Mechanical behavior of microcrystalline aluminum-lithium alloy under superplasticity conditions

Aluminum-lithium alloy 1420, which, after equal-channel angular pressing, has a grain size of about 3 mum, is shown to possess superplasticity in a temperature range of T = 320-395 degreesC upon tension at a constant relative strain rate of 10(-2)-10(-3) s(-1). The axial deformation at fracture can exceed 1800%. The data processing at such large deformations should be carried out using true strains epsilon (t) and stresses sigma (t). In the flow curve, a short stage of hardening is followed by a long softening stage. They can be described by the relation epsilon (t) similar to sigma (n)(t)exp(-U/kT) with a constant exponent n approximate to 2 and activation energies U approximate to 1 eV for the softening stage and U approximate to 1.4 eV for the hardening stage. The deformation is supposed to be controlled by grain-boundary sliding at the stage of softening and by self-diffusion in the bulk of grains at the hardening stage. (C) 2001 MAIK "Nauka/Interperiodica".