Microstructures and Tensile Properties of New Mg–0.9Zn–0.2Mn–0.5RE Alloys via Different Al Additions

Abstract

Effects of Al content on the microstructure and tensile properties of Mg–0.9Zn–0.2Mn–0.5RE (0.2Sm + 0.3La) alloy have been systematically investigated. In the as‐cast Mg–0.9Zn–0.2Mn–0.5RE alloy, intermetallic compounds are identified as Mg41Sm5, Mg12La, and Mg12(La, Sm) phases, while when Al is added, new Mg17Al12 and Al11(La, Sm)3 phase is formed instead of Mg12(La, Sm) phase. As Al content increases, Al11(La, Sm)3 phase increases and the morphology changes from a bright needle to a short rod in the as‐cast alloys. Al11(La, Sm)3 phase is broken and characterized as polygonal and rod shapes in as‐extruded alloys, and gradually increases in size and segregation as Al content increases, resulting in an increase in the ultimate strength and fluctuation of the average grain size, yield strength, and elongation. It should be noted that the as‐extruded alloy has good elongation (A ≈ 25.3%) with 3% Al content and good tensile strength (280 MPa ≤ Rm ≤ 300 MPa) with 6% and 9% Al content. Besides, the as‐extruded Mg–0.9Zn–0.2Mn–0.5RE–3Al alloy shows outstanding ductility due to the weakened texture of DRXed and sub‐structured grains and the high SF value in pyramidal <c + a> slip and basal <a> slip.