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Benefits of zinc-aluminum-magnesium coated products

Oct 09, 2022

The principle of zinc-aluminum-magnesium corrosion resistance and self-healing of scratches


Zinc Aluminum Magnesium Steel Coil has unique corrosion resistance, especially notch protection. It is divided into two cases for analysis: the plane without scratches and the cases with cuts and scratches.


1 When the surface of the galvanized aluminum-magnesium steel sheet is not scratched

The combined action of magnesium and aluminum contained in the coating will produce a dense oxide protective film with extremely high adhesion on the surface of the coating in long-term use, which will isolate the coating from the external corrosive environment and play the role of isolation and anti-corrosion. , to prevent corrosion of the coating. Magnesium is a more active metal than aluminum. It is extremely easy to be oxidized in the air. The oxide film formed by solid magnesium is also denser, which can effectively protect the internal organization and prevent further oxidation. Since magnesium is not the same as aluminum, it is evenly and finely distributed in the coating, so that the oxide film covers the entire surface of the coating, so that all the structures in the coating are protected.


2 When the coating is scratched or cut

The magnesium dissolved from the coating can form a fine and dense oxide film containing magnesium on the incision section, covering the scratched or exposed steel base at the incision, thereby improving its corrosion resistance. In this case, the anti-corrosion effect of zinc and the isolation and anti-corrosion effect of aluminum and magnesium can also be exerted. On this basis, because magnesium is very active, it can reduce the loose oxides on the surface of the steel plate and replace them with dense magnesium oxides, so that the exposed steel base is protected.


Corrosion resistance comparison between zinc aluminum magnesium and other coating types


1. Comprehensive data comparison

(1) The salt spray resistance test of the plane part is similar to that of the aluminum-zinc-silicon plate, which is about 10 to 20 times that of the galvanized plate, and 5 to 8 times that of the galvanized-5% aluminum alloy.

(2) The salt spray resistance test of the cut section, the bent part and the scratched part is better than that of the aluminized zinc silicon plate, the galvanized-5% aluminum plate and the galvanized plate.

(3) The ammonia resistance is 2 times that of galvanized sheet and 10 times that of Al-Zn-Si sheet.

(4) The acid and alkali resistance is similar to that of galvanized sheet, better than that of aluminized zinc silicon sheet and galvanized-5% aluminum sheet.

(5) When the coating is 90g/m2, the corrosion resistance is better than the 560g/m2 coating obtained by the hot dip plating method after processing into the workpiece.


2. Comparison of ZAM plate salt spray test

Compared with the red rust occurrence time of the ZAM plate and the other three common coatings in the salt spray test, the red rust occurrence time of the ZAM plate is the longest.


3. SD board exposure test comparison

The fracture state of SD board and other three common coatings in the outdoor exposure test after 8 months and 20 months is shown in the figure below. Corrosion is reduced instead.


4. ZM board parts cycle test comparison

The following is a group of comparative photos of auto parts made of ZM plates after the corrosion resistance cycle test. It can be seen that the corrosion resistance of ZM70 coated products is also better than that of Z100 coated products.

Type of coating Zinc Aluminum Magnesium

Analysis of the processing performance characteristics of Zinc Aluminum Magnesium Coated Steel Coil


1. Scratch resistance of the coating

The plane corrosion of the coated sheet mostly occurs at the scratch, and the scratch is an unavoidable phenomenon of the coated sheet, especially in the process of processing, if the coated sheet itself has good scratch resistance, it can be Avoid scratches to a large extent, thereby increasing its service life.


Scratch performance is expressed by the load generated by scratches. The measurement method is to place a sapphire test needle with a tip radius of 0.05mm perpendicular to the test site and move it under loads ranging from 0.0196 to 0.196N (2 to 20gf). The test site is 20mm. After that, it was visually observed whether or not scratches occurred at the test site, and the smallest load among the loads in which scratches occurred was taken as the scratch-resistant load.


After testing, ZAM plate is the best, and its load when scratching is about 1.5 times that of galvanized-5% aluminum, and more than 3 times that of galvanized and galvanized. This is because of the higher hardness of the coating. The Vickers hardness values ​​of the four coatings are shown in the table below.

Type of coating Plating hardness
ZAM 140Hv~160Hv
Hot dip plated 55% Al-Zn alloy 100Hv~110Hv
Hot dip Zn-5% Al alloy 80Hv~100Hv
Hot dip Zn plating 55Hv~65Hv

2. Weldability

Compared with hot-rolled and cold-rolled sheets, the welding performance of ZAM sheet is slightly worse, but it can still be welded with a reasonable process and achieve the due strength, which will not affect its use. For the welding part, it can be repaired with Zn-Al paint to achieve the effect similar to the normal coating.


3. Paintability

The paintability of ZAM is similar to that of aluminum-zinc-silicon and zinc-5% aluminum alloy coatings, and it can be painted to further improve the appearance and service life.


Competitiveness and irreplaceability of Al-Zn-Mg Alloy Coated Steel Coil


1 Core Competitiveness

As shown in the table below, the core competitiveness of this product is:(1) The surface protection ability overcomes the deficiency that galvanized products are easily scratched;

(2) The edge and scratch protection ability can produce products with a thickness of 3~8mm, and there will be no premature edge corrosion, and the galvanized sheet thickness exceeds 3mm will cause premature edge corrosion;

(3) The corrosion resistance of outdoor exposure is good, and the 300g/m2 coating can achieve a life of up to 30 years, while the 30-year life of galvanized sheet must exceed 800g/m2 on both sides, which cannot be produced at all.


2. Irreplaceability

The following occasions are only the use of zinc, aluminum and magnesium, and other products are irreplaceable:

(1) For long-term outdoor use, such as high-speed guardrails, the product specifications are required to be thicker and the surface coating is thicker. In the past, batch galvanizing had to be used. After the birth of zinc-aluminum-magnesium, continuous hot-dip galvanizing of aluminum-magnesium can be used. method, such products also include solar equipment brackets, bridge components, etc.;

(2) Where the roads in Europe and other places need to be sprinkled with salt, if other coatings are used to produce the car floor, it will be corroded quickly, and it must be made of zinc-aluminum-magnesium plates. Such cases include buildings such as beach villas;

(3) For special occasions that require acid resistance, such as poultry houses and troughs in farms, poultry manure is acidic, and zinc-aluminum-magnesium plates that are more resistant to pickling and corrosion must be used.

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