Nature of the internal friction peak in cold-worked dilute aluminum alloys

The origin of the internal friction peak observed for cold-worked aluminum alloys has been studied by the low-frequency torsion pendulum technique. Internal friction has been measured for pure aluminum of various grades and dilute alloys containing Li, Mg, Si, Fe, Ga or Ge. The peak appears at 210 K (for similar to 1 Hz) for unalloyed materials, as well as for the alloys, among which the peak is the largest for those with Si. The peak observed for "pure" aluminum is probably due to interaction between dislocations and impurities, such as Si. The peak exhibits asymmetrical shape when measured as a function of temperature (sharper on the low temperature side), and the activation energy and the preexponential factor of the relaxation rate tau(-1) are anomalously large. These features are discussed in the light of phenomenological models of anelastic relaxation for systems where anelastic elements interact strongly with each other.