Mechanism for enhancing the corrosion resistance in a spray deposition aluminum alloy Al-8.31Zn-2.46Cu-2.07Mg-0.12Zr

The ultra-high strength deformed aluminum alloy 7055 has been used as numerous components in aerospace field. Enhancing the corrosion resistance of 7055 alloy is always the emphasis and focus of current researches. In this article, we intentionally introduced an additional high-temperature pre-ageing process into the conventional T6 heat treatment of the spray deposited aluminum alloy Al-8.31Zn-2.46Cu-2.07Mg-0.12Zr to investigate the effect of pre-ageing time on the microstructure and property responses. We found that the corrosion resistance was significantly improved due to the formation of considerable amount of η phases, which served as the sites of grasping and releasing hydrogen atoms to reduce the concentration of hydrogen. The separated η phase formed on the grain boundary could break the consistency of original grain boundary, which would reduce the electrochemical driving force of intergranular corrosion and break the anode corrosion channel. The η phase on grain boundaries and (η′+η) inside grains were collectively served as positive electrode, while the matrix were served as the negative electrode, which leads to the etch of grain and grain boundary simultaneously.