The aerospace and automotive industries are seeking advanced materials with low weight-to-strength ratio, such as light alloy-based metal matrix composites (MMC) with nanoparticle rein-forcements. However, van der Waals and adhesive forces between nanoparticles result in large agglomerates that compromise the final properties of MMCs. Ultrasonic melt processing is a potential technology for de-agglomerating these clusters and producing samples with improved properties via grain refinement. This paper considers two hypotheses of cluster de-agglomeration: the breakup of a cluster due to the growth of gas contained in the cluster and the stripping of nanoparticles by pulsating neighbouring bubbles
