Grain refinement and enhanced mechanical properties of ZK20 magnesium alloy via hot extrusion and mischmetal addition

Tensile properties of as-cast and extruded Mg, ZK20 (Mg-2Zn-0.5Zr), and ZEK200 (Mg-2Zn-0.5Zr-0.5RE, where RE denotes the rare earth elements) alloys were studied. The addition of 0.5 wt% Ce-rich mischmetal to ZK20 alloy (to form ZEK200 alloy) refined the alpha-Mg grains, which resulted in the improvement of mechanical properties and tensile toughness. The fine microstructures introduced by hot extrusion significantly improved the mechanical properties, and hence, the wrought alloys were recommended for industrial applications. The grain size dependency of yield stress was successfully quantified by the Hall-Petch strengthening law, which resulted in the slope of 400 MPa mu m(-0.5). For the extruded condition, the higher tensile toughness of ZEK200 alloy compared to Mg and ZK20 alloys revealed that the addition of cerium-rich mischmetal was a favorable practice.