Dispersion of ceramic nano-particles in the Al-Cu alloy matrix using two-step ultrasonic casting and resultant strengthening

Abstract

The work describes the dispersion of the Al2O3 nano-particles in the Al-3Cu matrix using a novel two-step ultrasonic casting technique and characterization of the bulk nanocomposite. As a result of Al2O3 dispersion by the two-step process, significant grain refinement, change in the grain morphology, and change in the morphology of the CuAl2 phase were observed. The dispersion of nano-particles was uniform in a substantial fraction of grains. However, in the remaining grains, segregation near the boundary of Al-rich phase and CuAl2 was observed suggesting pushing from both the ends. The reduction in grain size and change in the morphology of CuAl2 were ascribed to the increased heterogenous nucleation rate due to the presence of Al2O3 nano-dispersoids. The distribution was explained on the basis of deagglomeration due to the cavitation and influence of Cu on— (a) the wettability of the Al-Cu with Al2O3, and (b) pushing of nano-particles by the solidification front. The strengthening upon the dispersion was elucidated in terms of a climbing mechanism, which has been proposed earlier in the literature. The increase in the ductility was attributed to the lower extent of the inhomogeneity as a result of two-step ultrasonication in the nanocomposite as compared to the base alloy.