Improving joint formation and tensile properties of friction stir welded ultra-thin Al/Mg alloy sheets using a pinless tool assisted by a stationary shoulder

In order to reduce or eliminate pin adhesion, a self-designed pinless tool with six-groove on a rotational shoulder was proposed to friction stir weld 6061-T6 Al and AZ31B Mg alloys. The assisted stationary shoulder can successfully improve surface formation, accelerate mechanical mixing, broaden welding process parameter window, heighten welding depth, and reduce the intermetallic compound layer thickness. Under the welding parameters of 40 mm/min, 1200 rpm, and 0.3 mm offset to Mg, sound joint with small flashes, sufficient Al/Mg mixture, and welding depth of 1 mm was obtained using the pinless tool assisted by the stationary shoulder. The maximum tensile strength of Al/Mg joint by the stationary shoulder reaches 124.1 MPa, which is 121.6% of that by the pinless tool. Some dimples appear on the fracture surface of the top region, presenting the existence of ductile fracture. Therefore, the pinless tool assisted by the stationary shoulder is greatly suitable for the welding of ultra-thin sheets of Al/Mg alloys.