Research on the Properties and Low Cycle Fatigue of Sc-Modified AA2519-T62 FSW Joint

The aim of this research was to examine the mechanical and fatigue properties of friction stir welded Sc-modified 5 mm thick AA2519-T62 extrusion. The joint was obtained using the following parameters: 800 rpm tool rotation speed, 100 mm/min tool traverse speed, 17 kN axial, and MX Triflute as a tool. The investigation has involved microstructure observations, microhardness distribution analysis, tensile test with digital image correlation technique, observations of the fracture surface, measurements of residual stresses, low cycle fatigue testing, and fractography. It was stated that the obtained weld is defect-free and has joint efficiency of 83%. The failure in the tensile test occurred at the boundary of the thermo-mechanically affected zone and stir zone on the advancing side of the weld. The residual stress measurements have revealed that the highest values of longitudinal stress are localized at the distance of 10 mm from the joint line with their values of 124 MPa (the retreating side) and 159 MPa (the advancing side). The results of low cycle fatigue testing have allowed establishing of the values of the cyclic strength coefficient (k′ = 504.37 MPa) and cyclic strain hardening exponent (n′ = 0.0068) as well as the factors of the Manson–Coffin–Basquin equation: the fatigue strength coefficient σ′(f) = 462.4 MPa, the fatigue strength exponent b = −0.066, the fatigue ductility coefficient ε′(f) = 0.4212, and the fatigue ductility exponent c = −0.911.