Achieving high strain rate superplasticity via severe plastic deformation processing

In this study, a thermomechanical process consisting of general precipitation and severe plastic deformation through equal channel angular extrusion (ECAE) was applied to a Zn-22 wt.% Al alloy to produce a microduplex structure for high strain rate (HSR) superplasticity studies. Microstructures, hardness, and superplastic properties of the Zn–Al alloy were studied by using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), recordable hydraulic press, and a tensile test with a hot stage. A work-softening phenomenon due to the occurrence of a grain boundary-sensitive dynamic recrystallization (DRX) was observed during the ECAE processing of the Zn–Al alloy at the extrusion temperatures investigated from -10 C to 50 C. An important discovery regarding the grain boundary-sensitive DRV was realized in this study such that through a progressive work-softening process the Zn–Al alloy will eventually exhibit HSR superplastic properties.