Macro/micro-structure and mechanical properties of medium-thick 2219 aluminum alloy joints fabricated by laser-assisted helium arc deep-penetration TIG welding

In this work, defect-free and structurally sound 13 mm thick 2219 aluminum alloy weld joint was fabricated using a novel laser-assisted helium arc welding method in deep-penetration mode. The weld formation, microstructure and mechanical properties of the weld joints were systemically investigated. It is found that helium arc with the assistant of laser can achieve a full-penetration weld with a deep penetration of 13 mm. The microstructural results show that the welding thermal cycle causes the complete dissolution of θ’ phases in the weld zone (WZ) and partially melted zone (PMZ), forming α-Al + θ eutectic structures. The subsequent argon arc capping weld introduces a secondary thermal cycle, which promotes the coarsening and coalescence of low-melting-point eutectics within the original backing welded joint, creating interconnected networks along the grain boundaries. Mechanical testing demonstrates a high-quality final joint with a tensile strength of 282.7 MPa and an elongation of 5.7%. The fracture paths shift from traversing the WZ in backing welds to being confined to the WZ/PMZ interface in final joints. This shift is driven by the geometric effect at the weld toe and the localized stress concentration induced by the coarse eutectic networks in the PMZ.