采用富铈混合稀土对Al-24%Si合金进行了变质处理,用扫描电镜对合金的硅相形貌与尺寸进行了研究,分析了变质效果及机理.结果表明:富铈混合稀土对合金中初晶硅及共晶硅均有良好的变质效果,变质后初晶硅平均尺寸由100 μm细化到50 μm左右,共晶硅细化成颗粒状或短杆状;初晶硅细化是通过稀土原子与氧原子反应生成稀土化合物(CeO2),它成为硅非均匀形核核心,生成了大量硅晶晶核来实现的;共晶硅细化是通过硅相生长界面前沿形成很强的稀土原子富集层,造成成分过冷降低硅生长速度来实现的.

Al-24%Si alloy was modified with cerium-rich mischmetal.The morphology and size of the Si phase were studied by using SEM,and the modification effect and mechanism were analyzed.The results show that after modification both primary Si in the alloy and eutectic Si had been well refined.The average size of primary Si could be reduced from 100 μm to 50 μm,and the eutectic Si could be transformed into granular or short rod.Cerium and oxygen could occur chemical reaction,and the product was CeO2,which could become the heterogeneous nuclei of primary Si,so as to produce numerous Si crystal nuclei.Eutectic Si was refined by the forming of cerium-rich layer at the growth interface,which led to the composition undercooling and reduce the growing speed of eutectic Si.