Microstructural Evolution During Superplastic Forming of Al-Li 8090 Alloy

Abstract

Commercial grade AA8090 Al–Li alloy sheet contained three layers of distinct microstructural features along thickness direction. The surface layer contained well recrystallized equiaxed grains with higher fraction of T {4 4 11}, Cu {1 1 2}, H {0 0 1} and CH {0 0 1} texture components whereas middle layer contained unrecrystallized elongated grains with higher fraction of brass {0 1 1}, CG {0 2 1} and goss{0 1 1} texture components. Superplastic forming of the separated surface and middle layers was carried out at constant pressure. Microstructure and texture evolution was studied at different location of the formed bulge. The extent of texturing or anisotropy was calculated from standard deviation of texture estimated normal anisotropy (R) values, Rstdev. At all conditions, in both the surface and middle layers, the texture randomization was found to be more at the apex than that at the edge of the bulge. The overall reduction in texturing was predominantly accompanied by weakening in strong texture components and strengthening in the weaker ones.