The Numerical Simulation Research Of The Global Ignot Macro Micro Coupling

It is still a very difficult problem to eliminate macro-segregation defect of heavy castings. In order to solve this problem completely, it is necessary to make a real coupling simulation of macro field with microstructure in the full domain of the casting. And one of the key techniques is to choose an appropriate numerical model to simulate the microstructure of castings, which is the focus of this paper.Firstly, on the basis of the former researches on CA(cellular automaton), a new capture model is presented concerning the KGT model. A new model is designed to selectively capture the neighbor cells according to the growing length of dendrite tip, which is capable of eliminating the anisotropy phenomenon occurring in growing cells, and removing the defect of losing liquid cells happened in the process of capturing liquid cells in the Zigzag model.Secondly, another CA growing model, named solute diffusion controlling model, is also investigated in the paper. The basic principle of the model is that the interface cells keep discharging solute to its neighbor cells in the process of solidification. The simulation results in this paper shows its good accordance with the experiment.On the basis of the above two CA model research, in order to determine which one is the more appropriate model to be used to simulate the macro segregation, three criteria were put forward, they are: 1) the model is able to present CET process. 2) the model is capable to describe the secondary dendrite(to predict type A and V segregation). 3) the model is able to calculate the solute distribution during the dendrite growing process.According to the above three criteria, through the contrast calculation of the microstructure of Al-4.7% Cu alloy ingot, we find that: 1) when the cell’s size is generated in 100μm×100μm, both models are able to display the CET process, and there is no significant difference in grain size. Neither of the two models is capable to show the secondary dendrites in this cell size. 2) The solute diffusion model is able to present the morphology of secondary dendrite in 10μm×10μm cell size(micro scale), while KGT model cannot. 3) In both cell size, solute diffusion model shows clearly the solute distribution contour in every grain, while the solute distribution calculated by KGT model is blurring. Based on the above study, we know that the solute diffusive model should be a good model to be collected.Finally, further research for the diffusion controlling model has been done, such as the influence of initial temperature, cooling rate and the average nucleation undercooling degree to the directional solidification of dendrite growth. The simulating results show that the three factors can affect dendrite microstructure. It’s advised to set appropriate assembling parameters to control microstructures. The numerical simulation result is coincident with the results calculated by analytical models, which shows that the solute diffusion controlling model can be used as a basic model for predicting A and V type macro-segregation in ingot/ continuous casting slab.