Settling and clustering of silicon carbide particles in aluminum metal matrix composites

The settling of 14-μm silicon carbide particles in an aluminum-silicon alloy was monitored with an electrical resistance probe to measure thein situ particle voluem fraction. The rate of settling was much greater than expected from hindered settling of single 14-μm particles. From the observed settling rate, an equivalent hydrodynamic diameter and density of clusters of particles were deduced, 38 μm and 2740 kg/m3, respectively. Other work was analyzed with the same procedure; it was concluded that if the stirring prior to settling were intense, then the clusters would be smaller than with weaker stirring. The implications for foundry practice and mechanical properties are discussed.