The Numerical Simulation Research Of Non-Modified Al-Si Eutectic Alloy Ingot Microstructureignot Using Cellular Automaton Method

A two-dimensional CA(Cellular Automaton)model was developed for simulating the microstructure of the binary elements eutectic alloy.In the model,the curvature undercooling and the constitutional undercooling have been taken into account.Using this model,the growth process of Al-Si eutectic is studied,and the influences of different curvature undercooling and different heat transfer coefficient on the eutectic growth of AlSi eutectic are discussed.The simulation results show that curvature undercooling has little influence on the eutectic growth of Al-Si.When transfer coefficient between mould and external environment was increased,needle-like eutectic silicon distribution became more intensive and thinner and more different in length.The silicon morphology in the eutectic alloy under the non-modification condition were investigated.The results of simulation and experiments show that: 1)in the surface region of the ingot,because of the great undercooling,the Si phase is in the shape of short and thick rod,and distributed densely,which is similar to that of the fine grain layer of the ingot of the single phase solid solution.2)In the region neighboring to the ingot surface layer,the Si phase was of long needle shape and distributed sparsely,which was similar to that of the columnar crystal zone of single phase solid solution.3)In the central area of the ingot,the Si phase was needlelike,and the width was uniform,which was similar to the central equiaxed crystal region formed in the ingot of single phase solid solution.The above results were in agreement with our pouring experimental results.We can say that the model describe the growth of Al-Si eutectic well.On the other hand,the simulation of Al-Si hypoeutectic Al-7wt%Si alloy ingot was studied with CA model.Using three sets of different sizes of grid to compute the temperature field primary alpha phase growth process and eutectic growth process respectively.Coupled with the modified liquidus slope formula which variate with temperature,the alpha primary dendrite growth progress was simulated.With the modified liquidus slope formula,the primary alpha phase morphology under different curvature undercooling calculation and distribution of the solute on 850 K was analyzed.Afterwards,the eutectic growth process among primary alpha dendritic was studied,and the eutectic silicon morphology and experiment were compared.Simulation results show that the curvature undercooling has influence on primary alpha phase morphology,and the solute distribution on 850 K is reasonable in the results with application of the modified liquidus slope formula.The error between actual solute concentration and theory of solute concentration is less than 0.01%.Eutectic silicon morphology w is in good agreement with experimental results.