Residual Stresses in Welded Joints Made by Friction Stir Welding

Friction stir welding (FSW) is a relatively new welding process that has already been widely used for structural joints in the aerospace, transportation, shipbuilding, and other industries. Although it requires sophisticated equipment, it is believed that, compared to traditional arc welding processes, it provides less heating of the joint metal and a lower level of residual stresses and strains. Information on residual stresses is required to predict welded structures’ strength and service life. In this paper, we investigated the features of residual stresses in a butt FSW joint made of a heat-strengthened aluminum alloy. A mathematical model for determining residual stresses at the FSW was developed, and the effect of the aluminum alloy softening during welding heating on residual stresses was considered. Comparison of the calculated and experimental data on the distribution of residual longitudinal stresses in the specimens made by FSW showed their satisfactory level of correspondence. It is important to note that a high level of residual tensile stresses close to the yield strength of the annealed metal was determined.