Particle sedimentation during processing of liquid metal-matrix composites

A novel electrical resistance probe technique to measure thein situ volume fraction of ceramic particles in molten metals was applied to the measurement of sedimentation rates of 90-µm-diameter silicon carbide particles in molten aluminum. The results indicate that the rate strongly depends on volume fraction; the time to clarify a 0.15-m depth increased from approximately 60 to 500 seconds as the particle volume fraction increased from 0.05 to 0.30. Maps showing the changes in volume fraction throughout the melt were generated. A multiphase hydrodynamic model was developed to describe the sedimentation. Using volume fraction-dependent drag coefficients from work in aqueous systems, the model was able to simulate the experimental results remarkably well. The experimental and modeling results indicate that there was little agglomeration or network formation during sedimentation. The implications of the results for solidification and particle pushing are discussed.