Chromium-free passivation solution for black passivation treatment of galvanized layer and preparation method thereof

Abstract

The invention relates to a chromium-free passivating solution used for the black passivation treatment of a zinc plating and a preparation method thereof. The preparation method is characterized by comprising the following steps: weighting boric acid, sodium silicate and potassium persulfate according to the total volume of the passivating solution to ensure that 1L of the passivating solution contains 5-10g of boric acid, 4-8g of sodium silicate and 3-6g of potassium persulfate, dissolving the components in 10-20 times of water by weight respectively, mixing the three solutions evenly after complete dissolving to prepare a solution A; then weighting cerium nitrate according to the total volume to ensure that 1L of the passivating solution contains 2-4g of cerium nitrate, dissolving cerium nitrate in 10-20 times of water, weighting hydrochloric acid according to the total volume to ensure that 1L of the passivating solution contains 10-25mL of hydrochloric acid, adding hydrochloric acid in the cerium nitrate solution to prepare a solution B; then slowly adding the solution B in the solution A, mixing evenly, weighting hydrogen peroxide according to the total volume to ensure that 1L of the passivating solution contains 9-10mL of hydrogen peroxide, adding hydrogen peroxide in the mixed solution of the solution A and the solution B to obtain a solution C; weighting cobalt chloride, ammonium molybdate or sodium molybdate according to the total volume to ensure that 1L of the passivating solution contains 5-8g of cobalt chloride, 8-15g of ammonium molybdate or 8-15g of sodium molybdate, dissolving in 10-20 times of water to obtain a solution D; and adding the solution D in the solution C, mixing evenly, adjusting the solution with water to reach the total volume, adjusting the pH value of the passivating solution with phosphoric acid to 2.0, and aging for 24 hours. The film has the advantages of black luster, uniformity, glossiness and no dark or spots and the like.

Description

technical field [0001] The invention relates to a chromium-free passivation solution for black passivation treatment of galvanized layer and a preparation method thereof. Background technique [0002] Galvanizing is an effective anti-corrosion method for steel parts, but the zinc coating is prone to white rust in humid air, and then red rust, which affects the corrosion resistance of the galvanized layer and reduces the service life of the galvanized workpiece. In order to further improve corrosion resistance, galvanized parts must be passivated. [0003] The black passivation of the galvanized layer is mainly composed of copper salt black passivation and silver salt black passivation. Copper salt black passivation generally uses copper sulfate as the blackening agent, adding chromic anhydride, acetic acid and other components, the passivation process is easy to operate, the time is short, and the blackening speed is fast. If the passivation time is longer, the passivation...

AI Technical Summary

Problems solved by technology

Although this method obtains a black passivation film, the time for white rust to appear in the neutral salt spray test of the passivation film is only 13 to 18 hours, and the time for red rust to appear is 72 hours, which is far from meeting the passivation requirements of the workpiece.