Upward and downward unsteady-state directional solidification of a hypoeutectic Al-3wt.%Mg alloy

Solidification thermal parameters, such as growth rate, cooling rate and dendrite arm spacing (λ), have been measured in a hypoeutectic Al-Mg alloy directionally solidified under upward and downward transient heat flow conditions. The experimental setup used in this work consists of a water-cooled mould with heat being extracted from the bottom or the top, promoting upward and downward directional solidification, respectively. It is shown that the dendritic arm spacing are not significantly affected by interdendritic convection for both solidification configurations and single growth laws are proposed for both cases. The Bouchard- Kirkaldy model is shown to overestimate the experimental primary dendritic arm spacing, despite fitting properly the secondary dendrite arm spacing.