A methodology for the study of Friction Stir Welded butt joints applied to unweldable aerospace aluminium alloys

Weight reduction is a constant improvement point for the aerospace sector. The joining of difficult to weld materials such as 2xxx and 7xxx aluminium series alloys has attracted the attention to Friction Stir Welding (FSW) in this field. This solid state welding process has already been presented as an environmentally friendly alternative for riveted joints and conventional welding operation in the automobile sector. Unfortunately, its application on the aeronautical sector is not completely studied at the moment and concerns about its quality and in-service behaviour have delayed its implementation. This paper stablished a methodology to study the effect of the welding parameter and applied it to a structural aluminium AA2024-T3, covering the design of the testing bench, the tool, the process monitoring and the analysis of the quality and main mechanical properties of the joint. The results showed the impact of the welding parameters on the quality of the joint. The burr and the roughness were optimised for 850 rpm and the forces were reduced up to 30% for this rotational speed. Similarly, the mechanical properties were reduced by up to 61.5% and 45% compared to the base material for the UTS and microhardness respectively.