A LOW TEMPERATURE COLD WORK INTERNAL-FRICTION PEAK IN Al-0.5 Wt % Ga

An internal friction peak (around - 84° C, f = 0.8 hz) was observed in Al-0.5 wt % (0.19 at %) Ga cold-drawn to 12% reduction in area at 20°C. This peak was stable when measurements were taken below 20°C with decending and ascending temperatures and the height of the peak decreased after an anneal at elevated temperatures. It disappeared completely after an anneal at 200°C. The peak height first increased and then decreased with the amount of cold-working at 20° C and a 12% reduction in area seems to be close to the optimum amount of cold-working. The activation enthalpy associated with this internal friction peak measured with the method of changing of frequency is 0.85 ± 0.05 eV. A dislocation-kink dragging model is suggested in which the mobile agents that interact with dislocation kinks are Ga atom-vacancy pairs. The effect of the temperature of previous deformation on the behavior of the internal friction peak is discussed. It is contemplated that the broadening of the peak when the previous plastic deformation was made at -196°C may be due to the formation of Ga atom-divacancy pairs.