Large depth to width ratio friction stir welding joint obtained by novel designed tool with double pin

A novel welding tool with a double pin structure was proposed to solve the problem of difficult weld formation with a large depth to width ratio (DWR). Experiments revealed that the novel welding tool could achieve non-defect joints for four common engineering aluminum alloys (2A12-T6/5052-H32/6013-T6/7075-T6), with a DWR of 0.59-0.67. Due to the difference in the direction of material flow between the upper pin and the pin effect, impact slow flow zone was formed in the joint center. The maximum ultimate tensile strength of the 7075-T6 aluminum alloy double pin friction stir welding (DPFSW) joint reached 450.38 MPa, which was 85.8% of the base material. Analysis of the tensile fracture location revealed that the stirring zone of the advancing side and weld nugget zone occurred local blockage, resulting in joint failure.