Impact of buoyancy on the growth of equiaxed grains in Al–Cu

Abstract

Equiaxed dendritic growth in grain refined Al–Cu (15, 20, 25 wt-%Cu) has been studied in-situ during directional solidification by means of high resolution synchrotron X-ray video microscopy. At these compositions, the α-Al grains have a lower density than the surrounding melt and experience buoyant forces which affect their growth rates and morphologies. A model has been derived, based on Scheil conditions to account for solute transport across the solid-liquid interface, and a spherical envelope approximation to the dendrite morphology in order to simplify both the interface geometry of the growing crystals and the Stokes drag exerted upon them during motion. The model was compared with experimental results to evaluate its present merits and to devise possible routes for further improvement and development.