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采用金相显微镜、扫描电镜观察了稀土变质的过共晶Ａｌ－Ｓｉ合金中共晶Ｓｉ的形貌。结果表明：稀土在过共晶Ａｌ－Ｓｉ合金中对共晶Ｓｉ的变质不同于稀土在共晶或亚共晶Ａｌ－Ｓｉ合金中的变质作用，即在初晶Ｓｉ周围存在不完全变质组织。产生该组织特征的原因是共晶Ｓｉ在初晶Ｓｉ表面形核生长以及稀土对共晶团中α（Ａｌ）和共晶Ｓｉ两相生长的抑制作用不同。指出了在过共晶Ａｌ－Ｓｉ合金中采用稀土变质时提高冷却速度和使初晶Ｓｉ均匀分布的重要性。
The morphologies of eutectic Si in the hypereutectic Al-Si alloy were characterized by metallographic microscope and scanning electron microscope. The results show that the modification of eutectic Si in hypereutectic Al-Si alloy is different from the modification of rare earth in eutectic or hypo-eutectic Al-Si alloy, ie, there is incomplete metamorphic microstructure around primary Si. The reason for this characteristic of the organization is that the eutectic Si forms nuclei on the surface of the primary Si and the effect of rare earth on the growth of α (Al) and eutectic Si in the eutectic is different. The importance of increasing the cooling rate and distributing the primary Si evenly in the hypereutectic Al-Si alloy is pointed out.