, med början med den termiska modellen där värmeledning av fast och flytande fas beräknades. Sedan skapades CFD-modellen genom att involvera drivkrafterna för flytande rörelse i svetsbassängen, dvs. naturlig konvektion och Marangoni-effekt. Slutligen laddades temperaturprofilen beräknad av CFD-modellen in i den mekaniska modellen för beräkning av termisk stress och töjning. De mekaniska resultaten krävdes i kriterier för att mäta känsligheten för het sprickbildning. De viktigaste resultaten inkluderar att Marangoni-effekten spelar en dominerande roll när det gäller att generera vätskeflödet och konvektivt värmeflöde i svetsbassängen, vilket förbättrar värmeavledningen och sänker temperaturen i arbetsstycket. Däremot är sådan temperaturreduktion orsakad av luftkonvektion, strålning och naturlig konvektion försumbar. Svetsbanan längre från den fastspända sidan upplever mindre tvärgående restspänning, men det föreslår inte nödvändigtvis högre känslighet för hetsprickning enligt de tillämpade kriterierna. Man kan dra slutsatsen utifrån aktuella resultat att dessa första modeller av lasersvetsningsprocesser fungerar tillfredsställande. Det finns fortfarande ett arbete att göra för att få full mognad för denna modell på grund av dess begränsning och vissa antaganden för enkelhetens skull.

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48

Oger, Loïc. "Corrosion sous contrainte et fragilisation par l'hydrogène d'alliages d'aluminium de la série 7xxx (Al-Zn-Mg) : identification des paramètres microstructuraux critiques pilotant l'endommagement à l'échelle locale." Phd thesis, Toulouse, INPT, 2017. http://oatao.univ-toulouse.fr/19559/19/OGER_Loic_1_sur_2.pdf.

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Dans un contexte normatif toujours plus sévère concernant les rejets automobiles polluants, la substitution des aciers par des alliages d’aluminium dans les structures des véhicules est en plein essor. Ce projet de thèse, qui s’inscrit dans un programme de développement de la société Constellium, cible plus précisément les alliages d’aluminium de la série 7xxx (Al-Zn-Mg) qui, malgré leurs propriétés mécaniques élevées, peuvent présenter une sensibilité à la corrosion sous contrainte (CSC) liée au phénomène de fragilisation par l’hydrogène (FPH). La compréhension des mécanismes mis en jeu dans ce type d’endommagement constitue donc une première étape vers une optimisation métallurgique en vue d’une industrialisation future de ces alliages dans le secteur automobile. La première partie de ces travaux est consacrée à l’étude de l’influence de l’état métallurgique de l’alliage 7046 sur son comportement en CSC et à l’identification des mécanismes de dégradation. Un lien direct a pu être mis en évidence entre l’abattement des propriétés mécaniques et les modes de rupture actifs et la quantité d’hydrogène dans l’alliage. Les deux modes d’endommagement observés, intergranulaire-fragile et transgranulaire-fragile, ont respectivement été attribués à un enrichissement en hydrogène aux joints de grains et au piégeage de l’hydrogène au niveau des précipités intragranulaires. Les interactions entre l’hydrogène et les précipités fins d’une part et les dislocations d’autre part, identifiés comme deux hétérogénéités microstructurales critiques vis-à-vis de la FPH, ont été étudiées à une échelle plus locale dans la seconde partie du travail de thèse. Les essais ont été réalisés sur des échantillons modèles, chargés en hydrogène en milieu H2SO4 sous polarisation cathodique et la profondeur de pénétration de l’hydrogène a été évaluée par SKPFM (Scanning Kelvin Probe Force Microscopy). L’ensemble des résultats obtenus met en évidence : 1/ un effet « barrière » des précipités fins et des dislocations sur la diffusion de l’hydrogène en relation avec un abattement des propriétés mécaniques moins important, 2/ un transport possible de l’hydrogène par les dislocations et 3/ l’efficacité du SKPFM pour déterminer précisément des coefficients de diffusion apparents de l’hydrogène. Ces résultats ouvrent ainsi de nouvelles pistes vers la compréhension des mécanismes de CSC dans les alliages Al-Zn-Mg.

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Zeghloul, Abderrahim. "Comparaison de la propagation en fatigue des fissures courtes et des fissures longues." Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb37619253w.

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50

Yeh, Sheng-Wen, and 葉聖文. "The Study Of Hot Cracking On The Scandium–Aluminum Alloys." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/69186729921134943071.

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碩士
國立交通大學
工學院精密與自動化工程學程
100
The “Spot-Varestraint Test” was applied to assess the sensitivity of four scandium–aluminum alloys –M6, M7E, M7B and M9H4 – to hot cracking from welding. In these experiments we applied Gaseous Tungsten Arc Welding (GTAW) without an added feeder. Samples with varied thermal cycles and with one or two welding energy inputs on the same welding seam were prepared, The stereoscopic microscope is used to observe hot cracking and the software for computer image acquisition and analysis measurement are used to measure and to analyze the length of hot cracks in the fusion and the heat-affected zones with varied augmented applied strains and thermal cycles. The optical microscopy (OM) and scanning electron microscopy (SEM) to observe the microstructure of crack formation with different amount of scandium the containing scandium aluminum for welding hot crack sensitivity. The results indicate that the number of cracks increases with increasing augmented strain. This phenomenon occurs in both the fusion and the heat-affected zones. The number of thermal cycles also has a significant influence on the heat-affected zone; the number of hot cracks increases, especially in the heat-affected zone of the metal weld, with increasing number of thermal cycles. The hot cracking sensitivity under different augmented strain and number of the thermal cycles shows that the crack length of M6 is the length, M7B and M7E an similar in the hot cracking sensitivity, the M9H4 is the shortest. The compositions of these four alloys show that M6, M7B and M7E have similar tendencies to be subject to hot cracking, greater than M9H4. With increasing number of thermal cycles, the hot cracks show the same tendency, M9H4 > M7E> M7B> M6. On cracking fracture surface, the experiment results show three distinct regions in the fusion zone, dendritic area (D area), dendritic-flat area(D-F area) and the flat area (F area), to confirmed the fusion zone belong to the solidification cracking. In the heat affected zone, the results indicate the brittleness fracture phenomenon along grain boundary on the fracture surface, and it is presented in the form of liquefied hot cracking. The EDS analysis for the partial melting zone shows M7B and M7E does not produce Cu and Mg segregation increases. These two kinds of alloys are purely grain boundary liquation.M6 and M9H4 have the Cu element segregation in the vicinity of grain boundaries, and are the Cu segregation increases with the number of thermal cycles. So that the M6 and M9H4 are segregation-induced liquation mechanism in the partially melted zone.

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