Friction stir welding of T-joints with dissimilar aluminium alloys: Mechanical joint characterisation

Friction stir welding (FSW) is a high reliability joining process creating excellent opportunities for new design concepts. This paper discusses T-joints composed by dissimilar aluminium alloys, a configuration suitable for reinforced panels where the skin is made of an aluminium alloy with higher toughness, and the web (reinforcement or stiffener) is made of a higher strength aluminium alloy, creating a good damage tolerant arrangement. A T-joint configuration was proposed non-including overlap interfaces between the workpieces. This T-joint also promotes a good flow among the materials of the different workpieces during the FSW process resulting in sound welds. Mechanical properties were measured achieving high efficiency values of joint static and dynamic strenght but with the drawback of the loss of elongation. Microstructural analyses of the weld zone were performed, and the results were compared with those of base materials and FSW butt joints evidencing the possibility of joining two dissimilar aluminium alloys in a T configuration. Additionally, the residual stress field, which is an important parameter for a more reliable design of integral structures, was evaluated with a semidestructive and a destructive method. The feasibility to weld T-joints with dissimilar aluminium alloys was demonstrated achieving good quality results, which can be used for structure reinforcement and optimisation.