Microstructure evolution, mechanical properties and deformation characteristics of ultrafine-grained annealed pure aluminum

In this paper, ultrafine-grained pure aluminum was first fabricated by heavy extrusion. Subsequently, the prepared samples were annealed at 350 oC for different times to tailor heterostructures with the aim of achieving strength-ductility balance. The microstructure characterization revealed that the annealed samples formed heterostructures composed of recrystallized coarse grains, retained ultrafine grains, and coarsening banded structure. Typical rolling texture components prevailed as annealing time was below 8 min. When annealing time exceeded 8 min, these texture components were gradually replaced by the Cube-oriented and random-oriented grains, and at the same time, abnormal grain growth occurred with a faster kinetic (growth exponent ñ3.4). Tensile tests indicated that 5–8 min annealed samples obtained a reasonable strength-ductility balance, which was higher than their counterparts predicted by the rule-of-mixture based on the recrystallization model. In addition, the macro-deformation characteristics of the heterostructured sample were comparatively studied using digital image correlation, while the micro-deformation behaviors were revealed by in-situ tension. The results showed that the heterostructured sample caused inhomogeneous deformation and significant geometrically necessary dislocations gradient at the hetero-boundaries. The loading-unloading-reloading tests found that the interaction of heterostructures induced a noteworthy hetero-deformation-induced (HDI) stress, thereby contributing to HDI strengthening.