As the lightest metallic structural material, magnesium alloys were widely used in automotive, aerospace, electronic equipment and other fields. Among commercial magnesium alloys, AM series were commonly used due to excellent ductility and energy absorption. However, their relatively poor strength greatly restricted their extended use. In order to improve mechanical properties of AM50 alloy, the Zn and Y elements were added into the AM50 alloy in the form of atomic ratio of 6∶1 by the permanent mold casting. The microstructure, solidification behavior and mechanical properties of AM50-x(Zn, Y) (x=0, 2, 3, 4, 5, mass fraction, %) alloys were investigated by OM, SEM, EDS, XRD, thermal analysis and tensile tests. The results indicated that addition of Zn and Y elements with an atomic ratio of 6∶1 to AM50 alloy, the microstructures were obviously refined, and the quasicrystal I-phase(Mg₃Zn₆Y) cannot form. In addition, the granular Al₆YMn₆ phase and fine Al₂Y phase were formed in the microstructure, and the size of Al₆YMn₆ phase increased with increasing the Zn and Y content. The Φ-Mg₂₁(Zn, Al)₁₇ phase with lamellar structure was formed around β phase when x≥3, and its amount increased with increasing the Zn and Y addition. Thermal analysis results show that the Φ-Mg₂₁(Zn, Al)₁₇ phase was formed at 354 ℃ by the peritectic reaction, in which the precipitation temperatures of α-Mg and β phase were decreased with the increase of x content. Due to the formation of Al₆YMn₆, Al₂Y and Φ-Mg₂₁(Zn, Al)₁₇ phases, the size and amount of the β phase was decreased. For AM50-4(Zn, Y) alloy, the microstructure was greatly refined, and the ultimate tensile strength, yield strength and elongation of the alloy reached to the maximum, 206.63 MPa, 92.50 MPa and 10.04%, respectively.