Fig. 1. Schematic of test device

Fig. 2. Macro-morphologies of weld cross sections under different scanning parameters. (a) f＝50 Hz, P＝1.8 kW, D＝2.5 mm; (b) f＝100 Hz, P＝1.8 kW, D＝2.5 mm; (c) f＝150 Hz, P＝1.8 kW, D＝2.5 mm; (d) f＝200 Hz, P＝1.8 kW, D＝2.5 mm; (e) f＝250 Hz, P＝1.8 kW, D＝2.5 mm; (f) f＝200 Hz, P＝1.5 kW, D＝2 mm; (g) f＝200 Hz, P＝1 kW, D＝1.5 mm

Fig. 3. Weld forming diagram of scanning laser overlap joint

Fig. 4. Influence of different scanning parameters on weld forming

Fig. 5. High-speed photographies in initial scanning period during circular scanning laser welding with laser spot indicated by arrow

Fig. 6. High-speed photographies of molten pools under different circular scanning parameters. (a1)－(a4) f＝50 Hz, D＝2.5 mm; (b1)－(b4) f＝200 Hz, D＝2.5 mm; (c1)－(c4) f＝50 Hz, D＝1.5 mm; (d1)－(d4) f＝200 Hz, D＝1.5 mm

Fig. 7. Spatters during circular scanning (f＝200 Hz，D＝2.5 mm)

Fig. 8. Molten metal flow at back edge of molten pool during circular scanning (f＝50 Hz, D＝2.5 mm)

Fig. 9. Dynamic flow of molten pool during circular scanning. (a) High speed photography in initial scanning period；(b) schematic

Fig. 10. Schematics of circular scanning energy distributions

Fig. 11. Comparison of energy distribution during circular scanning