Effects of pre-stretching on mechanical properties and corrosion behavior of superplastic formed 2A97 Al-Li alloy

Effects of pre-stretching on mechanical properties and corrosion behavior of superplastic formed 2A97 Al-Li alloy were investigated by using tensile test, intergranular corrosion test, electrochemical analysis, electron backscattering diffraction analysis and transmission electron microscopy. The results show that compared with T6 heat treatment, the T8 heat treatment effectively improves the strength by introducing more finer and more homogeneous T1 precipitations. And the pre-stretching strain has significant influence on the microstructure and properties of superplastic formed alloy. When the pre-stretching strain reaches 4 %, the cavities formed during superplastic forming are obviously elongated along the pre-stretching direction. During 4 %-8 % pre-stretching strain, the increment of strength gradually decreases, but the elongation drops sharply. When the pre-stretching strain reaches 8 %, the elongated cavities and cracked coarse second phases result in a slight decrease in strength. The corrosion behavior of samples after heat treatment with different pre-stretching strain are obviously different. The corrosion microscopy of T6 and T82 sample is pitting with intergranular corrosion (IGC) by the grain boundary precipitation free zones (PFZ) dissolving preferentially. After 4 %-8 % pre-stretching treatments, the corrosion microscopy is only pitting by the dissolution of the matrix around T1 precipitations. What's more, strength and corrosion resistance are both at a high level by 4 % pre-stretching treatment.