Flow Behavior and Microstructural Evolution of 7A85 High-Strength Aluminum Alloy During Hot Deformation
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7A85 aluminum alloy is defined as a member of high-strength 7xxx series aluminum alloy (Al-Zn-Mg-Cu alloy system) and its property levels are better than those of 7085 aluminum alloy due to its more optimized chemical composition and higher purity as well as special processing. Exceptional combinations of strength and fracture toughness together with lower quench sensitivity designate 7A85 aluminum alloy a suitable alternative to typical high-strength 7050 aluminum alloy as structural material for the aircraft structure components.[1,2] For the successful application of high-strength aluminum alloy in aerospace industries, the hot deformation is a necessary approach to make the critical components. On the one hand, the final microstructures and properties of products depend on hot deformation parameters, such as temperature and strain rate. On the other hand, microstructural changes of alloys in turn affect the flow behavior, and thus affect the hot forming process.[3–6] So, the studies on XINGANG LIU, SHUANG HAN, SHUAI YANG, MIAO JIN, and BAOFENG GUO are with the School of Mechanical Engineering, Yanshan University, Qinhuangdao 066004, P.R. China. LEI CHEN is with the National Engineering Research Center for Equipment and Technology of Cold Strip Rolling, Yanshan University, Qinhuangdao 066004, P.R.China. Contact e-mail: [email protected] TIANHONG MAO is with China National Er-zhong Group Company, Deyang 618000, P.R. China. Manuscript submitted October 8, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
deformation behaviors and microstructural evolution of high-strength aluminum alloy during hot working are significant and contributed to understanding the deformation mechanism of aluminum alloy under different hot working conditions. In the past, many investigations on the mechanical and microstructural behaviors of Al-Zn-Mg-Cu alloy during hot deformation were reported. On the microstructural evolution, in most of the previous reports, the occurrence of dynamic recrystallization (DRX) was observed after hot deformation.[7–9] Several DRX mechanisms at different deformation conditions were proposed, and continuous dynamic recrystallization(CDRX) characterized by converting subgrain structures to high-angle grains was considered to be more prone to occur.[10–12] Moreover, some reports [13–15] showed that the Zener–Hollomon parameter (Z-parameter), which is widely used to characterize the combined effect of strain rate and deformation temperature on the hot deformation process, determined the development of DRX in aluminum alloys. As reported, DRX only occurred below a critical Z-value. Deng et al.[16] found a continuous decrease in very low-angle boundaries with misorientation between 2 and 5 deg and a steady increase in the higher angle boundaries, especially with misorientation between 30 and 60 deg after hot deformation of 7050 aluminum alloy, when the Z-value decreased. On the mechanical characteristics, the constitutive equations for various 7xxx series aluminum alloys were developed from the experimentally m
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