Prediction of the solidification structure of casting and heterogeneous nucleation

The frequency of heterogeneous nucleation during the solidification of Al-Si binary alloy was estimated by comparing experimentally obtained macrostructures of castings with numerically simulated ones. A molten alloy was unidirectionally solidified from a water-cooled copper chill in an adiabatic mold. The location of colunmar to equiaxed transition (CET) in the solidified alloy ingot was measured. A numerical simulation for grain structure formation based on the Monte Carlo method was carried out, and the frequency of heterogeneous nucleation in the alloy was evaluated by producing similar structure with the experimental one. The frequency of heterogeneous nucleation was expressed as a probabilistic function with an exponential form of undercooling that deter-mines the probability of nucleation event in the simulation. The value of the exponent is regarded as the nucleation parameter. The nucleation parameter of Al-Si binary alloy varied with initial Sicontent.