LAUSR

Hot Form Quench (HFQ®) is an advanced technology for forming complex-shaped parts in automobile industry. In the present work, the effects of HFQ® conditions on microstructure evolution and bake-hardening (BH) response of AA7075 were investigated by means of transmission electron microscopy (TEM), x-ray diffraction, electron back-scattered diffraction and microhardness tests. The results show that, with pre-strain increasing, more η and η′ precipitates appear. The size of η′ changes little but η becomes larger. The reason for the high volume fraction of precipitates is the high-density dislocations which can act as the effective nucleation sites. Meanwhile, it is revealed that the effect of precipitation strengthening and dislocation strengthening has been enhanced gradually. Nevertheless, the solid-solution strengthening effect is weakened and the effect of grain boundary strengthening changes slightly. Compared with water quenching condition, more large-sized η phase appears easily in air-cooling condition, which was recognized as the reason for the decrease in hardness. As evidenced in the analysis of HRTEM and TEM, no precipitates existed in the sample with solid-solution state and a large number of Guinier–Preston (GP) zones were found in 10% pre-strain + pre-aging sample, indicating pre-aging enables to promote GP zone nucleation, which may bring an improvement in BH response.