New Chromium-Free Passivation Agent for Multicolor Zinc Coating on Carbon Steel

In this article, a novel chromium-free passivation agent contained sodium molybdate, sodium citrate, sodium phosphate, tannin, 1-hydroxyethylidene-1, 1-diphosphonic acid (HEDP) and cobalt nitrate was prepared. The component content of the chromium-free passivation agent was firstly determined by using the single variable method, and then optimized by the orthogonal array method. The results indicated that the optimal content of the passivation agent are sodium molybdate 15 g/L, sodium citrate 15 g/L, sodium phosphate 25 g/L, tannin 13 g/L, HEDP 14 ml/L and cobalt nitrate 11 g/L. In the neutral salt spray test, the corrosion life of the as-prepared passivation coatings can reach 46 h, implying the potential commercial application of this chromium-free passivation agent.