Experimental and Numerical Investigation on Strengthening Behavior of 7075 Aluminum Alloy Sheets in Hot Forming–Quenching Integrated Process

Abstract

7xxx-Series aluminum alloys have a wide application prospect in the automotive industry due to its higher strength than other series of aluminum alloy. However, little literature has been reported on the formability and strengthening behavior of 7xxx-series aluminum alloys for the structural components of body in white (BIW). In this paper, the formability and strengthening behavior of 7075-T6 were investigated systematically under hot forming–quenching (HFQ) integrated process. First, compound dies with rod-heated blank holder and water-cooled lower punch and upper die were set up for experiment. For low adhesion friction and high cooling rate, the optimum blanking temperature was determined as 400 °C. Second, forming state, thickness distribution, and temperature field were investigated through experiment and finite element simulations. A-pillar reinforcement panel was successfully manufactured based on the simulation results. The simulation data showed that the maximum thinning rate of the whole part is about 14.25%, and the maximum thickening rate is about 1.95%. Third, the formability and quench sensitivity of u7075-T6 were achieved through time–temperature–transformation (TTT) curves and continuous cooling precipitation (CCP) diagrams combined with the thermo-mechanical coupling simulation. Finally, the strengthening was measured by testing the tensile strength and Vickers hardness at different positions of formed parts after artificial aging process. The testing result showed that the strength of the formed parts after artificial aging at 120 °C for 24 h were 162.7–172.2 HV and 505–528 MPa, respectively.