Solidification of hypereutectic and hypoeutectic binary alloys with buoyancy and surface tension driven natural convection

Convection patterns and evolution of macrosegregation during solidification of hypereutectic and hypoeutectic NH4CL-H2O binary systems in rectangular side chilled ingots have been numerically investigated. Under the conditions of pure thermal/solutal convection, without a free surface, solidification of NH4CL 70%-H2O hypereutectic alloy is characterized by the formation of channels and A-segregates, while solidification of NH4CL 10%-H2O hypoeutectic alloy is characterized by the formation of circulation cells in the narrow melt and V-segregates. Surface tension effects during solidification of NH4CL 70%-H2O results in establishing a counterclockwise rotating cell at the cavity top, changing the number and orientation of developed channels, and creating an area of negative segregation at the cavity top. During solidification of NH4CL 10%-H2O, surface tension effects increase the intensity of flow and results in a higher degree of macrosegregation.