Solid-state intermetallic phase tranformations in 3XXX aluminium alloys

Abstract During homogenisation of direct chill cast ingots of Al alloys for beverage-can bodies, the degree of transformation of Al6(Fe,Mn) phase to α-Al-(Fe,Mn)-Si phase is important for subsequent processing. The morphology of the transformation and the associated local composition changes are studied using a range of electron microscope techniques, including energy-filtered transmission electron microscopy, convergent-beam electron diffraction and field-emission-gun scanning electron microscopy. Nucleation of the α-phase controls the rate of the transformation, which proceeds by eutectoid decomposition of the Al6(Fe,Mn) phase into α-phase and aluminium solid solution. The transformation requires intake of silicon from the surrounding matrix; intake of manganese is not required but does occur on continued annealing. A basic description is given of the transformation kinetics.