稀土Y和Sm对AZ91D镁合金组织与性能的影响

采用控制变量法研究单一稀土Y和复合稀土Y，Sm元素对AZ91D镁合金微观组织与力学性能的影响，分析稀土元素对AZ91D合金的细化机理。结果表明：复合添加稀土Y和Sm对AZ91D合金的作用效果明显好于单一添加稀土Y对AZ91D合金的作用效果，添加Y和Sm后，生成了块状相Al₂Y相和针状相Al₂Sm相，可以作为α-Mg的有效异质形核点。当加入量为0.8%（质量分数，下同）Y+1.0% Sm时，α-Mg晶粒尺寸最为细小，分布最为均匀，其合金的硬度、抗拉强度及伸长率分别为67.42HV，153.37 MPa和3.62%，改善了铸态AZ91D合金的室温力学性能，但是超过这个最佳添加量后，合金的室温力学性能开始下降。

Effect of Y and Sm on microstructure and properties of AZ91D magnesium alloy

The effects of solo rare earth Y and combined rare earth Y and Sm elements on the microstructure and mechanical properties of AZ91D magnesium alloy were studied by controlling variable method.The grain refinement mechanism of rare earth elements on AZ91D alloy was analyzed. The results show that the effect of combined addition of rare earth Y and Sm on AZ91D alloy is better than that of solo addition of rare earth Y significantly. More effective heterogeneous nucleation sites for α-Mg are achieved by adding Y and Sm to AZ91D alloy produced bulk phase Al₂Y and acicular phase Al₂Sm. When the addition content is 0.8% (mass fraction) Y and 1.0%Sm, the α-Mg grain size is the smallest and most uniform. The hardness, tensile strength and elongation of the alloy are 67.42HV, 153.37 MPa and 3.62% respectively, the mechanical properties of as-cast AZ91D alloy at room temperature are improved. However, the mechanical properties of the AZ91D alloy at room temperature decrease after exceeding this optimum addition.