1.What is the basic definition and production process of SGCC?
Core Features: SGCC uses cold-rolled steel as its substrate. A uniform zinc layer is formed on the surface through a hot-dip galvanizing process (immersing the steel in molten zinc). This process combines the formability of cold-rolled steel with the corrosion resistance of the zinc layer.
Production Process: Cold-rolled substrate (such as SPCC) → Degreasing and cleaning → Annealing (to restore plasticity) → Hot-dip galvanizing (zinc bath temperature approximately 460-470°C) → Air knife control of zinc layer thickness → Cooling → Passivation (optional, to improve corrosion resistance) → Finishing (flattening and shearing).
2.What are the parameters and anti-corrosion performance of SGCC zinc layer?
Zinc coating weight: Common specifications are 60g/m², 80g/m², 120g/m², and 180g/m² (total weight on both sides), corresponding to zinc coating thicknesses of approximately 8.5μm, 11.5μm, 17μm, and 25μm. The thicker the zinc coating, the stronger its corrosion resistance (for example, the salt spray resistance of a 120g/m² zinc coating is approximately 1.5 times that of a 60g/m² zinc coating).
Zinc coating structure: From the outside in, the hot-dip galvanized coating consists of a pure zinc layer (η phase), a zinc-iron alloy layer, and an iron-zinc alloy layer. The alloy layer is tightly bonded to the substrate and resists detachment.
Anti-corrosion principle: The zinc layer acts as a sacrificial anode, corroding preferentially while simultaneously forming a dense zinc oxide/zinc hydroxide protective film that blocks water and oxygen from reaching the substrate, providing dual protection.
3.What are the chemical composition and mechanical properties of SGCC?
Base Material Composition: Similar to SPCC, with carbon ≤ 0.15%, manganese ≤ 0.60%, phosphorus ≤ 0.035%, and sulfur ≤ 0.035%, ensuring excellent formability.
Mechanical Properties:
Tensile Strength: 270-370 MPa
Yield Strength: 130-250 MPa
Elongation: ≥ 20% (The zinc coating slightly reduces the base material's elongation, but still meets general forming requirements).
Performance Characteristics: Strength is similar to SPCC, with slightly lower ductility. However, the zinc coating provides significantly better corrosion resistance than bare steel.
4.What is the surface state and classification of SGCC?
Surface Treatment:
Regular Spangle: Features visible spangle crystals on the surface, offering a highly recognizable appearance at a low cost.
Minimized Spangle: Features fine, uniform spangles, making it suitable for painting or lamination, avoiding the uneven coating thickness caused by larger spangles.
Spangle-Free: Offers a smooth, nearly spangle-free surface, making it a preferred choice for applications requiring high aesthetics (such as appliance housings).
Passivation: Choose between chromate passivation (traditional, highly corrosion-resistant but containing hexavalent chromium) or chromium-free passivation (e.g., silane and titanium-zirconium based passivations), further enhancing fingerprint and corrosion resistance.
5.What are the performance characteristics and application areas of SGCC?
Core Advantages:
Excellent Corrosion Resistance: Compared to bare steel (such as SPCC), its service life in humid environments can be extended by 3-5 times.
Good Formability: Suitable for bending, stamping, welding, and other processes (be mindful of the potential for porosity caused by zinc evaporation during welding).
Cost-Effective: The hot-dip galvanizing process is mature, with lower costs than electroplating, making it suitable for mass production.
Typical Applications:
Construction: Roof panels, wall panels, keels, and brackets (for outdoor applications requiring weather resistance).
Home Appliances: Refrigerator back panels, air conditioner housings, and washing machine bases (requiring moisture and corrosion resistance).
Automotive: Chassis components and door frames (non-exterior components, with a focus on corrosion protection).
Industrial: Electrical cabinets, warehouse shelving, ventilation ducts, etc.