Mechanical behaviour of AA 2024 friction stir overlap welds

Purpose - To investigate the effect of different welding configurations on the mechanical properties of friction stir welding (FSW) overlap joints. The application of FSW in an overlap configuration could be an attractive replacement to the riveting process for assembly of fuselage primary structures due to the similarity in tolerance management. However, the mechanical properties of welded overlap joints are often inferior to the respective riveted lap-joint properties. Design/methodology/approach - In order to quantify the static and fatigue strength of FSW overlap joints, numerical and experimental investigation on overlap welds were performed in the current work. Several single shear overlap joints welding configurations were investigated, including single and multiple pass friction stir welds. The static and fatigue behaviour of these joints was assessed through tensile and fatigue tests. Findings - Static and fatigue behaviour were found to strongly depend on the welding process parameters and configuration. With respect to the static behaviour, it was found that values close to base material can be achieved. However, depending on configuration and process parameters, static properties can be as low as about 30% of the base material properties. As for the fatigue behaviour, the fatigue limit for all configurations tested was found to be unrealistic for structural applications. Originality/value - The distance between the outermost welds in multiple pass welds were found to influence the mechanical properties, although no direct relationship can be derived. Indications have been found but no clear conclusion has been reached with respect to the optimum configuration. In some cases, specimens with superior tensile properties exhibited reduced fatigue properties whereas the exact opposite effect was observed for other configurations.