Galvanization is a thin coating (5-8um) formed on the surface of iron. In a corrosive environment where iron is prone to oxidation reactions, zinc can be corroded before iron. Thereby play a role in protecting iron. Because the cost of galvanizing is low, it is used in various fields such as automotive steel plates, home appliances and building materials, and plays a very important role in preventing rusting of most steel products. Of course, most of the screws used in related fields also adopt this plating method.
Because galvanized materials are prone to oxidation reactions and have the property of discoloration, screw fasteners are usually chrome-plated after galvanizing, that is, they are immersed in a solution containing chromate to make the metal surface A chromate coating is formed. After the chromium plating treatment, the corrosion resistance of the metal surface is improved, and the appearance will become more beautiful. There are several types of chromate coatings:
1. Colored chrome (chrome plating). This is a surface treatment method whose main purpose is to improve corrosion resistance. The color is golden with some red. The surface treatment method with the main purpose of increasing gloss and improving aesthetics. The color is silver with blue, and black chrome (black zinc) refers to the surface treatment method for places that need to improve corrosion resistance and obtain black. The color is black with gloss. Green chrome plating is originally a surface treatment method with excellent corrosion resistance, and the color is dark green.
These chrome plating processes include a chromium metal called six valences in recent years. Because this hexavalent chromium is said to be harmful to the human body. Therefore, in the industrial fields such as the automobile industry and the electronics industry, people have begun to look for alternative treatment agents for hexavalent chromium and to formulate restrictions on hexavalent chromium.
At present, the most feasible alternative to hexavalent chromium that people have proposed is non-toxic trivalent chromium. The method of chrome plating with trivalent chromium is called trivalent chromium plating. Not only that, the use of chrome plating treatment agents is limited. In the movement, several important rules were formulated.
