The chemical polishing and chemical transformation of Aluminum ( electric )
1.The effect of chemical polishing or electro-polishing
Chemical polishing is an advanced finishing treatment. It can remove not only the slight mold marks and scrapes on the surface of aluminum products, but the rubbing striation, the layer of thermal deformation, oxide film, etc. may form in mechanical polishing, which increases the decorative effect of aluminum product by smoothing the rough surface into a bright one.
2.The principle of chemical polishing
Chemical polishing makes aluminum product’s micro projection preferentially solubilize before its depression by controlling the selective dissolution of aluminum product’s surface, with the purposes of brightening and smoothing the surface. The principle of electrochemical polishing is point discharge,which is similar to other kind of chemical polishing.
3.The effect of chemical transformation
Chemical transformation is mainly used for protecting aluminum and its alloys from corroding. It can be used as coating directly or under-coating of organic polymer, which can not only solve the problem of the adhesion between coating and aluminum but also improve the corrosion resistance of organic polymer coatings.
4.The principle of chemical transformation
In the solution for chemical treatment, the surface of aluminum and chemical oxidant will react to form chemical conversion coating . In this process, common chemical transformations can be divided into chemical oxidation, chromate treatment, chromate-phosphate process and chrom-free conversion.
5.The introduction of chemical transformation
The approach of chemical oxidation treatment is that aluminum can obtain a dense protective chemical oxidizing film in boil water. But as film forming rate and performance lack productivity. The chromium film of chromate treatment is the highest in corrosion resistance at present, which can be used in sprayed under-coating as well directly used as the final coating of aluminum alloy, with the disadvantage of causing serious environment pollution. Chromate-phosphate process can meet the requirement of sprayed under-coating and trivalent chromium is nontoxic, which mainly used in 3C products at the moment. Chrom-free conversion industrialization production mainly adopts chromium - free treatment of titanium-containing or (and) fluoride complexes of zirconium, which requires a degree of chemical pretreatment. Meanwhile, the actual results of chemical transformation cannot be judged by naked eyes as without chromium treatment film is colorless transparent. So reliable performance and strict controlled processing are more counted on. Above all, chemical transformation is most frequently used for chromate-phosphate process of 3C products.
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