Analysis on the formation mechanism of porous microstructure on aluminum grooves by ultrasonic cavitation treatment.

During the ultrasonic cavitation treatment, the morphology of groove surface can be changed obviously due to the cavitation impact. This study intends to investigate the formation mechanism of porous microstructure on the groove surface. Experiments were conducted to explore the effects of ultrasonic cavitation duration and clearance on the formation of microstructure on two types of aluminum grooves. Meanwhile, an acoustic-fluid coupling simulation is executed to analyze the acoustic pressure distribution and flow velocity characteristics under different ultrasonic treatment clearances. The results show that the porous microstructure appears preferentially at the bottom of the groove, and gradually extends to the peak as the treatment duration increases. The bottom corner of the groove is more susceptible to cavitation impact due to its smaller radius of curvature and higher flow velocity. The ultrasonic clearance mainly affects the distribution and size of the porous microstructure at the peak of the groove due to the variation of flow velocity. As the clearance decreases, the high-pressure region tends to concentrate and expand into the grooves, and the flow velocity also increases obviously. The higher flow velocity may accelerate the movement of bubbles to the grooves, thereby increasing the likelihood of cavitation impacts on the groove surfaces. And too smaller clearance also results in the smaller size of micro-hollows at the groove peak due to the relatively weak cavitation impact form the restricted cavitation bubbles. These results will contribute to the parameter optimization of the treatment process.