Characteristics of molten pool flow in adjustable-ring-mode laser welding of titanium alloys considering influence of groove gaps

Owing to inherent excellent specific strength, high specific modulus and good welding compatibility, TC4 titanium alloy has become the core material of crucial load-bearing structures in the field of aerospace industry. Nevertheless, during the narrow gap laser welding process, the interaction between the dynamic characteristics of molten pool and the geometric constraints is prone to induce the defects of incomplete fusion on the sidewall, which significantly affect the service performance of components. Ring-core adjustable laser technology is regarded as an advanced beam modulation approach, which can provide an innovative solution for improving narrow-gap welding quality by optimizing the spatial energy distribution to regulate molten pool behavior. In this study, with the integration of experiments with numerical simulations, a thermo-fluid coupling model was established to analyze the evolution of molten pool, while the relevant flow characteristics were revealed by the high-speed imaging and infrared thermal imaging. The experimental results demonstrate that the flow patterns of molten metal are significantly affected by the geometric constraints of groove sidewalls. Besides, the increase of groove gap width at a fixed ring-core ratio leads to the enhanced flow rate on the molten pool surface, and thereby the molten pool profile is shifted from concave to convex, resulting in the decreased fusion efficiency. In contrast, when the groove gap remains constant, the increase of ring-core ratio can effectively promote the wetting capability of molten pool on the sidewall, and thereby a stepwise improvement in fusion quality can be achieved.