Microstructural Characterization of Warm-Worked Commercially Pure Aluminum

The deformation microstructures of commercially pure aluminum deformed by plane strain compression to 50 pct thickness reduction at temperatures between 100 °C and 300 °C, under two strain rates, 5 × 10−2 s−1 and 5 × 10−4 s−1, have been characterized by transmission electron microscopy. As the deformation temperature increases, the deformation microstructure gradually changes from a checkerboard pattern into an equiaxed subgrain structure with increasing subgrain size. The fraction of geometrically necessary boundaries (GNBs) found in warm-worked aluminum is much less than that found at room temperature. The average misorientation of dislocation boundaries appears to be independent of deformation temperature and strain rate. The constancy of the average misorientations is a combined effect of the variation of the fractions of GNBs and incidental dislocation boundaries (IDBs) and the variation of the average misorientations of GNBs and IDBs. Scaling theory can apply to both boundary misorientations and subgrain sizes that formed at different temperatures and strain rates. Subgrain size distributions for different temperatures and strain rates all resemble a lognormal distribution.