Deformation Behavior and Mechanical Properties of AA7075 During Pre-hardened Aluminum Alloy Hot Forming Process

The long production cycle and high energy consumption limit the widespread application of the Hot Form Quench (HFQ^®) process. Hence, a novel hot stamping process was proposed, known as pre-hardened aluminum alloy hot forming (PAHF), which is of high quality, efficiency, and performance. In this project, the deformation behavior, microstructure evolution, and mechanical properties of AA7075 in PAHF were studied by uniaxial isothermal tensile tests and microstructure observations. The flow stress decreased with the increase of deformation temperature and the decrease of strain rate, exhibiting a thermal softening and strain rate sensitivity. The elongation reached at least 15.85% at higher temperatures, which was 50% higher than that at room temperature. At temperatures ≤ 400°C, AA7075 exhibited higher elongation in HFQ^® than in PAHF. However, the elongation in HFQ^® at 450°C/1 s⁻¹ decreased to 16%, comparable to the lowest in PAHF at 15.3%. At a deformation temperature of 200°C and a strain rate of 1 s⁻¹, the peak strength decreased from original 571.2 MPa to 450.9 MPa and decreased even more under other deformation conditions. The grain size remains unchanged after deformation. As the deformation temperature increased, the fracture characteristics in PAHF gradually evolved from intergranular fracture to ductile fracture.