Effect of Heat Treatment Conditions on Mechanical Properties and Precipitates in Sheet Metal Hot Stamping of 7075 Aluminum Alloy

Abstract

Due to the low formability at room temperature, the application of 7XXX aluminum alloy sheet is limited. The hot forming-quenching process is an effective technology for the forming of some complex-shaped aluminum alloy parts. In this study, heat treatment was integrated with sheet metal stamping to improve formability and strength of 7075 aluminum alloy sheet. The effect of different heat treatment parameters on the strength of 7075 aluminum alloy sheet was investigated under stamping and heat treatment integrated process, based on which the optimal heat treatment combination was determined. Furthermore, the evolution of precipitates with the variation of aging temperature and time was studied by transmission electron microscope. In addition, quenching under water-cooled dies was conducted for 7075 aluminum alloy sheet after solution heat treatment, in which the hardness under die quenching was compared with that of underwater quenching and air quenching. Finally, the tensile test illustrates that, after die quenching and successive artificial aging, the tensile strength of 7075 aluminum alloy sheet was achieved at around 548 MPa. Shear fracture with long strip step-shaped pattern was observed in aging state.