Superplastic forming at high strain rates after severe plastic deformation

An Al-3% Mg-0.2% Sc alloy was fabricated by casting and subjected to severe plastic deformation through equal-channel angular pressing to a strain of similar to 8. The grain size after pressing was similar to 0.2 mu m and inc reased to - 1.1 mu m when holding at 673 K for 10 min. Very high tensile el ongations were recorded at 673 K with a maximum elongation of similar to 22 80% when testing with an initial strain rate of 3.3 x 10(-2) s(-1) The stra in rate sensitivity was measured as similar to 0.5 at strain rates in the v icinity of 10(-2) s(-1). Small disks were cut from the rods after pressing and these disks were successfully formed into domes at 673 K using a biaxia l gas-pressure forming facility and forming times up to a maximum of 60 s. Measurements of the local thicknesses at selected points around the domes r evealed reasonably uniform thinning which is consistent with the high strai n rare sensitivity of this alloy. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. AII rights reserved.