Stepped-shoulder friction stir welding to alleviate weld thinning for dissimilar AA2195-T8/AA2219-T6 alloys

A stepped-shoulder friction stir welding tool containing a protruding inner shoulder and an outer shoulder was proposed to join AA2195-T8 Al-Cu-Li and AA2219-T6 Al-Cu alloys. The inner shoulder with a considerable plunge depth enhanced forging effect, and the outer shoulder with a low plunge depth prevented plasticized materials from overflowing out of welds, while the pin with milling facet promoted material flow. The sound joint with a weld thinning of 0.05 mm (about 0.8% of the workpiece) was obtained. The interface between the two materials was free of cavities and kissing bond. The joint fractured in thermo-mechanically affected zone on the side of AA2219-T6 alloy. The tensile strength reached 352 MPa, equal to 81.7% of base AA2219-T6 alloys.