The structure of a partially solid alloy

Abstract

An apparatus is described that permits continuous production of partially solidified slurries of Sn-15 pct Pb alloy. The slurries thus produced can be cast into ingots semi-continuously. Results of earlier fundamental studies carried out on a high temperature viscometer are verified by an extensive number of experiments carried out in this apparatus. The three important process variables affecting structure and viscosity of a slurry are: average shear and cooling rates during primary solidification and volume fraction solid in the slurry. Increasing the average cooling rate makes the primary solid particles smaller and more uniform in size, but increases the amount of entrapped liquid in each particle. Increasing the average shear rate affects particle size and uniformity of size similarly, except this effect is noted only at low cooling rates. Primary solid particle size in a vigorously agitated slurry is approximately the same as primary dendrite arm spacing in a conventional casting solidified at equivalent cooling rate. As the volume fraction solid in a slurry increases, so do its primary solid particle size and viscosity.