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

A brief review of orientation imaging microscopy and an overview of the res ults of investigations related to textural evolution during superplastic de formation of a recent series of superplastic grade aluminium alloys, and sp ecifically 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, wh ereas the midthickness layer was dominated by brass (011)< 211 > type textu re. In the course of superplastic deformation, textural weakening occurred, the rate and extent of which were different in the surface and centre regi ons, depending upon whether the two layers were deformed separately or as a composite in the full thickness tensile specimen. Textural weakening was g enerally 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 s tages of deformation, whereas the conventional mechanism for superplastic d eformation is thought to be operating during the later stages.