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The attenuation of sound at a frequency of 5 megacycles has been found to reach a maximum in aluminum at 155 °K. Combination of this result with the work of Bordoni, who obtained a maximum at 40 kilocycles and 100 °K., gives an activation energy in agreement with the value calculated by Mason for a dislocation relaxation process. The maximum is greatly increased by plastic deformation. The velocities of sound for annealed and cold-worked aluminum show a maximum difference about 155 °K., again indicating a dislocation mechanism. The maxima are superimposed on a background attenuation mostly caused by scatter at grain boundaries and diffraction.
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Hutchison et al. (1956) studied this question.
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