Crack path and fracture analysis in FSW of small diameter 6082-T6 aluminium tubes under tension-torsion loading

This paper reports part of the work done in a research project aimed at developing an optimised process to join 38 mm diameter tubes of 6082-T6 aluminium alloy using friction stir welding (FSW), and then to determine the fatigue performance under tension, torsion and tension–torsion loading conditions. The final outcome of the project is intended to be guidance for fatigue design of small diameter aluminium tubes joined by FSW, and this paper presents information on crack path and defects under the various loading conditions. Crack path analysis was performed using both low magnification stereo microscopy and scanning electron microscopy, in order to identify crack initiation sites, the direction of crack propagation and the interrelated influence of microstructure and weld geometry on the crack initiation path.