Influence of grain size in the near-micrometre regime on the deformation microstructure in aluminium

The effect of grain size on deformation microstructure formation in the near-micrometre grain size regime has been studied using samples of aluminium prepared using a spark plasma sintering technique. Samples in a fully recrystallized grain condition with average grain sizes ranging from 5.2 to 0.8μm have been prepared using this technique. Examination in the transmission electron microscope of these samples after compression at room temperature to approximately 20% reduction reveals that grains larger than 7μm are subdivided by cell block boundaries similar to those observed in coarse-grained samples, with a similar dependency on the crystallographic orientation of the grains. With decreasing grain size down to approx. 1μm there is a gradual transition from cell block structures to cell structures. At even smaller grain sizes of down to approx. 0.5μm the dominant features are dislocation bundles and random dislocations, although at a larger compressive strain of 30% dislocation rotation boundaries may also be found in the interior of grains of this size. A standard 〈110〉 fibre texture is found for all grain sizes, with a decreasing sharpness with decreasing grain size. The structural transitions with decreasing grain size are discussed based on the general principles of grain subdivision by deformation-induced dislocation boundaries and of low-energy dislocation structures as applied to the not hitherto explored near-micrometre grain size regime.