The compound influence of melt thermal treatment

including melt mixing and melt superheating

and strontium modification on silicon phases in Al-20Si alloy was investigated.The results show that with only strontium modification

the primary silicon in the alloy is modified weakly

and the morphology change of the eutectic silicon can be ignored.The low temperature Sr modified Al-10Si melt mixed with the high temperature Al-30Si melt in the ratio of 1:1

nuclei number in Al-20Si melt is increased

resulting in the significant refinement of primary Si phase.And then

mixed melt is treated by superheating to 1 000 ℃

and the average size of the primary silicon is decreased to approximately 14 μm

and the morphology of the eutectic silicon is changed from long needle-shape into short fiber-like.