Research On The Key Techniques Of The Micro Modeling Of Casting Alloys Structure For Solidification

In the paper, a method of solving Johnson-Mehl equation for Monte_Carlo Steps (MCS) is studied. A model basing on Johnson-Mehl equation is developed for solving the Monte_Carlo Step time. Meanwhile, physical reality of Monte_Carlo Step (MCS) is studied. First time, a model based on the physical reality of Monte_Carlo Step, is developed for solving the Monte_Carlo Step time during the solidification. Two-dimensional computations are performed for the Al-4.5%Cu casting solidification simulation with realistic Monte_Carlo Step time. A method of simulation for treeing in binary alloys with Cellular Automaton is studied. In the paper, a model basing on Cellular Automaton is developed for Simulation of treeing during solidification. Two-dimensional computations are performed for Al-4.5%Cu crystal growth with Cellular Automaton. Some key problems in the numerical computation of the model are resolved, the mechanism of the dendritic growth during solidification of the alloy is discussed, and a favorable base for prediction of mechanical property of casting is established. Phase-field method can be used to describe the complicated morphologies of dendritic growth without explicitly tracking the complex phase boundaries. It is expected as a powerful tool to describe complex phase transitions in non-equilibrium state. It is the frontier domain of the numerical simulation during solidification processes at present. A new phase-field method for two-dimensional simulations of binary alloy solidification is studied. A model basing on solute conservative in every unit, is developed for solving the solute diffusion equation during solidification. Two-dimensional computations are performed for ideal Ni-Cu dendritic growth into an isothermal and highly supersaturated liquid phase. The relationships between material properties and phase-field parameters can be determined at a thin-interface limit condition. The dependence of simulation results upon the mesh size, the interface anisotropy and noise is investigated, and how to choose the values of these key parameters is determined. The governing equations are discretized on uniform grids using the Finite Difference method, and a double grid method is used for the mesh slice to save the time. The thermal governing equation is numerically solved using an alternating direct implicit (ADI) method, which is unconditionally stable. These methods are put forward to optimize the numerical computation of the Cellular Automaton and phase-field models, which improve the calculating efficiency. For the simulation results being displayed realistically, the visualization in the simulation of solidification is investigated, and the numerical methods of some key parameters in the dendritic growth are put forward. A software system for the visualization of microstructure simulation results is developed using the MFC technique, which realize the computer display of simulation results, and can integrate with the computational program of the Cellular Automaton and phase-field models to realize dynamic display of the simulation results. Experimental study on the solidification process of Al-Cu binary alloys is used to validate the CA simulations of this dissertation. The results indicate that the dendrite morphologies and solute profiles under different cooling times, which are obtained in the experiment, agree well with the results of CA simulation qualitatively.