Oscillating laser welding of ultra-thick titanium alloy using new flux-cored filler wire: Process stability, microstructural evolution and mechanical properties

Abstract

A new type of flux-cored filler wire was designed by synchronously optimizing Mo and Fe elements, and it was applied to narrow gap laser oscillating wire filler welding (NG-LOWFW) of ultra-thick titanium alloy, the effects of process parameters on the stability of welding process, microstructure and mechanical properties of welded joint were studied by experiment and numerical simulation. The results show that the oscillating laser and the liquid bridge transition mode could increase heat exchange between molten pool surface and external environment, resulting in high undercooling conditions, reduced thermal gradient, and guarantee the stability of the welding process effectively, the microstructure evolution of ultra-thick welded seam is uniform, the grain size is refined and the welding defects are restrained effectively. Moreover, Mo and Fe elements could further enhance the wetting and spreading mobility of liquid metal during welding, which contributes to the synergistic optimization of strength and toughness of ultra-thick welded joint, up to 935 MPa and 25 J. The research outcomes provide a new route for welding ultra-thick titanium alloy, which benefits further welding process and optimization.