Microstructural evolution and deformation mechanism of 5A90 Al-Li alloy during superplastic deformation

The microstructural evolution and deformation mechanism of 5A90 Al-Li alloy sheets during superplastic deformation were studied by optical microscopy, scanning electron, electron back scattering diffraction and high temperature tensile test. The results show that the elongation of the specimen, which is recrystallized at 450℃ for 30 min before the tensile test, could increase from 480% to 880% at an appropriate superplastic condition of 475℃/8×10-4s-1. The superplastic mechanisms of 5A90 Al-Li alloy sheets are explored by investigating the microstructural evolution. The misorientation increases and dislocation activity plays a key role at the initial stage (ε≤0.59). Dynamic recrystallization begins to occur when the true strain reaches 0.59. With recrystallization, the misorientation between grains becomes larger and grain boundary sliding (GBS) starts at this stage (0.59<ε<1.55). With larger true strains (ε≥1.55), grain continues to grow with a stable microstructure, and superplastic mechanism is dominated by GBS.