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

Abstract

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.