Fig. 1. Schematics of laser welding. (a) Laser welding; (b) molten pool morphology

Fig. 2. Schematics of sampling position and size of specimen. (a) Sampling position; (b) size of tensile specimen

Fig. 3. Weld morphologies under different heat inputs. (a)(a1)(a2) Low heat input (90 J/mm); (b)(b1)(b2) medium heat input (150 J/mm); (c)(c1)(c2) high heat input (200 J/mm)

Fig. 4. Effect of heat input on molten pool dimension. (a) Schematic of typical molten pool; (b) corresponding dimensions under different heat inputs

Fig. 5. Microstructures under different heat inputs

Fig. 6. Schematics of microstructure growth conditions during molten pool solidification process. (a) Constitutional supercooling condition; (b) expansion stage of columnar grains; (c) formation stage of equiaxed grains; (d) weld grain distribution

Fig. 7. IPFs, PFs, and distribution histograms of grain sizes and misorientation angles under different heat inputs

Fig. 8. Sub-grain structures at WS bottom and secondary dendrites at centerline of WS under different heat inputs. (a)(d) Low heat input (90 J/mm); (b)(e) medium heat input (150 J/mm); (c)(f) high heat input (200 J/mm)

Fig. 9. Tensile test results of weld seam under different heat inputs. (a) Stress-strain curves; (b) tensile strength and elongation

Fig. 10. Fracture morphologies under different heat inputs. (a) Low heat input (90 J/mm); (b) medium heat input (150 J/mm); (c) high heat input (200 J/mm)