Synchronous improvement of strength and corrosion resistance by an improved variable-rate non-isothermal aging process in Al-Zn-Mg-Cu alloy

Overcoming the trade-off between high strength and excellent corrosion resistance of Al-Zn-Mg-Cu alloys is a challenging problem. In this study, a variable-rate non-isothermal retrogression and re-aging (VNRRA) process has been proposed to solve this problem in AA7085 aluminum alloy and is compared with conventional isothermal aging treatments (T6, T77, and T73 tempers) in detail. This improved aging process consists of a slowly heating stage at low temperature, a rapidly heating stage at elevated temperature and an isothermal aging stage at 120 degrees C, and can synchronously improve the strength and corrosion resistance of Al-Zn-Mg-Cu alloy. Precipitation behaviors, mechanical properties and corrosion resistance have been systematically investgated. Compared with T6 temper, the VNRRA sample exhibits higher hardness and yield strength, which can be attrubuted to the high-density eta' precipitates that fully grow up but are not severely coarsened in Al matrix. Meanwhile, the corrosion resistance of the optimal VNRRA specimen is comparable with that of T77-treated specimen, which is closely linked with the discontinuous distribution of Cu-rich GBPs.