Annealing behavior of aluminum after low-temperature severe plastic deformation

Severe plastic deformation (SPD) processes have received less attention at low temperatures (sub-zero and cryogenics). Hence, in this study, SPD of a commercially pure aluminum (AA1050) through Multi-Directional Forging (MDF) at Low-Temperature (LTMDF) and Room-Temperature (RTMDF) is investigated for different strains. Multi-directionally forged (MDFed) samples were annealed at 150, 250, 350, and 450 degrees C for 1 h, and some samples were stored at room temperature for periods up to 1 year. Results show that the hardness values and flow stress of LTMDFed aluminum are higher than those of RTMDFed ones. The ratio of yield strength to hardness for LTMDF is similar to that for RTMDF. Surprisingly, the work-hardening exponent of LTMDFed aluminum is higher than that of RTMDFed samples, which probably can be due to the increase in mobile dislocation fraction as a result of suppression of dynamic recovery. Microstructural evolutions, hardness, and flow stress changes of annealed samples indicate that LTMDFed samples are more affected than RTMDFed ones and have weak thermal stability because of the non-equilibrium microstructure. The study of self-annealing suggests a rather dramatic decrease in the hardness values of LTMDFed samples during a one-year period, which is not tangible for RTMDFed ones. LTMDF leads to grain coarsening during self-annealing, presumably owing to extended static recovery at room-temperature.