57Fe MÖssbauer spectroscopy of intermetallic phases in D.C. cast aluminium

Abstract

Direct-chill (D.C.) casting is a widely used technique for casting industrial aluminium alloy ingots. Commercial purity alloys contain small amounts of iron and silicon. During casting, intermetallic phases are formed inter-dendritically from the final liquid to solidify. Since the solidification rate varies substantially with position in the ingot various phases can form, ranging from the equilibrium phase Al{sub 3}Fe{sub 4}, to increasingly metastable phases, such as Al{sub 6}Fe, Al{sub x}Fe, Al{sub m}Fe or alpha-AlFeSi, as the solidification rate increases. The phases formed may influence the ease of processing and the final gauge properties of the material. Fe Moessbauer spectroscopy has been used previously to identify the intermetallic phases in situ in aluminium from Bridgman grown model alloys. Also variable temperature studies have been carried out on the phases extracted from the alloys by butanol dissolution. The work reported in this paper demonstrates how the Moessbauer data obtained from the previous studies can now be used to identify and quantify the proportion of different phases formed in ingots prepared by direct-chill casting and subsequent heat treatments.