Evolution of Fe-Rich Intermetallics in Al-Si-Cu 319 Cast Alloy with Various Fe, Mo, and Mn Contents
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AL-SI cast alloys have attracted much attention in the automotive industry owing to their excellent castability and combination of strength and ductility. Further, their high strength-to-weight ratio, high thermal conductivity, and good machinability make them perfect candidates for various manufacturing areas and technology fields.[1–3] In aluminum cast alloys, Fe is often regarded as the most common but inevitable impurity because it can be easily introduced but difficult and expensive to be removed in the commercial practice.[4,5] Various Fe-rich intermetallics can precipitate during solidification owing to the extremely low solubility of Fe in Al at room temperature compared with its highly solubility in liquid Al. Numbers of Fe-rich intermetallics have been reported for different Al alloys, e.g., Al3Fe, Al6Fe, and AlmFe.[6–11] Regarding Al-Si cast alloys, the two most commonly encountered Fe-rich intermetallics are generally Chinese script Al8Fe2Si (a-Fe) and platelet Al5FeSi (b-Fe).[12]
LANFENG JIN, KUN LIU, and X. GRANT CHEN are with the Department of Applied Science, University of Quebec at Chicoutimi, Saguenay, QC G7H 2B1, Canada. Contact e-mail: [email protected] Manuscript submitted December 18, 2018. Article published online May 30, 2019. 1896—VOLUME 50B, AUGUST 2019
Owing to the platelet morphology of b-Fe, they can block metal feeding and thus generate many porosities during solidification,[13] therefore make alloys more easily fractured under tensile loads,[2,4,14] and then lead to the decreased ductility and strength.[15] Chinese script Fe-rich intermetallics are less detrimental to mechanical properties.[2,16] Therefore, the modification of Fe-rich intermetallics from platelet into Chinese script has attracted much attention in Al-Si cast alloys. Rapid solidification[17,18] and melt superheating[19] can promote the formation of Chinese script Fe-rich intermetallics instead of platelet ones during solidification. However, these methods are limited in the practical application as they can promote hydrogen absorption and increase manufacturing costs. Up to date, chemical modifications of Fe-rich intermetallics are more promising and popular. Some alloying elements such as Cr,[20] Co[21] have been reported to be effective either in hindering the platelet b-Fe growth or transferring the morphology of Fe-rich intermetallics from platelet into Chinese script. In the foundry practice, Mn is one of the most economical and effective elements to neutralize the detrimental effects of Fe.[2] However, there are still controversies on the influence of Mn on Fe-rich intermetallics. For instance, some researchers[22,23] have stated that an Mn/Fe ratio of 0.5 is sufficient to fully modify the b-Al5FeSi phase, whereas Seifeddine and Johansson et al.[24] reported that even for an Mn:Fe ratio of 2:1, the b-Al5FeSi phase cannot be completely replaced by the a-Al15(FeMn)3Si2 Chinese script phase.
METALLURGICAL AND MATERIALS TRANSACTIONS B
One of the likely reasons can be the different variants of Fe-rich intermetallics, in pa
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