Eutectic morphology of Al-7Si-0.3Mg alloys with scandium additions
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Author list: Pandee P., Gourlay C.M., Belyakov S.A., Ozaki R., Yasuda H., Limmaneevichitr C.
Publisher: Springer
Publication year: 2014
Journal: Metallurgical and Materials Transactions A (1073-5623)
Volume number: 45
Issue number: 10
Start page: 4549
End page: 4560
Number of pages: 12
ISSN: 1073-5623
eISSN: 1543-1940
Languages: English-Great Britain (EN-GB)
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Abstract
The mechanisms of Al-Si eutectic refinement due to scandium (Sc) additions have been studied in an Al-7Si-0.3Mg foundry alloy. The evolution of eutectic microstructure is studied by thermal analysis and interrupted solidification, and the distribution of Sc is studied by synchrotron micro-XRF mapping. Sc is shown to cause significant refinement of the eutectic silicon. The results show that Sc additions strongly suppress the nucleation of eutectic silicon due to the formation of ScP instead of AlP. Sc additions change the macroscopic eutectic growth mode to the propagation of a defined eutectic front from the mold walls opposite to the heat flux direction similar to past work with Na, Ca, and Y additions. It is found that Sc segregates to the eutectic aluminum and AlSi2Sc2 phases and not to eutectic silicon, suggesting that impurity-induced twinning does not operate. The results suggest that Sc refinement is mostly caused by the significantly reduced silicon nucleation frequency and the resulting increase in mean interface growth rate. ฉ 2014 The Minerals, Metals & Materials Society and ASM International.
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