1.How many levels of "corrosion" are there in the environment?
Low corrosion: basic protection, a thin zinc layer is enough
Medium to low corrosion: medium zinc layer, anti-condensation corrosion
Moderate corrosion: thicker zinc layer, resistant to atmospheric pollutants
High corrosion resistance: thick zinc layer + surface treatment, resistant to salt spray / industrial exhaust gas
Extremely high corrosion resistance: Extra thick zinc layer + coating, strong corrosion resistance
2.How to choose the type of galvanizing layer?
Hot-dip galvanizing (GI): The steel sheet is immersed in molten zinc to form a zinc layer (uniform thickness and strong adhesion). The zinc layer acts as a sacrificial anode to protect the steel sheet and is suitable for most outdoor environments (C2-C5).
Examples include building roofs, automobile chassis, and outdoor brackets.
Electrogalvanizing (ZE): The zinc layer is deposited by electrolysis (thin thickness and high uniformity). Its corrosion resistance is weaker than hot-dip galvanizing and is only suitable for dry indoor environments (C1), requiring additional paint for enhanced protection.
Examples include home appliance interiors and precision instrument casings.
Galvanizing alloying (GA): After hot-dip galvanizing, the zinc layer and steel sheet are subjected to high-temperature treatment to form a zinc-iron alloy (high hardness and excellent weldability). Its corrosion resistance is slightly lower than GI, but it is scratch-resistant and suitable for applications subject to frequent contact, such as automobile bodies (C2-C3).
3.How to choose the thickness of the galvanized layer?
The thickness of the zinc layer is expressed as "total zinc content on both sides (g/m²)". The thicker the layer, the longer the corrosion resistance life (under the same environment, doubling the zinc layer thickness can extend the life by 1.5-2 times).
4.How can surface treatment be used to enhance corrosion resistance and applicability?
Passivation: After galvanizing, a chromate or chromium-free passivation layer (such as silane) is applied to reduce "white rust" (an initial corrosion product) on the zinc layer and extend the corrosion resistance period (suitable for C3-C4 environments).
Oil Treatment: The surface is coated with anti-rust oil to temporarily protect the zinc layer (during transportation/storage). It must be removed before use (suitable for short-term protection in all environments).
Color Coating: An organic coating (such as polyester or fluorocarbon paint) is applied over the zinc layer to create a "zinc + coating" dual protection, significantly improving corrosion resistance (suitable for C4-C5 highly corrosive environments, such as coastal building exteriors).
5.What are the selection steps?
Determine the environmental corrosion level: Based on humidity, salinity, and contaminants, determine whether the environment is classified as C1-C5.
Determine the type of galvanizing: Hot-dip galvanizing (GI) is preferred for outdoor applications, while electroplating (ZE) can be an option for simple indoor applications.
Match the zinc coating thickness: Select the appropriate zinc content based on the corrosion level (e.g., Z275 or higher for C4).
Additional surface treatments: Passivation or color coating can be applied to enhance corrosion resistance in highly corrosive environments.
Based on processing requirements: For complex forming, choose a deep-drawing grade like DX53D; for simple processing, choose a standard grade like DX52D.