Effects of different Si content and cooling rate on particle agglomeration and mechanical properties of SiCp/Al-Si composites were investigated by SEM （scanning electron microscope）. The results reveal that when Si content in matrix alloy is less than 12%

with increasing in Si content

SiC particle agglomeration in the composites can be distinctly relieved

however

when Si content in matrix alloy is more than 12%

with increasing in Si content

its relief can be neglected. SiC particle in Al-7Si alloy is repelled into eutectoid to cause particle agglomeration in sand casting while it is uniformly distributed in the microstructure in graphite mold casting since high cooling rate restricts the movement of SiC particle. Mechanical properties of the composites are decreased with increasing in Si content in matrix alloy

however

it can be greatly improved with increasing in cooling rate.