Grain size in the semi-continuous casting 7050 aluminum alloy could be refined significantly with imposing ultrasonic power.Cavitation bubble co-vibrating mechanism in the aluminum alloy melt was analyzed by theoretical calculation and experiment based on crystallization thermo-dynamics and kinetics.The results reveal that cavitation effects can greatly increase the vibrating energy of grain nuclei

which is responsible for the refinement of grain size as a result of apparently increase the vibrating frequency of the nuclei.The effect of cavitation is quantitatively analyzed for energy transfer and change of vibrating frequency of the nuclei in 7050 aluminum alloy during semi-continuous casting process.In addition

effects of frequency of cavitation bubble and its initial equilibrium radius on nuclei vibrating frequency and nucleation in aluminum alloy melt with ultrasonic treatment were approached.