Fig. 1. Ultrafast laser precision micromachining system and microtexture preparation principle

Fig. 2. Schematic of pulse green laser welding device and overlap welding

Fig. 3. Copper/steel welded joint hardness measurement chart and tensile specimen. (a) Microhardness measurement diagram; (b) tensile specimen

Fig. 4. Morphologies of stainless steel surface before and after texturization. (a) Initial surface state; (b) surface state after laser etching

Fig. 5. Surface roughness of stainless steel before and after surface texturization

Fig. 6. Groove depth, width and depth-to-width ratio at different laser power

Fig. 7. Surface morphology, cross-sectional shape and geometric size of microtexture at different laser power. (a1)-(a5) Surface morphology; (b1)-(b5) cross-sectional shape; (c1)-(c2) geometric size

Fig. 8. Texture depth, width and depth-to-width ratio at different etching times

Fig. 9. Surface morphology, cross-sectional shape and geometric size of microtexture at different scanning times. (a1)-(a5) Surface morphology; (b1)-(b5) cross-sectional shape; (c1)-(c2) geometric size

Fig. 10. Microstructures of copper/surface untextured 304L stainless steel laser overlap welded joint. (a) Whole view; (b) enlarged view of region A; (c) enlarged view of region B; (d) enlarged view of region C

Fig. 11. Microstructures of copper/surface textured 304L stainless steel laser overlap welded joint. (a) Whole view; (b) enlarged view of region A; (c) enlarged view of region B; (d) enlarged view of region C

Fig. 12. EDS line scanning of the bottom part of molten pool of copper/surface untextured 304L stainless steel laser overlap welded joint. (a) Line scanning position; (b) EDS result

Fig. 13. EDS line scanning of the bottom part of molten pool of copper/surface textured 304L stainless steel laser overlap welded joint. (a) Line scanning position; (b) EDS result

Fig. 14. Microhardness distribution curves of welded joints

Fig. 15. Relationship between tensile strength and groove depth of copper/steel overlap welded joint

Fig. 16. Tensile fracture morphology of copper/steel laser overlap welded joints. (a) Untextured joint; (b) textured joint (groove depth:89.91 μm)