The annealing and aging effects of high temperature internal friction in pure aluminum

By using an inverted torsion pendulum we investigated the effects of annealing and aging on high temperature internal friction in pure aluminum. In 99.9 wt.% aluminum we found only one internal friction peak, and its height decreased gradually and finally disappeared with increasing annealing temperature. In 99.993 wt.% aluminum, two internal friction peaks were observed; one vanished and was accompanied by the appearance and development of the other with increasing annealing temperature. The later peak was reproducible during the annealing–aging–annealing cycle. In 99.999 wt.% aluminum, only one internal friction peak was found and the peak height decreased when the specimen was aged at room temperature. We think that the high temperature internal friction peaks in pure Al originate from the stress relaxation across grain boundary and the annealing and aging effects on them were associated with the condensing of impurities on grain boundaries and depend on the interaction of impurities with grain boundaries.