The influence of rolling direction on the mechanical behavior and formation of cavity stringers in the superplastic Zn-22% Al alloy

Abstract

The superplastic Zn-22% Al eutectoid alloy was tested over a range of strain rates at 503 K using specimens machined with the rolling direction perpendicular to the tensile axis. It is shown that the mechanical properties of the alloy, including the elongations to failure, are essentially identical to those obtained when the rolling direction is parallel to the stress axis. Inspection after failure showed that cavities are formed in stringers and, as in the same alloy tested with the rolling direction parallel to the tensile axis, these stringers are aligned parallel to the stress axis. The results demonstrate that the cavities are not nucleated primarily at impurity or oxide particles, nor do they grow from pre-existing microvoids which may be introduced during thermomechanical processing. The cavities are located preferentially at the α/β interfaces and at the associated triple points, and it is probable that they were nucleated at triple points and grain boundary ledges during bursts of grain boundary sliding.