Study on the effect of ultrasonic melt treatment on the grain refinement of aluminum alloy based on the principle of acoustic reflection

Ultrasonic melt treatment, as an important method for controlling metal solidification, can significantly improve the microstructure and properties of materials. However, due to the limited range of ultrasonic action, its application in the horizontal continuous casting process has been restricted. An L-shaped ultrasonic probe is designed using the idea of acoustic reflection, the effect of its structural on the microstructure of aluminum alloys is studied and the mechanism of grain refinement is analyzed. The results show that the aluminum microstructure near the corner and the end of the L-shaped ultrasonic probe is significantly refined, the grain size was reduced by more than 60 % compared with the sample without ultrasonic treatment, and the refining range expands with the increase of ultrasonic power. Ultrasonic waves reflect and refract at the graphite/aluminum interface, accompanied by a wave-type conversion that generates refracted transverse waves and reflected longitudinal waves. These two wave types act on the aluminum melt near the corner and the end of the L-shaped probe, respectively. The cavitation and acoustic streaming induced by ultrasound are the primary mechanisms for refining the solidification structure of the aluminum alloy.