Role of geometrically necessary dislocations on mechanical properties of friction stir welded single-phase copper with medium stacking fault energy

Abstract

The contribution of geometrically necessary dislocations (GNDs) and grain boundaries (GBs) on the mechanical properties of different zones in a friction stir welded pure copper joint is unveiled. This representative and simple medium stacking fault metal is selected to decouple the contributions of complex microstructure (precipitates, second phases and phase transformation) and focus only on GNDs and GBs. The GNDs density is much higher in the weld compared to the base material but similar in the thermomechanically affected zone (TMAZ) and the stir zone (SZ). Their difference is rather related to the dislocation distribution: in the grain interior in the SZ and near the GBs and grain interior in the TMAZ. In comparison to the TMAZ, the higher strength and elongation of the SZ results from the formation of finer grains and sharp-clean grain boundaries issued from continuous dynamic recrystallization.