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/B 4 C composites containing three types of B 4 C particle sizes (56.9   µm, 4.2   µm and 2.0   µm) were synthesized and studied. For a constant value of volume fraction of B 4 C, the composite with coarse reinforcement particles exhibited a relatively homogeneous and discrete distribution of the B 4 C particles while the composites with fine reinforcement exhibited agglomeration of the B 4 C particles. The composite with the smallest B 4 C particles possessed the highest yield strength and fracture strength. Quantitative analysis of the strengthening mechanisms revealed that smaller B 4 C 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 B 4 C. In addition, the different spatial distributions of the B 4 C particles contributed to different fracture mechanisms in the composites.