Published online by Cambridge University Press: 10 February 2011
High-angle grain boundaries are generally deemed necessary for superplasticity in metals. In polycrystalline materials the grain boundary character must be described in terms of a probability distribution rather than by a single parameter, and little has been reported on the relationship between this distribution and fine-grain superplasticity. For aluminum alloys that exhibit continuous recrystallization the results of computer-aided electron backscatter diffraction analysis have shown that bimodal grain boundary disorientation distributions are present in as-processed material and persist during subsequent annealing. Such distributions may be simulated by computer methods based on a model of the microstructure which assumes that deformation banding occurs during deformation processing. High-angle boundaries (≥30°) develop in association with deformation banding while boundaries of lower disorientation (<30°) develop by dislocation reaction within the bands. Improved understanding of the grain boundary types associated with various microstructural transformation mechanisms will aid the design of processes to produce superplastic microstructures.