Microstructural Evolution and Property Evaluation of In Situ Al–MgAl<inf>2</inf>O<inf>4</inf> Nanocomposite Prepared by γ-Al<inf>2</inf>O<inf>3</inf> and Ultrasonication-Assisted Impeller Mixing

Abstract

In situ Al–MgAl2O4 nanocomposite billet is prepared by the reaction of γ-Al2O3 with molten Al and ultrasonication-assisted impeller mixing. The microstructure of the composite shows homogeneously distributed MgAl2O4 crystals alongside their clusters in the Al matrix. Microstructural analysis reveals MgAl2O4 crystals distributed from 20 nm to 4 μm in size. The hardness is found to vary within the composite from 50 Hv for the matrix to 140 Hv for the particle cluster regions. The grain size is reduced from 1000 μm in reference metal (commercially pure Al [CPAl]) to 100 μm in the composite. The compression strength of the composite is increased substantially and higher strain-hardening effect in comparison with Al is noticed in the compression test. The signatures of extensive plastic deformation such as dislocation pileups, deformed grains, grain boundary pinning, and so on are observed in the composite via transmission electron microscopy. Damping properties of as-cast composite are higher than those of CPAl in the temperature range from room temperature (RT) to 350 °C. After rolling the composite, the damping capacity (Tanδ) of the composite is found to increase marginally after 150 °C. Higher damping is found to reoccur after the annealing treatment of the composite.