1.What is the difference between anti-corrosion mechanism and the nature of corrosion resistance?
Galvanized Coil (GI): Sacrificial Anodic Protection
Zinc is more chemically active than iron. When the coating is damaged or a cut exposes the iron base, the zinc acts as a "sacrificial anode," corroding before the iron, thereby protecting the steel underneath. This protection is active and comprehensive, lasting until the zinc layer is completely consumed.
Advantages: Excellent protection against cuts.
Disadvantages: Zinc consumption is relatively rapid in corrosive environments.
Galvanized Coil (GL): Primarily Barrier Protection
Aluminum rapidly forms a dense protective film of aluminum oxide (Al₂O₃) in air. This film is highly stable and effectively blocks the intrusion of moisture and oxygen, acting as a strong physical barrier.
The zinc component in the coating provides localized sacrificial anodic protection, especially at the site of the coating damage.
Advantages: Due to the stability of aluminum, the overall corrosion resistance is very long, making it particularly suitable for environments with high humidity, coastal areas, and industrial acid rain.
Disadvantages: Due to the high aluminum content, its sacrificial anode effect is not as rapid and long-lasting as pure zinc, so its incision protection ability is relatively weak.
2.What is the heat resistance of galvanized coils and galvanized coils?
Galvanized Coil: When temperatures exceed 200°C, the zinc layer begins to weaken, becoming "zinc embrittlement," and its protective properties decline. Therefore, it is not suitable for use in high-temperature environments.
Alu-Zn Coil: Aluminum's high melting point gives it excellent heat and oxidation resistance, allowing it to withstand extended use below 315°C without sacrificing performance. This makes it an ideal choice for high-temperature components such as chimneys, ovens, and dryers.
3.What is the difference in appearance between galvanized coil and galvanized coil?
Galvanized Coil: After solidification, the surface forms a characteristic shiny crystal pattern known as "zinc spangles." These can be categorized as large or small.
Alu-zinc Coil: Due to the presence of aluminum and silicon, its surface crystallizes to form a unique silver-gray, mottled pattern that resembles fish scales or marble, creating a more aesthetically pleasing finish.
4.What is the difference in processability between galvanized coil and galvanized coil?
Galvanized Coil: The coating is relatively soft and has good adhesion, making it less susceptible to noticeable coating detachment during bending and stamping, and offering excellent formability.
Alu-Zn Coil: The coating is hard and brittle, and prone to micro-cracks during aggressive processing (such as sharp-angle bending). While this generally does not affect corrosion resistance (as it primarily provides barrier protection), it can affect deep drawing.
5.How to choose?
Choose Galvanized Coil (GI) when:
Excellent cut protection is required (e.g., exposed edges after cutting).
Cost is a primary consideration.
The operating environment is not subject to high temperatures.
Complex deep drawing or forming processes are required.
Typical Applications: General building structural members, cable trays, ventilation ducts, and general hardware.
Choose Galvalume Coil (GL) when:
Extended service life and enhanced corrosion resistance are sought, especially in harsh environments (coastal and industrial areas).
High temperature resistance is required (e.g., for roofing and stove components).
Special aesthetic requirements (e.g., unique surface patterns are preferred).
Typical Applications: Building roofing/exterior walls (a premium base material for color-coated steel sheets), granaries, automotive exhaust pipe insulation, and oven and barbecue grill casings.