Influence of Friction Stir Welding on Microstructure and Fatigue Life of 6082-T6 Aluminum Alloy

This work investigates the effects of friction stir welding (FSW) on the microstructure and mechanical behavior of 6082-T6 aluminum alloy joints. A combination of mechanical testing (tensile strength, fatigue crack growth per ASTM E-647, and microhardness measurements) and advanced microstructural characterization (optical and scanning electron microscopy, elemental analysis via X-ray fluorescence) was used to evaluate the welded assemblies. The weld zones namely the stir zone (nugget), thermomechanically affected zone (TMAZ), heat-affected zone (HAZ), and base metal (BM) exhibited significant differences in grain structure and elemental distribution. Dynamic recrystallization was observed in the nugget, while grain coarsening and softening occurred in the HAZ, particularly on the advancing side. Fatigue tests revealed a decrease in crack growth resistance in the welded joint compared to the base metal, especially under high stress intensity factors. The presence of iron-rich inclusions in the weld region suggests material transfer from the tool, potentially affecting long-term joint performance. Although FSW provides a sound and defect-free joining process for this alloy, local mechanical weakening remains a concern. The findings emphasize the importance of optimizing process parameters to improve structural integrity and fatigue durability.