Synergistic effects of Zn content and solution treatment duration on the corrosion behavior of highly alloyed Al–Zn–Mg–Cu alloys

Abstract

Highly alloyed Al–Zn-Mg-Cu alloys with elevated Zn contents are promising candidates for next-generation ultra-high-strength structural applications. In this work, five Al–Zn–Mg–Cu-Zr alloys containing 8–12 wt.% Zn were fabricated, and two solution treatment durations (1 h and 2 h) were employed to investigate their effects on corrosion behavior. The results indicate that the alloys primarily consist of α-Al and MgZn2 phases. After hot rolling and T6 treatment, the MgZn2 phases become fragmented and are discontinuously distributed within the matrix and along grain boundaries. The increased solution treatment duration promotes the dissolution of MgZn2 phases and improves matrix homogeneity. Electrochemical measurements reveal that corrosion resistance is influenced by Zn content in a non-monotonic manner, whereas the alloys subjected to the longer solution treatment consistently exhibit superior corrosion resistance. Immersion and intergranular corrosion (IGC) tests show that corrosion damage is dominated by uniform corrosion and pitting corrosion rather than IGC. The maximum pit depth increases with increasing Zn content but decreases with prolonged solution treatment. The overall corrosion behavior is governed by the combined effects of MgZn2 secondary phases, matrix electrochemical activity, and the evolution of the corrosion-product layer. These findings provide insight into the corrosion mechanisms of highly alloyed Al–Zn–Mg–Cu alloys and offer guidance for optimizing the balance between alloying level and corrosion resistance.