Superplasticity at Room Temperature in Zn-22Al Alloy Processed by Equal-Channel-Angular Extrusion

Abstract

Equal-Channel-Angular extrusion (ECAE) has been conducted at room temperature in order to develop an ultrafine-grained structure in a Zn-22 mass% Al eutectoid alloy. The microstructures had an equiaxed and homogeneously distributed Al-rich and Zn-rich duplex-phase and its average grain size was about 0.35 μm. This alloy exhibited a large elongation of 240% albeit at room temperature and a high strain rate of 10−2 s−1. A grain-size-dependent phenomenon was also observed at lower strain rates. The activation energy was close to that for grain boundary diffusion. It was apparent that the deformation behavior at room temperature is consistent with that observed in conventional superplasticity. From the results, it was concluded that the dominant deformation mechanism was grain boundary sliding accommodated by dislocation movement controlled by grain boundary diffusion.