HIGH-TEMPERATURE INTERNAL-FRICTION IN ALUMINUM STUDIED BY ISOTHERMAL MECHANICAL SPECTROMETRY

Isothermal mechanical spectrometry experiments (10(-4) Kz to 100 Hz) were carried out on strain hardened aluminum samples after recovery annealing between 300 and 700 K. For lower annealing temperatures (up to 480 K), internal friction spectra exhibit only a low-frequency background. Above 480 K, a relaxation peak stands out progressively against the background. The peak corresponds to the traditional intermediate temperature peak (ITP). Its height increases for annealing below 580 K and decreases above that temperature: the relaxation parameters undergo large changes after successive annealings. The peak is attributed to dislocation segment motion in dislocation pile-ups created by strain hardening and modified by recovery annealing.