Understanding the influence of ultrasonic streaming on solidification of AZ80 magnesium alloy during direct-chill casting using a transient coupling modeling

In this modeling, the influence of ultrasonic streaming on physical fields during direct-chill (DC) casting of AZ80 magnesium alloy is investigated by a transient 2D axisymmetric mathematical model, which couples the ultrasonic field, fluid flow and temperature field using COMSOL Multiphysics software. The influences of input acoustic pressure, inserted depth and shape of ultrasonic horn on physical fields are discussed systematically. Compared with the DC casting, the ultrasonic casting (UC) has more turbulent melt flow, uniform temperature gradient, and shallow liquid sump. The acoustic streaming driving force dramatically changes the melt flow and temperature distribution. The increase of input acoustic pressure from 0.2 MPa to 2.2 MPa enlarges the affected area of ultrasonic streaming. However, a further increase of input acoustic pressure to 4.2 MPa has sight effects on physical fields. With the increase of inserted depth of ultrasonic horn from 10 mm to 50 mm, the circulation caused by ultrasonic streaming is enlarged. The convex surface of the ultrasonic horn promotes the transverse flow of melt compared with the flat horn. Therefore, the transverse temperature gradient and depth of liquid sump are decreased.