Environmentally-friendly black chrome-silver-free zinc-plating passivation solution and preparation method thereof

The invention provides black passivation solution for zinc-plating post treatment. 1 liter of black passivation solution consists of 10 to 20g of sodium silicate, 20 to 30g of copper sulfate, 0.5 to 1.5g of nickel sulfate, 0.5 to 1.5g of ferrous sulfate, 1 to 3g of sodium acetate, 20 to 40mL of glacial acetic acid, 3 to 7mL of sulfuric acid (98 percent) and the balance of water. A zinc-plating material processed by the passivation solution has a uniform, bright and black appearance and high corrosion resistance, is free of rust for over 200h through a neutral salt spray test and can achieve the same effect as that achieved by the conventional black chrome-silver-contained passivation process in appearance and performance. The passivation solution has the advantages of thoroughly solving the problem of environment pollution caused by a chromium salt used by the conventional black zinc-plating passivation process, eliminating the use of a silver salt at the same time and greatly reducing the cost thereof by substituting silicate for the chromium salt as a main film-forming material and a copper salt, a nickel salt and a ferric salt for the silver salt as a blackening agent, along with stability and reliability and high film-forming efficiency.