Friction Stir Welding of the Butt Joints of Al-Mg-Si Aluminum Alloys

The mechanical properties and the structure of the butt joints of Al-Mg-Si alloys made by friction stir welding are investigated. The ultimate tensile strength of the joints is found to be 0.82-0.87 depending on the alloy grade after welding. Fracture is shown to occur through the thermomechanical action zone on the side of tool motion. The bending angle of the joints (170 degrees-180 degrees) significantly exceeds the values typical of fusion welding. The hardness distribution in the joints has a W-shape characteristic of these alloys. Artificial aging after welding is shown to cause an increase in the strength coefficient of the joints to 0.92-0.96 at a bending angle of 160 degrees-170 degrees. Complete heat treatment, including quenching and artificial aging, is found to cause noticeable buckling of the welded joints and to be accompanied by a decrease in the strength and plastic properties of the joints because of grain growth in the mixing and thermomechanical action zones. After this treatment, the microhardness distribution within the welded joints is found to decrease and level off.