Study On Adsorption Deposition Of Zn-20%Sn Mechanical Plating Process And Coating Preparatio

Zn-Sn plating,with a potential between zinc and tin,has both the sacrificial anode characteristics of zinc metal and the isolation effect of tin,and has good resistance to sulfur dioxide atmosphere and chloride ion corrosion in corrosion resistance tests,and is considered to be an ideal substitute for toxic lead-cadmium layers.With the development of Zn-Sn plating process technology,the characteristics of Zn-Sn plating under different systems vary,among which mechanical deposition is of interest to researchers for its non-hydrogen embrittlement,process flexibility,and easy adjustment of plating thickness.The salt spray resistance of mechanically galvanized tin layer is affected by the tin content in the coating.When the tin content is 20%to 30%the mechanically galvanized tin composite coating can exert a strong protective performance,and it is reported that the mechanical galvanized tin layer is3 to 4 times more resistant to salt water and salt spray corrosion than the mechanically deposited pure zinc layer,which is currently mainly used for drill-tail screws and screw fasteners,and is particularly effective in service in maritime climates,and has been incorporated into It has been incorporated into the relevant technical standards of some coastal countries.In this paper,the adsorption deposition process of Zn-Sn powder during mechanical plating was studied by electrochemical method,and the change of potential on the substrate surface during the formation of mechanical plating solution environment was measured by open-circuit potential.The adsorbed Zn-Sn powder was characterized by scanning electron microscopy（SEM）and energy dispersive X-ray spectrometry（EDS）,and a Zn-Sn layer of about 30μm was prepared on the iron substrate by mechanical plating.The Zn-Sn layer consists of zinc powder particles physically stacked with tin powder particles and filled with reduced tin,and the tin content in the layer is 20%-40%.The prepared Zn-Sn composite coating was characterized and analyzed using scanning electron microscopy（SEM）,X-ray photoelectron spectroscopy（XPS）,X-ray diffractometer（XRD）,polarization curves（Tafel）,electrochemical impedance（EIS）,and energy dispersive X-ray spectrometry（EDS）.The results of the paper are as follows:The open circuit potential（OCP）of steel substrate,pure zinc substrate,and pure tin substrate fluctuates significantly with the introduction of additives;the deposition process of tin powder on steel substrate in the plating solution environment is mainly affected by the chemical traction and carrying effect of zinc powder;the final potential of pure tin substrate is substantially negatively shifted by 0.46 V compared to the potential in water,which is favorable to the adsorption agglomeration of zinc powder;the final potential of zinc substrate is less affected by the formation process of plating solution;open circuit The circuit results indicate that the ionic concentrations of Sn²⁺and H⁺are directly related to the process of the plating solution reaction,and that excess Sn²⁺hinders the deposition and adsorption of zinc powder.The best adsorption deposition of elemental tin is achieved at p H=1 and an electrical conductivity of 4.87（ms/cm）,and the tin content of the deposited powder reaches the highest value of 43.9%.The Zn-Sn composite coating with tin content in the range of 20%～40%was successfully prepared on the surface of Q235 steel substrate by mechanical method using Zn-Sn blended powder as raw material,and sulfuric acid was selected as activator by the activation experiment results;the best material addition scheme for the preparation of Zn-Sn composite coating was optimized by orthogonal test:15:10（zinc-tin mass ratio）,8 g（stannous sulfate）,5:1（activation water outside the barrel to sulfuric acid concentration ratio）,6 ml（composite surfactant）,6 g（EDTA）,8 g（sodium hypophosphite）,3 times（thickening times）.（concentration ratio of activation water to sulfuric acid）,6 ml（complex surfactant）,6 g（EDTA）,8 g（sodium hypophosphite）,3 times（number of thickening）,and the Zn-Sn composite coating under this scheme has excellent salt corrosion resistance.In the Zn-Sn composite coating,the tin powder and zinc powder are agglomerated and co-deposited,and the dotted flocculated reduced tin covers the surface of the zinc powder and fills the interstices of the coating,making the coating more compact;the self-corrosion potential and corrosion current of the Zn-Sn coating are positively shifted by 68 m V and decreased by 189.9μA/cm^-2,respectively,compared with the pure zinc layer;the reduced tin has a good shielding effect on the zinc powder,and together with the inert tin powder,the diffusion of corrosion products is inhibited,thus improved the corrosion resistance of the Zn-Sn coating,the plating polarization resistance increased by 1118Ω/cm²,and the appearance of white rust and red rust time increased by 24 h and 240 h,respectively,compared with the pure zinc layer;the Zn-Sn composite coating mainly relied on the formation of Zn（OH）₂and Sn（OH）₂.