Influence of particle size and spatial distribution of B4C reinforcement on the microstructure and mechanical behavior of precipitation strengthened Al alloy matrix composites

We report on an investigation of the influence of reinforcement particle size on the microstructure and mechanical behavior of Al metal matrix composites. In our work, Al 7075/B4C composites containing three types of B4C particle sizes (56.9 µm, 4.2 µm and 2.0 µm) were synthesized and studied. For a constant value of volume fraction of B4C, the composite with coarse reinforcement particles exhibited a relatively homogeneous and discrete distribution of the B4C particles while the composites with fine reinforcement exhibited agglomeration of the B4C particles. The composite with the smallest B4C particles possessed the highest yield strength and fracture strength. Quantitative analysis of the strengthening mechanisms revealed that smaller B4C particles lead to larger values in strain gradient strengthening as well as CTE mismatch strengthening, which are significantly correlated to the geometrically necessary dislocations caused by the presence of B4C. In addition, the different spatial distributions of the B4C particles contributed to different fracture mechanisms in the composites.