1.What is the recommended zinc coating thickness for inland dry/low pollution areas?
Recommended zinc coating thickness: 120-180g/㎡ on both sides (corresponding to a zinc coating thickness of approximately 17-25μm, considered a medium-weight zinc coating).
Core Logic:
In environments like these, where there's no significant salt spray or acid-base corrosion, only basic outdoor protection is required. A zinc coating of 120-180g/㎡ protects against rain and minor dust damage through its sacrificial anodic action. Combined with the commonly used exterior wall coatings of fluorocarbon paint or polyester paint (a dual zinc + coating protection), the coating can achieve a service life of 15-20 years.
Additionally, this zinc coating (primarily pure zinc) offers balanced workability, meeting common exterior wall requirements for right-angle bends (such as curtain wall stud splicing) and mildly curved surfaces (such as decorative exterior wall panels), and is less susceptible to cracking or peeling during processing.
Typical Applications: Curtain wall studs and exterior decorative panels (such as pre-painted galvanized sheet substrates) for residential and office buildings in inland cities.
2.What is the recommended thickness for coastal/high humidity areas?
Recommended zinc coating thickness: 200-275g/㎡ on both sides (corresponding to a zinc coating thickness of approximately 28-38μm, considered a heavy-duty zinc coating).
Core Logic:
Salt spray (Cl⁻ ions) in coastal environments is a primary corrosion source for galvanized steel. Salt spray accelerates the sacrificial anodic reaction of the zinc coating. If the zinc coating is too thin (<200g/㎡), zinc depletion and substrate corrosion (manifested as bulging and paint peeling on the exterior wall panels) may occur within 3-5 years.
A heavy-duty zinc coating of 200-275g/㎡ significantly extends the zinc coating depletion cycle. Even in salt spray environments, combined with protective coatings, the service life can reach 20-25 years.
Note: If exterior wall components require frequent welding (such as splicing large curtain wall steel frames), alloyed zinc coating (ZF) is recommended. (At the same thickness, alloyed zinc coatings are less likely to produce zinc vapor pores during welding, and after welding, the zinc layer and substrate bond tightly, reducing the risk of weld corrosion.) Typical applications: exterior wall steel frames of high-rise buildings in coastal cities, exterior wall decorative panels in coastal resorts, and exterior wall rainwater pipe supports in rainy areas.
3.What is the recommended zinc coating thickness for industrially polluted areas?
Recommended zinc coating thickness: ≥300g/㎡ on both sides (corresponding to a zinc coating thickness of ≥42μm, approaching super-heavy-duty zinc coating).
Core Logic:
Acidic and alkaline mist (such as SO₂ and NOx) in industrial environments directly damages the zinc coating's "white rust barrier" (zinc oxide and zinc hydroxide are easily soluble in acids and alkalis), leading to persistent corrosion of the exposed zinc layer.
A thick zinc coating of ≥300g/㎡ provides a sufficient "sacrificial anode reserve" to slow corrosion. It must also be combined with a special corrosion-resistant coating (such as polyvinylidene fluoride (PVDF)) to achieve a service life exceeding 15 years.
Processing precautions: Thick zinc coatings (especially pure zinc coatings) are prone to "zinc accumulation cracking" during bending. Preheating (to 60-80°C) or selecting a "soft substrate" (to reduce substrate hardness and improve overall ductility) is recommended.
Typical applications: Exterior wall panels for industrial buildings and exterior wall studs for public buildings near chemical plants.
4.How does the zinc layer structure affect the long-term stability of exterior wall elements?
Preferred applications include exterior wall decorative panels (requiring complex curved surface forming) and non-welded spliced components (such as snap-on wall panels). Pure zinc coatings offer excellent ductility, a smooth finish after processing, and lower cost than alloyed zinc coatings.
Preferred applications include exterior wall load-bearing steel frames (requiring welded splicing) and components exposed to vibration (such as exterior wall supports near cooling towers). Alloyed zinc coatings offer strong bonding to the substrate, eliminate zinc vapor pores during welding, and are less susceptible to zinc peeling during vibration, preventing weld rust or component delamination.
5.What is the logic behind selecting the zinc layer for cold-rolled galvanized steel for building exterior walls?
Final zinc coating thickness = Environmental corrosion intensity (core) + Processing requirements (auxiliary) + Cost budget (balance)
Inland dry areas: 120-180g/㎡ (primarily pure zinc layer);
Coastal/high-humidity areas: 200-275g/㎡ (pure zinc layer or alloyed zinc layer, with alloying preferred for welded components);
Industrial polluted areas: ≥300g/㎡ (pure zinc layer requires preheating, or alloyed zinc layer).