Fig. 1. Schematic of welding path formed by circular swing of beam

Fig. 2. Influence of welding speed and M² on weld surface morphology and weld morphology. Surface morphology: (a) M²=1.18, v=228 mm/s; (c) M²=1.18, v=255 mm/s; (e) M²=1.25, v=228 mm/s; (g) M²=1.25, v=262 mm/s; (i) M²=2.39, v=175 mm/s; (k) M²=2.39, v=215 mm/s; (m) M²=6.6, v=77 mm/s; (o) M²=6.6, v=84 mm/s; (q) M²=6.74, v=60 mm/s; (s) M²=6.74, v=120 mm/s; (u) M²= 11.6, v=40 mm/s; (w) M²=11.6, v=67 mm/s. Melting depth and width: (b) M²=1.18, v=228 mm/s; (d) M²=1.18, v=255 mm/s; (f) M²=1.25, v=228 mm/s; (h) M²=1.25, v=262 mm/s; (j) M²=2.39, v=175 mm/s; (l) M²=2.39, v=215 mm/s; (n) M²=6.6, v=77 mm/s; (p) M²=6.6, v=84 mm/s; (r) M²=6.74, v=60 mm/s; (t) M²=6.74, v=120 mm/s; (v) M²=11.6, v=40 mm/s; (x) M²=11.6, v=67 mm/s

Fig. 3. Influence of M² on weld penetration and weld width

Fig. 4. Influence of M² on laser welding efficiency and CPK value. (a) Welding speed; (b) CPK value

Fig. 5. Influence of M² on energy distribution characteristic in laser welding of aluminum. XOY plane: (a) M²=1.18; (d) M²=1.25; (g) M²=2.39; (j) M²=6.60; (m) M²=6.74; (p) M²=11.6. XOZ plane: (b) M²=1.18; (e) M²=1.25; (h) M²=2.39; (k) M²=6.60; (n) M²=6.74; (q) M²=11.6. YOZ plane: (c) M²=1.18; (f) M²=1.25; (i) M²=2.39; (l) M²=6.60; (o) M²=6.74; (r) M²=11.6

Fig. 6. Influence of M² on extreme difference in energy density and occupied space line density. (a) Extreme difference;(b) occupied space line density