The Preparation And Mechanisms Study Of Cu-Sn Alloy Coated Ferrous Powder

The oil-containing bearings generally take iron-bronze mixed powder as raw materials, which inevitably bring out imbalance component and microscopic structure, form hard phase and lead to product properties degradation, make too much noise when bearing operated and reduce its working life. In order to overcome the disadvantages of blending power on the machine, and solve the problems caused by imbalance chemical component and microscopic structure in oil-containing bearings. The composite powders of Cu/Sn two metal coating on the iron matrix are prepared by immersion plating and electroless plating, which contain 20%Cu and 2%Sn with good bond strength and antioxidation ability. Meanwhile, the vacuum heat treatment is applied to the composite powder to make the Cu/Sn coating alloying, and finally obtain the Cu-Sn alloy-coated iron powder.The testing methods including XRD, EDXRF and analytical chemical titration, are adopted to qualitatively and quantitatively analyze the components of the Cu/Sn coating. The SEM and metallographic Microscopy are adopted to observe the sectional microscopic structure and surface topography to estimate coated quality. Through orthogonal experiment, the effect of each factor on the coated quality was studied, and the processing parameters were optimized. Through kinetic test, the effects of temperature, initial concentration and pH value of solution on displacement rate have also been discussed.The research shows that the optimal technology of immersion plating tin on Cu/Fe composite powder are Stannous Chloride-5g/L, citric acid-30g/L, pH value-1.2, bath temperature-85⁹0℃. The Kinetic experiment clarify that the reaction rate is obviously affected by the bath temperature and pH value. And the reaction rate speed up with the increase of temperature and slow down with the reduction of pH value. The displacement reaction system is controlled by Chemical Section. The kinetic data obey the law of the first order reaction rate. And the reaction can be presented by the following equation: lnk=-9.64/T+21, Ea=80.1 kJ/mol. Adding appropriate stabilizer (FS-1) of plating tin is the best effective way to enhance the stability of plating solution.The optimal technology of electroless plating copper on Sn/Fe composite powder are copper sulphate-12g/L, formaldehyde-12ml/L, EDTA·2Na-25g/L, pH value-13, bath temperature-45℃. The Kinetic experiment clarify that the reaction rate speed up with the increase of the copper sulfate concentration, reducing agent concentration, bath temperature and pH value and slow down with the decrease of complexing agent concentration.The vacuum heat treatment experiment shows that the Cu/Sn alloying system contains two diffusion mechanisms, one is melting-dissolving-separating, another is diffusion-solid solution. Moreover, alloying extent increases with the increasement of temperature and time. When the heat treatment temperature reaches 600℃and heat insulation for one hour, the Cu/Sn coating alloying completely, and mainly contains three metallic compounds: C₈₁Sn₂₂, Cu_5.6Sn and Cu₂₀Sn₆.