Influence of heat treatment on phase distribution and micro-galvanic corrosion in AZ91 and Mg-Gd-Y Alloys: A comparative analysis

This comprehensive study investigated the microstructure evolution and corrosion mechanisms of AZ91 and MgGd-Y alloys subjected to various heat treatments, including as-cast, T4, and T6 conditions, revealing differences between Mg-Al and Mg-RE. It was found that the corrosion resistance of AZ91 improved with heat treatment, with T6 demonstrating the highest resistance. In contrast, the Mg-Gd-Y alloy displayed a different trend, with T4 treatment resulting in the poorest corrosion resistance due to the presence of noble phases that exacerbated micro-galvanic corrosion. Scanning Kelvin probe force microscopy (SKPFM) measurements revealed significant potential differences between phases, elucidating their contributions to corrosion behavior. Owing to the nonuniform distribution of the second phase, the AZ91 alloy predominantly experienced localized corrosion, with the resulting corrosion product film exhibiting a porous and fragile structure. In contrast, in the Mg-Gd-Y alloy, the second phase formed an interconnected skeleton framework that actively contributed to oxidation film formation, thereby generating a compact and protective corrosion product film.