High strain rate behavior of ultrafine-grained Al-1.5 Mg

The high strain rate behavior of ultrafine-grained Al-1.5 Mg alloy produced by the equal channel angular pressing technique is investigated in this work. High strain rate compression tests were performed in a split Hopkinson pressure bar to achieve nominal strain rates of around 2000 s(-1) at temperatures ranging from 300 to 523 K. In addition to un-interrupted Hopkinson bar tests, strain rate change tests were carried out using a flange and sleeve arrangement on the incident bar. The results obtained at the high strain rates were compared with those at low strain rates from an earlier study. It was seen that at the strain rate of 2000 s-1 the transition from hardening to softening (with respect to the coarse grained alloy), was shifted to higher temperatures. The strain rate sensitivity for the ultrafine-grained alloy was higher as compared to the coarse grained alloy for the entire range of testing. The increased strain rate sensitivity and the average subgrain size measured after testing at 473 and 523 K, suggest an active role of grain boundaries in the process of deformation. The possible reasons for softening at the low strain rates and its suppression at the high strain rates are discussed. (C) 2008 Elsevier B.V. All rights reserved.