A Mössbauer investigation of phases formed in Al-Fe alloys

Abstract

During the semi-continuous casting of aluminium alloy ingots, the solidification rate varies substantially with position in the ingot. For commercial purity alloys, which contain small amounts of iron and silicon, intermetallic phases are formed inter-dendritically from the final liquid to solidify, and comprise typically 1% of the microstructure. The development in the work reported in this paper is that the phases of interest have been extracted from super-purity based, Bridgman Grown model aluminium-iron binary alloys by dissolving the aluminium matrix in butanol. This has the advantage of providing the pure phase and thus increases the proportion of iron (and Fe-57) which gives an improved signal to noise ratio for Moessbauer spectroscopy. Using phases extracted in this way, detailed variable temperature Moessbauer studies have been carried out on Al{sub 13}Fe{sub 4} and Al{sub 6}Fe. The variation with temperature of the isomer shift and absorption area were obtained. This enabled the recoil-free fractions of the two phases to be determined. With this information it was then possible to determine the proportion of Al{sub 13}Fe{sub 4} and Al{sub 6}Fe in an extracted sample containing both phases, and in a rod of the aluminium containing both phases in situ.