Effects of welding current on microstructure evolution and mechanical behavior of WC-Co/X32 steel joints by resistance spot welding

The Co-depletion zone in WC-Co welding joint is the main failure zone for joints by resistance spot welding (RSW), which is crucial to explore novel processes to inhibit the Co-depletion zone and enhance its mechanical properties. In this study, WC-Co/X32 steel joints were prepared by RSW under the various welding currents, with the aim of improving the mechanical behavior. The microstructure in the joint zone was evaluated by SEM, micro XRD, TEM, shear strength tests and nano-indentation tests. The experimental results showed that with the increase of welding current, the flow of WC to the fusion zone was accelerated due to the diffusion and evaporation of the Co element, the number of porosities in the fusion zone increased and cracks developed near the fusion zone around the WC-Co side, reducing nano-indentation behavior including the elastic modulus and hardness. A suitable thickness of reaction layer is produced at the joint interface when the welding current is 850 A, and the shear stress increases by 122 % and 36 % respectively compared with other parameters.