Study On The Process And Properties Of Cyanide-free Electroplating Silver Nickel Alloy

In the 21st century,China vigorously promoted military-civilian integration.As the heart part of complex equipment and instruments,conductive ring is widely used in military products.It is required to be 100 million RPM in five years for military products and 50 million RPM for civil products.Ag-Ni alloy has high conductive property,mechanical property and chemical property,which meets the application of conductive ring coating for military and civil products.So far,the most mature Ag alloy electroplating process is still the century-old cyanide electroplating.However,cyanide,as a highly toxic chemical,has the potential danger of serious harm to the environment and workers.Therefore,a cyanide-free electroplating conductive ring coating process is developed,which not only meets the requirements of environmental protection and clean production,but also complies with a series of international and national relevant regulations.Firstly,the basic formula of Ag-Ni bath was studied.The optimal concentration of Ag/Ni main salt was determined by Hall cell test,and then the auxiliary complexing agent was selected by single factor test.Finally,the dosage of main salt and complex complexing agent was optimized by orthogonal test,and the basic formula of the optimal plating solution was determined:0.3 mol/L of nickel sulfate hexahydrate,0.03 mol/L of silver mesylate,1.5 mol/L of potassium iodide,30 g/L of succinic acid and 30g/L of glycine.The optimal electroplating process was investigated by single factor test:temperature35℃,p H 5.5,cathode current density 1.0 A/dm~2,electroplating time 8-12 min.Secondly,the basic bath additives were studied.The single factor experiment was used to select the brighteners and surfactants suitable for the base bath.The results showed that adding different concentrations of brighteners saccharin,polyethylene glycol,β-naphthol in the base bath and different concentrations of surfactants OP-10,polyvinylpyrrolidone,α,α’-bipyridine in the base bath had obvious effect on improving the coating.Saccharin,polyethylene glycol,polyvinylpyrrolidone,α,α’-bipyridine were selected for orthogonal complex test,and the optimal additive complex results were obtained as follows:saccharin 0.3g/L,polyethylene glycol 4g/L,polyvinylpyrrolidone 4g/L,α,α’-bipyridine 0.03g/L.Finally,the properties of the optimized solution and coating were tested.Compared with cyanide electroplating,the electroplating environment of this system is safer.The stability and deep plating ability of the electroplating bath are good.Through heating and bending method,it is found that the adhesion between the coating and the substrate is good,and the coating has no blistering phenomenon.By SEM and EDS analysis of the coating,it was found that silver and nickel could not be intersoluble,forming a simple mechanical mixture.Compared with the copper substrate,the hardness of the coating is increased by 9.8%and the wear resistance is also significantly enhanced.By fitting the polarization curve and impedance curve,it is found that the corrosion resistance of Ag-Ni coating is improved nearly 163 times.The surface specific resistance test system was used to test the electroconductivity of the coating.It was found that the ASR of the silver nickel coating was 0.82mΩ/cm~2 at room temperature,and it had very good electrical conductivity.