The hypereutectic Al-18Si

Al-20Si

Al-22Si（weight fraction） alloys were prepared by the controlled diffusion solidification（CDS）

and effects of different mixing ways and high silicon alloy overheating temperatures on the size

morphology and distribution of primary silicon in hypereutectic Al-Si alloys were investigated.The results show that effect of liquid-liquid mixing way is superior to liquid-solid mixing way in improving primary Si.With the increase of the overheating temperature

the size of primary silicon is decreased with round morphology and uniform distribution.At the same overheating temperature

with increasing in the content of silicon in the alloys

the size of primary silicon is increased with the slightly change of morphology.Especially

the microstructure of liquid Al-25Si alloy with 900 ℃ overheating mixing with liquid pure Al at 660 ℃ exhibits desirable

where the primary silicon size is only 34.3 μm

and the length-width ratio is 1.48.