Modeling of microstructural evolution with tracking of equiaxed grain movement for multicomponent Al-Si alloy

A new model for the simulation of microstructure evolution of multicomponent alloys with equiaxed dendritic and eutectic morphology has been developed based upon the mixture-theory model (continuum approach). The model can account for the effects of natural convection, solidification contraction, solidification kinetics, and grain movement on the solidification microstructure evolution. The novelty of this model is that it includes tracking of equiaxed dendritic and eutectic grains movement during solidification and, thus, eliminates the assumption of uniform grain size in a given volume element, which is standard in current advanced solidification models. This is achieved through the implementation of continuous nucleation laws and of a grain distribution function over the volume element, in addition to solid transport simulation through the energy equation. To track grain movement, rules of tracking grain movement are proposed. The model deals with nonequilibrium solidification and describes competitive growth of primary and eutectic phases. The proposed model was implemented to simulate the microstructural evolution of an Al-Si-Mg alloy (A356) during solidification. An equivalent pseudobinary approach was developed to calculate the solidification parameters required in modeling of this multicomponent alloy. Computational experiments with the new model have demonstrated that significant variations in the volumetric grain density exist throughout the casting because of natural convection. These differences can be traced with the proposed grain tracking technique but not with current solidification models.