Study on High-Temperature Mechanical Properties and Forming Limit Diagram of 7075 Aluminum Alloy Sheet in Hot Stamping
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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.
Keywords7075-T4 aluminum alloy sheet FLD Flow behavior HFQ NTSF transition
The joint support from the National Natural Science Foundation of China (Grant No. 51475280) and the Shanghai Automotive Industry Science and Technology Development Fund (Grant No. 1610) is gratefully acknowledged.
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