Evaluation of Dislocation Density for 1100 Aluminum with Different Grain Size during Tensile Deformation by Using In-Situ X-ray Diffraction Technique

Ultra-fine-grained (UFG) aluminum with a grain size of 260 nm was fabricated by annealing a severely plastically deformed A1100 alloy. The resulting UFG aluminum exhibited a 0.2% proof stress (sigma(0.2)) that was four times larger than that predicted by the conventional Hall-Petch relation. In this study, the UFG aluminum, the fine-grained aluminum with a grain size of 960 nm and the coarse-grained aluminum with a grain size of 4.47 mu m were prepared. The change in the dislocation density, rho was investigated during tensile deformation using in-situ X-ray diffraction measurements at SPring-8. It was found that as the strain increased, the rho changed in four distinct stages. The first stage was characterized by elastic deformation, and little change in the rho occurred. For the coarse-grained aluminum, this stage was almost absent. In the second stage, the rho rapidly increased until the stress reaches sigma II in which the plastic deformation begins to occur at a constant strain rate. In the third stage, only a moderate change in the rho occurred. Finally, in the fourth stage, the rho rapidly decreased as the test pieces underwent fracture. Additionally, it was found that the sigma(0.2-sigma 1) was followed by the conventional Hall-Petch relation in all grain size range.