Improvement on both strength and ductility of Mg−Sm−Zn−Zr casting alloy via Yb addition

Abstract Effects of 2 wt% Yb addition on microstructures and mechanical properties of Mg−3.5Sm−0.6Zn−0.5Zr (SmZK410) casting alloy under as-cast, solution-treated and peak-aged conditions were thoroughly investigated. Yb addition has outstanding grain refinement effect, with grains being refined from ∼48 μm to ∼27 μm. Furthermore, the dominant intermetallic phase was changed from lamellar Mg 3 Sm to divorced Mg 24 RE 5 by Yb addition. Moreover, Yb addition remarkably improves the alloy's ageing hardening response. Transmission electron microscopy (TEM) observations indicate that the dominant precipitate in the peak-aged SmZK410 alloy is basal γ’‘, while both fine prismatic β’’ and basal γ’’ along with a coarse tridentate precipitate which is consisted of ordered β’‘/β′ stacking coexist in the alloy with Yb addition. These changes due to Yb addition result in clear improvement on both strength and ductility of the SmZK410 alloy at both room temperature and high temperatures. Thereby, the alloy with Yb addition exhibits high tensile yield strength of 228 MPa and a satisfactory elongation of 5.7%, thus more excellent strength-ductility balance than other conventional Mg−RE based casting alloys.