Study On The Process Of Low Phosphorus Electroless Nickel Phosphorus Plating

As one of the most widely used and mature technologies in the surface treatment industry,electroless nickel plating technology is used in aerospace,marine,machinery,electronics fields and so on.Low-phosphorus electroless nickel plating,one of the new development directions of electroless nickel plating technology,has great potential in the field of electronic computers,instead of chromium plating coating and alkali industry with its excellent brazability,demould properties and hardness.However,the process has not been scaled up due to technical problems such as plating cost,bath stability and bath maintenance,therefore the study of low-phosphorus electroless nickel plating process has great industrial value.In this paper,the plating rate,the mass fraction of phosphorus in the coating,the hardness and the porosity are chosen as evaluation indexes.Firstly,the plating process parameters and the composition of the plating solution of the low-phosphorus electroless nickel plating process are determined to obtain the basic formula and optimize it by orthogonal experiment.In order to further improve the plating hardness of the coating and reduce porosity of the coating,adding nanoparticles to the low-phosphorus system and determining that the addition of nano-TiO₂ can maximize the hardness of the coating.Finally,the auxiliary complexing agent and surfactant are selected.Comparing the developed low-phosphorus electroless nickel plating formula with the high-phosphorus formula,the results show that:1.According to system experiments the optimal low-phosphorus electroless nickel plating formula is:the optimum molar ratio of main salt and reducing agent values 0.50,lactic acid values 18 g·L^?1,propionic acid values 4 g·L^?1,ethylenediamine values 4 ml·L^?1,sodium acetate values 15 g·L^?1,thiourea values 2mg·L^?1,sodium dodecyl sulfonate values 60 mg·L^?1,nano-TiO₂ values 1 g·L^?1,plating solution pH values 4.8±0.1,loading ratio values 1 dm²·L^?1,plating time values1 h,plating temperature values 85±1°C,the deposition rate values 23.62μm/h,the plating phosphorus content values 3.53%,the plating hardness is 561.4 HV and porosity is as low as per square centimeter of 0.35.2.Comparing the low-phosphorus electroless nickel plating formula with the high-phosphorus electroless nickel plating solutions and coatings,it is found that the deposition rate of the low-phosphorus formula is 22.0-25.0μm·h^?1,the phosphorus content is 3.81%,and the hardness was 561.4 HV.The high-phosphorus formula has a deposition rate of about 12μm·h^?1,a phosphorus content of 12%,and a hardness of468.2 HV.What’s more,after heat treatment at 400°C for 1 h the low-phosphorus coating has a hardness of 691.8 HV,the deposition rate after 4 MTO remains at 13.3μm·h^?11 and the phosphorus content is maintaining at 3.5%-5%.After heat treatment at300°C for 1h,the hardness of the high-phosphorus coating is 591.4 HV and the deposition rate after 4 MTO is maintaining at 9μm·h^?11 and the phosphorus content is13.8%.It’s can be found that the corrosion resistance of the two coatings increases significantly after heat treatment,and the red rust begins to appear in the two types of coatings after 72 hours of neutral salt spray test.Through comparison,the low-phosphorus electroless nickel plating process has the same excellent plating solution and coating performance with high-phosphorus process,so it has certain industrial practical value.