Enhanced corrosion resistance and mechanism of a novel Mg-4Li-6Zn-1Y-0.2Ca alloy through cross-rolling and Ca microalloying

Abstract

In this study, a novel Ca-microalloyed Mg-4Li-6Zn-1Y-0.2Ca alloy was developed to address corrosion issues associated with the fragmentation of icosahedral quasicrystalline phase (I-phase) eutectic pockets and the non-uniform distribution of precipitates in conventionally processed Mg-Li-Zn-Y alloys. The effects of cross-rolling (CR) at reduction ratios of 20 %, 40 %, and 80 % on the microstructural evolution and corrosion behavior were systematically investigated. Cross-rolling significantly promoted dynamic recrystallization, reducing the average grain size from 59.6 μm in the annealed state to 2.4 μm at 80 % reduction. It also fragmented and dispersed coarse secondary phases (I-Mg₃Zn₆Y, W-Mg₃Zn₃Y₂, and Ca₂Mg₆Zn₃), while promoting the uniform precipitation of nanoscale LiMgZn particles. As the reduction ratio increased, corrosion behavior shifted from severe localized attack to more uniform degradation. Annealed samples formed loose and discontinuous Mg(OH)₂/CaCO₃ corrosion layers that provided limited protection, whereas the CR80 % samples developed compact and continuous Mg(OH)₂-based layers incorporating CaCO₃ and Li₂CO₃. Consequently, the corrosion rate of the CR80 % sample decreased to 1.34 mm/y, representing a 77 % reduction compared to the annealed state (5.71 mm/y). This improvement is attributed to the refined microstructure and uniform distribution of LiMgZn precipitates, which enhanced the compactness and integrity of the corrosion product layer, thereby improving corrosion resistance.