Fig. 1. Schematic of experimental platform for laser welding in vacuum

Fig. 2. Images of plasma plume captured by high speed camera under different pressures. (a) 101 kPa; (b) 80 kPa; (c) 50 kPa; (d) 20 kPa; (e) 5 kPa

Fig. 3. Average grayscales and area pixel ratios of plasma plume under different pressures. (a) Average grayscale; (b) area pixel ratio

Fig. 4. Relationship between each factor and porosity

Fig. 5. Effects of each factor on penetration depth and depth-width ratio. (a) Penetration depth; (b) depth-width ratio

Fig. 6. Cross-sections of welds under different laser powers. (a) 6 kW; (b) 8 kW

Fig. 7. Cross-sections of welds under different welding speeds. (a) 1.0 m·min-1; (b) 1.4 m·min-1

Fig. 8. Pore distributions under different pressures. (a) 101 kPa; (b) 15 kPa; (c) 5 kPa

Fig. 9. Microscopic features of pores in middle-bottom parts. (a) Pore morphology; (b) fold of pore wall; (c) deposits in pore

Fig. 10. Schematic of pool flow patterns. (a) Normal pressure; (b) vaccum

Fig. 11. Pore distributions under different laser powers. (a) 6 kW; (b) 8 kW

Fig. 12. Pore distributions under different welding speeds. (a) 1.4 m·min-1; (b) 1.0 m·min-1

Fig. 13. Weld surface formations and cross-sectional morphologies under different pressures