Numerical Simulation Of Solidification Process Of Alloy Under Natural Convection Based On Lattice Boltzmann-Cellular Automata Model

The effect of natural convection on the solidification process of alloys is a frontier issue in current numerical simulation of solidification field.In this paper,the lattice Boltzmann-cellular automaton(LBM-CA)model is established to study the single-phase solid solution alloy's solidification process through coupling the flow field,temperature field,solute field with microstructure.The main research contents are as follows:The LBM-CA model was established to calculate the flow field,temperature field,solute field and microstructure of single phase solid solution.The correctness of the model is verified by two schemes:(1)The classical example of the natural convection in the closed cavity was calculated to prove the correctness of the flow field by the LBM model;(2)The growth process of single dendrite under natural convection was calculated.The numerical solution is compared with the Kurz boundary layer theory solute concentration and LGK analytical solution of the dendritic tip velocity to verify the correctness of the LBM-CA model.On the basis of the above,the LBM-CA model is appied to simulate single grain surrounded by four grains and a large number of grains growth under natural convection.The results show that natural convection has a significant change in the crystal morphology for the five grains,the dendrite grow rapidly at the upstream and slowly at the downstream;For a large number of grains,natural convection is suppressed and it played a role in homogenizing the solute.Then,the ingot CET(columnar-equiaxed crystal transformation)process under and without convection was simulated by the LBM-CA model.The effects of natural convection on the CET position and grain scale were compared,the change of natural convection intensity during the solidification process was analyzed.The results show that(1)natural convection makes the CET position in advance and refines the grains.In addition,the intensity change of natural convection is increased first and then decreased until it disappears.(2)natural convection causes the formation of a large number of nuclei in the cental region of the ingot,rather than layer formation.(3)compared with no convection,natural convection changes the distribution of the temperature field,which will promote the upgrading and progress of commercial software.Comparing with the relevant pouring experiments,it is found that the simulated microstructure and component segregation are in good agreement with the experimental results.Finally,the dendritic remelting phenomenon of the solidification process was studied by the LBM-CA model.It was found that the multiple remelting can suppress the growth of the columnar crystals and increase the equiaxed.