Abstract: The ultrasonic dilution mechanism was analyzed through studying the fabrication process of the Zn-Al alloy matrix composites by high-intensity ultrasonic dilution of XD composites.The results show that the mechanism of ultrasonic dilution of the XD composites is the result of the cooperative effects of the acoustic cavitation and high speed acoustic streaming in the Zn-Al alloy melt. The instantaneous high temperature caused by the acoustic cavitation can promote the element’s diffusion between the interface of XD composites and the Zn-Al alloy melt.The instantaneous high pressure breaks off the long rod-like TiAl₃ phase protruding along the XD composite/ Zn-Al interface,and drives the gathering particles out of the net of the rod-like TiAl₃ phase. On the other hand,the intensitive agitation caused by the acoustic streaming thins the interface area and makes the short rod-like TiAl₃ phase and fine particles (Al₂O₃ and TiB₂) homogeneously disperse in the Zn-Al alloy melt.On the basis of the results, the models of the element diffusion and dilution process of the XD composites into the Zn-Al alloy melt were established.