Iron in nature exists in the form of various oxides. It is smelted (reduced) to iron, but according to the principle of thermodynamics, the oxidation of iron is a self-process. Therefore, at the same time when steel is produced, corrosion of steel occurs. Statistics show that the economic loss of metal corrosion in developed countries each year accounts for about 1.5% -4.2% of their gross national product. Corroded metals account for about 15% of production each year. At normal temperature, the forms of corrosion are mainly chemical corrosion and electrochemical corrosion.
Chemical corrosion refers to the damage caused by the direct chemical reaction between the surface of the metal substrate and the non-electrolyte. The reaction is characterized by the direct oxidation-reduction reaction between the atoms on the surface of the substrate and the oxidant in the non-electrolyte to form corrosion products.
Electrochemical corrosion refers to the damage caused by the electrochemical reaction between the surface of a metal substrate and an ion-conducting electrolyte. Any corrosion reaction by electrochemical mechanism includes at least an anode and a cathode reaction, and forms a loop with an electron current flowing through the interior of the metal substrate and ions in the electrolyte. Electrochemical corrosion is the most common and common corrosion. Corrosion of metals in the atmosphere, sea water, soil, and various electrolyte solutions falls into this category.
There are many ways to control and prevent metal corrosion. Among them, the method of preventing corrosion by isolating steel and external media by covering the coating is more common in thin plates. These cover coatings are mainly divided into two types: metal plating and non-metal coating.
Color coated steel plate coating features
The galvanized varieties used for color-coated steel plates for construction are galvanized and alloy coated products. Their performance differences and uses are as follows:
The hot-dip galvanizing referred to here refers to hot-dip galvanized pure zinc. It is most widely used in construction. Before it was used as a color-coated substrate, it has been widely used in the construction industry and is currently the main variety of color-coated substrates for construction. Excellent corrosion resistance. Suitable for making building exterior panels. It can process a variety of levels such as general molding, stamping and deep drawing.
The coating composition of this product is approximately 55% aluminum, 1.5% silicon, and the rest is zinc. It is characterized by excellent atmospheric corrosion resistance, 2-6 times that of galvanized sheet, and excellent corrosion resistance. It also has high temperature corrosion resistance of aluminum plate, smooth surface and good appearance, but the forming and welding properties of the plating layer are slightly worse. It is suitable for building exterior panels, and can be processed in various levels such as general molding and mechanical bite.
Hot-dip galvanized aluminum
The composition of the coating is 5% aluminum, 0.1% mixed rare earth elements, and the rest is zinc. It is characterized by good coating formability and atmospheric corrosion resistance 2-3 times that of hot-dip galvanized sheet. Good applicability and welding performance. Compared with hot-dip galvanized steel sheet, zinc flower is small and rarely used in bare state.
The purity of the coating is high, so the corrosion resistance of the coating at the same thickness is better than that of hot-dip galvanized products. According to the test, under the same conditions, according to the American standard (ASTMB 114), the red rust resistance time of a micron coating is 12 hours for electrogalvanizing and less than 10 hours for hot galvanizing. However, it is very difficult to obtain a thick electro-galvanized coating (large power consumption, high cost, and technical difficulty). As a color-coated substrate, the use of electro-galvanized is also mainly applied to home appliances, steel furniture, doors and windows, and the like.
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