The hypereutectic Al-18Si alloy was prepared by CDS technology

and the effects of precursor alloying component and mixing methods on the size

morphology and distribution of primary silicon phase in the alloy prepared were investigated by OM（optical microscope）.The results show that

at fixed overheating temperature of precursor Al-Si alloy

under solid pure Al mixing with liquid Al-25Si

the desirable microstructure in the alloy can be obtained

where the average size of primary Si is 11.68 μm with shape factor of 1.608.The analysis reveals that

at the same mixing method

the refining effect is increased with increasing in Si content.With a higher Si content in precursor Al-Si alloy

liquid Al mixing with liquid Al-Si alloy can weaken segregation of primary Si and refine grain size

while with a lower Si content in precursor Al-Si alloy

solid pure Al mixed with liquid precursor Al-Si alloy is a acceptable method.