SUPERPLASTIC FORMING AT HIGH STRAIN RATES AFTER SEVERE PLASTIC DEFORMATION

摘要

An-3/100 Mg-0.2/100 Sc alloy was fabricated by casting and subjected to severe plastic deformation through equal-channel angular pressing to a strain of ~ 8. The grain size after pressing was ~ 0.2 βm and increased to-l.1 βm when holding at 673 K for l0 min. Very high tensile elongations were recorded at 673 K with a maximum elongation of ~ 2280/100 when testing with an initial strain rate of 3.3 x l0~2 s~-l. The strain rate sensitivity was measured as ~ 0.5 at strain rates in the vicinity of l0~-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 thick- nesses at selected points around the domes revealed reasonably uniform thinning which is consistent with the high strain rate sensitivity of this alloy.