Flow behavior of a superplastic Zn–22% Al alloy processed by equal-channel angular pressing

A Zn–22% Al eutectoid alloy was processed using equal-channel angular pressing (ECAP) to reduce the grain size to ∼0.8 μm. A maximum elongation of ∼2230% was recorded in tensile testing at 473 K at a strain rate of 1.0 × 10−2 s−1. The significance of grain boundary sliding was evaluated by measuring the offsets in surface marker lines for samples pulled to an elongation of 30% at three different strain rates. The highest sliding contribution was recorded under testing conditions corresponding to the maximum superplastic elongation. Detailed measurements showed that relatively high sliding offsets were recorded at the Zn–Zn and Zn–Al interfaces whereas the offsets were smaller at the Al–Al interfaces. The measurements show that grain boundary sliding is a major flow process during superplastic deformation in the Zn–22% Al alloy processed by ECAP.