Fig. 1. Keyhole and molten pool shape when welding speed is 3.0 m·min^-1.(a) Three-dimensional morphology of keyhole; (b) temperature field of molten pool longitudinal section

Fig. 2. Keyhole and molten pool shape when welding speed is 6.0 m·min^-1.(a) Three-dimensional morphology of keyhole; (b) temperature field of molten pool longitudinal section

Fig. 3. Keyhole shapes at different time when welding speed is 3.0 m·min^-1. (a) t+1 ms; (b) t+5 ms; (c)t+10 ms

Fig. 4. Keyhole shapes at different time when welding speed is 6.0 m·min^-1. (a) t+1 ms; (b) t+5 ms; (c) t+10 ms

Fig. 5. Variation curve of keyhole depth at different welding speeds

Fig. 6. Flow field images of molten pool at different time when welding speed is 3.0 m·min^-1. (a) t+1 ms; (b) t+5 ms; (c) t+10 ms

Fig. 7. Flow field images of molten pool at different time when welding speed is 6.0 m·min^-1. (a) t+1 ms; (b) t+5 ms; (c) t+10 ms

Fig. 8. Variation of flow velocity of H-spot liquid metal with time at different welding speeds