The effects of ultrasonic power on solidification microstructure and mechanical properties of hypereutectic Al-Mg-Si alloy were investigated.The results indicate that the primary Mg

2

Si can be refined and the mechanical properties of alloy can be enhanced under the ultrasonic treatment with 600 W and 1 000 W. When the ultrasonic power reaches 1 400 W

some high solid solution coarse microstructure appears near the primary Mg

2

Si phase in spite that the size of primary Mg

2

Si becomes finer

which is attributed to the local overheat caused by high power ultrasonic treatment

resulting in the degradation of mechanical properties.