Formation and mechanical properties of 6082-T6 aluminum alloy joint via bobbin-tool friction stir welding

Bobbin-tool friction stir welding (BT-FSW) was used to realize welding of 10 mm thick 6082-T6 aluminum alloy sheet. Characteristics of thread processing on the surface of pin was conducive to inducing single shear deformation of material around the pin, increasing complexity of deformation of material around the pin while improving strain rate, and thus helping to weaken microstructure of material in the area of BT-FSW joint. The results showed that when rotational speed was 300 r/min, welding speed was 400 mm/min and press-in depth was 0.5 mm, BT-FSW joints with good surface and internal macroscopic shape were obtained, and macroscopic shape of welded joints was typical “dumbbell”. Under the influence of high degree of plastic deformation, dynamic recrystallization of grains in BT-FSW joints occurred, resulting in fine equiaxed grains. Due to different distribution of friction heat input in different areas of welded joints, hardness distribution of welded joints exhibited typical W shaped distribution. Tensile strength of welded joints was about 77% of base material and elongation was about 69% of base material.