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What's the Hot-dip Aluminized Steel
2021-12-08
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Introduction to " Hot Dip Aluminized steel"

" hot-dip aluminized steel" is a new type of coating process in which steel products are placed in molten aluminum at a certain temperature and immersed for a proper time to form an alloy aluminum layer on the surface of the steel.

Hot-dip aluminized steel has both the high strength of the steel matrix and the corrosion resistance, wear resistance and high temperature resistance of the aluminum layer. Its corrosion resistance is 5-10 times that of galvanized steel; in terms of resistance to sulfide and heat corrosion. Its performance is better than 18-8 stainless steel. Therefore, it can bring obvious economic benefits to users.

The characteristics of metallographic structure of hot-dip aluminized steel

Hot-dip aluminized steel makes the bond between iron and aluminum atoms, which are tightly combined by metal bonds, as shown under the microscope, from the outside to the inside, there is an aluminum oxide film, an aluminum layer, and an alloy layer. The sequence formed the plating layer. In the case of carbon steel, the plating layer is in close contact with the base material in a band-like structure.

Hot-dip aluminized steel makes the bond between iron and aluminum atoms, which are tightly combined by metal bonds, as shown under the microscope, from the outside to the inside, there is an aluminum oxide film, an aluminum layer, and an alloy layer. The sequence formed the plating layer. In the case of carbon steel, the plating layer is in close contact with the base material in a band-like structure.

The performance of hot-dip aluminized

Corrosion resistance:

The corrosion resistance of aluminized steel is exerted by the corrosion resistance of the aluminum oxide film, the corrosion resistance of the aluminum layer itself, the corrosion resistance of the alloy layer, and the electrochemical corrosion protection principle between the aluminum layer, the alloy layer and the base material.

(1) Weather resistance

Aluminized products can be used for a long time in corrosive environments such as humid ocean areas, industrial zones and sulfur hot springs.

Comparison of corrosion test results of galvanized and aluminized steel mg/cm2.

Test name Test condition Galvanized steel Aluminized steel.

(2) Seawater resistance

Hot-dip aluminized steel has good corrosion resistance to seawater, not only in the marine environment, but also in the sea and waves. The corrosion resistance of aluminized steel is excellent in salt water. The following table lists the corrosion test results of 3 kinds of steel in 3% NMacl aqueous solution.

(3) Water resistance

Since the coating of aluminum-plated products has anti-corrosion effect as a cathode, the aluminum oxide passivation film and alloy layer formed on the aluminum surface are both corrosion-resistant. Therefore, the aluminized products have extremely strong water resistance. Due to the differences in water quality, pH, temperature, and flow rate, there are also certain differences in the anti-corrosion and durability of aluminized products.

(4) Stress corrosion resistance and crack prevention

If some special steels, carbon steels, etc. are placed in aqueous solutions (low-resistance media) containing chlorides, sulfates, nitrates, etc., stress corrosion cracking will occur. If they are plated with aluminum, they can be prevented. This is because in a low-resistance medium, the aluminum-plated layer functions as a sexual anode, and it will not crack before the coating disappears. In the experiment of using aluminum-plated tubes such as heat exchangers, no matter what kind of heat exchangers, they have shown several times the durability.

(5) Medicines and other corrosive aqueous solutions

The resistance to aqueous solutions of aluminized products depends on the depth of the ions in the water, the depth of the organic substances contained in the water, and the water temperature.

For organic acid, nitric acid, sulfuric acid (3), ammonium water, ammonium salt less than 1% and more than 20%. It has corrosion resistance to hydrogen sulfide water, sulfurous acid aqueous solution, urea water, salt water, calcium chloride, and sulfur-containing hot spring water.

Heat resistance

(1) High temperature oxidation resistance

Ordinary steel will oxidize rapidly at a high temperature of 550 degrees Celsius, while aluminized steel has strong high temperature oxidation resistance and high temperature corrosion resistance. This is because the dense oxide film on the aluminum surface prevents the diffusion of oxygen, and the alloy layer itself (described in the following reaction formula) also has strong heat resistance.

(2) Carbon leaching resistance

The alloy layer on the surface of aluminized steel can suppress the intrusion and diffusion of carbon. In addition, it can prevent decarburization of the base material (steel) even in a high-temperature reducing gas environment.

(3) High temperature vulcanization resistance

The sulfide resistance of hot-dip aluminum plating is very good, even better than chromium, especially for hydrogen sulfide.

Welding of hot-dip aluminized products

When aluminum-plated steel needs to be welded, special aluminum-plated welding rods (produced in China) can be used, and the corrosion resistance of the welded parts is the same as that of aluminized steel. During welding, the aluminum layer diffuses and penetrates at high temperature, and the base material is also protected.


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