Effect of extrusion temperature on the microstructure and mechanical properties of low Zn containing wrought Mg alloy micro-alloying with Mn and La-rich misch metal

A new low Zn containing Mg-1.5Zn-0.4Mn-0.9LaMM (La-rich misch metal) alloy with excellent mechanical properties is developed. The alloys with superior high strength and respectable ductility (the maximum of UTS reaches 353 MPa and corresponding EL 19.4%) are fabricated by mold casting and indirect extrusion. Effects of extrusion temperature on the evolution of microstructure, mechanical properties and extruded texture are investigated by SEM, XRD and TEM analysis. The addition of LaMM is found to produce typical bimodal structure of fine DRXed (dynamic recrystallized) grains and elongated un-DRXed grains when extruded at relatively low temperature. The relatively high strength is primarily due to the grain boundary strengthening and precipitation strengthening, moreover the large hard elongated deformed grains functioning as in-situ strength-reinforcement fibers also apparently contribute to the strength improvement. The equixal, refined DRXed grain structure and comparable different extruded texture component with traditional AZ31 and other alloys with similar microstructure are believed to enhance its ductility.