Effect of high volume fraction of B4C particles on the microstructure and mechanical properties of aluminum alloy based composites

In this work, we have evaluated the effect of high volume fraction of B4C particles (>20 vol.%) on the microstructure and mechanical behavior of Al-2024 matrix composites. The composites were fabricated by mechanical milling of the matrix and the reinforcements together followed by hot extrusion. Mechanical milling resulted in significant grain refinement of the Al-2024 matrix phase (∼35.4 nm), while hot extrusion provided the combined advantage of homogenous dispersion of the reinforcement in the matrix as well as clean and strong interface between the two phases. After consolidation at 823 K, the grain size of the Al matrix has grown up partially, while the grains around B4C particles are still at nano-scale because of the large difference in the coefficients of thermal expansion (CTE) between the matrix and the reinforcement. The microhardness and compression strength of the composites reinforced by the B4C particles are 260 and 950 MPa, respectively, which are almost twice as high as that of the matrix. The superior mechanical properties are attributed to the refined microstructure of the matrix and the homogeneous dispersion of the B4C particles.