Effect of graphene on microstructure and mechanical properties of U-MIG-welded galvanized steel

In present study, Graphene nanoparticles (GNPs) are incorporated into the steel plate by dip coating technology, and the steel plate is welded by a composite welding process combined with an ultrasonic generator and a MIG welding machine (U-MIG). Joint samples of different contents of GNPs were obtained. After welding, the microstructure of the welded joint is characterized by OM, SEM, XRD, and RAMAN and compared with the bare sample. The results show that a certain amount of graphene nanoparticles can be evenly distributed in the center of the weld area, and the grains in the center of the weld are significantly refined. Using the nanoindentation technique to study the microhardness of the weld cross section, the hardness of the weld center has increased due to the addition of graphene; compared with the bare sample, the maximum enhancement rate of the GNPs coating sample is ∼ 125.6%. The enhancement of the strength of the composite material is achieved by a variety of strengthening mechanisms, such as non-uniform nucleation, pinning effect, and hindering dislocation movement. This improvement in mechanical properties is attributed to the uniform dispersion of the hybrid particles and the refinement of the matrix grains and the good interface combination between the hybrid particles and the matrix.