Fatigue strength improvement of GMAW T-welds in AA 5083 by friction-stir processing

The aim of this study is to verify to what extent the friction stir processing (FSP) can improve the fatigue behaviour of GMAW welds in aluminium alloys. In fact these welds often have problems such as: formation of porosity, distortion, loss of mechanical strength and deterioration of their fatigue behaviour. In this study the FSP technology is applied to GMAW T-fillet welds performed on 5083-H111, 6 mm thick aluminium alloy plates. The FSP effects were studied by metallographic analysis as well as hardness, tensile and fatigue tests and the fatigue-fractured surfaces were analysed using scanning electron microscopy (SEM). The fatigue tests were done under constant loading for two stress ratios, R = 0 and R = −1, and variable loading with spectrum shape exponent of ν = 2 and ν = 5 with the stress ratios R = 0 and R = −1. The FSP slightly increases the hardness and Rp0.2 of toe microstructures, but reduces the elongation on fracture of tensile specimens. However, the fatigue strength of the welded joints is significantly improved because of the grain refinement, porosity removal and reduction in stress concentration promoted by the weld toe radius increase.