On the multistage nature of deformation of the microcrystalline aluminum-lithium alloy 1420 under superplasticity conditions

The constant-rate tensile deformation and creep of aluminum-lithium alloy 1420 with a grain size of 3 µm (obtained by equal-channel angular extrusion) exhibiting superplasticity at temperatures of 600–670 K and relative-deformation rates of 10^?2–10^?3 s^?1 are considered. It is shown that, upon tension at a constant rate V _m, a steady-state segment appears in the true stress σ_t-true strain ?_t dependence, which is described by the expression $\dot \varepsilon _t \sim \sigma _t^n \exp ( - U/kT)$ with constant coefficients, and that the rate of deformation $\dot \varepsilon _t$ is close to the creep rate at comparable stresses and strains. The conclusion is made that, upon deformation under superplasticity conditions, an equilibrium structure is formed, which remains unaltered in the process of further deformation until the sample goes over (because of geometrical conditions) to a prefracture state.