Texture analysis of the transition from slip to grain boundary sliding in a continuously recrystallized superplastic aluminum alloy

An investigation was conducted into the phenomenon of continuous recrystallization in a superplastic Al–5%Ca–5%Zn alloy. The as-processed microstructure includes adjacent regions that have lattice orientations corresponding to the symmetric variants of the most prominent texture component, {2 2 5}〈5 5 4〉. This orientation is near the copper, or C, component, {1 1 2}〈1 1 1〉. A cellular dislocation structure with highly disoriented cell walls was present within these regions. Continuous recrystallization during static annealing resulted in the development of distinct boundaries accompanied by retention and sharpening of the texture and the development of a bimodal grain boundary disorientation distribution. The high-angle boundaries (50–62.8°) are the interfaces between grains having lattice orientations as symmetric variants of the texture, while the low-angle boundaries (2–15°) correspond to a cellular structure within the variants. Such a structure persists during superplastic deformation over a wide range of temperature and strain rate conditions. Both dislocation creep and grain boundary sliding operate simultaneously in response to the applied stress under all testing conditions investigated. The relative contribution of each of these mechanisms varies depending on the testing conditions. This is a consequence of the presence of the variants in the microstructure and their persistence during deformation. Fiber texture formation was not observed during either longitudinal or transverse deformation.