Abstract: The ductility of Al Si15Cu alloy is extremely susceptible to the large Si particle size, which makes the mechanical properties of the alloy decrease. The effect of ultrasonic vibration time on hypereutectic Al Si15Cu alloy has been studied. The results show that ultrasonic vibration can efficiently refine the primary Si particles in Al Si15Cu alloy. Ultrasonic vibration refines the primary Si particles by creating cracks inside the Si particles. Ultrasonic vibration at an appropriate time causes hard particles such as intermetallic compounds to collide with the primary Si, resulting in further fragmentation and refinement of the Si particles. The primary Si grains of the alloy is in uniform distribution and refinement state after ultrasonic vibration, which can overcome the problem of poor deformation of the alloy. Compared with the untreated alloy, the mechanical properties of the treated alloy are significantly improved.