Grain refinement of AZ31 by (SiC)P: Theoretical calculation and experiment

Grain refinement of gravity die-cast Mg-alloys can be achieved via two methods: in situ refinement by primary precipitated metallic or intermetallic phases, and inoculation of the melt via ceramic particles that remain stable in the melt due to their high thermodynamic stability. In order to clarify grain refinement mechanisms and optimize possible potent refiners in Mg-alloys, a simulation method for heterogeneous nucleation based on a free growth model has been developed. It allows the prediction of the grain size as a function of the particle size distribution, the volumetric content of ceramic inoculants, the cooling rate and the alloy constitution. The model assumptions were examined experimentally by a study of the grain refinement of (SiC)P in AZ31. Additions of (SiC)P result in significant grain refinement, if appropriate parameters for ceramic particles are chosen. The model makes quantitatively correct predictions for the grain size and its variation with cooling rate.