Effects of Sm content on microstructures and mechanical properties of casting Mg-Y-Nd-Sm-Zr alloys

The microstructures and mechanical properties of Mg-5Y-2Nd-xSm-0.5Zr (x = 0, 1, 3, 5) alloys were investigated. The results indicated that a new Mg41Sm5 phase was generated in the as-cast Sm-containing alloys. As the Sm content was increased, the grain of a-Mg matrix was refined and the amount of second phases at the grain boundary increased. After the solution and aging treatment, a large number of beta' phases precipitated, the alloys mainly consisted of alpha-Mg, Mg24Y5, Mg41Nd5 and Mg41Sm5. The grain size significantly reduces from 80 mu m to 23 mu m with the increasing of Sm content. Under all conditions in this paper, Mg-5Y-2Nd-3Sm-0.5Zr alloy had the best mechanical properties. The tensile strength and elongation of the aged Mg-5Y-2Nd-3Sm-0.5Zr alloy were 296.9 MPa, 4.78% room temperature and 279.4 MPa, 6.43% at 250 degrees C, respectively. The mechanical properties of this alloy is obviously superior to the commercial WE54 alloy with equivalent total rare earth content, which has excellent heat resistance and can be reliably applied below 250 degrees C. The improving of the mechanical properties is mainly due to grain refining strengthening, solid solution strengthening and precipitation strengthening of the beta'-Mg41Sm5 phase.