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 increased to - 1.1 mu m when holding at 673 K for 10 min. Very high tensile elongations were recorded at 673 K with a maximum elongation of similar to 2280% when testing with an initial strain rate of 3.3 x 10(-2) s(-1) The strain rate sensitivity was measured as similar to 0.5 at strain rates in the vicinity 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 biaxial 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 revealed reasonably uniform thinning which is consistent with the high strain rare sensitivity of this alloy. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. AII rights reserved.