Ultrafine-grained Al samples of purity grades 2N7 and 4N were prepared by hydrostatic extrusion. The changes in structure and properties in the grain growth regime after annealing were studied in terms of the role of grain boundary structure. Important differences in grain growth kinetics were observed at annealing temperatures higher than 620 K and grain growth is shown to be dependent on the predominant type of grain boundary. This interpretation is supported by the results of mechanical testing and Hall–Petch analysis, leading to the conclusion that the parameters σ0 and k are more strongly dependent on grain boundary structure than on material purity.
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