A Computational and Experimental Study of Ultrasonicated Phase Separation Process for Liquid Al–Bi Immiscible Alloy

A numerical model coupling ultrasonic cavitation with acoustic streaming for the liquid phase separation process of immiscible alloys within ultrasonic field was developed to predict the nucleation, growth and migration dynamics of secondary phase droplets. In the specific case of one-dimensional ultrasound propagating inside Al–10 wt pct Bi immiscible alloy, the sound pressure sharply attenuated along the wave propagation direction, making the cavitation area gathered near ultrasonic horn, whereas the acoustic streaming exhibited a symmetric vortex structure with a jet formed along the center line. The high pressure in the cavitation area significantly accelerated the homogeneous nucleation of secondary (Bi) droplets, while the acoustic streaming effect promoted the heat transfer and reduced the temperature gradient to weaken the Marangoni migration of the secondary phase. It also restrained the Stokes motion of secondary (Bi) droplets by markedly accelerating the migration speed opposite to the sedimentation direction, leading to a homogeneous distribution of refined (Bi) droplets on (Al) matrix. The simulated volume fraction and size distribution of secondary (Bi) droplets were in good agreement with the results of comparative solidification experiments, securing that the numerical model is valid to predict the liquid phase separation characteristics of immiscible alloys under various ultrasonic conditions.