Thermal Stability of an Al‐6061 Alloy Processed by High‐Pressure Torsion

The occurrence of static recrystallization (SRX) and grain growth (GG) is examined in an Al‐6061 alloy processed by high‐pressure torsion for 10 turns at room temperature during isochronal heat treatment in the temperature range of 473–723 K for 30 min. The results demonstrate a normal GG behavior in which the mean grain size continuously increases with increasing annealing temperature from 0.44 ± 0.1 μm (deformation state) to 8.7 ± 0.8 μm at 723 K. Coincidentally, the Vickers microhardness decreases from 155 ± 3 (deformation state) to 43.5 ± 4.1 Hv _0.1 after annealing at 573 K due to SRX and then reaches a steady state up to 723 K due to GG. A texture analysis reveals the gradual development of a C shear component in the SRX stage (523–623 K) and its dominance in the GG stage (673–723 K). The activation energy for SRX obtained through differential scanning calorimetry analyses is equal to 85.4 ± 4.2 kJ mol ⁻¹ , indicating a dominance by grain boundary self‐diffusion. The activation energy for GG is estimated by the Arrhenius equation as 68.4 ± 2.4 kJ mol ⁻¹ , indicating the poor thermal stability of the high‐pressure torsion‐processed Al‐6061 alloy.