In this study, the hot extrusion process was applied to stir cast aluminum matrix–SiC composites in order to improve their microstructure and reduce cast part defects. SiC particles were ball milled with Cr, Cu, and Ti as three forms of carrier agents to improve SiC incorporation. Large brittle ceramic particles (average particle size: 80 μm) were fragmented during ball-milling to form nanoparticles in order to reduce the cost of composite manufacturing. The experimental results indicate that full conversion of coarse micron sized to nanoparticles, even after 36 h of ball milling, was not possible. Multi modal SiC particle size distributions which included SiC nanoparticles were produced after the milling process, leading to the incorporation of a size range of SiC particle sizes from about 50 nm to larger than 10 μm, into the molten A356 aluminum alloy. The particle size of the milled powders and the amount of released heat from the reaction between the carrier agent and molten aluminum are inferred as two crucial factors that affect the resultant part tensile properties and microhardness.