During the solidification of a liquid containing dispersed second phase particles, particles are either rejected or engulfed by the advancing solid-liquid interface. Theories have been proposed on the mechanisms on particle pushing by a freezing front. However, the critical growth velocities predicted are much smaller than actually found experimentally. This article evaluates mechanisms on particle pushing. A specially selected alloy system, an Al-Ti-B master alloy, was chosen to evaluate particle pushing under various solidification conditions. The final distribution of the particles in ingots was examined. It is concluded that most of the particles are pushed by the dendritic solid liquid interface under cooling conditions varying a few orders of magnitude. Mechanical disturbance, such as fluid flow in the remaining liquid of the mushy zone, promotes particle pushing by the growing solid.
Keywords: Particle pushing, solidification, Aluminum alloys, and metal-matrix composites
Experimental study of the solid-liquid interface in a yield-stress fluid flow upstream of a step