Overview -: Microtextural evolution during superplastic deformation of AA 8090 Al-Lialloy

A brief review of orientation imaging microscopy and an overview of the results of investigations related to textural evolution during superplastic deformation of a recent series of superplastic grade aluminium alloys, and specifically the results of the authors' study on microtextural evolution in AA 8090 Al-Li alloy, are presented. It was observed that the surface layer of the AA 8090 alloy sheet was dominated by S (011)< 634 > type texture, whereas the midthickness layer was dominated by brass (011)< 211 > type texture. In the course of superplastic deformation, textural weakening occurred, the rate and extent of which were different in the surface and centre regions, depending upon whether the two layers were deformed separately or as a composite in the full thickness tensile specimen. Textural weakening was generally more extensive at higher test temperatures and lower strain rates. Based on textural evolution and the presence of a large proportion of low angle boundaries, and their near elimination at larger strains, dislocation slip could be considered to be the dominant mechanism during the initial stages of deformation, whereas the conventional mechanism for superplastic deformation is thought to be operating during the later stages.