The impact of matrix microstructure and reinforcement size (micron vs. nano-size) on the compressibility of Al-SiC powder mixtures and hardness of Al/SiC composites

In the present study, four series of Al-6061/SiC composites synthesized via powder metallurgy technique were used to investigate the impact of the matrix grain size and/or the size of reinforcing particles on enhancing the compressibility of powder mixtures and hardness of the composites. In two series, the as-received Al powders have micron-sized grains mixed with either nano-sized or micron-sized SiC particles. For the other two series, the Al powders were initially milled to convert their grain size to nano-scale before mixing with either nano-sized or micron-sized SiC particles. The powder mixtures containing 1, 2, and 3 vol.% of SiC particles were cold pressed and hot extruded. The decreased compressibility in all of the four series of Al/SiC powder mixtures with increased SiC content attributed to the enhanced portion of the hard and non-deformable SiC particles in the powder mixtures resulting in a reduced degree of plastic deformation. Increment the SiCn content from 0% to 3% resulted in a significant increase in the microhardness of 20h planetary ball milled powders accompanied with decrease compressibility of powders. The composites were subjected to Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and X-ray diffraction (XRD) studies as well as density and hardness measurements. Metallographic studies and density measurements confirmed significant densification with no indication of voids in the samples’ microstructures after hot extrusion. The results revealed that matrix microstructure, as compared with the size of the reinforcing particles, was more influential in enhancing the powder compressibility and composite hardness.