Fig. 1. Schematic of laser focus rotation spot welding process

Fig. 2. Spot weld morphology and molten pool state versus welding time. (a) 0.037 s; (b) 0.2 s; (c) 0.4 s; (d) 0.6 s; (e) 1.0 s; (f) 1.8 s

Fig. 3. Spot weld size versus welding time

Fig. 4. Influence of focus rotation frequency on spot weld morphology. (a) 30 Hz; (b) 50 Hz; (c) 70 Hz; (d) 90 Hz; (e) 110 Hz

Fig. 5. Spot weld size versus focus rotation frequency

Fig. 6. Spot weld quality versus laser power under two spot welding processes. (a) Width-depth ratio; (b) porosity repression

Fig. 7. Microstructure of spot weld under traditional laser spot welding process. (a) Fusion line zone; (b) columnar grain zone; (c) centered equiaxed zone

Fig. 8. Microstructure of spot weld under focus rotation spot welding process. (a) Fusion line zone; (b) columnar grain zone; (c) central zone

Fig. 9. Microhardness of spot weld under two spot welding processes. (a) Tradition; (b) focus rotation