Effect of Sm on Microstructure, Mechanical Property and Lattice Constant of As-Cast Mg-11Gd-2Y-0.6Al Alloy

Mg-11Gd-2Y-xSm-0.6Al (x = 0, 1, 3, 5) alloys were prepared in electromagnetic induction furnace by gas protection. The crystal structure, microstructure and mechanical properties of as-cast Mg-11Gd-2Y-xSm-0.6Al alloys were studied by X-ray diffraction, metallographic microscope, scanning electron microscopy and tensile testing. The results show that the main phases of Mg-11Gd-2Y-xSm-0.6Al alloys are alpha-Mg matrix, Mg5Gd, Mg24Y5 and Mg41Sm5. The addition of Sm refines the microstructure and increases the number of second phase in the grain boundary. The diffraction peaks of the cylindrical plane (100)(alpha-Mg), base plane (002)(alpha-Mg) and conical plane (101)(alpha-Mg) are shifted to a low angle. The offset of diffraction peak and the lattice constant of alpha-Mg increase with the increase in Sm content. The crystal axis ratio decreases with the increase in Sm content. When the addition of Sm is 3%, the ultimate tensile strength reaches to 240 MPa, which increases by 17.07%. The improvement in mechanical properties is mainly attributed to the grain refinement and the decrease in the crystal axis ratio of alpha-Mg.