Study On Electroless Ni-Cu-P Ternary Alloy Plating And Gradient Composite Electroless Plating Based On Ni-Cu-P

Corrosion leading to premature failure of the material, and as a result, not only causes heavy losses of the national economy, but also becomes a major inducement for all kinds of accidents. Improving the corrosion resistance of the material, will effectively improve the life of the materials and reduce the probability of accidents, so as to achieve intrinsic safety.Surface treatment is one of the most economical and effective technologies to improve the corrosion resistance of the materials. As a new cost-effective, energy saving, and environmental friendly surface engineering technology, the electroless plating can give materials excellent corrosion, wear and other comprehensive performance, therefore developed to be an important research area of the material protection technology.Q235 carbon steel as substrate, the plating system of Ni-Cu-P and its graded composite coating were studied systematically. The main contents and conclusions are as follows:1) Study of Ni-Cu-P Ternary alloy electroless plating solution effective components selection, formula optimization and plating process. Choose the bath stability, plating rate,coating surface quality, hardness, porosity and Cu, P and Ni element content as the main technical indicators, based on the results of screening effective ingredient, finally determined the nickel sulfate and copper sulfate as main salts, sodium hypophosphite as reducing agent,sodium citrate as complexing agent, and the best bath formulation are as follows:C6H5Na3O7·2H2O 17.5g/L, NiSO4·6H2O 25g/L, CuSO4·5H2O 1.5g/L, NaH2PO2·H2O 23.7g/L,CH3COONH4 15g/L, C4O6H4KNa·4H2O 5g/L, C2H3O3 Na 5g/L. The optimal parameters are:pH=7.50, T=80±1℃.2) Study on composite electroless plating technology based on Ni-Cu-P plating The samples of Ni-P, Ni-Zn-P, Ni-Cu-P coatings were prepared respectively based on the optimum conditions obtained in the pre-optimization. Open circuit potential curve was tested in 3.5wt%NaCl solution. The results of open circuit potential test are: Ni-Zn-P<Ni-P<Ni-Cu-P.According to the sacrificial anode composite gradient coating preparation principle, throughprocess optimization of composite, Ni-P/Ni-Zn-P, Ni-Cu-P/Ni-P, Ni-Cu-P/Ni-Zn-P gradient composite coatings were prepared successfully. The research results show that: both the Ni-Zn-P deposited on Ni-P coating surface, or Ni-P, Ni-Zn-P deposited on Ni-Cu-P coating surface, the intermediate activation are critical in determining the quality of composite plating.The optimum process conditions are activation 20 s in 50ml/LHNO3+150ml/LH2O2 solution at room temperature.3) Typical sample performance analysisThe typical sample obtained under the optimum technological conditions were analyzed by EDS, SEM, micro-hardness tester, XRD, Porosity testing, Immersion corrosion test and potentiodynamic polarization curve. EDS analysis results showed that the coating composition are as follows: Ni-P coating, P 7.95%, Ni 92.05%; Ni-Zn-P coating, P 6.17%, Zn14.81%, Ni 79.02%; Ni-Cu-P coating, P 9.27%, Cu 11.02%, Ni 79.71%. Through appearance analysis and cross-sectional microscope observation, the results indicate that the coatings and the substrate combining closely, interface without gaps and defects, coatings compactness and thickness uniform distribution. Through micro-hardness analysis, the results indicate that the hardness of Ni-P, Ni-Zn-P, Ni-Cu-P, Ni-Cu-P/Ni-P, Ni-Cu-P/Ni-Zn-P, Ni-P/Ni-Zn-P depositing layer respectively is 481.50 HV, 278.6HV, 530.7HV, 604.8HV, 364.5HV, 333.9HV.XRD analysis show that the deposits are both amorphous coating, and the amorphous feature of composite coating is more obvious compared to corresponding single-layer coating.The result of Eocp-t test and PDP(potential dynamic polarization test) indicate that all the coating are cathodic coating, but the open circuit potential of the coatings was significantly different;Different coatings can variably reduces the corrosion current density, improve the corrosion properties of the material,wherein the composite coating reduced greatly. Porosity testing and50℃, 3.5wt% NaCl solution immersion corrosion test results show that porosity of the composite coating is lowest, and has the best corrosion protection ability.