Development of ultrafine-grained microstructure and low temperature (0.48 Tm) superplasticity in friction stir processed Al-Mg-Zr

Friction stir processing (FSP) was applied to extruded Al-4Mg-1Zr to produce fine-grained microstructure with grains sized 0.7-1.6 mu m. Low temperature deformation behavior was investigated at 175 degrees C and initial strain rates of 5 x 10(-5)-3 x 10(-3) s(-1). Low temperature superplasticity was observed in ultrafine-grained material. A maximum superplastic elongation of 240 % was obtained in ultrafine-grained (0.7 mu m) ESP sample at an initial strain rate of 1 X 10(-4) s(-1) where a maximum strain rate sensitivity of 0.34 was observed. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.