Simulation Of Dendrite Growth In The Presence Of Fluid Flow By Cellular Automaton

The fluid flow in the melt changes the temperature field and concentration field, further influences the nucleation and growth procedure and finally affects the solidification microstructures and properties of the casting metals during the solidification processes. In order to study the mechanics of the fluid flow affecting on the growth of the dendrites, a Cellular Automaton (CA) model, which includes the dendrite tip growth kinetics in the presence of fluid flow and the decentred growth algorithm describing the evolution of the growth envelope of the grains in the flow field, is developed and applied to predict the solidification morphologies of Al-Si binary alloy in the forced flow field.It shows that the dendrite tip velocity is larger in the upstream direction than that in the downstream direction, which is embedded in the algorithm of the dendrite tip growth kinetics. The solidification morphologies of the multi-grains which are nucleated at the mold surface are predicted by the above CA model. It can be seen that with the increase of the fluid flow intensity, with the decrease of the nucleation density and the decrease of the undercooling, the dendrites are inclined to grow towards the upstream direction and the deflection angle, which is the angle between the dendrite growth direction and the direction perpendicular to the nucleation surface, is increased. The fluid flow intensity, the nucleation density and the undercooling are regarded as the internal parameters effecting the dendrite growth in the forced flow field and the influences of the fluid flow intensity on the dendrite growth dominates the influences of the other two. The predicted relationships of the deflection angle versus the flow velocity and the solidification rate agrees with the empirical relations of Okano.Further, the CA model combining the algorithm of the growth, the transport, the impingement and sticking to the mold surface for the single cluster, which is formed by one or more grains, and the two clusters in the flow field is developed and applied to the evolution of the growth of the two nucleuses in the melt. This makes it possible for the present CA model to predict the microstructures and morphologies in the presence of fluid flow during the realistic solidification processes.