Research On Electroplating Process Of Copper-tin Alloy And Its Properties In Methyl Sulfonic Acid System

As a substitute for nickel electroplating process,copper-tin alloy has advantages of bright appearance,high densification,good corrosion resistance,moderate hardness,low cost and good non-proliferation performance.It is one of the most widely used alloy plating layers and with the nickel coating in the decorative field is eliminated gradually,copper-tin alloy becomes more and more favored.When the mass fraction of tin is 8%¹5%,a high decorative imitation gold coating can be formed by electroplating copper-tin alloy on the workpiece surface.Since cyanide electroplating solution of copper-tin alloys has been limited due to its toxicity,it is imperative to study and develop a kind of non-cyanide copper-tin alloy plating solution with simple process,environmental-friendliness and excellent performance.In this paper,thermodynamics was used to analyze the stability of the methanesulfonic acid copper-tin alloy plating solution.The stability of the plating solution was optimized by using a large anode and a small cathode,increasing the content of hydroquinone,changing stannous sulfate to stannous methanesulfonate.Through preliminary selection of additives,the feasibility of golden copper-tin alloy plating under this system was realized.It was found that additives F-28 and PPDH had a good effect on enlarging the operable current density range,especially when F-28 was higher than 0.6 ml/L,bright golden plating can be obtained in the range of 0.8 and 2.0 A/dm2.The composition of the plating bath and the range of process parameters that can be used to achieve imitation gold plating were initially screened by visual observation: 0.12 to 0.14 mol/L Cu²⁺,0.02 to 0.03 mol/L Sn²⁺,and the optimal copper to tin ratio: 5:1,room temperature,stirring speed: 45⁶0 r/min,current density: 0.8².0 A/dm2.Secondly,on the basis of the result of preliminary screening,spectrometer?EDS?,scanning electron microscopy?SEM?,filter paper method,and electrochemical tests were used to study the effects of bath composition and process conditions on the performance of the coatings and.Excellent imitation gold coating performance by optimizing: 0.13 mol/L CuSO₄,0.025 mol/L?CH₃SO₃?₂Sn,2 mol/L MSA,0.01 mol/L hydroquinone,25?,stirring speed 45⁶0 r/min.Under the optimal conditions,the influence of the amount of additives F-28 and PPDH on the coating properties was studied.The results showed that: high-density F-28 had abilities of fine crystallization,leveling and widen the current density range;the PPDH with concentration of 0.6 ml/L also had the abilities of graining refinement and stabilize the appearance of coating,but did not have a leveling effect.Finally,the electrochemical behaviors of copper,tin and copper-tin alloy deposition were investigated by linear sweep voltammetry,chronopotentiometry and electrochemical impedance spectroscopy;and the impact mechanism of bath composition,process conditions and additives F-28 and PPDH was discussed according to the electrodeposition process.The results showed that the reduction of Cu²⁺ and Sn²⁺ can be promoted by each other to achieve co-deposition.However,due to the large difference in the exchange current densities between the two,it was difficult to achieve the requirement of gold-plated electroplating in the absence of additives.The reason that additive F-28 had a good modification effect on imitation gold electroplating was mainly due to its ability to inhibit reaction of tin deposition and hydrogen evolution and its ability to increase the co-defining limiting current density,while additive PPDH refined the plating grain by increasing the polarization of copper plating.