Development of grain structure during superplastic deformation of an Al-Zn-Mg-Cu-Zr alloy containing Sc

Recent studies have shown that a suitably thermomechanically processed Al-Zn-Mg-Cu-Zr-Sc alloy having an essentially unrecrystallized grain structure may be subjected to superplastic deformation at a temperature and strain rate combination of 475 degrees C, 1.9 x 10(-2) s(-1) to obtain a total elongation of 650%. The present work demonstrates that the utilization of two-step strain rate at 425 degrees C during superplastic deformation of a similarly thermomechanically processed alloy increases the total elongation value to as high as 916%. The beneficial effect of two-step strain rate could further be realized at 350 degrees C to obtain a total elongation of 438%. Using electron backscattered diffraction, the present work provides a systematic assessment of the changes in (i) percentage recrystallization and (ii) recrystallized grain size with percentage elongation in the material superplastically deformed using both one- and two-step strain rates. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.