Study The Process And Performace On Chromium-free Colour Passivation For Zinc Coating

Electro-galvanized process is one of the important measures of metal corrosion, and is widely used in transportation, aerospace, the machinery manufacturing and other industries. However, serious pollution galvanized the industry, its main pollutants from galvanized after passivation process. Currently galvanized passivation process on the market are mainly two: hexavalent and trivalent chromium on the salt passivation, with chromate passivation.Chromate passivation process stable, mature,and have excellent appearance and corrosion resistance,is widely used in industrial production. But the solution may hexavalent chromate and trivalent chromium on the environment and caused great harm to the human body, in order to solve the electroplating industry, environmental on hazards, truly environmentally harmless, research and development of the environmentally on friendly chromium-free passivation fluid replacement chromate passivation solution to solve the problem of environmental pollution hazards electroplating industry fundamentally promote the development of green passivation process is necessary.This paper studies the development of an environmentally friendly chromium-free passivation process silicate color. The passivation process using sodium silicate as a main, agent, an auxiliary film-forming agent added, the oxidizing agent and a complexing agent to improve the corrosion resistance and improving the appearance of the passive film passivation film Experiment to determine the color of silicate passivation process through single factor and orthogonal experiments recipe ingredients and passivation process conditions parameters are on the summarized below: Na2SiO3-9H2O19g/L,(98%)H2SO43ml/L,H2O28ml/L,CuSO41.9g/L,NaF6g/L, NaNO3l4g/L, passivation temperature with30℃, PH values:2.5with the passivation time:60S, Passivation film, the appearance of color obtained after the passivation process, uniform, bright, and good corrosion resistance, by5%NaCl solution, the white neutral salt spray test average time was around76hours rust, corrosion and trivalent chromium salts color passivation process quite.Color silicate passivation film was subjected to corrosion tests, the main use of neutral salt spray test, copper sulfate drip experiment, brine immersion test and electrochemical testing and other means, until the sample data show not passivated compared to silicate color passivated samples greatly improved the corrosion resistance of zinc layer, and corrosion resistance of trivalent chromium salts quite; through adhesion tests found attached silicate passivation film passivation process color efforts to meet national standardsUsing scanning electron microscopy (SEM) observations of silicate colored microscopic surface passivation film found silicate surface passivation film good repair defects zinc coating surface and the surface forming a network structure, and chromic acid a dense network structure of the passivation film forming salts compared silicate passivation film mesh structure is relatively loose, no strong dispersing chromate film corrosion current capability, but also effectively silicate passivation film dispersed corrosion current, protect galvanized layer. XPS composition obtained by the test element with the passivation film mainly Zn4Si2O7(OH)2·2H2O and colloidal SiO2, ZnO, Zn(OH)2and the like exist in the form of compounds, these compounds are deposited on the zinc layer is formed on the surface passivation film protect the zinc coating.Over silicate color passivation process of industrial experiments, the process stability and maintenance of passivation solution to inspect the results show that the impact of the various components of the solution to stabilize the size of the passivation solution of H2SO4,Na2SiO3, NaF,H2O2, CuSO4,NaNO3. By periodically added to the passivation solution must have a sodium silicate solution and sulfuric acid, can effectively improve the silicate passivation solution for industrial life. Respectively silicate color passivation of industrial production tested at different plating system, find the basic rack and barrel plating system has been passivation film appearance and corrosion resistance are better than good acidity rack and barrel plating effect.In summary,the color green silicate passivation process with no pollution, low cost, good stability, the passivation film passivation process has been the appearance and corrosion resistance initially meet the requirements of industrial production, by further industrial experiments, is expected to completely replace chromate passivation process color, and has broad market prospects.