Constitutive Modeling of Hot Deformation Behavior of the AA6063 Alloy with Different Precipitates
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INTRODUCTION
THE 6xxx series aluminum alloys are widely used in automotive and aerospace applications because of their high strength-to-weight ratio.[1–5] During the manufacturing of these alloy products, the cast ingots are deformed by successive hot deformation (rolling/extrusion) passes.[6] As precipitation hardening is a main strengthening mechanism in these alloys, the distribution of solute atoms in the matrix, which are mainly affected by predeformation heat treatment and the hot deformation conditions, plays a key role in the alloy strength and work hardening/softening behavior.[7,8] The thermomechanical treatments applied during the hot deformation also affect the resulting microstructure and therefore the final alloy properties.[9–14] Hence, in order to achieve the desired final microstructures and properties, it is necessary to carefully control the thermal and thermo-mechanical treatments. One method of understanding the relationship between the microstructure and properties of the alloy in the thermomechanical treatment is to employ a physically based model that predicts the microstructural evolution at each stage of the treatment. In particular, the prediction of flow behavior is the main necessity in hot deformation modeling. Although several studies concerning the hot flow behavior of aluminum alloys have been carried out in the past,[8,15–19] to our knowledge, there is no mechanism-based model to predict the flow behavior of heat-treatable aluminum alloys under hot deformation conditions by considering the preaging treatment, NOZAR ANJABIN, Ph.D. Candidate, and ALI KARIMI TAHERI, Professor, are with the Department of Materials Science and Engineering, Sharif University of Technology, Tehran 11365-9466, Iran. HYOUNG SEOP KIM, Professor, is with the Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang 790-784, South Korea. Contact e-mail: [email protected] Manuscript submitted February 5, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS A
preheat conditions, and work hardening, as well as, work softening at different conditions of deformation. The flow strength of the age-hardenable aluminum alloy at high temperature is often described by an empirical constitutive equation,[8,15] or by an artificial neural network (ANN) method[20,21] which considers only the effect of deformation parameters on flow stress. The effect of the concentration of alloying elements in the matrix has also been introduced by incorporating a solute-dependent parameter in empirical constitutive equations,[18] but the effect of precipitates on the hot flow stress has not been considered in that study. Furthermore, these methods do not account for the microstructural evolution during deformation in the aluminum alloys. On the other hand, there have been a vast number of investigations on modeling static aging,[22,23] and also the precipitates’ dissolution while heating the aged alloys.[22,24] For example, Vermolen et al.[24] proposed the finite volume method to handle the dissolution of p
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