Enhanced ductility and deformation mechanisms of ultrafine-grained Al-Mg-Si alloy in sheet form at warm temperatures

Ultrafine-grained Al-Mg-Si alloy processed by high-ratio differential speed rolling exhibited significantly enhanced tensile ductility at warm temperatures (493-553 K). The dominant deformation mechanism of the alloy was found to be pipe-diffusion-controlled grain boundary sliding associated with a stress exponent of 4. According to the analyses based on Hart's necking criterion, in addition to increased strain rate sensitivity, increased strain hardening by accelerated dynamic grain growth notably contributes to the ductility of ultrafine-grained aluminum. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.