Prediction of bending limits in friction-stir-processed thick plate aluminum

Friction-stir processing (FSP) was used to modify surface microstructures, to enhance the bending of thick-plate 6061-T6 and 7050-T7451 aluminum alloys. Plates were bent at room temperature into a V-shaped die, to various angles. Bending performance in the friction-stir-processed plates was significantly better than that in the base plates, where processing caused localized softening of the pretensile surface of the plate. A finite-element model of the plate-bending process was developed, to predict the bending limits of both the unprocessed base plates and of the friction-stir-processed plates. For the friction-stir-processed plates, the model employed a mesh divided into two or more zones; one zone was for unprocessed base material and other zones were for the processed material or for material that was affected by the heat of processing. The model used both the von Mises and the Latham and Cockroft criteria to predict bending limits. The bending-limit predictions were reasonably accurate, provided the gradient in true stress-strain behavior through the plate thickness was well characterized.