Morphology transformation of eutectic silicon in Al-Si alloy during solid solution was observed by OM and SEM. The results show that the granulation effect of silicon phase is obviously controlled by the cast structure of eutectic silicon and the modification can greatly promote the granulation of silicon phase during the solid solution treatment. The modified and unmodified eutectic silicon phases have different 3D morphologies after solid solution treatment

in which the former is granular and the latter is lathy. Some phenomena in the morphology transformation of eutectic silicon and their mechansims were approached.