Optimization of the microstructure and mechanical properties of heterogeneous Al-Al2O3 nanocomposites

Abstract

High-energy ball milling and hot-press sintering were employed to synthesize heterogeneous aluminum (Al) matrix nanocomposites reinforced by 5 vol.% alumina (Al2O3) nanoparticles. The heterogeneous structure was formed by the nonuniform distribution of Al2O3 nanoparticles in Al matrix, and it composed of an isolated irregular soft phase (pure Al) and a continuous hard phase (Al reinforced by Al2O3 nanoparticles). It was found that the size of soft phase is optimized with increasing ball milling time, resulting in an increase in the yield strength and ultimate strength, as well as retained failure strain. It is worth noting that the ultimate strength of heterogeneous Al nanocomposite with milling time of 20 h (referred to as Heter-20) reached 610 MPa under compression testing. In particular, the introduced soft phase exhibited severe plastic deformation and interface microcracks under compression, which led to higher failure strain (∼30% for Heter-20) and toughness compared to traditional homogeneous Al matrix composites. Furthermore, coexistence of brittle and ductile fractures was observed in the heterogeneous Al nanocomposites under quasi-static compression.