Study For Preparation, Performance And Mechanism Of Non-chrome Zinc-Aluminum Coating

Because of excellent performance and non-pollution during the producing, Dacromet coating has attracted widely attention since it was introduced into China in 1990's. But, as require of the protection for environment, Dacromet coating will be forbidden in not further future. It's mainly because of the using of chromate which can induce cancer. So, it's necessary to find a substitute for chromate. Nowadays, there are only three kinds of non-chrome Zinc-Aluminum coating, and they are not widely used because of high prices and technical monopolization. Considering these reasons, a non-chrome zinc-aluminum coating was developed based on Dacromet technology, its performance was tested, and the anti-corrosion mechanism were discussed.Firstly, the basic components were selected, such as dispersant, thickener as well as other assistants. The selection of substitute for chrome was the key and most difficult work in the paper. After lots of tasting experiments and failure, it was included that chromate can only be substituted by at least two reagents, one as the binder, the other as the corrosive depressant. Then, these two reagents were selected; the cohesion and the anti-corrosion experiment showed that they can work. And, the non-chrome zinc-aluminum coating was prepared.In order to optimize the coating, the orthogonal test was designed in which the results were evaluated by the appearance, cohesion and anti-corrosion performances. The influence of each component on coating's performance was researched by extreme difference. And then, the coating with optimal performances was prepared. The processing parameters of preparation for non-chrome coating were studied, such as swing, drying and solidifying processes. The influences of proportion and particle size of zinc and aluminum powder were also researched by contrasting different coatings.After the researches on the components and preparation process, the non-chrome zinc-aluminum coating with the best performances was prepared. The anti-corrosion performance, heat resistance, cohesion as well as porosity of the coating were tested. And the appearance and microstructure of the coating were observed by LYCRA microscope and Philips XL30 SEM. The element of the coating was researched by EDAX.According to the microstructure of the coating, electro-chemical experiments and scratch test, the anti-corrosion mechanism of non-chrome coating were discussed in four aspects: physical shield, corrosion inhibiting, cathode protection and self-repair. The anti-corrosion mechanism for intact coating and scathed coating were also discussed.The non-chrome zinc-aluminum coating has a prosperous future, although lots of works have been done in this paper, there still a great deal of work need to do before it will be used in industry.