Effect of deformation induced precipitation on grain refinement and improvement of mechanical properties AA 7055 aluminum alloy

- Pre-deformation accelerated the formation/refinement of deformation induced precipitates (DIPs).
- Low angle grain boundaries transition model has been proposed for grain refinement.
- DR treated alloy displays superior elongation than CR treated alloy in T6 state.

An improved TMT (thermomechanical treatment) double step hot rolling (DR) including low-temperature pre-deformation, intermediate short-term annealing and final hot rolling, was proposed to manufacture fine grained AA7055 sheets. Microstructural analysis results show that the low temperature pre-deformation can accelerate the formation and spheroidization of fine precipitates which can exert great drag force to the migration of grain boundaries and dislocations so as to promote the formation of high density dislocation cells and accommodate sufficient deformation storage energy subsequently. Then, these dislocation cells may turn into polygon sub-grains by short-period intermediate annealing. With the final hot rolling, low angle grain boundaries (LAGBs like sub-grain boundaries) were gradually transferred into high angle grain boundaries (HAGBs) and fine-grained structures were obtained. Tensile testing results reveal that samples processed by the optimal DR processing (300 °C/60% + 430 °C/5 min + 430 °C/50%) display superior tensile plasticity than the conventional hot rolling (CR) samples without strength loss, which could be correlated with the fine grained structure of the DR sample. It indicates that the present DR processing may be a good alternative to efficiently produce fine grain structured heat-treatable aluminum alloys.