Wire-based refill friction stir spot welding with the modified sleeve towards non-thinning and high mechanical properties joint

The inherent issues of weld thinning, hook-induced stress concentration, and the weak region of bonding ligament severely impaired the general appearance and mechanical properties of the refill friction stir spot welding (RFSSW) joint. Herein, wire-based refill friction stir spot welding (W-RFSSW) and modified sleeve were devised to achieve non-thinning and well-formed 5A06/2219 aluminum alloy lapped joints with ER5356 wires. The weld thinning was compensated by paraxial feeding wire through the clamp sidewall. The trapezoidal groove in the modified sleeve functioned like mechanical "shovels," promoting vertical material flow and mixing, which subsequently increased shear strain and heat generation. Internal formation and material flow were improved by severe plastic deformation effect of the modified sleeve. The joint formation, microstructural evolution, mechanical properties and thermal cycle measurements of joints produced by all three methods: conventional RFSSW, W-RFSSW, and W-RFSSW with modified sleeve, were systematically investigated. Compared to conventional RFSSW joint, W-RFSSW with a modified sleeve joint’s properties enhanced from 8015 ± 2438 N to 13106 ± 143 N, increasing by 63.5 %. The hook angle increased from 59° to 117°, mitigating stress concentration at the hook. This method provided a novel approach for material-deficient joints and significantly enhanced joints with hook mitigation and sufficient material flow.