Corrosion resistant and high-strength dual-phase Mg-Li-Al-Zn alloy by friction stir processing

Abstract

Magnesium is the lightest structural metal, and alloying with lithium makes it even lighter. However, multi-phase Mg-Li alloys typically undergo rapid corrosion, and their strength decreases at room temperature due to natural age-softening. Here, we engineer a rapidly degrading dual-phase Mg-Li-Al alloy to be durable via friction stir processing followed by liquid CO2 quenching. The best performing alloy has a low electrochemical degradation rate of 0.72 mg·cm−2· day−1, and high specific strength of 209 kN·m·kg−1. We attribute this electrochemical and mechanical durability to its microstructure, which consists of a refined grain size of approximately 2 µm and dense nanoprecipitates. This microstructure suppressed the formation of the detrimental AlLi phase, and an aluminium-rich protective surface layer also formed. This processing route might be useful for designing lightweight and durable engineering alloys.