Comparative Study of Fatigue Properties in Friction Stir Welded Dissimilar Aluminium Alloys (AA5083-H111 and AA6061-T6) Using an Optimized Tool Pin Profile Versus a Standard Design Tool

Abstract

Friction stir welding (FSW) is a solid-state joining technique particularly effective for welding dissimilar aluminium alloys, such as AA5083-H111 and AA6061-T6. While the influence of FSW tool design on joint properties is acknowledged, the detailed comparative analysis of fatigue properties using different tool designs remains underexplored. This study fills this gap by examining the effects of a standard tool and an innovative tool design with longitudinal cylindrical grooves and circular grooves on the tool shoulder that are compatible with the thickness of the alloy to be welded. The tool designs were optimized using a systematic Design of Experiments (DOE) approach, focusing on enhancing mechanical properties and fatigue life through controlled tool features and process parameters. The tensile strength of the welded joints was quantitatively assessed, revealing that joints produced with the novel tool (S1) achieved a significantly higher tensile strength of 317 MPa (±15 MPa), compared to 285 MPa (±13 MPa) for the standard tool (S2). This improvement is linked to the novel tool's optimized heat generation and material flow characteristics. Moreover, the microstructure and hardness across the weld zones were evaluated to further understand the impact of tool design on the welding outcomes. Fatigue tests were conducted on samples from both tool types at seven different stress levels. The fatigue life, represented through S-N curves, showed that at an applied stress of 160 MPa, specimens welded with the novel tool withstood up to 9,328,980 cycles before failure, surpassing the 7,589,146 cycles endured by the standard tool, indicative of superior fatigue resistance. These results highlight the critical role of tool design in enhancing the FSW process for dissimilar aluminium alloys, demonstrating both the scientific rigor and innovative scope of the study.