Microstructure and enhanced mechanical properties of hybrid-sized B4C particle-reinforced 6061Al matrix composites

Abstract In the present work, the microstructure and elevated-temperature tensile properties of 6061Al alloy and 6061 Al matrix composites reinforced with bimodal-sized (micron + nano) B4C particles or monomodal micro-sized B4C particles are investigated. The results demonstrate that nanoscale B4C (n-B4C) particles are present both at the grain boundaries and within the grains in the composite. Due to the presence of n-B4C particles, there is a decrease in matrix grain size and recrystallization region percentage, and an increase in proportion of low angle grain boundaries. The combined mechanical property and theoretical analyses reveal that n-B4C particles play a significant role in hindering the dislocation movement and limiting the grain boundary slip during tensile deformation, causing an increase in ultimate tensile strength of the annealed composite with bimodal-sized B4C particles at elevated temperatures. The analysis shows that dislocation glide and climb are responsible for the elevated-temperature strengthening mechanism associated with the n-B4C particle addition. For the annealed composites, the ductile fracture of matrix is the primary failure mode at elevated temperatures.