稀土元素Nd对过共晶Mg-Si合金中Mg 2 Si粒子的变质作用

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Mg 2 Si粒子的变质作用与机理。结果表明：随着Nd含量的增加，初生Mg 2 Si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Mg 2 Si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Mg 2 Si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Mg 2 Si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Mg 2 Si粒子中的白色粒子由NdMg 2相转变为NdSi和NdSi 2化合物。因此，适量的Nd元素可以有效地细化初生Mg 2 Si粒子。

Modification of Mg2Si in Mg-Si alloys with neodymium

The modification effect of neodymium （Nd） on Mg2Si in the hypereutectic Mg-3%Si （mass fraction） alloy was investigated by optical microcopy, scanning electron microscopy and X-ray diffraction. The results indicate that the morphology of the primary Mg2Si transforms from coarse dendrite into fine polygon with increasing Nd content. The average size of the primary Mg2Si significantly decreases to about 10 ~ma with increasing Nd content up to 1.0%, and then becomes coarser again. The modification and refinement of the primary Mg2Si are mainly attributed to the poisoning effect. The NdMg2 phase in the primary Mg2Si transforms into NdSi and NdSi2 compounds as the Nd content exceeds 3.0%. Therefore, it is reasonable to conclude that the proper Nd （1.0%） addition can effectively modify and refine the primary Mg2Si.