Modeling of Strain Hardening in the Aluminum Alloy AA6061
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THE influence of aging on mechanical properties of Al-Mg-Si alloys is often viewed for its effect on yield strength. The influence of aging on the work-hardening behavior is, however, also very important from industrial and scientific viewpoints. Understanding the behavior of materials during deformation is essential in optimizing production processes, which are based on forming, e.g., deep drawing and rolling. There are mainly two aspects in work hardening: dislocation accumulation and dislocation annihilation.[1–6] Modeling and interpreting the work-hardening behavior of Al-Mg-Si alloys is much more complex than for singlephase alloys. This complexity is due to the presence of precipitates and their related solute distribution. Precipitates alter the mean free path of dislocations. They can also actively act as sites where dislocations are pinned and accumulated. Another important effect of precipitates is their influence on the solute content in the matrix. Alloying elements in solid solution are known to decrease the dynamic recovery rate by changing stacking fault energy or causing solute drag effects.[7] The workhardening behavior of Al-Mg-Si alloys is also influenced by the nature of precipitates. Shearable precipitates, for example, might lead to flow localization on the glide planes, where the precipitate strength is decreased ABBAS BAHRAMI, Post-Doc Researcher, and ALEXIS MIROUX, Senior Researcher, are with the Materials innovation institute (M2i), Delft University of Technology, Mekelweg 2, 2628 CD, Delft, The Netherlands, and also with the Department of Materials Science and Engineering, Delft University of Technology. Contact e-mails: [email protected], [email protected], JILT SIETSMA, Professor, is with the Department of Materials Science and Engineering, Delft University of Technology. Manuscript submitted August 29, 2012. Article published online January 12, 2013 METALLURGICAL AND MATERIALS TRANSACTIONS A
because of shearing during deformation. Non-shearable precipitates, on the other hand, might store both elastic energy and dislocations, leading to larger hardening rates compared to single-phase alloys. In addition to the effects of the nature of precipitates, their morphology can also be very important. Lath-shaped precipitates, for example, support larger local elastic stresses and thus give higher contribution to the hardening of alloys as compared to the precipitates of spherical morphology.[8] Several physically based approaches have been proposed to model work hardening of metallic materials, from simple one-variable models, like the Kocks, Mecking, and Estrin, KME, model,[9] to models including a more refined description of the microstructure.[3] Application of these models to simulate work hardening of Al-Mg-Si alloys has been reported.[6–12] These applications used numerical methods to calculate the microstructure and flow stress change with deformation. In the present paper, a simple analytical work-hardening model is derived, based on the KME approach, coupled with a precipitation model and
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