Strain rate sensitivity of flow stress and its effect on hot rolling texture development

It is well known that during the hot rolling of Al-alloys a strong B-orientation (011)[lt]211[gt] develops at the mid layer. Furthermore, in hot rolled Al-plates a strong through thickness texture gradient arises. These effects are most pronounced in high strength Zr-containing Al-alloys (7XXX, 8XXX series) which do not recrystallize during hot rolling and where the strong texture causes a marked anisotropy of the mechanical properties. A pronounced B-orientation was also observed in other hot rolled Al-alloys. According to common Taylor type deformation models, i.e. full constraints (FC) or relaxed constraints (RC) with free [var epsilon][sub 13] and/or [var epsilon][sub 23]-shear, which have been successfully applied to interpret cold rolling textures in Al, such a very strong B-orientation ought not to arise. In order to explain the occurrence of a strong B-orientation several approaches have been proposed: (1) The B-orientation is often assumed to exhibit the lowest stored energy. During hot deformation this leads to a reduced rate of recrystallization for the B-orientation, when compared to the other rolling orientations S (123)[lt]634[gt] and C (112)[lt]111[gt]. Such behavior has indeed been observed in Al-Li model alloys, which are very effectively inhibited by Zr and thus, selective recrystallization can be neglected. (2) Itmore » has been shown that dislocation slip on planes other than (111) can result in the development of the B-orientation. Final evidence for the occurrence of such non-octahedral slip, however, is still missing, at least for high deformation rates as during rolling.« less