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通过金相、扫描电镜和电子探针等方法研究了稀土Er和Gd复合变质对过共晶Mg-3.2Si合金组织和力学性能的影响,并探讨了其变质机理。结果表明,在过共晶Mg-3.2Si合金中,添加约0.6%的Er时,初生Mg2Si相的尺寸由150μm减小到40μm,其形态由粗大树枝状变为不规则多面体形状;在此基础上,继续添加0.6%的Gd,可获得20~30μm的多面体初生Mg2Si相,变质效果最佳;但稀土添加过量,会出现过变质现象。其变质机理是稀土在初生Mg2Si相表面富集,影响其生长过程并改变其生长方式;合金凝固时,稀土Er、Gd的晶体结构相同,形成了连续固溶体。当加入0.6%的Er和0.6%的Gd时,合金的抗拉强度与伸长率分别达到112 MPa和3.2%。
The effects of rare earth Er and Gd composite modification on microstructure and mechanical properties of hypereutectic Mg-3.2Si alloy were studied by means of metallographic examination, scanning electron microscopy and electron probe. The mechanism of metamorphism was also discussed. The results show that the size of the primary Mg2Si phase decreases from 150μm to 40μm with the addition of about 0.6% Er in the hypereutectic Mg-3.2Si alloy, and the morphology changes from coarse dendrites to irregular polyhedrons. Based on this, On the other hand, the addition of 0.6% Gd can obtain 20-30μm polyhedral primary Mg2Si phase with the best metamorphism. However, excessive addition of rare earth may cause metamorphism. The metamorphic mechanism is the enrichment of rare earth on the surface of primary Mg2Si phase, which affects its growth process and changes its growth mode. When the alloy is solidified, the crystal structures of rare earth Er and Gd are the same, forming a continuous solid solution. When adding 0.6% Er and 0.6% Gd, the tensile strength and elongation of the alloy reached 112 MPa and 3.2% respectively.