Effect of Forming-Die Temperature on Microstructure and Mechanical Properties of AA7075 Alloy During HFQ® Process

Hot forming quenching-integrated process (HFQ®) has aroused widespread attention as a new stamping technology recently for producing complex-shaped structural parts. Forming-die temperature plays a critical role on tailoring the microstructure and mechanical properties of the final hot formed parts. In this paper, the HFQ® + pre-ageing (PA) + simulated baking (SB) process was used for AA7075 alloy to investigate the changes in microstructure and mechanical properties as a function of forming-die temperature ranging from 25 to 400 °C. The results show that the volume fraction of η′ precipitates drops and part of η′ phase becomes coarsened after HFQ® + PA + SB process with 25–200 °C forming dies, when compared with the base metal. As forming-die temperature ranges from 300 to 400 °C, a large number of η phase can be found. The overall mechanical properties of U-shaped parts were compared under various forming-die temperature. The forming-die temperature of 200 °C was selected where the AA7075 alloy U-shaped parts exhibit good combination of strength and ductility, i.e., the value of PSE being approximately 7534 MPa·%, which suits for the industry production.