Restrictions of physical properties on solidification microstructures of Al-based binary alloys by cellular automaton

Abstract

The solidification microstructure evolution and the Columnar to Equiaxed Transition (CET) during Al-Si and Al-Cu binary alloy solidification processes are analyzed by the help of Cellular Automaton-Finite Difference (CA-FD) model. The effects of the physical properties, except the effects of the nucleation parameters and the operation parameters, on the cooling curves, the dendrite growth, the solidification morphologies and the CET of the Al-Si and Al-Cu binary alloys are emphatically discussed. Results show that the solidification morphologies are internally influenced by the physical properties related to the dendrite tip growth kinetics. Besides the solute diffusivity in liquid D L and the growth restriction parameter Q=mC°(kS/L-1), the Gibbs-Thomson coefficient r shows a great effect on dendrite tip growth rate. Their effects on the dendrite tip kinetics are ordered as m[k S/L-1)>I>DL. The growth rate can be predicted efficiently by the present simplified expression based on GGAN model combining several physical parameters and the local undercooling, which clearly shows the physical meaning of the constant coefficients in the simplified expression based on KGT model. The equiaxed ratio related to the solidification morphologies can also be evaluated as a function of those physical properties. © 2010 ISIJ.