Microstructural evolution and superplastic deformation mechanisms of as-rolled 2A97 alloy at low-temperature

The microstructure and texture evolutions of 2A97 Al-Li alloy with initial unrecrystallized structure during superplastic deformation were investigated. A total elongation of 300% was obtained at 390 degrees C at an initial strain rate of 3 x 10(-3) s(-1). The initial banded structure gradually transformed into a recrystallized structure, characterized by equiaxed grains, random boundary misorientation distribution and a weak texture at high strains. The true strain-stress curve exhibited three stages: work hardening (stage I), steady-state (stage II), and deformation instability regions (stage III). The corresponding deformation mechanisms varied at different stages. The strain rate sensitivity index (m) remained constant of 0.35 and the texture density increased with strain at stage I, where the dislocation creep and subgrain rotation were the dominant mechanisms. During stage II, the m-value increased to 0.44, and the texture density decreased drastically with strain. The combination of grain boundary sliding (GBS) and dislocation creeep could explain the behavior of the alloy. Grain growth and cavitation resulted in the decrease in m-value at stage III, where GBS was the main deformation mechanism.