X-Ray Videomicroscopy Studies of Eutectic Al-Si Solidification in Al-Si-Cu |
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Authors: | R H Mathiesen L Arnberg Y Li V Meier P L Schaffer I Snigireva A Snigirev and A K Dahle |
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Affiliation: | (1) Department of Physics, NTNU, N-7491 Trondheim, Norway;(2) Department of Material Science, NTNU, N-7491 Trondheim, Norway;(3) SINTEF Materials & Chemistry, N-7465 Trondheim, Norway;(4) Department of Physics, NTNU, Institut fur Strukturphysik, Technical University Dresden, D-01060 Dresden, Germany;(5) Norsk Hydro Sunndalsora, N-6600 Sunndalsora, Norway;(6) Experiments Division, ESRF, F-38043 Grenoble, France;(7) Department of Materials Engineering, University of Queensland, Brisbane, QLD, 4072, Australia |
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Abstract: | Al-Si eutectic growth has been studied in-situ for the first time using X-ray video microscopy during directional solidification (DS) in unmodified and Sr-modified Al-Si-Cu
alloys. In the unmodified alloys, Si is found to grow predominantly with needle-like tip morphologies, leading a highly irregular
progressing eutectic interface with subsequent nucleation and growth of Al from the Si surfaces. In the Sr-modified alloys,
the eutectic reaction is strongly suppressed, occurring with low nucleation frequency at undercoolings in the range 10 K to
18 K. In order to transport Cu rejected at the eutectic front back into the melt, the modified eutectic colonies attain meso-scale
interface perturbations that eventually evolve into equiaxed composite-structure cells. The eutectic front also attains short-range
microscale interface perturbations consistent with the characteristics of a fibrous Si growth. Evidence was found in support
of Si nucleation occurring on potent particles suspended in the melt. Yet, both with Sr-modified and unmodified alloys, Si
precipitation alone was not sufficient to facilitate the eutectic reaction, which apparently required additional undercooling
for Al to form at the Si-particle interfaces. |
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