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The hot-dipped galvanized series of coated steels or steel strips are used in our trade or processing, such as galvanized, aluminum-zinc, zinc-aluminum-magnesium, and other coatings. According to some foreign publicity materials, about half of the world's zinc production is used for surface anti-corrosion treatment of steel and steel products (including immersion anti-corrosion of various zinc series coatings and a large number of whole steel parts).
Different hot-dipped galvanized coated steels have different characteristics and trade statuses
The zinc content of the plating solution in the hot-dipped galvanizing pot is not less than 99%, which is currently the most economical type of anti-corrosion coating.
Pure zinc coated steel sheets are divided into two types, those with zinc spangles and without zinc spangles, and their corrosion resistance is almost the same. If spraying or painting is needed in the future, the products without zinc spangles will be more beautiful while usually most thick zinc layer products have zinc spangles (for example, the weight of the zinc layer is 275g/m2 on both sides).
According to news, South Korea's Pohang has exported 600g of hot-dip galvanized steel coils with a zinc layer to the Chinese market. However, because the ultra-thick zinc layer affects the welding assembly, the cost is not as low as that of the overall immersion plating of the parts. And the pure zinc coating cannot protect the cut surface of the steel sheet well, so the sales in China are not very good.
The plating solution contains about 55% aluminum and about 1.6% silicon, and the remaining component is zinc. The corrosion resistance of aluminum-zinc coating is higher than that of pure zinc coating in most environments. Aluminum-zinc coating steel coils are all spangled. Excellent steel mills can produce even and beautiful spangles for direct use in home appliances, but the aluminum-zinc coating also has some shortcomings.
The welding performance of aluminum-zinc coated steel is not as good as that of pure zinc. In especial, when electric resistance welding is adopted, the molten coating metal will stick to the electrode tip. Because the hardness of the bonded metal after melting is relatively high, the removal efficiency of ordinary grinding tools is very low, which will cause the electrode tip scrapped. For the above reasons, please make the welding as little as possible.
In addition, the protection of the aluminum-zinc coating on the cut-off of the steel plate is far inferior to that of the pure zinc coating (and far less than the zinc-aluminum-magnesium coating). Therefore, the operator needs to take some measures to prevent corrosion of the cut-off opening (such as painting and sealing).
It is a coating product with excellent comprehensive performance. It was successfully developed and mass-produced by Nisshin Steel Corporation in Japan in the early 21st century, and the patent and trademark ZAM were registered.
The corrosion resistance of zinc-aluminum-magnesium-coated steel is much higher than that of zinc coating and aluminized zinc. The protection of the cut-off is effective, and the welding performance is also very good. It is said that the purpose of its development is to replace certain stainless steel.
