Effect of high-intensity ultrasonic field on process of semi-continuous casting for AZ80 magnesium alloy billets

Under the high-intensity ultrasonic field, AZ80 magnesium alloy was semi-continuously cast. The effects of ultrasonic intensity on the as-cast microstructures and mechanical properties were investigated. The results show that the microstructures of the alloy cast under high-intensity ultrasonic field are fine and uniform, and the grains are equiaxed, rose-shaped or globular with an average size of 257 μm. High-intensity field significantly decreases the grain size, changes the morphologies of the β-Mg17Al12 phases and reduces their area fraction. It is also shown that a proper increase in ultrasonic intensity is helpful to obtain fine, uniform and equiaxed as-cast microstructures. The optimum ultrasonic parameters are that frequency is 20 kHz and ultrasonic intensity is 1 368 W. The mechanical tests show that the mechanical properties of the as-cast AZ80 magnesium alloy billets cast under ultrasonic field are greatly improved, and with increasing the ultrasonic intensity, the mechanical properties of the entire alloy billets are much higher and more uniform than those of the alloy without ultrasonic field.