1. Principle of corrosion resistance and self-healing of scratched cuts of zinc, aluminum and magnesium. First, a theoretical analysis is carried out. ZAM board has unique corrosion resistance properties, especially cut protection properties. The analysis is divided into two situations: the plane situation without scratches and the situation with cuts and scratches.
1 When the ZAM surface is not scratched, the combined action of magnesium and aluminum contained in the coating will produce a dense oxide protective film with extremely high adhesion on the surface of the coating during long-term use, which will isolate the coating from the external corrosive environment. It plays the role of isolation and anti-corrosion to prevent corrosion of the coating. Magnesium is a more active metal than aluminum and is extremely easily oxidized in the air. The oxide film formed by solid magnesium is also dense, which can effectively protect the internal tissue and prevent further oxidation. Because magnesium is different from aluminum, it is evenly and finely distributed in the coating, so that the oxide film covers the entire coating surface, so that all the structures in the coating are protected.
2 When the coating is scratched or cut, the magnesium dissolved from the coating can generate a fine, dense oxide film containing magnesium on the cut section, covering the exposed steel base in the scratched or cut area, thereby improving its resistance. corrosive. In this case, the sacrificial anti-corrosion effects of zinc and the isolation anti-corrosion effects of aluminum and magnesium can also be brought into play. On this basis, because magnesium is very active, it can reduce the loose oxides on the surface of the steel plate and replace them with dense magnesium oxides, thereby protecting the exposed steel base. As shown in the figure below, in the newly formed incisions of the ZAM plate, the exposed steel base will be oxidized in the corrosive environment, and initial red rust will appear. However, as time goes by, the magnesium and zinc dissolved from the coating and Aluminum and other elements will turn red rust into a gray-black oxide film, which has a denser structure and protects the fracture site from further oxidation. The ZAM incision site protection principle incision exposure test shows that the fracture surface shows a certain red color in the early stages of the test, but The redness will not develop seriously, and after 3 years, the original redness will turn into gray-black. After testing, it was found that the oxide film at the fracture site contained complex components such as zinc, magnesium, aluminum, oxygen, iron, chlorine, and sulfur.
Comparison of corrosion resistance between zinc, aluminum and magnesium and other coating types:
(1) The salt spray resistance test of the flat part is similar to that of galvanized silicon plate, about 10 to 20 times that of galvanized plate, and 5 to 8 times that of galvanized -5% aluminum alloy.
(2) The salt spray resistance test of the cut section, bent section and scratched section is better than that of galvanized silicon plate, galvanized -5% aluminum plate and galvanized plate.
(3) The ammonia resistance is 2 times that of galvanized sheets and 10 times that of galvanized silicon sheets.
(4) The acid and alkali resistance is similar to that of galvanized sheets, and better than galvanized silicon sheets and galvanized-5% aluminum sheets.
(5) When the coating is 90g/m2, the corrosion resistance is more superior than the 560g/m2 coating obtained by hot-dip plating after processing into the workpiece.
