Abstract
The orientation dependence on recovery has been studied in cold-rolled and annealed polycrystalline high-purity aluminium (99.99 wt%), binary Al-0.25Mn and commercial purity aluminium. The growth mechanisms were found to be independent of the alloy system and the microchemistry only influences the coarsening kinetics. Orientation-dependent subgrain growth, mainly studied in high-purity aluminium and measured in lamellar bands of uniform orientation, occurs in three distinct ways, depending of the size of the local orientation gradients. Following the evolution in average subgrain size and boundary misorientation by detailed electron backscatter diffraction (EBSD) characterization during annealing, it was found that the rate of subgrain growth in Cube- and Goss-oriented grains were faster than in the typical deformation texture components, particularly after an incubation time when discontinuous subgrain growth occurs. In commercial purity aluminium, general orientation-independent subgrain growth is faster than the orientation-dependent growth because more growth occurs in regions near high-angle grain boundaries separating differently oriented lamellar bands. It appears as if subgrains misoriented by more than 3.5° have a growth advantage over less misoriented subgrains, typically in the interior of lamellar bands. While the average boundary misorientations are decreasing, the individual boundary misorientations are increasing.
Highlights
Softening of deformed metals typically takes place by recovery, recrystallization and grain growth
The recrystallization behaviour was very heterogeneous, as exemplified by the two data sets obtained at 220 ◦ C predicting both extended recovery and recovery followed by recrystallization
At 240 ◦ C there are two curves which seemingly depict fast recrystallization but on closer inspection, the hardness value at 1000 s is more appropriate for an extended recovery process
Summary
Softening of deformed metals typically takes place by recovery (i.e., dislocation annihilation and notably, subgrain growth), recrystallization and grain growth These phenomena have been extensively studied, during the late 80s and 90s due to the introduction of the electron backscatter diffraction (EBSD) technique for scanning electron microscope (SEM) characterization. This at-the-time new method made detailed studies of the substructure possible with far better statistics than previously achieved by transmission electron microscopy (TEM) and led to an improved description of the softening mechanisms, including the development of several softening models [1,2,3]. This effect is not exclusive for grain boundaries but subgrain boundary mobilities (misorientation < 15◦ ) are reduced by elements like Si and Fe in solid solution [5,10,11,12,13,14]
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