Achieving superplasticity at high strain rates using equal channel angular pressing

Abstract

Equal channel angular pressing (ECAP) is a processing procedure in which a sample is pressed through a die containing a channel bent into an L shaped configuration. This procedure introduces a high strain into the sample without any change in the cross-sectional area and it may be used to attain an ultrafine grain size with dimensions lying typically within the submicrometer range. This paper describes a series of experiments where ECAP was applied to a commercial Al–Mg–Li–Zr alloy having an initial grain size of ∼400 µm. The results demonstrate a refinement in the grain size of this alloy to a size of ∼1 µm and it is shown that these small grains are stable up to temperatures >600 K because of the presence of β′-Al₃Zr particles. The stability of these ultrafine grains at elevated temperatures provides an opportunity to achieve superplastic ductilities in this alloy at very high strain rates: for example, the measured elongations to failure under optimum pressing conditions exceed 1000% at a strain rate of 10^-1 s^-1 when testing at temperatures above 600 K.