The hypereutectic Al-20 Si alloys were modified by P and rare earth element La

and effects of P and La on the modification of primary silicon phase in the alloys were investigated.The experimental results indicate that the addition of P can refine greatly primary silicon phase in hypereutectic Al-20 Si alloy.The primary silicon phase in modified alloys is changed into fine granule from coarse block shape in unmodified alloys and well-distributed in matrix.The optimal refinement on the primary silicon phase can be obtained when the content of P is 0.06%

where the average size of primary silicon phase is decreased from 122μm to 25μm.However

with the addition of 0.09% P

the primary silicon in the alloy can be coarsened.The complex modification of P-La can further improve the refining effect of primary silicon.The optimal refinement on eutectic silicon in the alloy can be observed when the content of La is0.9%

while with La of 1.2%

over-modification effects can be observed.