A New Iron-Rich Intermetallic-Al m Fe Phase in Al-4.6Cu-0.5Fe Cast Alloy
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is one of the most widely observed iron-rich intermetallics in AA1xxx and AA5xxx wrought aluminum alloys.[1–4] It was reported to precipitate at a high cooling rate compared with other iron-rich intermetallics, such as Al3Fe and Al6Fe in Al-Fe-Si ingots.[1,3,5] The composition of AlmFe varies with m between 4.0 and 4.4.[1,4] Its crystal structure is body-centeredtetragonal with lattice parameters a = 0.884 nm and c = 2.160 nm.[1,4,5] To date, AlmFe has not been reported in A206 cast aluminum alloys. In this family of alloys, platelet Al7Cu2Fe is usually the most frequently observed ironrich intermetallic. It was even reported to be the only kind of iron-rich intermetallic present in the fully solidified microstructures of the A206 family of alloys containing 0.03Fe-0.36Mn,[6] 0.07Fe-0.24Mn,[7] 0.23Fe0.2Mn,[8] and 0.62Fe-0.8Si-0.04Mn[9] (all alloy compositions are in weight percent unless indicated otherwise). In addition to Al7Cu2Fe, a Chinese script Al-Cu-FeMn-Si intermetallic, named Mn-bearing iron intermetallic, was observed in Al-4.52Cu-0.30Fe-0.67Mn alloy by Tseng et al.[10] Recently, Liu et al.[11,12] systemically investigated the solidification characteristics of the ironrich intermetallics in a A206 cast aluminum alloy with 0.3Fe and found that both platelet b-Fe (including preeutectic Al7Cu2(FeMn) and eutectic Al7Cu2Fe) and Chinese script a-Fe (Al15(FeMn)3(SiCu)2) may be K. LIU, PhD Candidate, and X.-G. CHEN, Professor, are with the Department of Applied Science, University of Que´bec at Chicoutimi, Chicoutimi, PQ G7H 2B1, Canada. Contact e-mail: [email protected] X. CAO, Adjunct Professor, Department of Applied Science, University of Que´bec at Chicoutimi, is also a Research Officer, Aerospace Manufacturing Technology Center, Institute for Aerospace Research, National Research Council Canada, Montreal, PQ H3T 2B2, Canada. Manuscript submitted August 15, 2011. Article published online January 5, 2012 METALLURGICAL AND MATERIALS TRANSACTIONS A
present in the fully solidified microstructures, depending on the Mn/Fe and Si/Fe ratios. A206 cast alloys have been widely used in automotive and aerospace industries. However, they usually require extremely low Fe contents, normally lower than 0.10 to 0.15 pct, significantly increasing the cost and limiting its wide applications.[13,14] To reduce the cost, recycled aluminum alloy material needs to be reused but causes a significant increase in iron levels. In the present work, the solidification mechanisms of A206 cast aluminum alloy with 0.5 pct Fe were investigated. Chinese script AlmFe phase was observed, for the first time, in the A206 Al-Cu cast alloys. Commercial pure Al (99.7 pct), pure Mg (99.9 pct), Al-50 pct Cu, Al-25 pct Fe, and Al-50 pct Si master alloys were used to prepare the experimental alloy with the compositions of Al-4.58Cu-0.28Mg-0.51Fe-0.07Si0.003Mn. The final compositions of the experimental alloy were analyzed by using an optical emission spectrometer. During the experiments, the molten alloy was gently stirred to homogenize and avoid the entrainment of s
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