Understanding the highly dynamic phenomena in ultrasonic melt processing by ultrafast synchrotron x-ray imaging

Abstract

In this paper, we present some highlighted findings from our recent research on real-time and in situ studies of the fundamentals of ultrasonic melt processing, including (1) ultrasonic bubble implosion, oscillation in liquid and semi-liquid (semi-solid) metals and their interactions with the growing solidifying phases; (2) enhanced acoustic metal flow and their impact on the liquid-solid metal interface. The real time experimental phenomena were interpreted with the aid of calculating the propagation of acoustic pressure in liquid metals using the Helmholtz equation and bubble wall pressure and velocity profile during bubble oscillation using the classical Gilmore model. The research provides unambiguous real-time evidence and robust theoretical interpretation in elucidating the dominant mechanisms of microstructure fragmentation and refinement in solidification under ultrasound.