Effect of Surface Texturization on Microstruture and Mechanical Properties of Laser Welded Copper/Steel Joint

 Shang Da-zhi, Zhang Jian, FENG Aixin, Zhou Yuan-hang, Tang Jie, Chen Feng-xian. Effect of Surface Texturization on Microstruture and Mechanical Properties of Laser Welded Copper/Steel Joint[J].中国激光,2020,47(09):1-11.

Abstract

To improve the overlap welding strength and metallurgical compatibility of copper/steel transition joints, a dissimilar metal microtexture-melting laser overlap welding method was proposed. Firstly, ultrafast green laser was used to prepare microtexture on the surface of steel matrix to improve the wettability and bite strength of steel side interface during welding. Then, pulsed green laser was used to weld copper/steel fusion lap on the surface of microtexture. Finally, the morphology, joint structure, bonding interface, tensile properties and fracture mechanism of microtexture were studied. The results show that under high laser power and etching times, the degree of thermal ablation increases and the internal quality of the groove deteriorates easily. Surface texturization has a significant effect on the microstructure and tensile strength of the joint. The surface texturization can strengthen the mass transfer and enhance the diffusion of copper to the bottom of the molten pool (steel side), which is conducive to the formation of higher copper content of α-Fe, γ -Fe solid solution, resulting in higher microhardness of the bottom of the molten pool. When the groove depth is 89.91 um, the tensile strength of the textured joint is the highest, which is 112.5MPa, 19.5% higher than that of the untextured joint. The fracture mechanism of the joint is ductile fracture. The tensile properties of joint are improved by solution strengthening, fusion volume increasing and vortex occlusion.