Microtextural Evolution during Superplastic Deformation in AA8090 Al-Li Alloy

Abstract

Evolution of microtexture during superplastic deformation (SPD) of an AA8090 SPF grade sheet was investigated. The SPD was performed by tensile testing at 530°C and at a strain rate of 1x10 - 3 /sec, and the microtexture was analyzed by electron back scatter diffraction technique based Orientation Imaging Microscopy (OIM). Prior to the onset of SPD, there was a variation in distribution of different types of textures across the thickness of the sheet. The center location had a predominantly brass-type texture, whereas the surface location had a copper-type texture. The subsequent microtextural determination in samples deformed to various strain levels showed that, there occurred grain growth, grain shape change and textural weakening. The magnitude of these three microstructural changes continuously increased with the amount of SPD. However, there was no evidence of a development of any new type of texture following the deformation. A sample was also statically heated at a higher temperature of 570°C and for a longer time of one hour to simulate the grain growth to the same level as occurred during SPD. It was observed that without deformation the original grain morphology and textures did not change. Therefore, it was concluded that discontinuous recrystallization did not occur during static annealing, and the texture weakening that occurred during SPD was the result of deformation itself and not due to grain growth.