The experimental procedure for observing the low frequency anomalous internal friction peaks in Al-0.5% Cu alloy was systematically investigated in order to be able to obtain reproducible results. It is shown that, when the specimen is plastically deformed on a tensile testing machine to a suitable extent and then the internal friction measured in the course of aging at a suitable temperature, an aging internal friction peak exhibiting an anomalous amplitude effect may be observed. After the specimen has been "sufficiently" aged and its internal friction has reached a steady value, an amplitude internal friction peak at a given temperature can be observed when the strain amplitude for measuring internal friction is successively increased. Furthermore, when the internal friction of the "sufficiently" aged specimen is measured at higher temperatures with a given strain amplitude, a temperature internal friction peak exhibiting an anomalous amplitude effect may be observed. These experimental results demonstrated conclusively the existence of the previously observed amplitude internal friction peak at a given temperature and of the temperature internal friction peak exhibiting an anomalous amplitude effect.In order to find out why the anomalous internal friction peaks previously observed in Al-0.5% Cu alloy have a poor reproducibility, the effect of strain amplitude upon the appearance of the amplitude internal friction peak, as well as the effect of the amount of the previous plastic deformation upon the appearance of the aging internal friction peak and the temperature internal friction peak was systematically studied. An analysis was made on the experimental conditions for the appearance of these anamolous internal friction peaks.The observed experimental results concerning the anomalous internal friction peaks can be explained in a qualitative manner with a model in which the solute atom "atmosphere" was assumed to be dragged along with the dislocation. The concrete model and its theoretical analysis will be reported in a later paper.
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