Study On Codeposition Of Sn-Ni Alloy And Its Composite

Sn-Ni alloy is widely used in industry and daily life due to its excellent appearance and excellent properties.With the development of science and technology and the improvement of coating performance requirements,the traditional Sn-Ni alloy plating process has been continuously improved and developed.Aiming at the green and pollution-free bath,simple process formulation,wide range of work,easy operation and high quality,a simple pyrophosphate solution system was used to study the technological conditions of electrodepositing Sn-Ni alloy on copper substrate and the corrosion resistance of alloy coating.The electrochemical behavior of nickel–tin electrochemical codeposition from pyrophosphate bath was studied by linear dynamic potential scanning method.The effects of the concentrations of P₂O₇^4-,auxiliary complexing agent,NH₄Cl and saccharin sodium on the electrodeposition behaviors of Sn-Ni deposit were analyzed.The results of dynamic potential scanning method showed that the complexion of P₂O₇^4-with metal ions increases the cathodic polarization of metal deposition.The negative shift of deposition potentials of Sn and Ni ions in pyrophosphate bath is contributed to the Sn-Ni codeposition.The auxiliary complexing agent in electrolyte bath plays roles of broadening the range of the working current density of the bath for bright layer and inducing the codepostion of Ni and Sn in electrolyte.The additive NH₄Cl has a function of depolarization,contributes to the codeposition of Sn and Ni.Saccharin sodium in electrolyte inhabits the discharge of Ni²⁺and Sn²⁺homogeneously.The effects of bath composition and process conditions on the composition of tin-nickel alloy electroplated by pyrophosphate were studied by Hull cell experiment and constant current experiment.Surface morphologies and compositions of Sn-Ni deposits were obtained by scanning electron microscopy?SEM?with X-ray photoelectron diffraction?EDX?.The results showed that the composition of plating bath and operation parameters have an effect on the composition of the coating.The Sn²⁺:Ni²⁺molar ratio has the greatest effect on the nickel content of the Sn-Ni alloy coating.When Sn²⁺/Ni²⁺is 0.6¹.8?molar concentration ratio?,the nickel content of the obtained Sn-Ni alloy coating ranges from 31wt.%³7wt.%and the composition is relatively fixed.Through optimization,the best formula for plating Sn-Ni alloy in pyrophosphate solution system is[P₂O₇^4-]:[Sn²⁺+Ni²⁺]molar ratio 1.6²?molar concentration ratio?,total molar concentration of metal ions 0.25⁰.35mol·L^-1,Sn²⁺:Ni²⁺molar ratio 0.6²,auxiliary complexing agent 20³0g·L^-1,NH₄Cl 8¹2g·L^-1,saccharin sodium 0.5³g·L^-1,pH 8¹0,temperature 35⁴5?,DK 0.3⁴A·dm^-2.Under this process specification,the stability,dispersing power and covering ability of bath are good,and a bright and compact Sn-Ni alloy layer can be obtained.The co-deposition of Sn-Ni alloy belongs to non-equilibrium co-deposition.Salt spray test and electrochemical method were used to test the corrosion resistance of tin nickel alloy coating.The effect of nickel content on the corrosion resistance of Sn-Ni alloy coatings in 10%H₂SO₄ acidic environment was analyzed and discussed.The corrosion behavior of Sn-Ni alloy coatings with the nickel content of31wt.%in 5%NaCl was also discussed.The results showed that:Compared with single metal tin,the coating has excellent corrosion resistance.and it can exist stably in acidic and neutral environment.The Sn-Ni alloy containing 31wt.%³7wt.%has excellent corrosion resistance.Finally,the corrosion resistance of Sn-Ni/graphene fluoride composite coatings was studied,and the effect of the concentration of graphene fluoride on the properties of the composite coatings was discussed.The experimental results show that:When the concentration of fluorinated graphene is 300mg·L^-1,the composite coating has the best corrosion resistance.The addition of fluorinated graphene can refine the grain and improve the corrosion resistance of the coating.