Research On Environmentally Friendly Electroplating Process Of Low Tin Copper Alloy

As one of the important alloy plating species,electroplating copper-tin alloy is a mature traditional nickel-substitution process.Copper-tin alloy has the advantages of good workability,good toughness,strong welding reliability,good physical and mechanical properties,simple and easy to master process.The deposition rate of copper-tin alloy coating is fast.When the mass fraction of tin in the coating is 8%～15%,the surface of the coating is dense and flat,the surface is golden yellow,and it is widely used in decoration due to its good corrosion resistance and moderate hardness field.The traditional process uses cyanide electroplating of copper-tin alloy,but its application is limited due to toxicity and instability of the plating solution.Therefore,it is imperative to study an environmentally friendly copper-tin alloy electroplating process with simple process and excellent performance.This thesis first studied the formulation of the environmentally friendly electroplating low-tin copper alloy plating solution,and tested the performance of the coating by changing the ratio of tin to copper,the amount of citric acid,and the amount of resorcinol.The results showed that the surface can be obtained under the conditions of 10g/L stannous sulfate,30g/L copper sulfate,50g/L ammonium sulfate,20g/L citric acid,1g/L resorcinol,20g/L ammonia,and p H 6.0.Copper-tin alloy coating with bright,good compactness,and the tin content of the coating controlled within 15%.Using VEGA3 XMU scanning electron microscope,it is found that when the ratio of tin to copper is 1:3,the distribution of crystal clusters is more uniform,and the coating surface is obviously flat.Phase analysis of the coating with a 6100 X-ray diffractometer found that the coating is composed of Cu_13.7Sn,Sn and Cu.The corrosion resistance of the coating was tested with a CHI660e electrochemical workstation.When the ratio of tin to copper is 1:3 the best.Then,on the basis of the determined formula composition,single factor test and orthogonal test are carried out on the process conditions.The VEGA3 XMU scanning electron microscope was used to observe the surface morphology of the coating,and the CHI660e electrochemical workstation was used to test the corrosion resistance of the coating.It was found that when the current density is 1.2A/dm²,the time is 25min,and the temperature is 30℃,the coating surface is smooth and fine,and the color is uniform.Bright,the coating has good corrosion resistance.Phase analysis of the coating using a6100 X-ray diffractometer found that the coating was composed of Cu_13.7Sn,Sn and Cu.The filter paper method was used to calculate that the porosity of the coating was low and the coating surface had good compactness.Finally,the three-electrode system was used to test the cyclic voltammetry curve and chronoampere curve of the sulfate system containing copper,tin alone and copper-tin ions.Cyclic voltammetry results show that the reduction of Cu²⁺is a one-step reduction,the reduction range is-0.54V～-1.58V,and the oxidation range is-0.62V～0.83V.The reduction of stannous ions in this system is also a one-step reduction,the reduction range is-0.39V～-1.49V,namely Sn²⁺→Sn⁰.During the positive scanning process,an oxidation peak appears under the potential of 0.24V.This oxidation peak corresponds to The oxidation of tin,Sn⁰→Sn²⁺.Moreover,the reduction processes of copper,tin,and copper-tin ions in the sulfate system are all irreversible processes under the control of diffusion.The chronoamperometry results show that when the two ions of copper and tin co-exist in the sulfate system,the chronocurrent at the potentials of-0.22V,-0.23V,-0.24V,-0.25V,-0.26V,-0.27V,respectively The dimensionless curve after the non-dimensional processing of the curve conforms to neither the three-dimensional instantaneous nucleation nor the three-dimensional continuous nucleation.It is a complex nucleation process.