Recovery Kinetics in Commercial Purity Aluminum Deformed to Ultrahigh Strain: Model and Experiment

A new approach to analyze recovery kinetics is developed from a recent model, and microstructural observations are introduced to supplement hardness measurements. The approach involves two steps of data fitting, and the second step of fitting enables an estimation of the apparent activation energy for recovery. This approach is applied to commercial purity aluminum (AA1050) cold rolled to ultrahigh strain (99.6 pct reduction in thickness) and annealed at temperatures from 413 K to 493 K (140 °C to 220 °C). The annealing data fit the recovery model well, and the analysis shows that the apparent activation energy increases during recovery and approaches 190 kJ/mol at the end of recovery, suggesting that solute drag is an important rate-controlling mechanism. The recovery rate for the highly strained Al is found to be higher than that for Al deformed to a lower strain, an effect which is related to an increase in the stored energy (driving force). These findings form the basis for a discussion of recovery mechanisms and the increase in the apparent activation energy during annealing, suggesting an application of the model when optimizing the structure and strength through annealing of nanostructured materials produced by high strain deformation.