Microstructural Evolution and Property Evaluation of In Situ Al–MgAl₂O₄ Nanocomposite Prepared by γ‐Al₂O₃ and Ultrasonication‐Assisted Impeller Mixing

Abstract

Synthesis of nanocomposites is challenging due to the difficulties in achieving homogeneous distribution of reinforcing particles in metal. In this paper, an in‐situ Al‐MgAl2O4 nanocomposite billet was prepared by the reaction of ɣ‐Al2O3 with molten Al and ultrasonication‐assisted impeller mixing. The microstructure of the composite showed homogeneously distributed MgAl2O4 crystals alongside their clusters in the Al matrix. Microstructural analysis revealed MgAl2O4 crystals distributed from 20 nm to 4 μm in size. The hardness was found to vary within the composite from 50 Hv for the matrix to 140 Hv for particle cluster regions. The grain size was reduced from 1000 μm in reference metal (CP Al) to 100 μm in the composite. The compression strength of the composite was increased substantially and higher strain hardening effect in comparison with Al was noticed in the compression test. The signatures of extensive plastic deformation such as dislocation pileups, deformed grains, grain boundary pinning etc. were observed in the composite via transmission electron microscopy. Damping properties of as‐cast composite were higher than those of CP Al in the temperature range from room temperature to 350 °C. After rolling the composite up to 40% reduction, the damping capacity (Tanδ) of the composite was found to increase marginally after 150 °C. Higher damping was found to reoccur after the annealing treatment of the composite. The improvement in damping capacity at RT was possibly influenced by the micron sized MgAl2O4 and at higher temperatures by the nano‐sized MgAl2O4 crystals. The reoccurrence of higher damping in the annealed composite underlined the stability of finer grains due to the grain boundary pinning by nano‐sized MgAl2O4 crystals. The studies on the damping property of the composite displayed the benefits of having dual size distribution of MgAl2O4 crystals (nm and μm) in the composite.This article is protected by copyright. All rights reserved.