Recrystallization and superplasticity in aluminum alloys

There are two distinct microstructural transformation routes that enable superplastic response in aluminum alloys. One involves changes that occur gradually and homogeneously throughout the deformation microstructure during annealing, and which have been described as continuous, or insitu, recrystallization. The reactions proceed with little or no migration of high-angle boundaries and generally small changes in the orientations within the deformation texture. Grain boundaries develop as grains subdivide during deformation processing, as well as via recovery within the deformation microstructure during annealing. The other route is comprised of recrystallization processes involving heterogeneous formation and subsequent growth of grains by the migration of newly-formed high-angle grain boundaries. The stable end orientations in the microstructure developed during deformation processing undergo large changes that result in the disappearance of deformation texture components and the appearance of recrystallization texture components. Results of investigations into the evolution of microtextures and grain boundary misorientations by means of computer-aided electron backscatter diffraction (EBSD) analysis methods for alloys representing each of these different routes will be summarized and implications to processing of Aluminum alloys for superplasticity will be discussed.