Effects of P-RE compound modification on tensile properties at room temperature and fracture morphology of hypereutectic Al-20Si alloy were investigated.The results show that both primary Si phase and eutectic Si phase in the Al-20Si alloy with P-RE modification are refined effectively

where primary Si is converted into the near-spherical structure

and eutectic Si phase is transformed into the particle or short rod-like one.Meanwhile

the size of the primary Si phase and eutectic phase is decreased from approximately 100 μm to 10

1

5 μm and to lower than 1μm

respectively.Tensile strength of the alloy with P-RE modification is improved by approximately 100% compared with that of the matrix alloy.The fracture morphology of the alloy modified is composed of fine cleavage plane and tearing edge

dimple among the cleavage plane.In addition

plenty of dimple bands gathered in boundary among cleavage steps can be observed.