A near-isotropic ultrafine-grained Mg-Gd-Ag alloy with high strength-ductility synergy

Abstract

It is challenging to develop Mg alloys with high strength-ductility synergy and isotropic mechanical properties. An industrial-scale ultrafine-grained (UFG) Mg-10.6Gd-2Ag wt. % alloy with excellent strength-ductility synergy and near-isotropic mechanical behavior was made by an industrial-scale rotary die equal channel angular pressing (RD-ECAP). The microstructure of the UFG alloy involves the primarily submicron α-Mg grains with an average grain size of 760.5 nm and the high-density submicron β phase (Mg5Gd) precipitates (267.8 nm). Room temperature tensile tests results reveal that the UFG alloy exhibits an over three times tensile yield strength, near two times ultimate tensile strength, and more than one and a half times elongation along three orthogonal test directions than the as-cast Mg alloy. The improvement of strength is linked to the effect of the grain boundary strengthening as well as the precipitation strengthening. The enhanced ductility is ascribed to the ultrafine grains with low dislocation density, which provide a degree of dislocation storage capacity and facilitates multiple potential deformation modes. The near-isotropic mechanical behavior stems from the weak texture and multiple deformation modes.