In-depth Study on the Relationship between Composition and Performance of Galvalume Steel Coil

In fields such as building curtain walls, appliance housings, and photovoltaic brackets, galvalume steel coils are gradually replacing traditional galvanized steel coils as the mainstream choice due to their dual advantages of corrosion resistance and cost-effectiveness. Whether it’s the Galvalume Steel Coil Price, a key consideration in engineering procurement, or the ASTM A792 Galvalume specification clearly defined in production standards, the differences in core performance stem from the precise control of composition. Today, we’ll start with composition analysis to unravel the performance secrets of galvalume steel coils (including Galvalume Roll, Steel Coil Galvalume, etc.).
I. Core Composition Analysis of Galvalume Steel Coil
The performance of galvalume steel coils is determined by both the “base material” and the “coating.” Different component proportions directly affect the applicable scenarios of the final product. For example, the composition design of Galvalume Steel Coil Az150, which requires high corrosion resistance, differs significantly from that of ordinary Galvalume Coil.
1. Coating Composition: The “Golden Ratio” of Aluminum, Zinc, and Silicon

Aluminum-zinc coating is not a single metal, but an alloy system of aluminum (55%), zinc (43.5%), and silicon (1.5%). This ratio is the optimal solution verified through long-term practice:
* Aluminum (Al): The “corrosion-resistant core” of the coating. Aluminum forms a dense Al₂O₃ oxide film on the surface of the steel coil, which can resist corrosion from harsh environments such as acid rain and salt spray. This is the key reason why aluminum-zinc coated steel coils have 3-5 times higher corrosion resistance than ordinary galvanized steel coils;
* Zinc (Zn): Plays the role of “sacrificial anode protection.” When the coating is scratched, zinc will preferentially react with oxygen to prevent the base steel from rusting. At the same time, the presence of zinc can also improve the ductility of the coating, making it easier for Galvalume Roll to bend and stamp;
* Silicon (Si): Solves the problem of “coating adhesion”. Silicon can inhibit the reaction between aluminum and iron to form brittle and hard Fe-Al intermetallic compounds, reducing the risk of coating peeling. The stabilizing effect of silicon is especially important for thicker Galvalume Steel Coil Az150 (AZ150 represents 150g of coating weight per square meter).
2. Substrate Composition: The “Basic Guarantee” of Low-Carbon Steel

The substrate of galvalume steel coils is mostly low-carbon steel (carbon content ≤0.12%), supplemented with small amounts of manganese (0.3-0.6%) and phosphorus (≤0.045%): Carbon (C): Excessive carbon content will make the substrate too hard, making it prone to cracking during processing; too low a content will reduce the strength of the steel coil. Therefore, the carbon content of low-carbon steel must be strictly controlled within the “strength and processability balance range”; Manganese (Mn): A small amount of manganese can improve the yield strength of the substrate without significantly affecting ductility, making it suitable for load-bearing applications (such as steel coil galvalume for photovoltaic brackets); Phosphorus (P): Phosphorus increases the brittleness of steel, therefore the phosphorus content in the substrate must be strictly limited, which is also one of the indicators clearly specified in the ASTM A792 Galvalume standard.
II. The Relationship Between Composition and Key Performance Characteristics Understanding the composition allows us to clearly see why some Galvalume Coils are suitable for outdoor construction while others are suitable for appliance liners—the essence lies in the performance differences resulting from compositional adjustments.

1.Corrosion Resistance: Aluminum Content Determines “Protection Level” Corrosion resistance is the core competitiveness of galvalume rolls, and its relationship with composition is particularly direct: When the aluminum content of the coating increases from 50% to 55%, the density of the Al₂O₃ oxide film significantly improves. In salt spray environments at the seaside, the corrosion time of the steel coil can be extended from 10 years to over 20 years. If the silicon content is below 1%, it will lead to a decrease in the adhesion between the coating and the substrate, making the coating prone to blistering in salt spray tests; if it is above 2%, it will increase the brittleness of the coating, thus reducing corrosion resistance durability. This is also why Galvalume Steel Coil AZ150 has stronger corrosion resistance than AZ100 (100g coating per square meter) – not only is the coating thicker, but the aluminum-zinc-silicon ratio is also better suited to high protection requirements.
2.Mechanical Properties: Substrate Composition Dominates “Strength and Processability”
Strength: For every 0.1% increase in the manganese content of the substrate, the yield strength of the steel coil can increase by 5-8 MPa. Therefore, for Galvalume Steel Coil used in load-bearing applications, the manganese content is controlled at 0.5-0.6%.
Processability: For applications requiring complex stamping, such as appliance casings, substrates with a carbon content ≤0.1% are selected, while the silicon content of the coating is reduced to around 1.5% to prevent coating cracking during stamping. 3. High Temperature Resistance: Aluminum’s Advantage of “High Temperature Stability”
The melting point of aluminum (660℃) is much higher than that of zinc (419℃), therefore, the high temperature resistance of aluminized zinc steel coils is far superior to that of galvanized steel coils:
In environments below 200℃ (such as oven linings), the coating performance is stable;
Even under short-term high temperatures of 300℃, the Al₂O₃ film can prevent coating oxidation, which is the core reason why Galvalume Roll is suitable for chimneys and high-temperature pipe cladding.

III. The Relationship Between Composition, Performance, and Galvalume Steel Coil Price

Many people wonder during procurement: Why can the price difference of Galvalume Coil of the same specifications reach 100-200 RMB/ton? In essence, the price difference reflects the cost of the components: Coating cost: The market price of aluminum is 2-3 times that of zinc. Therefore, the higher the aluminum content in the coating (e.g., AZ150 compared to AZ90), the higher the cost, and the higher the Galvalume Steel Coil Price. Base material cost: The higher the manganese content and the lower the phosphorus content in low-carbon steel, the higher the smelting cost, and the higher the corresponding Galvalume Steel Coil price. Standard cost: Products conforming to the ASTM A792 Galvalume standard have stricter component tolerance control (e.g., aluminum content deviation ≤ ±1%), a higher scrap rate during production, and a price 5-8% higher than non-standard products. IV. Practical Application Case: The Importance of Composition Selection

A coastal construction project compared two types of galvalume steel coils: Ordinary Galvalume Coil (50% aluminum, 1% silicon): Localized corrosion appeared after 3 years of use; Galvalume Steel Coil Az150 (55% aluminum, 1.5% silicon), conforming to ASTM A792: No significant corrosion after 5 years of use, and no deformation during typhoon impact (superior mechanical properties). The project ultimately chose the latter. Although the initial price of Galvalume Steel Coil was 150 RMB/ton higher, the service life was extended by more than 10 years, resulting in a lower overall long-term cost.

Conclusion: The composition design of galvalume steel coils is a process of “precisely matching requirements”: AZ150 (high aluminum, high silicon) is chosen for high corrosion resistance; low silicon, low carbon substrates are chosen for complex processing; and ASTM A792 standard products are chosen for export projects. With the future development of the photovoltaic and new energy industries, composition optimization (such as adding trace amounts of rare earth elements to improve corrosion resistance) will become an important development direction for aluminized zinc steel coils, further expanding their application boundaries.