Zinc-Aluminum-Magnesium Coated Steel Plates – the Frontier of Anti-corrosion in Steels

1. What is zinc-aluminum-magnesium steel?

Definition: Zinc-aluminum-magnesium is a kind of alloy metal, which is mainly used for surface anti-corrosion treatment of steel and steel products, including coatings of various zinc series and anti-corrosion immersion of a large number of whole steel parts. Initially, the metal used for the surface anti-corrosion treatment of steel products is pure zinc. With the improvement of technology, alloy metals such as aluminum-zinc alloy and zinc-aluminum-magnesium alloy have appeared one after another, which greatly enhanced the corrosion resistance effect of the metal layer.

2. Composition and classification of Zinc-Aluminum-Magnesium Steels

Zinc-aluminum-magnesium coated steel sheet refers to a coated steel sheet in which a certain amount of Al, Mg is added to the existing hot-dip galvanized coating or a certain amount of Mg is added to the hot-dip galvanized coating. It has high performance of corrosion resistance and high trimming protection.

A generalized analysis of magnesium-containing coated steel plate for commercial applications shows that the Mg content in most coatings is less than or equal to 3%. Hence, according to the aluminum content of the coatings, the zinc-aluminum-magnesium coatings can be divided into the following types:

• l Low-aluminum Zn-Al-Mg coating, with aluminum content of 1-3.5%: This coating is formed by adding a certain amount of aluminum-magnesium and other elements on the basis of hot-dip galvanizing. The coated steel plate has also been tested in a color coating unit, and low-aluminum zinc-aluminum-magnesium plate has also been successfully developed. The coating is an upgraded version of the corrosion resistance of the hot-dip pure zinc coating, which is referred as BZM coated steel plate and its color coated plate.

• l Medium-aluminum Zn-Al-Mg coating, with aluminum content of 5~11%.

• l High-aluminum Zn-Al-Mg coating, with aluminum content of 55%. The coating is formed by adding certain magnesium and other elements on the basis of hot-dip aluminum-zinc. The coated steel plate has also been tested in a color coating unit, and the color coated steel plate with a high-aluminum zinc-aluminum-magnesium substrate has been successfully developed. This coating is an upgraded version of the corrosion resistance of the hot-dip aluminum-zinc coating, which is referred to as BAM coated steel sheet and its color coated sheet.

3. Comparison between Galvanized (GI), Aluzinc, and Zn-Al-Mg Steels?

Pure zinc coating is a kind of economical anti-corrosion coating, with a zinc content of not less than 99%. It can be further divided into galvanized steel with or without spangles, and these two types have almost the same level of corrosion resistance. However, if the steel plates need to be sprayed or painted later, those without spangles will have a more pleasant aesthetic. The thick zinc layer products usually have spangles (for example, the weight of the zinc layer is 275g/m² on both sides).

Aluminum-zinc coating is an alloy metal, in which the aluminum content is 55%, and the zinc content is 43.5%, with remaining component being silicon. Generally, the corrosion resistance of aluminum-zinc coating is 2-6 times better than pure zinc coating of the same weight. The surface of the galvanized steel coil can be modified by production technology to produce beautiful and uniform spangles, which can be directly used for exterior building or household appliances.

But there are also some disadvantages of aluminum-zinc coating:

First, the welding performance of the aluminum-zinc coating is not as good as that of pure zinc, so the welding process should be minimized in use;

Second, the protection of the aluminum-zinc coating on the cut of the steel plate is less than that of the pure zinc coating, and far less than that of the zinc-aluminum-magnesium coating.

The zinc-aluminum-magnesium coating has an excellent all-rounder performance. Its manufacturing cost is only slightly higher than Aluzinc coating, while its corrosion resistance is much better. In addition, it also has good performance to protect the cut of the steel plate, and the welding performance is equivalent to galvanized steels.

Currently, application cases of the Zn-Al-Mg steel plates are emerging in the market. At the same time, Zn-Al-Mg color-coated steel plate are also being mass-produced and widely used.

In the future, as the requirements for materials in construction and various industries gradually increase, zinc-aluminum-magnesium coated steel sheets may gradually replace the aluminum-zinc steel sheets in the market.

At CUMIC, we are constantly adapting our products and services to your processes for maximum efficiencies in your best interest. If you'd like to know more about Zn-Al-Mg coated steels, don't hesitate to leave a message below or reach us via marketing@cumic.com!