Investigation of intermetallics in hypoeutectic Al–Fe alloys by dissolution of the Al matrix

During the non-equilibrium solidification typical of DC (direct chill) castings a range of cooling rates occur from the surface to the casting center, and can cause the formation of metastable intermetallic phases (AlmFe, Al6Fe, etc.) in addition to the stable Al3Fe phase. The extensive presence of the plate-like Al3Fe phase in the as-cast structure adversely influences the mechanical properties of Al–Fe alloys, since this morphology is more likely to induce microcracks than the fibrous Al6Fe phase. The aim of this study was to present a method of characterization of AlFe intermetallics which is based on the dissolution of the aluminum matrix in distilled 1-butanol. Optical microscopy and SEM analysis of the undissolved intermetallics have permitted characterization of the morphology, distribution, size and chemical composition of both Al3Fe and Al6Fe phases. The results have shown that Al6Fe prevails for growth rates VL and cooling rates T˙L higher than 0.7 mm/s and 1.5 K/s, respectively.