The effects of modification treatment with single additions and combined additions of rare earth elements Nd and Ce on the microstructure and properties of Al-20Si hypereutectic Al-Si alloy were investigated by SEM

micro-hardness tester and universal tensile machine.The results reveal that with Nd addition

primary Si size in the alloy is decreased firstly and then increased

so the tensile strength of the alloy is increased firstly and then decreased.With Ce content increasing

primary Si size is decreased slowly at first and then dramatically decreased

and tensile strength of the alloy is increased continuously.The primary Si size is not refined with compound addition of 0.4% Nd and 0.7% Ce

which is relative with the Nd inhibiting refinement of Ce on primary Si.With controlling Na addition at a fixed range and adding Ce over critical range

primary Si can be refined obviously.