Effect of Thermomechanical Processing on Microstructure, Texture Evolution, and Mechanical Properties of Al-Mg-Si-Cu All
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lloy sheets have been increasingly used in the automotive industry due to their excellent properties, such as favorable strength-to-weight ratio, high formability, good corrosion resistance, and age-hardening response. Because heat-treatable Al-MgSi-Cu alloys possess high deep drawability before stamping and relatively high strength after paint baking through precipitation or age hardening, they have great potential for usage in car body outer panels.[1–3] The competition between aluminum alloys and steels is becoming more and more intense in the automotive industry, and the weaker deep drawability of Al-MgSi-Cu alloys in the fully annealed condition may restrict their application.[4] Therefore, improvement of their deep drawability is crucial. The deep drawability is conventionally characterized by the normal anisotropy X.F. WANG is with the Faculty of Mechanical Engineering and Mechanics, Ningbo University, Zhejiang 315211, P.R.China. Contact email: [email protected] M.X. GUO, Y. CHEN, J. ZHU, J.S. ZHANG, and L.Z. ZHUANG are with the State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, P.R.China. Manuscript submitted January 28, 2017. METALLURGICAL AND MATERIALS TRANSACTIONS A
(average r value) and the planar anisotropy (Dr value), and materials with high average r and low Dr values usually show good deep drawability.[5] Crystallographic textures are known to influence the deep drawability significantly. In general, some textures, such as a c fiber texture ({111}huvwi) or random texture with relatively high r and low Dr values, are suitable for deep drawability.[6–8] Numerous research results[9–14] have revealed that textures are controlled by a variety of processing parameters and chemical composition. In recent years, many attempts have been made to optimize textures. It has been well documented[9–11] that intermediate annealing, solution heating rate, and final cold rolling reduction after intermediate annealing have significant effects on the microstructure, texture, and r values of Al-Mg-Si-Cu alloys. It was found that the intermediate annealing with moderate temperature, solution treatment with high heating rate, and low final cold rolling reduction always tend to develop relatively weak textures and result in high r values. In addition, some alloy elements, such as Fe, Mn, Zr, Cr, and Zn, also play important roles in microstructure and texture development. It was demonstrated[7] that coarse Fe-rich phases are favorable for grain refining and texture weakening. Zhuang et al.[13] reported that some dispersoid-forming elements, such as Mn, Zr, and Cr, could
refine the grain structure due to the pinning effect and weaken CubeRD and Goss {110}h001i orientations. According to previous observations,[14] it appears that, compared with the Zn-free alloy sheet, the sheet with high Zn content possesses a coarser grain structure, stronger recrystallization texture, and lower r value after solution treatment. It is commonly accepted that a specific alloy alwa
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