Effects of Casting Parameters on Macrosegregation in 2024 Alloy During Direct-chill Casting Based on Numerical Simulation

The extended continuum mixture model considering the floating grain motion was applied to calculate the macrosegregation of large-size billet of 2024 aluminum alloy during direct-chill (DC) casting. Transport equations of mass, momentum, species and heat were solved simultaneously with the Scheil-Gulliver micro-model. The effects of casting parameters (billet size, casting speed, casting temperature and intensity of secondary cooling zone) on macrosegregation were calculated in nine cases. Influence of casting parameters on the transport mechanisms for macrosegregation formation was discussed. The results demonstrate that the processing parameters directly affect the shape and dimension of the sump, thereby affecting the final segregation patterns. The billet size and casting speed play the most important roles. A larger billet size usually means a slower cooling rate and a deeper and wider sump, which results in severe segregation in the billet center. The sump depth dramatically increases with the increase of the casting speed. Therefore, higher casting speed promotes greater macrosegregation. Nevertheless, the sump depth increases slightly with increasing the casting temperature.