LOW FREQUENCY INTERNAL-FRICTION PEAKS AS A FUNCTION OF STRAIN AMPLITUDE IN COLD-WORKED DILUTE ALUMINIUM ALLOYS

Abstract
Low frequency "amplitude peaks"(Q^-1 as a function of strain amplitude) were observed in cold-worked dilute aluminum alloys at low strain amplitudes. Such amplitude peaks appeared in conjunction with a temperature peak (Q^-1 as a function of temperature) and a strain-aging peak (Q^-1 as a function of strain-aging time of the cold-worked specimen. The very pronounced drop in Q^-1 on the high strain amplitude side of the amplitude internal friction peaks observed can not be explained simply by the G-L model. These three coexisting internal friction peaks cannot be elucidated in terms of thermally assisted de-pinning of dislocations because the solute atoms involved are mobile as indicated by the appearance of an aging effect. These peaks can only be annealed out at an elevated temperature, so that they are quite different from the Hasiguti peaks which disappear after annealing atrelatively low temperatures. A dislocation-kink-atmosphere-dragging model was suggested in which the solute atoms clustered around a kink are assumed to be dragged along the kink (or dislocation core) during the to and fro sidewise motion of the kink under the action of the applied alternating stress. If the sidewise motion of the kink proceeds too fast so that the solute atoms cannot follow the moving kink, then the solute atom atmosphere will be left behind and the internal friction drops down. Mathematical analysis of such an atmosphere-dragging model by dislocation-kinks is in progress.