Preparation And Properties Of Mechanical Galvanized-graphene Composite Coating

With the rapid development of science and technology,mechanical galvanized protection layer has been widely used in automotive,Marine,aerospace and high-speed railway manufacturing of high-strength steel fasteners,because of the coating no hydrogen embrittlement,environmentally friendly process and so on.Graphene consists of a single layer of carbon atoms arranged closely in a honeycomb structure.Its unique two-dimensional sheet structure and large specific surface area make it a material with excellent strength,electrical and thermal conductivity.,this thesis mainly adopts the method of mechanical plating process to add ink dispersion,plating zinc-graphene composite coating was prepared,using field emission scanning electron microscopy（FESEM）equipped with energy spectrum),Raman spectroscopy（RS）,X-ray diffraction analysis and research on the organizational structure of the composite coating and graphene depositional mechanism,adopting ac impedance spectra,polarization curves and salt spray test to study the different graphene content,sodium dodecyl sulfate（SDS）content on the properties of the coating morphology and impact,the results showed that:Through comparative analysis of SDS and SDBS dispersants,it can be found that SDS can well disperse graphene in mechanical plating solution,making it difficult for graphene flakes to agglomerate in the plating solution.In the preparation process of zinc-graphene composite coating,the base layer is established first,and better composite coating can be obtained by adding graphene dispersion solution in stages.（1）Through comparative analysis of SDS and SDBS dispersants,it can be found that SDS can well disperse graphene in the mechanical plating solution,making it difficult for graphene sheets to agglomerate in the plating solution.In the preparation process of zinc-graphene composite coating,the base layer is established first,and better composite coating can be obtained by adding graphene dispersion solution in stages.（2）During the establishment stage of the composite coating base,chemical reactions such as Fe+H⁺=Fe²⁺+H₂,Zn+H⁺=Zn²⁺+H₂,Zn+Sn²⁺=Zn²⁺+Sn and Fe+Sn²⁺=Fe²⁺+Sn occurred,and the Zn-Sn composite coating was deposited on the substrate surface.After the addition of Sn SO₄,tin ions play an induction role,promoting the agglomeration of zinc particles and adsorption and deposition on the substrate surface.During the coating thickening stage,Zn+Fe²⁺=Zn²⁺+Fe and Zn+M²⁺=M²⁺+Fe chemical reactions continuously deposited zinc powder on the surface of the substrate to increase the coating thickness.The graphene flakes were deposited in the composite coating at the thickening stage by adsorbing the surface of the composite coating and the surface of the adsorbed zinc particles.（3）Of mechanical galvanizing-graphene composite coating surface,cross-section and fracture analysis of the microstructure,mechanical plating composite coating of nanoscale graphene sheets mainly inclusions within the group that algal zinc powder mass of codeposition,Mosaic glass bead under the action of impact,adsorption in the surface of the zinc particles in the composite coating codeposition three ways doping in the composite coating.（4）When the graphene content of the plating solution is 0.2g/L,the composite coating has A good morphology and excellent performance,with A high microhardness value of 54.5 HV and A uniform hardness distribution.The corrosion potential of the composite coating sample is slightly negative than that of the pure zinc coating,but the corrosion current density decreases by 351 A/cm².The excellent conductivity of graphene flakes plays the role of electric bridge in the coating,promoting the formation of stable passivation film by sacrificial anode of zinc powder particles.Compared with the passivation interval of pure zinc coating,the passivation interval increases by 490 m V,effectively blocking the diffusion and erosion of corrosive medium,and inhibiting the pitting corrosion behavior of composite coating.Graphene has an excellent physical barrier effect,filling the pores of the coating and effectively preventing the penetration of corrosive media.R_coatresistance increases by5 times.The time of white rust in salt spray resistance test was 12 h longer than that of pure zinc coating.After 500 h,large area of red embroidery appeared in pure zinc coating,but no red embroidery appeared in composite coating.（5）When the amount of SDS added in the plating solution is 0.2 g,best for the comprehensive performance of composite coating,graphene sheets reach saturation adsorption of SDS alkyl chain and graphene sheets parallel vertical adsorption,adsorption to the repulsion between the graphene sheets maximum,dispersion in the sedimentary environment is best,minimize the composite coating porosity,surface is smooth and dense,composite coating hardness and corrosion resistance of the best,but too little and too much addition ratio of SDS,leads to low graphene dispersion effect and reduce the thickness of the composite coating,composite coating internal defects increase,reduce the strength of the composite coating and corrosion resistance.