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过共晶Ａｌ－Ｓｉ合金五瓣初晶硅具有简单多面体原子团簇凝并形核的特点，热力学分析表明，低温熔体中预存的四面体和八面体硅原子团簇以五重孪晶关系凝并是一自发过程．凝并后的多面体具有生长成五瓣星状初晶硅的内在条件．小于晶核临界尺寸的原子团簇凝并后可成为稳定的五瓣星状初晶硅生长的晶核．
The five-element primary Si of hypereutectic Al-Si alloy has the characteristics of simple polyhedron atomic cluster condensation and nucleation. The thermodynamic analysis shows that the tetrahedral and octahedron silicon clusters pre-existing in the low-temperature melt are condensed in a five-fold twins relationship Is a spontaneous process. The condensed polyhedron has the inherent condition of growing into five star primary silicon. Clusters of atoms smaller than the critical size of the nucleus can become stable nuclei for the growth of five primary star-shaped silicon.