将Zn和Y元素以原子比为6∶1的形式加入AM50合金中, 并采用金属型铸造成形, 利用OM, SEM, EDS, XRD, 热分析法及拉伸实验研究了AM50-x(Zn, Y) (x=0, 2, 3, 4, 5, 质量分数, %)合金的显微组织、凝固行为及力学性能. 结果表明: 向AM50合金中按原子比为6∶1的形式加入Zn和Y元素后, 组织得到明显细化, 组织中并未形成Mg₃Zn₆Y准晶相, 而是形成了颗粒状的Al₆YMn₆相和细小的Al₂Y相, 其中Al₆YMn₆相尺寸随着Zn和Y元素含量的增加而增大; 当x≥3时, 在组织中β相的周围逐渐形成层片状的Φ-Mg₂₁(Zn, Al)₁₇相, 且其数量逐渐增加. 热分析结果表明, Φ-Mg₂₁(Zn, Al)₁₇相约在354 ℃通过包晶反应形成, 其中α-Mg和β相析出温度随着x的增加而降低. 由于Al₆YMn₆相、Al₂Y相和Φ-Mg₂₁(Zn, Al)₁₇相的形成, 使得β相的尺寸减小、数量减少; 当x=4时, 合金组织最为细小, 且合金力学性能达到最优, 其抗拉强度、屈服强度和伸长率分别为206.63 MPa, 92.50 MPa和10.04%.

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.