LOW-TEMPERATURE INTERNAL-FRICTION PEAKS IN COLD-WORKED AL-CU SOLID-SOLUTIONS

The low-temperature composite internal friction peak previously observed in cold-worked Al-Cu solid solutions is now distinctly resolved into two separate peaks. Effect of copper content and annealing on these two peaks (the relaxation peak R and the phase transformation peak P) is studied. The R peak exhibits a pronounced amplitude effect but the Arrhenius relationship still holds giving a linear correlation factor 0.99. The activation energy associated with the R peak in Al-0.29 wt% Cu is found to be (0.61 +/- 0.10) eV with tau(0) = 2 x 10(-14) s. A complementary behaviour is found between the R peak and the room temperature peak (P1 peak): one rises while the other sinks. This gives a strong support to the proposition that the R peak and P1 peak are associated with the stress induced migration of copper atom-vacancy pairs and of copper atoms in the stress field of moving dislocations (kinks), respectively.