Modeling And Numerical Simulation Of Heterogeneous Nucleation And Growth Behavior Of Primary Al During Solidification Of Al-Cu Alloy

Al-Cu alloy has been widely used in aerospace,automobile,aircraft and other industries because of its excellent comprehensive mechanical properties.In the process of alloy processing and preparation,the solidification microstructure will directly affect the performance of the material.In recent years,the progress of numerical simulation technology and the perfection of solidification theory make it a powerful tool to study the solidification process.By establishing the correct mathematical physics model and using the powerful computing power of computer,the evolution process of alloy solidification structure under various factors can be simulated.In this paper,based on cellular automata method,Visual Studio 2015 MFC platform and C++ computer programming language are used to simulate the growth and evolution process of microstructure during solidification of Al-Cu alloy.The effects of non-uniform temperature field,Ti solute diffusion and dendrite rotation induced by semi-solid stirring process on grain nucleation and growth are investigated.(1)Based on the free growth model,the heterogeneous nucleation and growth behavior of Al-Cu alloy under the non-uniform temperature field was simulated by coupling the nonuniform temperature field with the nucleation and growth model,and the microstructure evolution of single core and multi-cores under different heat dissipation conditions and the internal non-uniform temperature field are simulated respectively.The simulation results under different heat dissipation boundary conditions show that the heterogeneous nucleation cores near the heat dissipation boundary is activated earlier,the dendrite arm is the more developed.Under the condition of internal non-uniform temperature field,the undercooling of the nucleating core is higher than that of other melt areas,and it is easier to be activated.This model pays attention to the effect of temperature distribution on heterogeneous nucleation,which is more accurate and fit to the experiments.(2)Based on the analysis of the refining mechanism of Al-Ti-B,it is found that the solute Ti plays a crucial role in refining the grain.A new model of α-Al grain nucleation and growth was established by coupling the diffusion field of solute Ti with Al-Ti-B intermediate alloy refinement.The effect of solute Ti on the nucleation and growth behavior of Al-Cu alloy heterogeneous nucleation cores was studied to better understand how solute Ti affects the grain refinement of aluminum alloy.(3)Based on the study of the formation mechanism of near-spherical microstructure in semi-solid forming,a dendrite rotation model is established in this paper.By periodically adjusting the growth direction of grains,the rotation of dendrites can be effectively controlled,so that the original dendrite symmetry structure is changed and the dendrites have obvious spiral growth.The coexistence of dendrite grains,rosaceous grains,and spherical grains was found very rarely in the multinucleate core simulation,which is in complete agreement with the experimental results,indicating that dendrite rotation is the key factor in the dendrite structure transformation from dendritic to rosaceous and spherical shape.