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

Abstract

Abstract: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% reduction in thickness) and annealed at temperatures from 413 K (140 °C) to 493 K (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 or 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.2

Mechanistic modelling of cryo-deformation and post-annealing of aluminium

“…In the curves of Figure 7, it can be seen that, up to the annealing temperature of 150°C for 1 h, dislocation density does not decrease significantly, which is an expected result [28]. At this temperature, SRV seems to have generally involved the removal of point defects.…”

“…The numerical constants and parameters used in this study are presented in Table 1. For the same material, the model constants used here have been previously corroborated in investigations on SPD and post-annealing [3,24,28,30,35,36,38,39].…”

“…For the same material, the model constants used here have been previously corroborated in investigations on SPD and post-annealing [3,24,28,30,35,36,38,39].…”

“…As it is clear, the model well covers the difference between RTMDF and LTMDF, as the rate of dislocations reduction in LTMDF is higher than that in RTMDF (shown for 1-pass samples in Figure 7). TEM images in [16,28] have already proved the reduction of dislocation density after annealing.

Figure 7 Curves of the dislocation density variations vs annealing temperature (°C) for MDFed aluminum (model results).

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“…SRV phenomenon facilitates dislocation movement, decelerates dislocation density, and decreases hardness and yield strength. So, it is crucial to determine annealing parameters such as annealing temperature and time, pre-applied strain (stored energy), the material's purity, and pre-deformation temperature [27,28]. Nes [29], Vandermeer and Hansen [30] are well-known for developing recovery annealing models which can compare favourably with the experimental data.…”