Microstructure evolution and mechanical properties of micro-/nano-bimodal size B4C particles reinforced aluminum matrix composites prepared by SPS followed by HER

With the advantage of micro-size and nano-size B4C particles, micro-/nano-bimodal size B4C particles have been widely used to fabricate excellent composites with high strength and ductility. In this study, micro-/nano-bimodal size B4C particles reinforced aluminum matrix composites with three different volume fractions (3%, 5% and 7%) were fabricated by spark plasma sintering (SPS) followed by hot extrusion and rolling (HER). The microstructure evolution and mechanical properties of as-SPSed, as extruded and as-rolled composites were investigated. Results show that the microscopic electrical discharge between the particles in SPS promotes the densification of composites. The maximum relative density of as-SPSed composites increases from 99.21% to 99.65% after HER. Nano-size B4C particles distribute mainly at the gap of 6061Al particles in as-SPSed composites, while the microstructure presents more homogeneous after HER. Pin effect of nano-size B4C particles stimulates dynamic recrystallization (DRX) and grain refining. Texture orientation of the 6061Al grain exists in the as-extruded and as-rolled B4C/6061Al NCs. No new phases are detected in composites in all deformation stages. The tensile strength of as-SPSed composites increases when compared with 6061Al matrix, and the tensile strength of as-rolled composites after hot extrusion is enhanced to 305 MPa. Fracture mechanisms of as extruded and as-rolled composites mainly include 6061Al matrix tear, particle/matrix interfacial tear and micro-size B4C particle fracture. (C) 2018 Elsevier Ltd. All rights reserved.