Synergistic enhancement of weld stability and mechanical performance in laser welding of titanium alloy by coupling ring-shaped mode and beam oscillation

Oscillating laser and ring-shaped laser modes have been proven effective in enhancing the process stability and joint quality of laser welding. However, their combined effects, along with the mechanisms of spatter suppression and microstructural regulation, remain largely unexplored. To address this, a novel ring-shaped mode oscillating laser welding (RMOLW) process was developed by integrating both beam modes. The influence of this novel process on the stability and microstructural characteristics of TC4 titanium alloy welds was investigated through comparative analysis. Results show that the proposed process improves the uniformity of energy density distribution along the welding path, thereby reducing undercut severity. The significant reduction in spatter is attributed to the ring-shaped laser enlarging the keyhole opening area to 0.76 mm², while beam oscillation induces stable vortex flow in the molten pool. Together, these effects effectively suppress spatter formation caused by keyhole collapse due to molten metal squeezing and covering the keyhole. The synergy between ring-shaped laser and beam oscillation reduced both the temperature gradient and cooling rate, leading to the formation of distinct microstructures in the weld zone. Due to the reduced undercut depth, the presence of strengthening basket weave microstructures, and a high fraction of high-angle grain boundaries, the welded joints produced by this novel process exhibit enhanced tensile strength and elongation. This study proposes a novel approach to enhance welding stability and microstructural characteristics, providing a foundation for advancing beam shaping strategies in laser welding.