Effects of aging mechanisms on the exfoliation corrosion behavior of a spray deposited Al–Zn–Mg–Cu–Zr aluminum alloy

Al–Zn–Mg–Cu–Zr alloys are very important aeronautical materials because of their low density, high strength, and high ductility. Corrosion failure is a significant factor causing aviation accidents, which should be investigated to develop an aeronautical material but has not been done yet. In this work, the effects of aging mechanisms on the exfoliation corrosion behavior of a spray deposited Al–Zn–Mg–Cu–Zr alloy were investigated. Natural aging (NA), single-stage aging (SA), and retrogression and re-aging (RRA) were treated on specimens before exfoliation corrosion testing. Corrosion attacks were evaluated using the optical microscope (OM) and scanning electron microscope (SEM). Corrosion mechanisms were deduced on the basis of polarization curve results and an equivalent circuit. The RRA sample exhibited the smallest corrosion attack among the three samples, while the NA sample showed the largest corrosion attack. Intergranular corrosion on grain boundaries was discussed to understand the exfoliation corrosion process in the RRA sample. The amount and size of precipitates in grain interior and grain boundary of RRA samples are larger than those in SA and NA samples, leading to the low corrosion susceptibility of the RRA sample.