What is the relationship between the zinc coating weight and zinc coating thickness of galvanized sheet?

What is the relationship between the "zinc coating weight" and "zinc coating thickness" of galvanized sheet? How do you convert them?
Zinc coating weight refers to the mass of the zinc coating per unit area (double-sided or single-sided), measured in g/m² (e.g., 80 g/m² and 120 g/m², usually refer to the total weight of both sides).
Zinc coating thickness refers to the physical thickness of the zinc coating, measured in μm (micrometers).
Conversion formula: Thickness (μm) = Zinc coating weight (g/m²) ÷ Zinc density (7.14 g/cm³) ÷ 10.
Example: Double-sided zinc coating weight 80 g/m² → Single-sided thickness = 80 ÷ 2 ÷ 7.14 ÷ 10 ≈ 0.56 μm.
7. What are the common galvanized sheet grades? What do they represent? Commonly used domestic steel grades follow GB/T 2518 (hot-dip galvanized steel) and GB/T 15675 (electrogalvanized steel). Taking GI as an example:
Q235-Z: Q235 is the base material (low-carbon steel with a yield strength of 235 MPa), and Z indicates hot-dip galvanizing.
DC51D+Z: DC51D is a cold-rolled base material (stamping grade), and +Z indicates hot-dip galvanizing. A zinc coating can be added later (e.g., DC51D+Z80, meaning a double-sided zinc coating of 80 g/m²).
HC340LA+ZF: HC340LA is a high-strength, low-alloy base material (yield strength of 340 MPa, stamping grade), and +ZF indicates zinc-iron alloying (GA).
8. What other types of galvanized steel are categorized by application? Downstream application scenarios can be categorized as follows:
Construction panels: such as roof panels, wall panels, and keels require a heavy zinc coating (120g/m² or higher) and wind load resistance;
Home appliance panels: such as refrigerator side panels and washing machine casings require minimal zinc spangles, high flatness, and easy painting;
Automotive panels: such as body panels (GA) and chassis components (GI) require high strength and excellent weldability;
Chemical panels: such as storage tanks and pipelines require acid and alkali resistance (may require additional coating) and a heavy zinc coating.
9. What are the core performance indicators of galvanized sheet? There are five key indicators for evaluating galvanized sheet quality:
Corrosion resistance: resistance to atmospheric corrosion and saltwater corrosion;
Mechanical properties: yield strength, tensile strength, and elongation of the substrate (affecting stamping formability);
Zinc layer properties: adhesion (ease of zinc detachment) and uniformity (no missing plating or thickness variation);
Surface quality: absence of defects such as scratches, pitting, missing plating, and black spots;
Processing properties: stamping, bendability, and weldability (especially for automotive applications).
10. How is the corrosion resistance of galvanized sheet tested? What are the commonly used methods? Three common testing methods are used, corresponding to different scenarios:
Neutral Salt Spray (NSS) testing: Samples are placed in a 5% sodium chloride solution mist environment (35°C) and the time it takes for white rust (zinc corrosion) and red rust (substrate corrosion) to appear is recorded. GI typically shows no white rust for 48-120 hours.
Damp Heat Testing: Samples are placed in an environment of 40°C and 95% relative humidity, observing corrosion to simulate a humid environment.
Outdoor Exposure Testing: Samples are placed outdoors in a natural environment (such as a seaside or industrial area) to track corrosion rates over a long period of time. This method is most closely aligned with actual applications, but the testing cycle is longer (1-5 years).