Superplasticity of a microcrystalline aluminum-lithium alloy under torsion

The deformation of an aluminum-lithium alloy under torsion in the temperature range 523-673 K at angular velocities of 0.322 and 0.0322 rad/s is studied. The shear strain gamma prior to failure is found to increase with decreasing strain rate, and its temperature dependence has a maximum at 553 K (gamma approximate to 30). The initial loading-induced jump in the dependence of the torque on the angle of rotation (stress-strain curve) is followed by a softening stage, which changes into a hardening stage or a stage with a constant torque at all temperatures except those near 673 K. The stress distribution over a cross section is analyzed, and the dependence of the shear-strain rate gamma on the stress tau and temperature T is found to be (gamma) over dot similar to tau(n) exp(-U/kT). The results are compared with those obtained earlier from tensile tests of this alloy. (C) 2003 MAIK "Nauka/Interperiodica".