Fig. 1. Schematic of welding experiment

Fig. 2. Images of tracer particle trajectories on molten pool surface. (a) Autogenous laser welding; (b) laser welding with filler wire

Fig. 3. Schematics of tracer particle trajectories on molten pool surface. (a) Autogenous laser welding; (b) laser welding with filler wire

Fig. 4. Molten pool surface fluctuation in autogenous laser welding. (a) High-speed camera image; (b) schematic

Fig. 5. Molten pool surface fluctuation in laser welding with filler wire. (a) High-speed camera image; (b) schematic

Fig. 6. Weld surface appearances. (a) Autogenous laser welding; (b) laser welding with filler wire

Fig. 7. Schematics of welding wire transition modes in laser welding with filler wire. (a) Liquid bridge transition; (b) droplet transition

Fig. 8. Droplet transition process in laser welding with filler wire. (a) High-speed camera image; (b) schematic

Fig. 9. Weld surface appearance for droplet transition in laser welding with filler wire

Fig. 10. Molten pool surface fluctuation states when wire feeding angle is 30°

Fig. 11. Molten pool surface fluctuation states when wire feeding angle is 60°

Fig. 12. Weld surface appearances under different wire feeding angles. (a) 30°; (b) 60°

Fig. 13. Longitudinal sections of welds under different wire feeding angles. (a) 15°; (b) 30°; (c) 60°

Fig. 14. Schematic of filler wire impact force on molten pool