Analysis of residual stresses in thick aluminum friction stir welded butt joints

► Residual stress on top surface presented “M” profile and peaked at 171 MPa. ► Stress on bottom surface presented inverted “v” profile and peaked at 99 MPa. ► Residual stress reached 243 MPa for the weld with tunnel defect. ► Residual stress decreased on top surface with the increase of rotary speed. ► Residual stress increased on bottom surface with the increase of rotary speed.