Damping of a high-purity aluminum single crystal at high temperatures

Isothermal mechanical spectroscopy has shown a relaxation peak at room temperature after 1% cold work in a single crystal of 5N aluminum. During the first heating sequence, the relaxation strength increased as the measurement temperature increased, and the Arrhenius plots of the relaxation rate did not give a straight line. However, in the subsequent measurements at various temperatures while cooling after annealing at 458 K, the relaxation peak showed a stable height and gave linear Arrhenius plots. This peak completely vanished after annealing at 673 K. Another peak appeared at a very low frequency in experiments above 650 K. In the measurements conducted at the same temperature but with different annealing temperatures, the frequency of the peak depended on the previous annealing temperature. The evolution of the peak and the relaxation parameters suggest that the first peak is due to fresh dislocations introduced by the cold work, and that the second peak is due to the motion of subgrain boundaries.