Nano-scale precipitate evolution and mechanical properties of 7085 aluminum alloy during thermal exposure

As a new generation of Al-Zn-Mg-Cu alloy, 7085 aluminum alloy is a promising structural material in the field of aerospace industry. However, research on its thermal stability is still lacking. In the present work, thermal exposure was carried out on the T7452-treated 7085 aluminum alloy under different temperatures (100 °C, 125 °C, 150 °C and 175 °C) for 500 h. Variations of tensile properties and hardness were exhibited. The microstructure, nano-scale precipitates and fracture characteristics of the alloy were investigated using optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that with the increase of exposure temperature, the strength and hardness increase first and then decrease while the elongation and the reduction of area increase continuously as compared to those of the non-thermal exposed alloy. The transformation from η′ phase to η phase during thermal exposure occurs continuously during thermal exposure. In addition, as the exposure temperature increases, the average dimensions of precipitates and the average spacing of neighbor precipitates become larger. The influence of precipitates on mechanical properties of the alloy is discussed.