THE EFFECT OF HEAT TREATMENT ON LOW TEMPERATURE INTERNAL FRICTION MAXIMA

Measurements of the attenuation of sound at a frequency of 5 megacycles have been made over the temperature range 100° to 200 ° K. on polycrystalline high purity aluminum subjected to various thermal and mechanical treatments. With samples annealed at 520 °C. a maximum in the attenuation versus temperature relation had been observed at 155 ° K. This maximum was greatly increased by small amounts of plastic deformation of the order of 1.0 to 1.5%.Aluminum initially annealed for extended periods at temperatures much closer to the melting point shows, however, either no increase in the attenuation maximum at 155 ° K. or, in extreme cases, no maximum in this region at all, after plastic deformation of the same order as before. It is believed that this indicates a dependence of the deformation-induced maximum on the distribution and possibly on the number of dislocations in the metal prior to deformation and on the arrangement of the dislocations after deformation.