Determination of recrystallization temperature of deformed high-purity Al assessed by internal friction technique

In this study, the recrystallization process in deformed high-purity aluminum was investigated by using the internal friction (IF) and hardness measurement. In the heating process, two IF peaks were detected when the heating rate is 2 °C/min: a sharp peak (P1 peak) at ~139 °C and a wide peak (P2 peak) at ~278 °C (0.5 Hz). In the subsequent cooling process, the P1 peak disappears while the P2 peak remains. The P2 peak shifted towards higher temperatures with increasing frequency and can be ascribed to grain boundary relaxation. For the P1 peak, however, its position did not change with increasing frequency but shifted towards higher temperatures with increasing heating rate in the range of 1–5 °C/min, and the corresponding modulus varied abnormally in the temperature range of 115–160 °C. These facts indicated that the P1 peak is a non-relaxational peak and can be ascribed to the recrystallization process. The recrystallization activation energy deduced via the shift of peak position with heating rate by using the Kissinger equation is 57± 3 kJ/mol, which is as same as that deduced from the classical isothermal recrystallization process as assessed by microhardness measurement. The classical isothermal recrystallization temperature can be deduced from the peak temperature of P1 peak by simply adjusting the heating rate. This provided a method to determine the recrystallization temperature via internal friction measurement in a continuously heating process, which needs only two or three samples.