Microstructure Simulation Of Al-Cu And Al-Si-Cu Alloy In Solidification Process

The control of grain structure is of primary importance in many solidification processes of castings, because the grain structure has influence on the quality of casting and mechanical properties. In the past, the microstructural evolution was researched mainly based on numbers of semi-empirical formulations and experiments, which brought great expense of costs and time. Otherwise, it can not provide a direct view of microstructure development. With the advent of high performance computing devices and new simulated techniques, numerical simulation has been considered as an effective tool for evaluation of microstructure evolutions during the solidification process.Numerical simulation experiences the stage of semi-quantitative simulation, fixed-points nucleation and deterministic model to quantitative simulation, random nucleation, and stochastic model. The method of microstructure simulation is the cellular automation-finite element (CAFE) model in this article. In the CAFE model, the growth kinetics of the dendrite tips and crystallographic orientation of grains are determined as a function of undercooling. The CAFE model is well suited to track the development of a columnar dendritic front in an undercooled liquid.This article has optimized and solved some problems of interface heat transfer, liquid-phase diffusion and nucleation which still exist in the microstructure simulation to further improve the accuracy of the CAFE model. The simulated results are in accord with the experimental ones well, and can accurately reflect equiaxed and columnar grains distribution, proportion and size. The main researches are shown as following(1) The interfacial heat transfer coefficients (IHTC) of Al-2%Cu, Al-2%Cu-9.75%Si and A356alloy are performed based on the inverse method of ProCAST and experimental temperature. The identified IHTC is taken into the CAFE method, which improve the accuracy of microstructure simulation with the constant IHTC. For verifying the IHTC, the temperature distribution was calculated by feeding the determined IHTC into the ProCAST with the same boundary conditions and then compared with the measured temperatures at the corresponding locations. In addition, the IHTC variation with time is analysed, and the differences of IHTC between Al-2%Cu alloy and Al-9.75%Si-2%Cu alloy are discussed. Otherwise, the IHTCs of the experiment with water-cooling system are resolved at different pouring temperatures by the inverse method.(2) The liquid-phase diffusion coefficients of Al-2%Cu alloy and Al-9.75%Si-2%Cu alloy are calculated by the Eyring model and Miedema model in different temperatures. The CAFE method is performed by the calculated liquid-phase diffusion coefficient, which improve the accuracy of the micro structure simulation based on the constant liquid-phase diffusion coefficients. The viscosity curve variation with temperature is introduced into the Eyring model. The self-diffusion coefficient is calculated by the Eyring model, and the liquid-phase diffusion coefficient is modified by the Miedema model. The liquid-phase diffusion coefficient of Al-9.75%Si-2%Cu alloy is calculated by the Eyring model, Miedema model and Toop model. In order to verify the feasibility of the model, the liquid-phase diffusion coefficients measured with experiments are compared with the calculated data by the Eyring model, Miedema model and Toop model.(3) According to the experimental conditions and casting material, the nucleation density and undercooling are discussed and selected based on the nucleation and growth model of CAFE in the microstructure simulation. The simulated results using the identified IHTC, calculated liquid-phase diffusion coefficients and suitable microstructure parameters are in accord with the experimental results of normal temperature mold well.