Fatigue Behavior of Friction Stir Welded Joints of Pure Copper with Ultra-fine Grains

In order to determine the long term durability of friction stir welded joints with ultra-fine grained microstructure, investigation of the mechanical response with specific emphasis on fatigue behaviour is critical. In this paper, fatigue behavior of friction stir welded joints of pure copper in low cycle; strain-controlled regime was investigated. Microstructural characterizations indicated the formation of recrystallized ultrafine-grained microstructure in the nugget zone (NZ) after friction stir welding. Fatigue properties were specified at a strain ratio of 0.1 with total strain amplitudes of 0.01, 0.1, and 0.2%. The results attained from the experiments demonstrated cyclic hardening effect at high strain amplitudes, while softening was observed in low strain amplitude of 0.01%. The hysteresis loops indicated the concavity along with the small portion of linear behavior after the reversal point. Localized deformation in the form of shear bands along with equiaxed cells and noticeable misorientation were observed on the fracture surface.