Predicting residual distortion of aluminum alloy stiffened sheet after friction stir welding by numerical simulation

► Structure (Al-alloy stiffened sheet) had an anti-saddle distortion state after FSW. ► Structure had the same distortion trends as sheet but deformation value is smaller. ► Deformation decrease in longitudinal direction of structure was more significant. ► Structure and sheet had the consistent plastic strain distribution after FSW. ► Stiffeners designed on sheet could reduce the buckling distortion of sheet.