Cellular growth during transient directional solidification of hypoeutectic Al-Fe alloys

Investigations have been made of the solidification structure of three hypoeutectic Al-Fe alloys, which were directionally solidified under unsteady-state heat flow conditions. The experiments have been carried out by using a casting assembly, which was designed in such way that the heat was extracted only through the water-cooled system at the casting bottom, promoting vertical upward directional solidification. A combined theoretical/experimental approach was used in order to quantitatively determine the solidification parameters: tip growth rate and cooling rate of Al-0.5 wt%Fe, Al-1.0 wt%Fe and Al-1.5 wt%Fe alloys castings. The experimental results include transient metal/mold heat transfer coefficients, h(g), determined from comparisons between the experimental thermal profiles in castings and the simulations provided by a finite difference heat flow program. Cellular microstructures prevailed along the entire castings for any alloy experimentally examined. The cell spacing variation with cooling rate and tip growth rate has been characterized by -0.55 and -1.1 experimental power laws, respectively. The experimental cell spacings were compared with the theoretical predictions furnished by cellular growth models. (C) 2008 Elsevier B.V. All rights reserved.