Types of Aluminized Steel Sheets
Overview
Aluminized steel sheets come in two main categories, each designed for specific applications:
- Category 1: Heat-Resistant Sheets
- These sheets can withstand high temperatures up to 640°C. They are made from low-carbon steel coated with a 20–25 micron thick Al-Si alloy, containing 6–8.5% silicon.
- Category 2: Corrosion-Resistant Sheets
- These sheets have a coating thickness two to three times greater than Category 1 and are primarily designed for corrosion resistance.
Both categories use hot-dip plating, forming a thin alloy layer between the steel and coating. Category 1 forms an Al-Fe-Si alloy layer, while Category 2 forms an Al-Fe alloy layer. However, Category 2 has reduced weldability due to its thicker, low-melting-point coating.
Features
Aluminized steel sheets combine the benefits of iron and aluminum, offering unique properties such as corrosion resistance, heat resistance, and thermal radiation reflection. These sheets are valued for their durability in environments exposed to thermal radiation, acid, condensate, and atmospheric corrosion. Components made from aluminized steel last 2 to 5 times longer than those made from galvanized steel, making them ideal for resisting SO2 and H2S corrosion.
High-Temperature Oxidation Resistance and Thermal Radiation Reflectivity
One key feature of aluminized steel sheets is their ability to reflect thermal radiation, which helps control and suppress heat. This performance is comparable to pure aluminum and superior to galvanized steel. Tests show that after four years outdoors, galvanized steel’s reflectivity drops to 5%, similar to a black body, while aluminized steel retains 55% reflectivity.
Aluminized steel also excels in high-temperature oxidation resistance. When the surface temperature reaches about 510℃, the aluminum coating prevents oxidation without discoloration. This makes it suitable for heat-resistant facilities exposed to corrosive condensate or combustion byproducts. Although the aluminum-iron-silicon alloy turns black between 510-677℃, the aluminum coating continues to protect the steel.
The steel base melts at 1580℃, much higher than the aluminum layer’s melting point of 654℃. Therefore, aluminized steel maintains its integrity longer than pure aluminum in fires, resisting and suppressing flame spread.
Disadvantages
The main disadvantage of aluminized steel sheets is their higher production cost compared to galvanized steel. However, they remain economical due to their extended service life. Additionally, aluminized steel is less suitable for certain processing applications compared to galvanized steel.
