Hot-dip aluminium plating technology involves immersing the substrate in molten aluminum, so that the aluminium forms a strong metal protective layer with the surface of the substrate. This process not only significantly enhances the corrosion resistance and high-temperature oxidation resistance of the material, but also improves its appearance and extends its service life. Due to these advantages, hot-dip aluminium is widely used in industries such as petrochemical, construction, and automotive.
Features and benefits of hot-dip aluminized coatings
Heat resistance
Hot-dip aluminized coatings are widely used due to their excellent high temperature resistance. For example, the heat resistance of carbon steel is increased from 550 °C to 1000 °C, and the aluminized layer can effectively prevent oxidation at high temperatures, especially when using aluminum-silicon alloy plating, the heat resistance is more prominent. This property makes hot-dip aluminium coatings widely used in high-temperature operating environments, such as industrial furnaces, exhaust pipes, etc.
Corrosion resistance
Hot-dip aluminium coatings are highly resistant to corrosion in industrial atmospheres (e.g. containing SO₂, H₂S, NO and CO₂) and perform well even in acid rain environments. Compared with hot-dip galvanized layer, the aluminized layer has better corrosion resistance and can effectively extend the service life of steel. This high corrosion resistance makes hot-dip aluminized steel often used in areas where corrosion resistance is critical, such as in the construction, marine and petrochemical industries.
Reflective properties
The hot-dip aluminum layer also has excellent light and heat reflectivity. This is due to the formation of a dense and smooth Al₂O₃ film on the aluminized surface, which remains highly reflective even after exposure to the sun. This property not only helps to reduce heat absorption, but also saves energy, so it is widely used in building materials.
Formation and preparation of hot-dip aluminized coatings
Formation of aluminum-iron compounds
According to the iron-aluminum binary state diagram, when steel comes into contact with liquid aluminum, the dissolution and chemisorption of iron and aluminum atoms occurs, forming different iron-aluminum compounds, such as FeAl and Fe₂Al₅. The formation process of these compound layers determines the microstructure and properties of hot-dip aluminized coatings. Among them, the alloy layer close to the steel matrix and the pure aluminum layer on the outer layer together form the aluminized layer.
Typical preparation process
Typical processes for hot-dip aluminium include uncoiling, oxidation, pickling, washing, reduction, hot-dip aluminization, and cooling. The steel is annealed and reduced in a reduction furnace to remove the oxide film and ensure that the surface of the steel is clean and can be well bonded with the molten aluminum. The process details will vary for different steel types, such as wire, strip and pipe, but the core steps are basically the same.
Effect of molten aluminium temperature and aluminium plating time
The temperature and dip time of the molten aluminium have a direct impact on the thickness of the alloy layer. Temperatures that are too high will accelerate the growth of the alloy layer, but beyond a certain temperature, the thickness will be reduced. The longer the dip plating time, the greater the thickness of the alloy layer, so the temperature and time need to be precisely controlled according to the specific process requirements.
Application of hot-dip aluminium coating
Architectural field
Hot-dip aluminized steel sheets are often used in the top floors, side panels, ventilation ducts and other buildings with excellent corrosion and heat resistance to keep these components in good condition in harsh environments. In addition, the high reflectivity of hot-dip aluminium steel also makes it a reliable material for building energy efficiency.
Automotive & Industrial
In automotive manufacturing and industrial equipment, hot-dip aluminized coatings are widely used in components such as exhaust systems and heat exchangers due to their good high temperature oxidation resistance and corrosion resistance. Especially in high-temperature corrosive environments, hot-dip aluminium coatings can significantly increase the service life of equipment.
Petrochemical and power industries
In the petrochemical and power industries, where many pieces of equipment are exposed to high temperatures and corrosive atmospheres, such as reaction towers, storage tanks, and pipelines, hot-dip aluminized coatings can extend the life cycle of these critical equipment and reduce maintenance costs.
summary
Overall, hot-dip aluminized coatings are a reliable steel surface treatment technology due to their excellent heat, corrosion and reflective properties. By reasonably selecting the coating material and controlling the process parameters, the performance of the aluminum plating layer can be optimized, so as to meet the requirements of different fields for the performance of steel.
