Effect of Brazing Filler Metals and Welding Parameters on Laser Welding-Brazing Joints of WC-Co to S1045

Abstract

Laser welding-brazing was used to join cemented carbide WC-Co and steel dissimilar materials. In this study, high-speed welding was adopted. The effect of welding parameters and brazing filler metals on the macrostructure, elemental diffusion, micro hardness and thermomechanical behavior was analyzed using optical metallography, scanning electron microscopy, electron probe micro-analysis, hardness test, and finite element method (FEM) based on thermo-elastic-plastic analysis. The experimental results show that increasing laser power is helpful to the increase of maximum welding speed. However, FEM also shows that increased welding speed leads to residual stress concentration, especial in the vicinity of jig. It is still a challenge to optimize laser power welding speed for a given brazing filler metal. The results show: when using pure copper, silver and nickel (thickness is less than 0.5 mm) as brazing filler metal, the combination, laser power of 1.2 kW and welding speed at 0.1 m/s, leads to complete penetration with good weld formation. However, when using Cu/Invar/Ni as brazing filler metal, laser power should increase to 1.7 kW if we still using a higher welding speed (0.1 m/s). Although a trial of high speed welding in laser welding-brazing exhibits feasibility, as-welded joints still have much more brittle risks due to the higher residual stresses.