Equal-load-bearing joining of alclad AA2024-T4 alloy stringers and skins in aviation via friction stir lap welding

Friction stir lap welding of stringers and skin is of great significance for aircraft weight reduction. A welding tool characterized by the conical threaded pin with triple milling facets was proposed to alleviate hook and cold lap defects in friction stir lap welded joints. Sound joints without weld thinning were achieved in AA2024-T4 alloy joints with the thickness of 1.5 mm and 1.2 mm. The design of the thread and triple facets effectively enhanced the material flow behavior, thereby suppressing the formation of hook and cold lap defects. The lap width was significantly broadened to 5 times of skin thickness towards better load-bearing capacity. The ultimate tensile strength of the joint reached 428.3 MPa, equivalent to that of the base material, which fractured at the base material far away from the welding zone.