Numerical Simulation Of Themotion Behavior Of Dendritesbased On CA-LBM Method

The movement of equiaxed grains in the melt is an important phenomenon in the solidification process of alloy,and it has an important influence on the microstructure and macrosegregation of castings.So far,the movement of equiaxed grains with real morphology is seldom considered in the simulation of microstructure of the ingot.In this study,the drift behavior of equiaxed grains is taken into consideration in the whole solidification process,which lays an important foundation for the accurate prediction of macro segregation of ingot.The main contents of this paper are as follows:A coupled model of CA-LBM for calculating the motion and growth of equiaxed grains is established.The model uses the CA method for the growth of the dendrite,the LBM for the momentum,mass,and heat transfer of the domain,the Ladd method for handling the solid-liquid interfaces and the equations of motion for tracking the motion of the solid phase.The accuracy of the model is verified by following examples:(1)Global equiaxed grains solidification is calculated and compared with the experimental results.The results show that the calculation of solute field is correct;(2)The simulation of a circular particle between two infinite and parallel walls proves the accuracy of boundary treatment;(3)The growth rate of the dendrite tip under pure diffusion is compared with the theoretical value to verify the accuracy of the model for the calculation of microstructures;(4)Two-dimensional computations of dendritic translation and rotation show that the shape preservation conditions are satisfied in this method.On the basis of the above,the growth and movement of a standard dendrite and a inclined dendrite were simulated with the established model.The results show that position of the dendrite changes under the influence of gravity.The movement of the standard dendrite will accelerate the flow velocity of the flow field and the dendrite arm at one end of the movement(downstream)grows faster than the dendrite fixed.When the dendrite is inclined and settles under gravity a slight rotation starts due to the asymmetry of growth.The rotation of the dendrite weakens the asymmetry of four dendritic arms.Then,the growth and movement of multi grains were simulated by this model,and the results show that in the solidification process,multi grains settle under the action of gravity,and accumulate in the computational domain at the bottom,forming a negative segregationregion.However,the Cu discharged from the Al-Cu alloy also sink to the bottom,so the bottom negative segregation can be weakened.Finally,the numerical model of calculating the motion and growth behavior of the equiaxed grains was applied to the simulation of the ingot CET process,and the effect of the dendritic motion on the CET process was researched.The results show that the motion of equiaxed dendrites impedes the growth of columnar dendrites and accelerates the CET transformation in the bottom.