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.

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.