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Differences Between GI, GL and ZAM

There are different kinds of galvanized products, including GI (pure zinc coating), GA (zinc-iron alloy coating), GL (55% Al-Zn coating), 5% AL-Zn (Galfan coating), aluminizing (pure aluminum coating and aluminized silicon coating), and ZAM (zinc-aluminum-magnesium coating). Here let’s review the differences between GI, GL and ZAM.

Differences Between GI, GL and ZAM

1. Coating Difference

GI is applied with a pure zinc coating; galvalume coating consists of 55% aluminum, 43.4% zinc, and 1.6% silicon by weight. While zinc-aluminum-magnesium steel is a new type of high corrosion-resistant steel. The coating mainly consists of zinc, plus 1.5%-11% aluminum, 1.5%-3% magnesium, and a trace amount of silicon.

2. Corrosion Resistance

In the same environment, the corrosion resistance of ZAM is the best, which is much better than that of GI and GL. The galvalume steel has better corrosion resistance compared to a galvanized coil of the same thickness. However, the hot dip GI sheet is the most economical anti-corrosion coating.

The corrosion resistance of GL coating is mainly due to the protective function of aluminum. When the zinc is worn away, the aluminum forms a dense layer of aluminum oxide, preventing further corroding the interior. But its alkali corrosion resistance is poor. In addition, the protection performance of the Al-Zn coating on the cutting area is much worse than that of the GI coating. In comparison, ZAM steel has strong chlorine resistance (salt/seawater/soil) and alkali corrosion resistance. Besides, Mg offers ZAM coating with high corrosion resistance and high cutting-edge protection performance. It has a self-healing function, which can guarantee no red rust for 20-30 years.

3. Appearance

Hot-dip galvanized steel has normal spangles, minimum spangles, and zero spangles. While galvalume steel also has spangles, which are more even and beautiful. The zinc-aluminum-magnesium steel looks finer and smoother.

Galvanized Sheet with Big Spangles

GI Sheet with Big Spangles

Galvanized Sheet With Spangles

Galvanized Sheet With Spangles

Galvalume Steel Surface

Galvalume Steel Surface

Production of SuperDyma Coil

Production of SuperDyma Coil

4. Substrate of Color Coated Steel

GI, GL, and ZAM are widely used as the base metal of color coated steel. But zinc magnesium aluminum steel is the most suitable material as the substrate of color-coated steel. Compared with PPGL, its corrosion resistance is much better. So it is widely used in the construction and home appliance industries.

5. Cost

The cost of GI is the cheapest, followed by GL and ZAM. But as for their corrosion resistance and service life, ZAM is the best, followed by GL and GI. You can choose a suitable material according to the use purpose, the use environment, and your budget.


At Wanzhi Steel, we have two hot-dip galvanizing lines, a galvalume, and a ZAM steel production line. Also, we offer slitting, profiling, cutting, and coil coating services. Our coated products, GI, GL, ZAM, PPGI, and PPGL are available in coils, sheets, and strips. Welcome to contact us for more details.

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