Creation of semisolid slurries containing fine and spherical particles by grain refinement based on the Mullins-Sekerka stability criterion

A non-agitation liquid processing approach for the production of semisolid magnesium slurries containing fine and spherical particles has been proposed on the basis of the Mullins-Sekerka stability criterion for spherical growth and recent advances in grain refinement of magnesium. It is shown that semisolid magnesium slurries containing fine and spherical particles are obtainable directly from the liquid state without agitation, via effective control of nucleation and growth by grain refinement with zirconium. The solid fraction can be varied in a wide range up to more than 50%. The formation of spherical primary magnesium particles is attributed to the combined effects of both dissolved and undissolved zirconium, which give rise to a high nucleation rate and a small undercooling when the melt contains a high level of dissolved zirconium and a sufficient number of suitably sized, undissolved zirconium particles. Grain refinement offers a promising non-agitation liquid processing approach for semisolid structure formation. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.