Abstract
The main purpose of this paper is to investigate both the columnar to equiaxed transition and primary dendritic arm spacings of Al-3wt.%Si alloy during the horizontal directional solidification. The transient heat transfer coefficient at the metal-mold interface is calculated based on comparisons between the experimental thermal profiles in castings and the simulations provided by a finite difference heat flow program. Simulated curve of the interfacial heat transfer coefficient was used in another numerical solidification model to determine theoretical values of tip growth rates, cooling rates and thermal gradients that are associated with both columnar to equiaxed transition and primary dendritic arm spacings. A good agreement was observed between the experimental values of these thermal variables and those numerically simulated for the alloy examined. A comparative analysis is carried out between the experimental data of this work and theoretical models from the literature that have been proposed to predict the primary dendritic spacings. In this context, this study may contribute to the understanding of how to manage solidification operational parameters aiming at designing the microstructure of Al-Si alloys.
Highlights
The fundamental understanding of the relationship between solidification parameters and the resulting structure is essential for the development of methods for quality castings
The main purpose of this paper is to investigate both the columnar to equiaxed transition and primary dendritic arm spacings of Al-3wt.%Si hypoeutectic alloy during the horizontal directional solidification in unsteady-state heat flow conditions
The following major conclusions can be drawn from this study, where Al-3wt.%Si alloy has been directionally solidified under unsteady-state heat flow conditions:
Summary
The fundamental understanding of the relationship between solidification parameters and the resulting structure is essential for the development of methods for quality castings. As the fluid flow in the interdendritic channels depends on these dendrite arm spacings, it is important to know the variation of these parameters during the solidification process to analyze microsegregation pattern which influences for instance the homogenization kinetics, ultimate tensile strength, ductility, toughness and yield tensile strenght of solidified alloys[12,13]. It is well known that dendrite fineness can be of even more importance than the grain size for the improvement of mechanical properties. These structures can be considered as an important object of investigation with respect to the directional solidification of metallic alloys
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