Grain boundary sliding in a superplastic zinc-aluminum alloy processed using severe plastic deformation

A Zn-22% Al eutectoid alloy was processed by Equal-Channel Angular Processing (ECAP) to produce a grain size of similar to 0.8 mu m. Tensile testing at 473 K gave a maximum elongation of similar to 2230% at a strain rate of 1.0 x 10(-2) s(-1). The significance of grain boundary sliding was evaluated by taking measurements of offsets in surface marker lines at an elongation of 30%. The highest sliding contribution was recorded under testing conditions corresponding to the maximum superplastic elongation. Detailed measurements showed that relatively large offsets occurred at the Zn-Zn and Zn-Al interfaces but there were smaller offsets at the Al-Al interfaces. It is concluded that grain boundary sliding is the dominant flow process during superplastic deformation.