Characteristics and differences between galvanized steel, galvalume steel, and zinc aluminum magnesium coated steel.

Galvanized steel (GI) is the first generation of coated steel. Its coating mainly contains zinc (over 99%). And it is currently the most widely used coating steel due to its longer history comparing with the other two.

Pure zinc-coated steel is divided into two types: spangle-free and regular spangle, and their corrosion resistance is almost the same. If spraying or painting is required later, products without spangle will be more beautiful; while products with thick zinc layers usually are spangled (for example, the zinc mass is 275g/m2 on both sides).

The coating mass of pre-galvanized steel can be 720g maximum. But please note, if the zinc layer is too thick, it will affect the welding assembly.

Galvalume steel (GL) is the second generation of coated steel. It is composed of 55% aluminum, 43.5% zinc, and a small amount of other elements. Its corrosion resistance is better than that of galvanized steel in most environments. But the weldability of GL is not as good as that of GI, especially when using electric resistance welding, the molten coating metal will stick to the electrode tip. Because the hardness of the metal adhered after melting is relatively high, the removal efficiency using ordinary grinding tools is very low, which will cause the electrode head to be scrapped, so the welding process should be minimized during use.

It should be noted that if rust occurs at a certain point of the GL sheet, if timely measures are not taken, the rusted area will gradually become larger and larger and eventually even the entire plate; whereas, even if rust occurs at a certain point of a galvanized sheet, it will not spread.

In addition, the protection of GL coating for the cutting section of GL steel sheet is far inferior to that of GI coating (although that of galvanized coating is not good either), so it is necessary to do anti-corrosion work on the cutting section, such as using anti-rust paint or zinc rich paint to seal it.

Zinc-aluminum-magnesium (Z-A-M) coated steel is the third generation of coated steel. Its coating is mainly composed of zinc, 1.5-11% aluminum, 1.5-3% magnesium and a small amount of silicon. This coating has comprehensive properties that far exceeds traditional coating of galvanized and galvalume steel.

Z-A-M coated steel was originally developed to replace some usage scenarios of stainless steel. Although stainless steel has good corrosion resistance, the cost is too high; and other zinc coated series steel is not as corrosion-resistant as stainless steel, and more importantly, for poor protection of cutting section or damaged coating.

Z-A-M coating has excellent red rust resistance and self-healing corrosion resistance of the cutting section, because the initial corrosion products of Z-A-M coating will flow and cover the exposed substrate. And at the same time, it also has far superior welding performance than galvanized and galvalume steel, which perfectly solves the shortcomings of ordinary coated steel that cannot effectively protect the cutting section, miss coating point, and coating damage. It can be said that it is one of the coated steel closest to stainless steel in terms of comprehensive performance.

Galvanized steel, galvalume steel, zinc aluminum magnesium coated steel can all be used in acid and alkali environments, but the effect of acid and alkali resistance is a bit different. Galvanized steel is often used in alkaline environments, while glavalume steel is better used in acidic environments. For Z-A-M coated steel, it has quite excellent corrosion resistance in both environments. Especially in C4 C5 and CX environments, Z-A-M coated steel is highly recommended.

Then there is the application of high zinc layer galvanized and galvalume steel, can consider in particular to be replaced by zinc aluminum and magnesium coated steel.

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