How to choose the appropriate zinc coating?
Step 1: Outline your core needs and determine your selection criteria. During the selection process, you need to clearly define the usage conditions and functional requirements. Then, parameter selection will be performed. Focus on three very important issues:
The type and thickness of the zinc coating vary depending on the corrosive environment and can be divided into the following four categories:
1. Low corrosive environment: Dry indoor environments (e.g., offices, ordinary warehouses) and unpolluted rural areas require lower corrosion resistance.
2. Medium corrosive environment: Urban outdoor environments, industrial areas (with less dust pollution), and high-humidity indoor environments (e.g., basements in southern regions) require basic corrosion protection.
3. High corrosive environment: Coastal areas (salt spray), heavy industrial areas (acidic gases and dust), and rainy and humid outdoor environments may require higher corrosion resistance.
4. Extreme corrosive environment: Chemical plants, offshore platforms, and other high-acid, high-alkali, and high-salt spray environments usually require high-performance coatings or alloy coatings.
Steel processing and forming requirements. The mechanical properties and coating adhesion of steel coils vary depending on processing needs:
Simple processing: For example, cutting and bending (e.g., building frames, simple electrical brackets), the processing performance of standard steel coils is sufficient;
Complex processing: In deep drawing (e.g., car door inner panels, microwave oven cavities), steel coils with good ductility and coating adhesion should be prioritized, as coating peeling or steel cracking may occur in such applications;
Special processing: In welding (steel structures), the impact on welding performance should be considered, such as pore defects caused by zinc vapor; or in spraying or printing (appliance casings), materials with a smooth surface and good adhesion should be used.
Service life and cost budget. The thickness of the zinc coating is directly related to its service life. A trade-off needs to be made between the minimum service life and cost. For short-term use (5-10 years), a thinner coating is recommended to minimize high maintenance costs; for long-term applications (15 years or more) and in sensitive areas with extremely high structural requirements (e.g., roofs and bridge components), a thicker coating or alloy treatment solution is recommended to reduce related costs. Step 2: Understand the core parameters and match performance to actual needs. After determining your goals, you must consider three main technical aspects that constitute the fundamental characteristics of steel coil performance:
Galvanizing layer thickness (zinc coating weight). The galvanizing layer thickness is usually expressed as “zinc coating weight per square meter (g/m²)” and is divided into single-sided and double-sided galvanizing. Thicker coatings improve corrosion resistance but also increase costs. Different application scenarios suggest different coating thickness ranges.
Substrate performance. The strength, elongation, and other parameters of the substrate determine the processing suitability of the steel coil:
General purpose (building fences, simple brackets): Use low-carbon steel substrates that are low-cost and easy to process, especially SPCC, DX51D, etc.;
Complex stamping (e.g., automotive parts, deep-drawn parts for home appliances): Use deep-drawing grade substrates (SECD, DC04) with elongation ≥30% to meet complex forming requirements;
Load-bearing structures (e.g., building keels, mechanical parts): Choose high-strength and durable substrates with a yield strength ≥280MPa to provide load-bearing stability.
Surface treatment methods: Various surface treatment methods are required, which produce different effects and should be customized according to the specific characteristics of the material used.
Passivation treatment: Provides good corrosion resistance, can withstand up to 72 hours of salt spray testing without white rust, suitable for humid environments;
Anti-fingerprint treatment: This technology forms an anti-fingerprint coating on various hardware surfaces, including electronic device casings, home appliance panels, and all other hardware that requires maintaining a high-quality surface;
Phosphating treatment: A process that improves paint adhesion to the surface, suitable for workpieces that require subsequent coating treatment;
Oiling treatment: This treatment prevents scratches during transportation and storage, but degreasing is required before processing.