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利用光学显微镜、扫描电镜及XRD物相分析研究稀土元素Nd对过共晶Mg-3%Si合金中Mg2Si粒子的变质作用与机理。结果表明:随着Nd含量的增加,初生Mg2Si粒子的形貌由粗大的树枝状转变为细小的多面体状。当Nd含量增至1.0%时,初生Mg2Si粒子被完全细化,尺寸约为10μm。然而,随着Nd含量的进一步增加,初生Mg2Si粒子反而又出现了粗化的现象。其变质机理主要是Nd元素富集于初生Mg2Si相的生长表面并抑制其优先生长晶向的生长,即中毒效应。当Nd含量超过3.0%时,初生Mg2Si粒子中的白色粒子由NdMg2相转变为NdSi和NdSi2化合物。因此,适量的Nd元素可以有效地细化初生Mg2Si粒子。
The modification and mechanism of rare earth element Nd on the Mg2Si particles in hypereutectic Mg-3% Si alloy were studied by optical microscopy, scanning electron microscopy and XRD. The results show that with the increase of Nd content, the morphology of primary Mg2Si particles changes from coarse dendrites to fine polyhedrons. When the Nd content increased to 1.0%, the primary Mg2Si particles were completely refined, the size of about 10μm. However, with the further increase of Nd content, the primary Mg2Si particles instead appeared roughening phenomenon. The metamorphic mechanism is mainly that Nd element is enriched in the growth surface of the primary Mg2Si phase and inhibits the growth of its preferential growth in the crystal orientation, namely the poisoning effect. When the Nd content exceeds 3.0%, the white particles in primary Mg2Si particles transform from NdMg2 phase to NdSi and NdSi2 compounds. Therefore, an appropriate amount of Nd element can effectively refine the primary Mg2Si particles.