Comparative study of recrystallization behaviour and nanoindentation properties of micro-/nano-bimodal size B4C particle-reinforced aluminium matrix composites under T6 and electropulsing treatment

Abstract

In this study, as-rolled micro-/nano-bimodal size B4C particle-reinforced aluminium matrix composites were subjected to T6 treatment (as-heated1) and electropulsing treatment (as-heated2). The recrystallization behaviour and nanoindentation properties of the as-rolled, as-heated1 and as-heated2 composites were investigated. Results showed that nanosized B4C particles were distributed uniformly in matrix, and the deformed grains accounted for the majority of as-rolled composites. After T6 treatment, fine recrystallized grains appeared around the microsized B4C particles due to the high dislocation density and large orientation gradient at the particle/matrix interface. The Al grains with dispersed, nanosized B4C grew slightly. After electropulsing at the same temperature, the deformed grains were replaced by completely recrystallized grains. This transformation was due to the extra driving force of recrystallization induced by electropulsing, indicating that the non-thermal effect played a dominant role. The texture orientation of the 6061Al grain existed in the as-rolled and as-heated1 composites, whereas that of the as-heated2 composites disappeared owing to full recrystallization. Compared with the as-rolled composites, as-heated1 and as-heated2 composites exhibited decreased microhardness owing to the coarse grains and residual stress release. The plasticity of as-heated2 composites was improved significantly according to the calculation of indentation work recovery rate based on the nanoindention results.