Microstructural Analysis and Process Parameter Optimization of Friction Stir-Welded AA8090 alloys for Enhanced Tensile Strength

Friction stir welding (FSW) has proven to be a dependable joining method for high-strength aerospace aluminium and titanium alloys that are challenging to weld using traditional fusion welding. One of the most crucial elements affecting heat generation, plastic flow, joint integrity, the resulting microstructure, and the mechanical properties is the design of the FSW tool. This study examined the effects of three controllable parameters: tool rotating speed (800, 1000, 1200), welding speed (50, 70, 90), and shoulder to pin diameter (D/d) ratio (3, 3.5, 4) on tensile strength in FSW operation on Aluminium 8090 alloys with hot-worked AISI H13 tool steel. A novel contribution is the systematic evaluation of the shoulder-to-pin diameter ratio (D/d) as one of the process parameters. Previous research largely focuses on tool pin shape or material, while this study uniquely isolates D/d as a variable, highlighting its contribution to weld quality and tensile strength. The studies were conducted on plates made of AA8090 alloy by applying the Taguchi technique. Using Minitab 16 software, a three-level, three-factor experiment design was created in accordance with the Taguchi orthogonal array L9. The results show that a rotational speed of 1200 rpm, a welding speed of 70 mm/min, and a shoulder to pin diameter of 3 are the optimal values for tensile strength. With a contribution of 68.6%, rotational speed is known to be the most important element based on the results. The second most important factor affecting the tensile strength of friction stir-welded AA 8090 alloys is the ratio of the shoulder to pin diameter (D/d) with a contribution of 16.9%. Ultimately, a tensile strength value model derived from FSW parameters was computed and validated by testing outcomes. SEM Fractography reveals the characteristic of brittle nature during tensile test. EDS spectrum exhibits presence of Cu, Mg and low Fe/Si content indicates good strengthening potential and minimal contamination.