Dynamic internal friction and evaluated activation volume for superplastic deformation in a Zn–5%Al alloy

The dynamic internal friction (DIF) during superplastic deformation of Zn–5wt.%Al eutectic alloy with an average grain size of 2 μm has been studied at strain rates of 10−6–10−4 s−1. The activation volumes Va for the superplastic deformation evaluated from the data of DIF are of the order of 10−27 m3, and decrease with the increase of strain rate or applied stress. The results indicate that the elementary process of grain boundary sliding during superplastic deformation is possibly associated with the motion of grain boundary dislocations surmounting the ledges.