Fig. 1. Welding equipments. (a) Remote laser welding system; (b) CMT welding equipment

Fig. 2. Schematic of weld cross-section

Fig. 3. Tensile sample. (a) Sampling position; (b) sample size (unit: mm)

Fig. 4. Metallographic structures and XRD pattern of FV520B steel base metal. (a) Metallographic structure of base metal etched by Marble's reagent; (b) metallographic structure of base metal after electrolytic corrosion in 20%NaOH solution; (c) XRD spectrum of base metal

Fig. 5. Morphologies of different areas on cross-section of laser backing welded joint. (a) Overall morphology; (b) center of upper fusion zone; (c) edge of upper fusion zone; (d) center of middle fusion zone; (e) edge of middle fusion zone; (f) coarse grain heat-affected zone; (g) fine grain heat-affected zone; (h) inter-critical heat-affected zone

Fig. 6. Appearance and size of filler weld

Fig. 7. Metallographic structures of different zones on cross-section of 1# weld. (a) At the vicinity of fusion line of filler welding; (b) FWFZ; (c) HAZ of laser welding; (d) HALWFZ near FWFZ; (e) HALWFZ far from FWFZ; (f) LWFZ near weld bottom

Fig. 8. Metallographic structures of different zones on cross-section of 2# weld. (a) At the vicinity of fusion line; (b) FWFZ; (c) HALWFZ near FWFZ; (d) HALWFZ far from FWFZ; (e) HAZ of filler welding; (f) LWFZ near weld bottom

Fig. 9. XRD patterns of laser welding fusion zone before and after CMT filler welding

Fig. 10. EDS line-scanning results of the area near fusion line of 1# weld

Fig. 11. Microhardness profiles on weld cross-section under various CMT welding parameters. (a) At horizontal direction; (b) at vertical direction

Fig. 12. Samples after tensile test

Fig. 13. Fracture morphologies of tensile samples

Fig. 14. Polarization curves of BM, OLWFZ and LWFZ