中文摘要：

采用扫描电镜、X射线衍射对合金组织进行观察,研究在Mg-3Si（质量分数/%,下同）合金陆续添加Zn,Nd,Gd,Y元素后微观组织演变规律。结果表明：Mg-3Si合金中Mg2Si粒子具有初生和共晶两种明显不同的形貌;添加3%Zn元素后的Mg-3.0Si-3.0Zn合金中,初生Mg2Si粒子粗化,共晶Mg2Si粒子完全消失;在Mg-2.0Nd-3.0Zn-3.0Si合金中,Nd元素的加入能有效地细化初生Mg2Si粒子并生成少量的Mg（41）Nd5粒子;继续添加Gd,Y元素后,在Mg-8.0Gd-4.0Y-2.0Nd-3.0Zn-3.0Si合金中的Gd5Si3和YSi等粒子急剧增加而Mg2Si粒子含量大大减少。通过Thermo-Calc热力学软件的热力学计算表明：Gd5Si3,YSi的吉布斯自由能低,Gd,Y原子与Si更容易形成化合物。在Mg-8Gd-4Y-2Nd-3Zn-3Si合金中,Gd5Si3,YSi,Mg2Si三种化合物的室温吉布斯自由能分别为-9.56×10^4,-8.72×10^4,-2.83×10^4J/mol,粒子的质量分数分别为8.07%,5.27%,1.40%。

英文摘要：

The microstructure of alloy Mg-3Si（mass fraction/%,same as below）after successive additions with different elements of Zn,Nd,Gd and Y was observed and the microstructure evolution was investigated by scanning electron microscopy and X-ray diffraction.The results show the primary Mg2Si particles co-exist with eutectic Mg2Si particles in binary alloy Mg-Si.With minor addition of Zn element,only primary Mg2Si can be found in ternary Mg-3Si-3Zn system while eutectic Mg2Si particles disappear.In quaternary alloy Mg-2.0Nd-3.0Zn-3.0Si,the addition of Nd element can effectively refine the primary Mg2Si particles and form some Mg（41）Nd5 particles.After continuous adding of Gd and Y elements into quaternary system,Gd5Si3 and YSi particles increase significantly in the alloy Mg-8.0Gd-4.0Y-2.0Nd-3.0Zn-3.0Si,while volume fraction of primary Mg2Si decrease significantly.Thermo-Calc calculation predicts that the Gibbs free energy for primary particles Gd5Si3,YSi is lower,and therefore Gd,Y atom and Si are more likely to form compounds.In Mg-8Gd-4Y-2Nd-3Zn-3Si alloy,room temperature Gibbs free energy for primary particles Mg2Si,Gd5Si3,YSi is-9.56×10^4,-8.72×10^4,-2.83×10^4J/mol,respectively,and the mass fraction of these particles is8.07%,5.27%,1.40%respectively.