Pinning effect of solute atoms on grain boundary dislocation dissociation

The dissociation of extrinsic grain boundary dislocations (EGBDs) in Al, Al-Mg and Al-Mg-Sn alloys was studied at various temperatures. While EGBDs were commonly observed in low- and high-angle boundaries in the alloy materials deformed to small strains, they could only be seen in low-angle grain boundaries in Al. Annealing of the lightly deformed alloy samples at 100 or 150°C led to the disappearance of the EGBDs with critical disappearance kinetics depending on grain boundary composition. A modified EGBD dissociation mechanism incorporating a solute drag effect has been developed in this work. Predictions based on the model agree reasonably well with the observed thermal behavior of the EGBDs in the three Al alloys.