Influence of retrogression and re-aging treatment on corrosion behaviour of an Al-Zn-Mg-Cu alloy

► Compared with T6 temper, the alloy under RRA temper is less susceptibility to IGC, EXCO and SCC, which indicating that the susceptibility of the Al-Zn-Mg-Cu alloy to IGC, EXCO and SCC can be decreased by the RRA process. ► The exfoliation corrosion susceptibility of the alloy was investigated by means of electrochemical impedance spectroscopy, and the relationship between exfoliation corrosion susceptibility and impedance spectroscopy was established. The appearance of two time constants indicates the onset of the delamination. Hence, the corrosion susceptibility of the alloy can be stated by comparing with the instant of the two time constants. ► Simulated EIS parameters are able to quantitatively determine the degree of the exfoliation susceptibility by equivalent circuit analysis. For instance, the polarization resistance of the porous layer (Rpo) for the RRA sample is higher than that of the T6 sample, which permits to conclude that the RRA treatment can increase the electrochemical corrosion resistance of the Al-Zn-Mg-Cu alloy.