Microstructure and properties of aluminium alloy 6082 formed by the Hot Form Quench process

During a process development trial, two identical structural automotive parts were formed from a rolled sheet of commercial 6082 Al alloy by Hot Form Quench (HFQ). The rapid transitional contact between the sheet and the die set during die closing imposed a range of complex cooling histories on different locations in the parts. After in-die quenching, one HFQ part was naturally aged at room temperature, while the other was peak-aged at 185 °C for 7 h. The microstructure was compared at two extreme locations; the flange, where die contact is instantaneous leading to immediate rapid cooling, and the sidewall, where the material cools more slowly in air before rapid quenching. After HFQ, some small quench induced grain boundary precipitates were observed in the sidewall specimen but not in the flange. However, subsequent artificial ageing led to a convergence of the microstructures. Consequently, hardness was found to be constant at both locations, and no loss of hardening potential was observed in either case compared with T6 sheet. Samples of the as-received material were subjected to selected quench-hold-quench-age experiments to mimic the HFQ microstructures. Tensile tests showed that the ductility and failure mechanism is insensitive to the small differences in grain boundary microstructure as observed in the HFQ component.