Research On The Electrochemical Performance Of Nickel Sealing Coating

Electroplated nickel has excellent wear resistance and corrosion resistance,and is widely used in all walks of life.However,the metal nickel is prone to cracks and pores during electroplating.Compared with the steel substrate,the nickel layer is a cathodic coating.In the corrosive medium,when there is a through hole between the coating and the substrate,a phenomenon of large cathode and small anode will occur,resulting in local corrosion of the base metal.Therefore,it is necessary to close the pores on the surface of the nickel plating layer.The compound electroplating technology can achieve a good sealing effect by introducing the second phase particles into the plating solution,thereby improving the corrosion resistance of the plating layer.SiO₂ and ZrO₂ are ceramic materials with stable physical and chemical properties,and are widely used as the second phase filler in Ni,Cu,Zn,Ag and Au plating layers.In this paper,low-carbon steel was used as the substrate,and the traditional electrodeposition technology was used to prepare the nickel-based composite coating.By adjusting the cathode current density and stirring method to determine the best electroplating process conditions,nickel coating with a uniform distribution of composite particles was obtained.The current density was 4 A/dm²,and Ni-ZrO₂ and Ni-SiO₂ composite coatings were prepared under electromagnetic stirring.The effects of the type and content of zirconium compound and the particle size and content of silica on the corrosion resistance of the composite coating were investigated,respectively.The type of zirconium compound added to the plating solution was changed,and a certain amount of zirconium oxychloride,hexafluorozirconate,zirconium nitrate,and zirconium dioxide sol were added to prepare a Ni-ZrO₂ composite coating.The effects of different zirconium compounds on the composition and corrosion resistance of Ni-ZrO₂ composite coatings were investigated using metallographic microscope,EDX,potentiodynamic polarization,electrochemical impedance spectroscopy.The results shows that the surface morphology and corrosion resistance of the composite coating prepared by adding 4 ml/L ZrO₂ sol to the plating solution are the best.Adding SiO₂ with different particle size and content to the plating solution,combined with field emission scanning electron microscope,X-ray diffractometer,potentiodynamic polarization,electrochemical impedance spectroscopy and salt spray test,the composition,structure,morphology and corrosion resistance of the composite coating was studied.The results show when the particle size and content of SiO₂ nanoparticles were 50 nm and 15 ml/L,Ni-50nm SiO₂ nano composite coating has the lowest orientation along the?200?crystal plane,the highest SiO₂ content,the lowest corrosion current and corrosion rate,and the highest corrosion resistance.The corrosion resistance of Ni-ZrO₂ and Ni-SiO₂ composite coatings prepared by experiment is better than that of pure nickel coatings.