1. What is the standard value for the zinc coating density of galvanized coils?
The standard density of the pure zinc coating (code Z) on galvanized coils is typically 7.14 g/cm³, a value widely used in engineering calculations and standard specifications. Based on the density of zinc, a 1-micron thick zinc layer corresponds to a weight of approximately 7.14 g/m². Therefore, the conversion relationship between zinc coating thickness and weight per unit area is: Thickness (μm) × 7.14 = Weight of zinc coating on one side (g/m²).
2. Are the zinc coating densities specified in different domestic and international standards consistent?
A: Different standards use slightly different values for zinc coating density, but they generally fall between 7.1 and 7.2 g/cm³. GB/T 2518 "Continuously Hot-Dip Galvanized and Zinc Alloy Coated Steel Sheets and Strips" uses 7.1 g/cm³ as the calculated density for pure zinc coatings; ISO 1460, the gravimetric method, uses 7.2 g/cm³ as the conversion method after coating peeling for thickness calculation; while in engineering practice, a large amount of data uniformly uses 7.14 g/cm³ as the conversion basis. Since the theoretical density of zinc itself is 7.14 g/cm³, this value has a stronger physical basis and is therefore the most widely used.
3. Are the density standards for aluminum-zinc and other alloy coatings the same as those for pure zinc?
A: No. The density of pure zinc coating is approximately 7.1~7.14 g/cm³, while the density of zinc-aluminum alloy coating (code ZA) is reduced to approximately 6.6 g/cm³ due to the addition of aluminum. The density of aluminum-zinc alloy coating (code AZ, commonly found on aluminum-zinc coated steel sheets, composition 55% aluminum - 43.4% zinc - 1.6% silicon) is even lower, approximately 3.75~3.8 g/cm³. Therefore, in actual engineering calculations, the corresponding density value must be selected according to the coating type; they cannot be used interchangeably.
4. How to convert between zinc layer density, coating thickness, and weight per square meter?
A: The conversion formula is: Zinc layer weight (g/m²) = Single-sided zinc layer thickness (μm) × Zinc density (g/cm³). Taking pure zinc density as an example (7.14 g/cm³), if the single-sided zinc layer thickness is 20 μm, then the single-sided zinc layer weight = 20 × 7.14 ≈ 143 g/m². In actual trade, the total weight of both sides is usually used. For example, the common Z275 coating has a total zinc content of 275 g/m², and its single-sided thickness is approximately 275 ÷ 2 ÷ 7.14 ≈ 19.3 μm. This conversion relationship allows for quick conversion between thickness and weight to verify whether product specifications meet requirements.
5. What is the effect of alloying elements on the density of the zinc coating?
A: The addition of alloying elements significantly alters the density of the zinc coating. Pure zinc has a density of approximately 7.1-7.14 g/cm³. When approximately 5% aluminum is added to form a zinc-aluminum alloy coating (ZA), the density decreases to approximately 6.6 g/cm³. When the aluminum content is increased to approximately 55% to form an aluminum-zinc coating (AZ, i.e., aluminum-zinc plating), the density further decreases to approximately 3.75-3.8 g/cm³. This lower density means that, for the same coating thickness, alloy coatings are lighter per unit area and consume less metal raw materials. Furthermore, different alloy compositions impart different corrosion resistance and processing characteristics to the coating. Users should select the appropriate coating type based on their specific application scenarios.