Simulation of dendritic remelting and fragmentation using coupled cellular automaton and Eulerian multiphase model

Dendritic structures are one of the most complicated forms of crystallization in nature and technology and strongly affect the properties of as-cast metals. The evolution of dendrites during solidification process is important for the optimization of materials structure and performance. Current computational models focus mainly on predicting the growth of dendrites, while neglecting the phenomenon of remelting and fragmentation. In this study, we develop, validate and apply a solute induced dendrite remelting model achieved by fully coupling cellular automaton (CA) and finite volume method (FVM). Our model successfully simulates the evolution of dendrites with both growth and remelting processes included. In comparison with other existing work, the present model is developed on the basis of an Eulerian two-phase model which allows us to treat the solid and liquid as two separate phases and for first time to fully describe the interactions of phase transformation, fluid flow, heat transfer and solute transport between those two phases. Our novel framework is applied on a single Al-4.5 wt% Cu alloy nucleus placed in undercooled melt. The results reveal that four stages of dendrite remelting exist, with the last stage leading to fragmentation. Fragmentation is shown to occur when the connection points between downstream dendrite arms and vertical primary dendrite arms are melted. No fragment is observed on the upstream side.