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

Plates of aluminum alloys 2219-T62 were joined in a butt joint by friction stir welding. The residual stresses on the top and bottom surfaces were measured using the hole-drilling strain-gauge method. In the test specimen, it was found that the residual stresses on the top surface peaked at about 171 MPa, while the value reached 243 MPa for the weld with tunnel defect and had the conventional “M” profile with tensile stress peaks in the heat-affected zone. Those attached on the bottom surface had the inverted “V” profile with tensile stress peaks in the weld centre and the corresponding value was 99.4 MPa. Meanwhile, with the increase of rotary speed, the longitudinal residual stress decreased on the top surface, but increased on the bottom surface.