Evaluation of mechanical behavior of nano-grained 2024 Al alloy during high pressure torsion (HPT) process at various temperatures

Highlights: ► HPT processing of 2024 Al alloy is performed at various temperatures. ► In situ torque measurements versus strain follow three distinct regions. ► Nano sized grains are produced at room and cryogenic HPT deformation. ► An overall increase of 3-fold in hardness is achieved at the tip of the samples. ► Aging precipitates have a significant effect on restoration process during HPT. - Abstract: The effects of high pressure torsion (HPT) processing at different temperatures on flow stress and hardness distribution of a 2024 Al alloy were studied. Using in situ torque measurements versus equivalent strain the flow stress of the material followed three distinct deformation regions at room temperature. In the first region the strength increases with strain and after taking a maximum at an equivalent strain of ∼8, the strength decreases with further straining in the second region. The third region appears at an equivalent strain of ∼22 or higher as a steady state where the strength remains unchanged. Transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) analysis were conducted on selected samples and influential effects of precipitates on flow stress and hardness were examined. It is proposed that restoration process in the second region of deformation and saturation region of deformation can significantly be affected by deformation temperature and aging precipitates. HPT deformation at −196 °C did not show any decrease in second region of deformation instead the strength is increased exponentially until the strain of ∼35 where saturation region of deformation starts. Nano sized grains of 50–70 nm were observed in saturation region of deformation with more than three folds increases in hardness.