The Numerical Simulationresearch On The Solidificationprocess Of Alloy Based On Threedimensional LBM-CA Model

The research of macro segregation of ingot/casting is a hot problem in the field of casting,and it is also a difficult problem.In view of the research process of macro segregation,numerical simulation has become the mainstream of macro segregation prediction of ingot.This is of great significance to the deep understanding of the formation of microstructure and the improvement of the performance of the castings during the solidification process.In this paper,a three-dimensional LBM-CA coupling model can be built to simulate the solidification process of the alloy,the CA model is used to calculate the growth of three dimensional dendrites,and the LBM model is used to calculate the flow field,temperature field and solute field in the solidification process,to study the growth behavior of dendrites under different influencing factors from three-dimensional simulations.The effect of natural convection on the solidification process of single-phase solid solution alloys was investigated.The main research contents completed and the conclusions reached are as follows:(1)First,according to the three-dimensional LBM-CA model constructed,the growth process of single dendrite under the pure diffusion condition in the cooled melt was simulated.The dendrite morphology,the steady state growth speed and the tip radius characteristic parameters of the simulation were compared with the LGK analytical solution and the dendritic morphology obtained from the related experiments.The results were in good agreement,which verified the rationality of the coupling model and the correctness of the simulation results.(2)Then the classic example is driven by the three-dimensional cavity cover to verify the correctness of the three-dimensional LBM model calculation fluid program.On this basis,the single-crystal growth process with different growth orientation under natural convection is calculated.The morphology of dendritic growth,the distribution of solute,the growth rate and the pure diffusion results are compared.The results show that natural convection affects the distribution of solute in the space,and solute from the upstream to the downstream side is transported,which promotes the growth of the downstream side,eventually,dendrite growth appears asymmetric.(3)The dendritic morphology and solute segregation with initial undercooling under three-dimensional natural convection is calculated.The results show that,when the initial undercooling is smaller,the asymmetry of the primary dendrite at the upstream and the downstream is more obvious,when the initial degree of subcooling is large,the dendrite grows faster,the solute is discharged from the solid phase to the interface frontier and the diffusion is not sufficient,making the concentration of the liquid solute between the dendrites high and the segregation more serious.(4)The two and three dimensional simulation results are compared under the natural convection conditions,the results show that the streamlines of natural convection melt can bypass the whole primary dendrite arm trunk under three dimensional conditions,and shuttle across the dendrite arm to form a three-dimensional spatial circulation.The thickness of the solute enrichment layer is thinner than that in the two-dimensional case.3D LBM-CA model can more reasonably reflect the flow of melt and the actual growth of dendrites.(5)On the basis of the above research,the whole solidification process of the ingot is simulated.The results show that in the early stage of solidification,natural convection accelerates the diffusion of solutes,promotes the nucleation of equiaxed grains in the center,and increases the possibility of grain refinement,making CET transformation ahead of time.In the later stage of solidification,the natural convection is suppressed due to the equiaxed crystal,the directional transport of solute is no longer obvious,and the solute distribution in the whole simulation area is more uniform.