A Comparative Study on Fatigue Response of Aluminum Alloy Friction Stir Welded Joints at Various Post-Processing and Treatments

The present study examines the fatigue of friction stir welded (FSW) aluminum 6061, 7075, 1060 joints followed by (i) in situ and sequential rolling (SR) processes, (ii) plastic burnishing (iii) solution-treatment artificial aging (STA), (iv) local alloying through depositing thin copper foils, and (v) inserting alumina powder in the weld nugget zone (NZ). The microstructural features and fatigue life of post-processed joints were compared with those of as-welded joints. The in situ rolling technique offered simultaneous rolling and welding operations of aluminum joints, while through the sequential rolling process, the top surface of FSW joints was rolled after the welding process. The fatigue life of in situ rolled samples was increased as the ball diameter of welding tool increased. The fatigue life of friction stir welded joints after a low-plasticity burnishing process was noticeably promoted. The addition of 1 wt.% alumina in the NZ of joints resulted in a significant elevation on fatigue life of friction stir spot welded joints, while an increase in alumina powder to 2.5 wt.% adversely affected fatigue strength. Weld NZ was alloyed through the insertion of copper foils between the faying surfaces of joints. This localized alloy slightly improved the fatigue life of joints; however, its effects on fatigue life were not as influential as STA heat-treated or in situ rolled joints. The microstructure of weld joints was highly affected through post-processing and treatments, resulting in a substantial influence on the fatigue response of FSW aluminum joints.