Study on High-Temperature Mechanical Properties and Forming Limit Diagram of 7075 Aluminum Alloy Sheet in Hot Stamping
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JMEPEG https://doi.org/10.1007/s11665-019-04436-x
Study on High-Temperature Mechanical Properties and Forming Limit Diagram of 7075 Aluminum Alloy Sheet in Hot Stamping Ruiying Gu, Qi Liu, Shichao Chen, Wurong Wang, and Xicheng Wei (Submitted January 4, 2019; in revised form September 10, 2019) To improve the formability of aluminum alloy sheets and avoid springback, a newly developed forming technique, HFQ (heat-forming-quenching), has attracted attention in the automobile industry. In this work, a high-temperature tensile test and the Nakazima hemispherical punch method were used to simulate the HFQ process to study the high-temperature flow behavior and formability of 7075-T4 aluminum alloy sheet. The results demonstrated that elongation to fracture was positively correlated with temperature, changing from 15% in the quenching state to 26.1% at 440 °C. Strain rate sensitivity was found to vary according to the strain rate due to the coupled competition between temperature and the strain rate. It was concluded that the necking to shear fracture transition of 7075 based on HFQ occurred at 358 °C. In addition, the forming limit of the alloy sheet decreased with the increasing waiting time. The temperature field distribution of the alloy sheet for different waiting times at a forming velocity of 10 mm/s was obtained by thermomechanical coupled simulations. Different modes of rupture indicated different thermomechanical behaviors due to the different initial temperatures under hot stamping. Keywords
7075-T4 aluminum alloy sheet, FLD, Flow behavior, HFQ, NTSF transition
1. Introduction Due to the stringent greenhouse gas emission standards and comprehensive promotion of the substitution of renewableenergy vehicles for traditional-fuel vehicles, an increasing number of automotive industries have emphasized their strategies of using lightweight materials to achieve fuel efficiency, emissions reduction and product recyclability (Ref 1). Within the last decade, 7000 series (Al-Zn-Mg-Cu) aluminum alloys have attracted many researchersÕ attention as a mass-saving replacement for some high-strength steels due to their excellent strength-to-density ratio, bend stiffness and corrosion resistance. Nevertheless, poor formability at room temperature (RT), high springback and high cost are the problems encountered in the application of 7000 series aluminum alloys. Therefore, various advanced hot forming processes are now under investigation to solve these problems. Heat-forming-quenching proposed by Garrett et al. (Ref 2) is one such promising hot processing technology that ensures the accurate fabrication of complex automotive parts and is applicable to any aluminum alloy sheet. This approach consists of a solution heat treatment
Ruiying Gu, Qi Liu, and Shichao Chen, School of Materials Science and Engineering, Shanghai University, Shanghai, PeopleÕs Republic of China; and Wurong Wang and Xicheng Wei, School of Materials Science and Engineering, Shanghai University, Shanghai, PeopleÕs Republic of China; and State Key Laboratory o
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