LOW-FREQUENCY "AMPLITUDE PEAKS" IN THE INTERNAL FRICTION ASSOCIATED WITH THE INTERACTION OF SUBSTITUTIONAL SOLUTE ATOMS WITH DISLOCA-TIONS IN ALUMINIUM ALLOYS

Low-frequency "amplitude peaks" and "temperature peaks" were observed inthe internal friction of dilute Al-Cu nd Al-Mg alloys around room temperature ata maximum surface-strain amplitude ranging from 5×10~(-7) to 1×10~(-5). This nom-alous internal friction showed a peculiar aging behaviour. An aging peak wasobserved in conjunction with the mplitude eak and the temperature peak. Suchpeaks have been observed repeatedly in: (1) heavily cold-worked specimens an-nealed ust rior to complete recrystallization; (2) fully annealed specimens cold-worked just after yielding; (3) fully annealed pecimens quenched from anelevated temperature. It is shown that the observed internal friction is associated with the nterac-tion of solute atoms (Cu and Mg in Al) with the mobile "fresh" dislocations pro-duced by cold-work or quenching. uch fresh dislocations contain a large numberof kinks. A modified dislocation atmosphere model was suggested in which thesolute atoms are assumed to be dragged along between two potential valleys dur-ing the to and fro sidewise motion of a ink under the action of the appliedalternating stress.