Achieving strength and ductility synergy via a nanoscale superlattice precipitate in a cast Mg-Y-Zn-Er alloy

Precipitation strengthening is one of the most promising methods to develop magnesium (Mg) alloys. However, the nerve-wracking fact is that the cast Mg alloys always have coarse second particles, which inevitably leads to a poor ductility. In this study, a novel nanoscale superlattice precipitate (NSP) with a superior strengthening effect is developed by rare-earth Er alloying. The newly-developed cast Mg-Y-Zn-Er alloy possesses a yield strength of 154 MPa, a tensile strength of 234 MPa, and a total elongation of ∼ 13%. The NSPs is systematically investigated, using transmission electron microscopy and first-principles calculations. The NSP with an average radius of 4 nm has a five periodic supercell structure enriched with Zn, Y, and Er atoms. The first-principles calculations indicate that Zn, Y, and Er atoms are apt to segregate on the (112¯1) plane. The excellent strength is contributed mainly by the ordering strengthening of the NSPs. The addition of Er enhances the multiplication of dislocations and the activation of 〈c + a〉 dislocation system during deformation, contributing to the ductility.