Grain boundary mobilities during recrystallization of Al–Mn alloys as measured by in situ annealing experiments

The influence of Mn on the mobilities of grain boundaries during recrystallization of Al–0.1 and –0.3 wt.% Mn alloys has been characterized by in situ SEM annealing experiments. Polycrystals of high purity, single-phase Al–Mn alloys were deformed in channel-die plane strain compression at room temperature to strains of 1.3. The specimens were in situ annealed in an SEM/EBSD in order to measure grain boundary mobilities at temperatures between 200 and 450 °C. Stable “loaded” boundary migration was observed in the 0.1 and 0.3% Mn alloys. However, unstable, partially “free”, boundary migration could also be found in the 0.1% alloy. The mobilities, deduced from the migration rates and the stored energies, were consistent with the solute drag theories of Cahn, Lücke and Stüwe. The diffusion rates controlling the solute drag were of the same order for both theories and the activation energy for boundary migration was found to be intermediate between that of solute diffusion in the lattice and along the grain boundaries.