Revealing internal flow behavior in adjustable-ring-mode laser welding of titanium alloys with a narrow gap structure

Adjustable-ring-mode laser welding (ARMLW) combining both a ring beam and a central Gaussian beam has shown good advantages and feasibility in manufacturing narrow-gap high-performance components. However, the flow dynamics within the molten pool of ARMLW remain unclear. This study investigated thermal characteristics and flow dynamics in ARMLW of Ti-6Al-4V with narrow-gap structure, carrying out experiment and simulation. The results demonstrated that the ARM laser expanded effective heat source distribution, thereby enhancing molten metal flow and sidewall fusion. With the increase of ring-core ratio, the fusion zone at the sidewall gradually enlarged, and the concave angle of molten pool surface profile was increased from 0.87° to 1.31°. However, the flow velocities at both the surface and cross-sectional regions of the molten pool exhibited a non-monotonic trend. The maximum surface velocity of 3.941 m/s and mid-pool velocity of 0.108 m/s were obtained at a ring-core ratio of 1.29, where the fluid flow capacity in the inner sidewall fusion zone was significantly enhanced.Phenomenon above resulted from the peripheral circulation flow induced by the ring laser beam around molten pool, which significantly modified the hydrodynamic behavior of the liquid metal within the fusion zone. This study is anticipated to advance understanding of the phenomena involved in the ARMLW of titanium alloys with narrow gap structure, and further establish a fundamental basis for optimizing the narrow gap laser welding process.