Superplastic deformation of Al-Li-Cu-Mg alloy sheet

Al-2.5 Li-1.2 Cu-0.6 Mg-0.12 Zr (wt%) alloy sheet was cold-rolled, solution heat-treated for 20 min at 510° C, prestrained by 3% and superplastically deformed at 450 to 540° C at strain rates between 1×10^–4 and 2.8×10^–1 sec^–1. The maximum elongation obtained was 300%. Significant cavitation occurred above about 0.5 strain at a rate (void volume/unit strain) of 4% at 540° C and 6% at 500° C. The onset of cavitation coincided with a reduction in the room-temperature tensile properties after reheat-treatment. During annealing at 500 to 540° C, grain coarsening near the sheet surface was associated with magnesium and lithium depletion. Superplastic deformation produced a fine equiaxed microstructure by dynamic recrystallization.