Abstract： The microstructure and mechanical properties of sand casting Mg-Gd-Y system alloys were investigated by optical microscopy（OM）, scanning electron microscopy（SEM）, energy dispersive spectrometer （EDS） and tensile tests, and the WE54 Mg alloy was also introduced as a comparison. The results show that the microstructure of as-cast Mg-Gd-Y system alloys were mainly composed of equiaxed dendrite of α-Mg solid solution, isolated island-like eutectic phase of Mg24（Gd,Y）5 at the grain boundaries, isolated square particles of Mgs（Gd,Y） and Zr-rich core playing a role in grain refinement. As the content of Gd addition to Mg-Gd-Y alloy increased, the ultimate tensile strength and yield strength increased gradually, while the elongation reduced gradually. The strength improvement was attributed to increase of the volume fraction of Mg2a（Gd,Y）5 at the grain boundaries. The strength of GW94 alloy was highest in present four alloys, and the tensile strength, yield strength and elongation at room temperature was 213.7 MPa, 156 MPa and 1.29%, respectively. The elongation of WE54 alloy was the highest, which may be due to its lamellar eutectic phase at the grain boundaries. The fracture modes of Mg-Gd-Y alloy and WE54 Mg alloy were both quasi-cleavage fracture.
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