Deformation pattern and strain hardening in a highly textured 8090 Al-Li alloy sheet

Abstract

Structure-deformation pattern analysis was made on a highly textured 8090 AI-Li alloy sheet deformed in tension. It is shown that the sharp beta-fiber type crystallographic texture induces a strong orientation variation in the mechanical properties and in the deformation structure. The soft orientation is 55 degrees in respect to the rolling direction (RD), while the hard orientation is parallel to the RD. Both results are predicted from the detected texture by the relaxed constrained Taylor deformation model (RC). Cellular dislocation substructure was observed in the samples deformed parallel to the RD. However, in the samples tested 55 degrees to the RD, coplanar dislocation arrangement was preserved even up to 30% elongation. In the hard orientation, the strain hardening ability is quickly exhausted. This is due to the effect of dynamic recovery occurring from the onset of deformation. In the soft orientation, the strain hardening is better sustained as a result of easy glide of the coplanar dislocations, on the primary slip systems, through the grain structure. The pattern of surface slip traces is compatible with the dislocation substructure arrangement observed by transmission electron microscopy (TEM).