Microstructures of Si-eutectic in Al-Si eutectic alloys modified with Sb were investigated by means of SEM.The result shows that microstructure of Si-eutectic may be changed from flake to fibrous staff by Sb

and Sb is similar to Na in modification;but in modifying ability Sb is weaker

more than Na

thus when Sb is used it need’s to cooperate with quickly cooling;flake and fibrous staff both are results of same growthing fashion of Si crystal

if growth speed of Si crystal is slower

staffs join each other by flank growth to form flakes

if the speed is extremely fast

staffs do not change because flanks are too late grown.