Chromium-free inactivating liquor for continuous galvanizing by hot-dip galvanized steel sheet

Abstract

The invention relates to a chromium-free passivation solution used for continuous hot dipping coating of galvanized steel sheet, which belongs to the technical field of metal surface treatment and corrosion prevention. The compositions and the mixed ratio in one liter of the passivation solution are as follows: 3 to 5 grams of molybdate, 5 to 15 grams of tungstate, 3 to 5 grams of tannic acid, 5 to 20 grams of citric acid, 10 to 30 grams of hydrogen peroxide, 10 to 30 grams of silicate, 20 to 30 grams of pH value regulator, and the balance being water. The chromium-free passivation solution has the following advantages: as no chromium is contained, the chromium-free passivation solution has no effect on a human body and the environment, and has low cost which is equivalent to that of a chromate passivation solution and is approximately 30 percent of that of the chromium-free passivation solution used in the prior art, thus the cost is less than one tenth that of the chromium-free passivation solution containing 80 to 160 grams of the molybdate per liter and 16 to 32 grams of the tungstate per liter in the prior art; besides, the salt spray corrosion resistance of the passivated galvanized steel sheet can meet the requirement of national standard with the corrosion area of a 72-hour neutral salt spray test less than 5 percent; and the chromium-free passivation solution not only does not change the prior process conditions, but also does not change the prior equipment in use.

Description

technical field [0001] The invention belongs to the technical field of metal surface treatment and anticorrosion, and in particular relates to a chromium-free passivation solution for continuous hot-dip galvanized steel sheets. Background technique [0002] Hot-dip galvanized steel sheets are widely used in fields such as automobiles, construction and home appliances. Under actual storage and / or use conditions, the surface of the galvanized layer often becomes dark gray due to corrosion, or white corrosion products are deposited. In order to prevent this phenomenon, it is necessary to passivate the galvanized sheet before use to improve its corrosion resistance and increase its bonding force with the coating. The traditional method of passivating the galvanized layer widely uses hexavalent chromate treatment process. This process has excellent corrosion resistance, self-healing effect and low price, and has always been favored by people. However, since hexavalent chromium...

AI Technical Summary

Problems solved by technology

However, the cost of organic passivation film formation process is high, the stability of the plating solution is poor, and the process of adding and maintaining the plating solution is complicated; some passivation processes even need to update and transform equipment

[0004] China Invention Patent Application No. 200810046857.4 discloses a chromium-free passivation solution for the surface of galvanized steel sheets. The composition of molybdate in the formula is 80-160g / L, and the composition of tungstate is 16-32g / L , compared with the chromate passivation solution, the cost has increased by more than 10 times, which is obviously difficult to bear for large-scale industrial production

[0005] Summing up the above situation, although many research institutions and manufacturers at home and abroad are unremittingly exploring the passivation solution used in the chromium-free passivation of the zinc coating, and have also proposed various schemes and solutions, but Compared with the chromate passivation solution, its biggest disadvantage is that the cost far exceeds the expectation under the condition of meeting the national standard

Therefore so far, there is still no chromium-free passivation agent (solution) that can meet the low-cost demand expected by users.