Precipitation behavior and properties of an Al-8.26Zn-1.95Mg-1.89Cu-0.08Sc-0.17Zr alloy with different dislocation morphologies via pre-treatment

Effects of pre-treatment (either pre-deformation or composed of pre-aging and pre-deformation prior to aging) on the dislocation morphologies and subsequent precipitation, corrosion behaviors, and mechanical properties of a novel Al-8.26Zn-1.95Mg-1.89Cu-0.08Sc-0.17Zr (wt.%) alloy were investigated. Pre-existing Al3(Sc, Zr) dispersoids can pin dislocations induced by pre-deformation before aging to form dislocation cells and cell walls. As a result, bimodal microstructures are formed during the subsequent aging process, with coarse precipitates dispersed along dislocation walls and fine precipitates inside dislocation cells. Meanwhile, dislocations pinned by Al3(Sc, Zr) dispersoids nearby grain boundaries inhibit the diffusion of solutes towards grain boundaries, which can modify grain boundary features by decreasing the potential difference between grain boundaries and grain interiors, and reducing precipitation-free zone width and grain boundary precipitate size. In particular, pre-aging prior to pre-deformation makes the dislocation distribution more uniform, which increases the volume fraction of nanoprecipitates without significant coarsening and further improves the grain boundary characteristics. Compared with the traditional T74 treated sample, these multiple microstructures significantly enhance the corrosion resistance of the alloy with less strength degradation. This study offers novel insights into the strengthening and corrosion mechanisms of pre-treated Al–Zn–Mg–Cu alloys with Zr and Sc microalloying.