Effect of addition of small amounts of samarium on microstructural evolution and mechanical properties enhancement of an as-extruded ZK60 magnesium alloy sheet

Abstract

The microstructure, texture evolution and mechanical properties of as-extruded Mg-5.5Zn-0.8Zr (wt.%) (ZK60) alloy with 1 % Sm addition were investigated. The results showed that the as-extruded ZK60-1Sm alloy consisted of α-Mg, Mg2Zn3, Mg7Zn3, Mg41Sm5 and (Mg, Zn)3Sm phases. The addition of 1 %Sm precipitated the Mg41Sm5 and (Mg, Zn)3Sm phases, which promoted the dynamic recrystallization (DRX) in the subsequent extrusion process and resulted in grain refinement. The microtexture and the orientation distribution characteristic implied that large amounts of <01–10> and <-12–10> slips were activated in ZK60-1Sm alloy during extrusion process, while only <01–10> basal slip was observed in ZK60 alloy. The non-basal slips led to more potential nucleation sites and a better coordination for the deformation, resulting in the better comprehensive mechanical properties of the as-extruded ZK60-1Sm sheet. Meanwhile, the as-extruded ZK60-1Sm alloy showed higher strength and ductility compared to ZK60 alloy. The ultimate tensile strength (UTS), the yield strength (YS) and the elongation to failure (EL) along the extrusion direction (ED) were enhanced by 11.7 %, 24.5 % and 26.2 %, respectively. The influence of fine grain microstructure, nanoscale Mg41Sm5 phase, micron scale (Mg, Zn)3Sm phase and texture evolution, contributed mainly to the strength of as-extruded ZK60-1Sm alloy.