| LI Hong-ling.Present Situation and Research Progress of Environment-friendly Dacromet Treatment Technology[J],52(10):115-123, 140 |
| Present Situation and Research Progress of Environment-friendly Dacromet Treatment Technology |
| Received:July 29, 2022 Revised:September 30, 2022 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2023.10.008 |
| KeyWord:environment-friendly dacromet coating chromate substitutes anti-corrosion mechanism nanoparticle |
| Author | Institution |
| LI Hong-ling |
Xinxiang University, Henan Xinxiang , China |
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| Abstract: |
| Dacromet coating is widely used in automobile, home appliance, architecture and petrochemical industry because of its non-hydrogen embrittlement, high temperature resistance, strong corrosion resistance, good adhesion, high permeability and strong coating ability. However, the Cr6+ content in the dacromet coating is limited due to its strong carcinogenic, teratogenic and mutagenic effects, and the hardness of dacromet coating is only 1H ~ 2H, the scratch resistance is poor, and the wear resistance is low. Therefore, the workpiece with such a coating is not suitable in the situation requiring high hardness and wear resistance. Under this background, the chromium-free dacromet technology is put forward. Chromium-free Zn/Al coating has become the trend of development. However, without chromate, the coating will lose self-repair capabilities, so the corrosion resistance is to be further improved. In addition, the hardness and wear resistance of chromium-free dacromet coating is not high enough, which limits the use of the coating. The chromium-free dacromet technology solves the pollution problem well, but the hardness and wear resistance of the coating are low, so the coating is easy to scratch. It is not possible to use chromium-free dacromet technology for workpieces requiring wear resistance. The workpiece is often scratched and worn during transportation, assembly and use. At the same time, the corrosion resistance of dacromet coating is also weakened in the high salt spray and high humidity environment, which affects the corrosion resistance of coating and the appearance of products. Therefore, it is urgent to improve the hardness and corrosion resistance of the coating by adding reinforcing phase to the non-chromium dacromet coating. In this work, the main components of dacromet coating solution (metal powders, solvents, chromate passivators and special organic compounds) and the effect of chromate (passivation, adhesion and self-healing) in dacromet coating were introduced. Then, the selection of chromate substitutes (non-chromate passivating agent-oxygen-containing salts and oxides, rare earth salts and organic binders-silane coupling agent, silane coupling agent + corrosion inhibitor, resin + corrosion inhibitor), and the formulation optimization of non-chromate passivating solution and nano-particle reinforced dacromet coatings were reviewed to improve the hardness and corrosion resistance of environment-friendly dacromet coatings in China and abroad. At present, there are many reinforcing phases including oxylate and oxide, rare earth salt, silane coupling agent, silane coupling agent + corrosion inhibitor, resin + corrosion inhibitor, which can improve the corrosion resistance of the coating. However, the research on nano-particles is limited. In the previous research, nano-particles can improve the hardness and wear resistance of coatings, but nano-ions have little effect on the corrosion resistance of coatings. Finally, the anti-corrosion mechanism of rare earth modified dacromet treatment technology is briefly introduced, the existing problems in the research of environment- friendly dacromet coatings are summarized, and the development trend of the dacromet coatings is prospected. On the basis of summary and analysis, it is pointed out that with the improvement of environmental protection requirements, the development of composite film-forming systems consisting of organic polymers (silane or resin) and rare earth salts with passivation and self-healing effects and nanoparticles will have great potential. |
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