A coaxial nozzle assisted underwater laser welding of 316L stainless steel

As a promising maintenance technique, underwater laser welding (ULW) technology aids in advancing oceanographic engineering. However, water has an attenuating effect on laser making direct ULW challenging, and water intrusion may deteriorate weld formation. This paper qualitatively analyzed the visualization of ULW welding process dynamics under varying water depths, based on image sequences recorded by a high-speed camera, and then focused attention on macro-forming characteristics of ULW joints. The results demonstrate that wet ULW fails when the water depth exceeds 6 mm due to the inability to establish a "beam channel", which is required for ULW to proceed. Thus, a self-designed coaxial nozzle was employed to minimize water interference in underwater environment, as demonstrated by numerical simulations. Porosity is sensitive to the welding parameters and can be minimized by lowering laser power, increasing velocity, and choosing a modest shielding gas flow rate. Pore formation is linked to the dynamic behavior of the local gas phase space, which is distinctive to the ULW processing. This work offered a comprehensive understanding of the ULW that was highly feasible.