Optimizing corrosion behaviours of an Al–Zn–Mg–Cu alloy through cold rolling and artificial ageing

The study optimizes the corrosion resistance of an Al–Zn–Mg–Cu alloy by changing the sequence of cold-rolling (CR) and artificial ageing (AR) processes. The samples are artificially aged at 150 ºC for 45 min and subsequently cold-rolled by the cumulative deformation of 10%, 20%, 30%, and 36%, which are denoted as CR + AR samples. In comparison, the CR + AR samples are cold-rolled by a cumulative 30% reduction in thickness and then aged at 150 ºC for various periods from 1 min to 8 h. The hardness of AR + CR samples increases from 158.7 to 213.4 HV with the increasing cumulative CR passes. But in the CR + AR group, it increases from 166.2 to 228.3 HV for 30-min ageing and decreases slightly with the ageing time. η phase precipitates during artificial ageing are the dominant strengthening factor. The improved corrosion resistance in CR + AR samples is mainly attributed to the formation of discontinuous grain-boundary precipitates that obstruct the anodic corrosion pathway. The optimal corrosion resistance is achieved by 30% cold rolling and ageing at 150 ºC for 8 h. This sample owns the highest impedance (ǀZǀ = 985.0 Ω cm²) and the most positive corrosion potential (E_corr = −0.748 V).