Numerical simulation of segregation in channel during horizontal solidification

A mathematical model for the segregation formation in channel during solidification process of binary alloys has been built and a set of expressions coupling the temperature and solid fraction with enthalpy is determined. The formation position and growth direction of the segregation during the horizontal solidification of NH4Cl-H2O with hypoeutectic and hypereutectic compositions are numerically studied based on the experiment. The simulation results show that the segregation originates from the mushy zone and the solute-rich liquid flows from mush into liquid. In order to supply the mass equilibrium in the channels, the fresher liquid may penetrate via the mushy zone from pure liquid region. The flow direction of solute-rich liquid in mush depends on its density. Because of the lower density of the rejected solute during the horizontal solidification of NH4Cl-70%H2O, channels grow slantways and upwards and A type segregates form in the upper region of mush. While the density of the rejected solute during the horizontal solidification of NH4Cl-90%H2O, channels grow slantways and downwards in the lower region of mush.