The hot-dip galvanized layer has a much better protective effect on steel than a paint or plastic layer.
1. When hot-dip galvanizing, zinc and steel are diffused to form a zinc-iron intermetallic compound layer, that is, an alloy layer. The alloy layer is metallurgically bonded to steel and zinc, and is more firmly bonded than lacquer and steel. The hot-dip galvanized layer exposed to the atmosphere will not fall off for decades and will be completely corroded.
2. When there is small crack or damage in the galvanized layer, zinc will continue to prevent cracking or steel rust in the form of sacrificial anode, which is the main feature of the galvanized layer superior to other coatings. The iron-zinc alloy layer contains more than 90% zinc, which has the same electrochemical protection effect on steel as zinc; and the hardness of the iron-zinc alloy layer is much higher than that of pure zinc (close to pure iron), so the coating resists collision and scratching. higher.
3. Since zinc can be dissolved in acids and alkalis, the hot-dip galvanizing layer can only be applied to general atmospheric and natural water environments. The galvanized layer produces slight electrochemical corrosion when exposed to air and water. The galvanized layer can last for many years in rural and air-clean areas, while the galvanized layer has a shorter durability in industrial stained areas and coastal areas. In addition, the thicker the coating, the longer the durability, and the durability is almost proportional to the thickness. The thickness of the coating can also be expressed in terms of the mass per unit area of zinc (g/m2), and the thickness of the 1 μm coating corresponds to the amount of zinc attached at 7.2 g/m2. There has been a large amount of data on the durability of the hot-dip galvanized layer. These data have some differences due to the specific test environment.
4. Since the plating layer is consumed in the application, when the iron-zinc alloy layer is gradually exposed, the surface of the plating layer becomes dull and dull. Moreover, the corrosion product contains a small amount of rust (ferric iron), which will cause the surface of the coating to have a local rust color. For the parts that are prone to dark coating, there is little or no pure zinc layer on the surface of the coating. This kind of "rust" will appear in the short-term use of the plated parts, but this does not affect its protection, but only affects the appearance.