Grain refinement mechanism in an Al-Si-Mg alloy with scandium
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Author list: Patakham U., Kajornchaiyakul J., Limmaneevichitr C.
Publisher: Elsevier
Publication year: 2012
Journal: Journal of Alloys and Compounds (0925-8388)
Volume number: 542
Start page: 177
End page: 186
Number of pages: 10
ISSN: 0925-8388
eISSN: 1873-4669
Languages: English-Great Britain (EN-GB)
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Abstract
Grain refinement of the primary aluminum (α-Al) phase in a hypoeutectic Al-Si alloy using scandium (Sc) was studied to identify the grain refinement mechanism. Optical microscopy (OM), Scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and electron backscatter diffraction (EBSD) techniques were extensively used in this study. We found that Sc refined grains of primary aluminum. However, the grain refinement efficiency of Sc was considerably lower than that of titanium (Ti) in the Al-Si-Mg foundry alloy. It was evident that the precipitated Sc-containing phases acted as heterogeneous nucleation sites for the primary aluminum phase. The Sc-containing heterogeneous sites are irregular in shape with sizes between 3 and 5 μm. At least three groups of nuclei based on their chemical composition were found, i.e., (i) Al and Sc, (ii) Al, Si, Mg, and Sc, and (iii) Al, Si, Mg, Sc, and Fe. Crystal orientation mapping showed primary aluminum dendrites with one orientation in each grain near Al 3Sc particles. The grain refinement mechanism of Sc for aluminum relies on heterogeneous nucleation of Al 3Sc particles, with less responsibly for grain growth restriction. Many intermetallic phases with Al, Si, Fe, Mg and Sc as their major components were found, and these phases could not effectively act as heterogeneous nuclei. © 2012 Elsevier B.V. All rights reserved.
Keywords
Grain refinement mechanism
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