FURTHER EXPERIMENTS ON THE HIGH-TEMPERATURE INTERNAL-FRICTION PEAK IN HIGH-PURITY SINGLE-CRYSTAL ALUMINUM

The internal friction peak around 365 degree C (with vibration frequency 1 Hz) previously observed in high purity single crystal aluminium is studied in 99. 999 wt% aluminium. It is shown that this peak occurs only in crystals prepared by static or dynamic strain annealing and subsequently annealed at a temperature higher than 550 degree C. Deformation at room temperature or under creep conditions suppresses this peak. Experiments show that this peak exhibits nearly the characteristic of a single relaxation process with an activation energy of 1. 84 ev, but exhibits an anomalous amplitude-dependent effect around the temperature region of the peak, although the absolute value of the anomalous internal friction is one order of magnitude smaller than that of the main relaxation peak. TEM observations show that the dislocation configuration responsible for the appearance of the 365 degree C peak is a uniformly distributed spatial dislocation network and that the breakdown of this network and the occurrence of some kind of dislocation substructure or cell structure seems to be responsible for the disappearance of this peak.