In situ quantification of the nucleation and growth of Fe-rich intermetallics during Al alloy solidification

Real-time in situ synchrotron X-ray tomographic microscopy was used to gain new insights into and quantify the nucleation mechanisms and growth kinetics of beta-Al5FeSi intermetallics during solidification of an aluminium A1-7.5Si-3.5Cu-0.6Fe (wt.%) alloy. Three new insights were obtained. First, the plate-like beta-intermetallics appeared to nucleate mainly on or near the primary aluminium dendrites and to a lesser extent off the oxide skin on the surface of the specimen. Second, for this alloy composition, beta-intermetallic formation was largely complete before the formation of Al-Si eutectic. Third, the beta-intermetallics formed via fast lateral growth, wrapping around and in between the primary dendrite arms. Further, the nucleation and growth dynamics of beta-intermetallics were quantified as a function of undercooling in a functional form that could be easily used in microstructural simulations. The frequency of intermetallic interaction mechanisms, such as plate nucleation vs. impingement and branching, were also quantified. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/3.0/).