Annealing Hardening For Commercial Pure Aluminum Processed By Cold Rolling

In this paper, the mechanical properties and micro-structural of commercial pure aluminum (99.7%) processed by Cold Rolling before and after the annealing were studied by uniaxial tensile testing, nanoindentation instrument and transmission electron microscopy.From the tensile testing experiments, the large equivalent strain aluminum appears obvious hardening after heat treatment and softening when subsequently deformation, which is in contrast to the typical behavior of coarse aluminum. Micro-structural investigation indicates that slight coarsening occurred during annealing and reduced the dislocation density, leading to an increasing in strength and a reduction in ductility. A subsequent cold rolling deformation may restore the dislocation structural and facilitate the yielding process when the aluminum is stressed. As a result, the strength decreases and the ductility increase. We predict that dislocation source-limited strengthening may play a key role in annealing hardening.A repeated stress relaxation test has been carried out to obtain the strain rate sensitivity, the apparent and physical activation volume of fine grain aluminum. The magnitude observed for these characteristic deformation parameters is very different from those of coarse-grained aluminum. This suggests that the thermally activated process in fine grain aluminum is different from the conventional forest dislocation cutting mechanism. From the very experiments, the heat treatment has impact on activation volumes, which implies the alteration of a microstructure in fine grain aluminum.Constant loading rate/load creep experiments were conducted on fine grain aluminum using nanoindentation instrument. The results indicated that the loading mode has an obvious effect on the nanoindentation creep properties. With increasing loading rate/load, total creep was increased.