INFLUENCE OF GRAVITY ACCELERATION ON MACROSEGREGATION AND MACROSTRUCTURE DURING THE UNIDIRECTIONAL SOLIDIFICATION OF CAST BINARY ALLOYS: A NUMERICAL INVESTIGATION

A comprehensive numerical approach was developed for modeling of macrosegregation during the solidification of cast binary alloy. The model accounts for the competition between dendritic (columnar and equiaxed) and eutectic structures through the use of the solidification-kinetics modeling for fraction of solid evolution. Microsegregation analytical calculations are performed assuming molecular diffusion in both solid and liquid. The coupling between the macroscopic and microscopic calculations is accomplished with the micro-latent heat method \[1,2]. A numerical analysis was performed of the thermosolutal convection effects on macrosegregation and macrostructure (grain structure) during the solidification of a liquid Pb-10 wt. % Sn alloy cooled from below in terrestrial and low-gravity (g) environments. Below 0.01 g , the macrosegregation tendency is insignificant. Freckles, fingers (which are caused by plumes), and channels enriched in Sn as well as isolated pockets poor in Sn develop for 1 g and sufficiently low thermosolutal Rayleigh number. For the simulation conditions used in this work (e.g., high thermal gradients), small effects of the thermosolutal convection on the solidification macrostructure were observed.