Microstructure and Mechanical Properties of Bobbin Friction Stir Welded Joint of 5 mm Thick 6082-T6 Aluminum Alloy

5 mm thick 6082-T6 aluminum alloy plates were butt-welded using the bobbin friction stir welding technique and the microstructure and mechanical properties of the joint were studied. The results show that after welding at the spindle speed of 500 r·min^-1 and welding speed of 400 mm·min^-1, the microstructure of the joint was dense. The grains in weld nugget zone was fine and even, while in the thermo-mechanical affected zone became long and narrow and in the heat affected zone became coarse. The tensile strength and yield strength of the joint was 232.75, 161.04 MPa, respectively, which were slightly lower than those (272,229 MPa, respectively) of base metal. The bending performance of the joint was qualified. The microhardness showed the W-shape distribution and the lowest value of the hardness appeared in the heat affected zone at the forward side, which was 67 HV. The hardness of the weld nugget zone was 77.6 HV.