The effect of pertinent processing parameters on the semi-solid microstructure was investigated in the course of preparing ZL101 Al Alloy semi-solid slurry by Ultrasonic Vibrating Method. The ZL101 melt in temperature of 630～660℃ was cast into a special-made metal cup

and exposed to ultrasonic vibration or isothermal holding for certain time. After examination and analysis of the microstructure of the samples

the following results are concluded: the primary α-Al crystals could be prepared with average grain diameter about 90μm and average shape coefficient above 0.5 by 144 s ultrasonic vibration; the average shape coefficient of grains would decrease at first

and then increase if isothermal holding with a short time of ultrasonic vibration beforehand; finer and rounder grains could be fabricated with the increase of the ratio of ultrasonic working time to rest time under the same other conditions. In addition

the mechanism of the ultrasonic vibration on metal melt is discussed preliminarily.