Investigation on synergetic effect of non-contact ultrasonic casting and mushy state rolling on microstructure and hardness of Al–Si–Al₂O₃ nanocomposites

The present work elucidates a novel way of processing Al–Si–Al₂O₃ bulk nanocomposites. The novel approach includes synergetic effect of non-contact ultrasonication and mushy state rolling for achieving appreciable uniformity in the distribution of nanoparticles in the metal matrix. A systematic study on the distribution of particles, the resultant microstructure, and also the resultant hardness in the nanocomposite has been presented. It is shown that the current methodology has resulted in enhanced distribution of nanoparticles in the metal matrix as compared to the earlier versions in the field. The structure of the nanocomposites has been explained on the basis of cavitation phenomena and particle pushing during solidification. The work also includes simulation using the Fluent platform to estimate the time available before the initiation of solidification to carry out effective deagglomeration and distribution of nanoparticles in the liquid melt using ultrasonic cavitation. Although the non-contact ultrasonic casting has resulted in a nearly uniform deagglomeration of nanoparticle clusters, a small number of agglomerates were present at the grain boundaries. Hence, the as-cast nanocomposites were deformed in the mushy state condition. An attempt has been made to explore the feasibility of enhancing the distribution of nanoparticles in the Al–Si matrix through semisolid state rolling. The synergetic effect has resulted in enhancement of the hardness of the material by 37%.