Thermally activated flow of dislocations in Al-Mg binary alloys

Thermally activated flow of dislocations has been studied in Al-Mg solid solutions under conditions of positive strain-rate sensitivity at 78 K. Thermodynamic deformation parameters determined from up-rate and down-rate changes show differences attributed to the density and types of effective obstacles intersected by the mobile dislocations. The alloys exhibit the stress equivalence of the apparent activation volume over the yield stress range as V∗∼σ0-0.75 under up-rate and down-rate changes. The stress equivalence holds throughout the onset of deformation up to failure where the corresponding relationships are: V∗∼σF-0.68 and V∗∼σF-0.5. The differences are attributed to the refinement of dislocation debris dominating down-rate change responses. An apparent activation volume equivalence of the work hardening is observed over the broad range of activation volumes, suggesting correspondence between thermally activated glide of dislocations over the obstacles and defect storage capacity of alloys. The thermodynamic conditions for plasticity limits are estimated in terms of the activation volume.