Abstract:The nucleation and growth of eutectic cell in hypoeutectic Al−Si alloy was investigated using optical microscopy and scanning electron microscopy equipped with electron backscattering diffraction (EBSD). By revealing the eutectic cells and analyzing the crystallographic orientation, it was found that both the eutectic Si and Al phases in an eutectic cell were not single crystal, representing an eutectic cell consisting of small ‘grains’. It is also suggested that the eutectic nucleation mode can not be determined based on the crystallographic orientation between eutectic Al phases and the neighboring primary dendrite Al phases. However, the evolution of primary dendrite Al phases affects remarkably the following nucleation and growth of eutectic cell. The coarse flake-fine fibrous transition of eutectic Si morphology involved in impurity elements modification may be independent of eutectic nucleation.

Key words: hypoeutectic Al−Si alloy; eutectic cell; nucleation; growth