Heterogeneous deformation of friction stir welded aluminum alloy 6061 in tension and high cycle fatigue

Purpose The investigations provide a basis for the optimization of the alloy 6061-T6 friction stir welding (FSW) process to improve the mechanical properties of welded joints. Design/methodology/approach The local deformation of the FSW joint in tension and fatigue test were experimentally investigated by digital image correlation (DIC) technique. Findings The local stress-strain behaviors of the sub-regions show that the plastic strain always concentrated at the heat affected zone (HAZ) on the advancing side both in tension and high cycle fatigue and eventually leads to the final fracture. The evolution of the plastic strain at very low stress is extremely slow and accounts for most of the total fatigue life. However, the local deformation exhibits a sudden increase just before the fatigue failure. Originality/value Based on the experimental data, the result indicates that the HAZ is the weakest zone across the weld and the strain localization in high cycle fatigue is very harmful and unpredictable for the FSW joints.