Study On The Influence Of Graphene Content On The Microstructure Of U-MIG Welding Seam Of Galvanized Steel Sheet

Galvanized steel sheet is a kind of steel with good corrosion resistance and toughness,which is widely used in automobile manufacturing and construction industries.However,galvanized steel sheets have always had problems such as spatter,cracks,and poor welding quality.In order to solve the problem of poor weldability of galvanized steel sheets,this article uses ultrasonic-assisted molten inert gas shielded welding welding method,using graphene nanoparticles as reinforcing materials to improve welding process and improve welding quality.In this paper,the method of dip coating is used to form a uniform and dense coating of different contents of graphene on the galvanized steel sheet,and the graphene is melted into the weld structure by the ultrasonic-assisted argon arc welding hybrid welding method.Scanning electron microscope(SEM),X-ray diffraction spectroscopy(XRD),Raman spectroscopy(Raman)and nanoindentation and other inspection methods were used to characterize the weld center,and the influence of graphene nanoplates(GNPS)on the joint structure and mechanical properties of galvanized steel plate welded by argon arc welding was studied.The experimental results show that the addition of graphene changes the microstructure of the weld center,and the uniformly dispersed graphene can effectively refine the grain structure at the center of the weld.In terms of mechanical properties,nanoindentation technology is used to test the microhardness of the weld.Due to the addition of graphene,the hardness at the center of the weld increases.Compared with ordinary welded joints,the highest enhancement rate of elastic modulus of welded joints with graphene added is about 125.6%of that of base metal welded joints.The increase in the strength of composite materials is achieved through a variety of strengthening mechanisms,including:uneven nucleation,pinning effects and hindering the movement of dislocations.This improvement in mechanical properties is attributed to the uniform dispersion of the hybrid particles and the refinement of the matrix grains,as well as the good interface combination between the hybrid particles and the matrix.In addition,this paper uses a first-principles method based on density functional theory to calculate the electronic structure and bonding between the iron atom and the graphene crystal structure.The calculation results show that after the optimization and convergence of the crystal structure of iron-doped graphene,due to the difference in the atomic radii of iron and carbon atoms,a certain distortion of the lattice constant occurs.By calculating the density of states,differential charge density and layout analysis,we can understand the electron orbital hybridization and bonding between iron atoms and graphene.The calculation results show that the crystal structure of iron-doped graphene exhibits metallic properties,and the charge transfer is mainly contributed by the 3d orbitals of Fe atoms and the 2p orbitals of C atoms,and orbital hybridization occurs in a certain area.The bonding of Fe atoms triggers the transfer of charge,which is mainly manifested as the charge transfer of Fe atoms to the surrounding carbon atoms.The bonding between the two forms a strong covalent bond and contributes to the stability of the crystal structure.