Tailoring Strength and Corrosion Resistance of Al-Zn-Mg-Cu Alloy by Double Aging Processes

This study investigated the effects of double aging processes on the tensile properties and salt spray corrosion resistance of an Al-Zn-Mg-Cu alloy. The mechanisms by which microstructural evolution influences these properties were elucidated using tensile testing, salt spray corrosion testing, electrochemical measurements, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results indicate that, under double aging processes, increasing the duration or temperature of either the first- or second-stage aging leads to a slight decrease in tensile strength but a significant improvement in salt spray and electrochemical corrosion resistance. This is attributed to the gradual coarsening of intergranular and grain boundary precipitates, a decrease in their number density, and a widening of the precipitate-free zone (PFZ). Furthermore, the second-stage aging exerts a more pronounced influence on the alloy’s properties and microstructure than the first-stage aging, and their quantitative contributions are systematically distinguished. The alloy treated with the 110 °C/3 h + 155 °C/20 h double aging processes exhibits the optimal overall performance, achieving a better balance between strength and corrosion resistance compared to conventional T6 treatment.