Effect of High Gravity on Freckle Formation and Convection in a Mushy Layer

Abstract

Nonlinear, time-dependent natural convection in a mushy layer during centrifugal solidification of binary alloys is investigated for low, moderate and high rates of rotation. Asymptotic and scaling analyses are applied to axisymmetric convection within the mushy layer and in vertical chimneys with small radius. These chimneys produce freckles in the final solidified material. Freckles are imperfections that reduce the quality of solidified materials. Results are obtained for several distinct regimes, corresponding to high or low Prandtl number melts and strongly or weakly time-dependent flow. In particular, conditions are determined under which convection and freckle formation can be eliminated, or at least reduced, by the rotational component of a high gravity environment.