Strain rate sensitivity and deformation kinetics of ECAPed aluminium over a wide range of strain rates

The strain rate sensitivity and apparent activation volume of aluminium processed by equal channel angular pressing for 1-8 passes are investigated at strain rates from 10(-3) to 10(3)/s. Constant strain rate tests performed in compression under both quasi-static and dynamic loading conditions show a continuously increasing strain rate sensitivity for the material subjected up to 8 passes of pressing. However, for the specimens subjected to the same number of ECAP passes, the dynamic strain rate sensitivity factor exhibits a 3- to 6-fold increase compared to the quasi-static value. This result suggests that the rate-controlling mechanism at high strain rates is different from that at low strain rates. Although the apparent activation volume under both quasi-static and dynamic loading conditions decreases with increasing pass number, the quasi-static activation volume for the Al ECAPed up to 8 passes is greater than 100b(3) (where b is the Burgers vector of aluminium) while the dynamic value is similar to 30b(3). Our experimental findings and analysis suggest that the deformation kinetics are controlled by the dislocation activations. The dominant rate-controlling mechanisms are suggested to be the forest dislocation cutting mechanism at quasi-static strain while viscous drag also plays an important role in the case of dynamic deformation. (C) 2012 Elsevier B.V. All rights reserved.