Revealing the mechanisms of exfoliation corrosion and stress corrosion cracking for an Al-Zn-Mg-Cu alloy after continuous retrogression and re-ageing treatment

Continuous retrogression and re-ageing (CRRA) treatment is designed to achieve an optimal balance between the strength and corrosion performance of an Al-Zn-Mg-Cu alloy. The findings suggest that intergranular corrosion predominantly affects the T6 sample, with extensive propagation into the bulk resulting in delamination and intergranular cracking. In contrast, crystallographic pitting dominates in the CRRA-treated sample, which effectively mitigates exfoliation corrosion and suppresses intergranular cracking. The different corrosion resistance between the T6 sample and the CRRA-treated sample is attributed to the disparate distribution of Cu in the alloy, which influences the corrosion rate, the types of corrosion and corrosion propagation path.