Effects of Al-10 RE master alloy on the microstructure and mechanical properties of as-cast Al-20 Si alloy were investigated.The experimental results reveal that the as-casting microstructure of Al-20 Si alloy mainly consists ofα-Al matrix

primary Si

eutectic Si and acicular Al11RE3 phase with adding Al-10 RE master alloy.The morphology of primary Si in the hypereutectic Al-20 Si is transformed from bulky to small blocky and globular shape with the increase of the Al-10 RE addition.It is found that with addition of 1.5%Al-10 RE

the average grain size with dispersive and homogeneous distribution of primary Si can be observed.Meanwhile

the tensile strength

elongation and micro-hardness of as-cast Al-20 Si alloy are increases from 98 MPa to 117 MPa

from 9.7%to 11.0%

from 70.93 HV to 87.76 HV

respectively.The RE element can change the growth morphology of primary Si

and fine grain size and generation of acicular Al11RE3 improve greatly the mechanical properties of the alloy.