Investigation on compressibility of Al-SiC composite powders

The consolidation behaviour of particulate reinforced metal matrix composite powders during cold uniaxial compaction in a rigid die was studied. Al-SiC powder mixtures with varying SiC particle size, ranging from nanoscale (50 nm) to microscale (40 mm), at different volume fractions up to 30% were used. Based on the experimental results, the effect of the reinforcement particles on the densification mechanisms, i.e. particle rearrangement and plastic deformation, was studied using modified Cooper-Eaton equation. It was found that by increasing the reinforcement volume fraction or decreasing its size, the contribution of particle rearrangement on the densification increases while the plastic deformation becomes restricted. In fact, when percolation network of the ultrafine reinforcement particles is formed, the rearrangement could be the dominant mechanism of consolidation. It was also shown that at tap condition and at the early stage of compaction where the particle rearrangement is dominant, the highest density is achieved when the reinforcement particle size is properly lower than the matrix (0.3<the size ratio<0.5) and the fraction of hard particles is relatively low (<10%). At high compaction pressures, the reinforcement particles significantly influence the yield pressure of composite powders, thereby retarding the densification.