Fig. 1. Schematics of Cu/Al/Cu sheet structure welding . (a) Welding fixing device; (b) laser scanning path

Fig. 2. Tensile shear diagrams of Cu/Al/Cu laminar sheet joint. (a) Lap diagram of joint; (b) schematic of shear force test

Fig. 3. Surface morphologies of Cu/Al/Cu laminar sheet joints under different welding speeds. (a)-(e) Optical mirror morphologies; (b)-(j) optical 3D structures; (k)-(o) SEM morphologies

Fig. 4. Cross-section morphologies of Cu/Al/Cu laminar joints under different welding speeds. (a)(f) 15 mm·s^-1; (b)(g) 18 mm·s^-1; (c)(h) 21 mm·s^-1; (d)(i) 24 mm·s^-1; (e)(j) 27 mm·s^-1

Fig. 5. Weld geometry characteristics of Cu/Al/Cu laminar structures. (a) Schematic of weld structure; (b) weld reinforcement and penetration depth

Fig. 6. Interfacial microstructures of typical Cu/Al/Cu laminar joints under different welding speeds. (a)-(c) 15 mm·s^-1; (d)-(f) 21 mm·s^-1; (g)-(i) 27 mm·s^-1

Fig. 7. Line scanning results of positions marked by arrows in Fig.6 under different welding speeds. (a)(b) 15 mm·s^-1; (c)(d) 21 mm·s^-1; (e)(f) 27 mm·s^-1

Fig. 8. Interfacial element distributions of Cu/Al/Cu laminar joints under different welding speeds. (a)-(d) 15 mm·s^-1; (e)-(h) 21 mm·s^-1; (i)-(l) 27 mm·s^-1

Fig. 9. Shear force test results of Cu/Al/Cu laminar joints under different welding speeds

Fig. 10. Fracture surface morphologies of typical Cu/Al/Cu laminar sheet joints under different welding speeds. (a)-(c) Optical mirror morphologies; (d)-(f) 3D features for Al-side fractures; (g)-(i) 3D features for Cu-side fractures

Fig. 11. SEM fracture surface morphologies of typical Cu/Al/Cu laminar sheet joints under different welding speeds. (a)(d) 15 mm·s^-1;(b)(e) 21 mm·s^-1; (c)(f) 27 mm·s^-1

Fig. 12. Failure mechanism diagrams of Cu/Al/Cu nanosecond pulsed laser welded joints under different welding speeds. (a) 15 mm/s;(b) 21 mm/s; (c) 27 mm/s