What is the difference between hot-dip galvanized steel and electro-galvanized steel?
A: The two processes and performance differ significantly. A detailed comparison is as follows:
| Comparison Dimensions | Hot-Dip Galvanized Sheet (Hot-Dip Galvanizing) | Electrogalvanized Sheet (Cold-Dip Galvanizing) ||----------|--------------------|--------------------|| Process Principle | The substrate is immersed in molten zinc (approximately 450°C). Zinc and iron react to form an alloy layer and a pure zinc layer. | Under electrolysis, zinc ions are deposited on the substrate surface, forming a pure zinc layer. || Zinc Layer Thickness | Thicker (usually 40-150 g/m² per side) | Thinner (usually 5-20 g/m² per side) || Adhesion | Strong (the alloy layer adheres tightly to the substrate and does not easily fall off) | Weak (the pure zinc layer has poor adhesion to the substrate and is easily scratched and falls off) || Corrosion Resistance | Strong (suitable for outdoor, humid environments) | Weak (suitable for dry indoor environments, such as appliance linings) || Cost | High | Low |
What is "Zinc-Aluminum-Magnesium Galvanized Sheet"? What are its advantages over ordinary hot-dip galvanized sheet?
A: Zinc-aluminum-magnesium galvanized sheet is an alloy coating with aluminum (Al) and magnesium (Mg) added to the zinc coating. Its advantages include: salt spray resistance 3-5 times that of ordinary hot-dip galvanized sheet (especially resistance to chloride ion corrosion, suitable for coastal environments); a denser zinc layer and stronger "self-healing ability" after scratching (surrounding zinc, aluminum, and magnesium migrate to the scratched area, delaying rusting of the substrate).
What is the purpose of "passivation treatment" on galvanized sheet?
A: Passivation treatment forms a dense "passivation film" (such as a chromate film or a chromium-free passivation film) on the surface of the zinc coating. Its functions are to: prevent the zinc layer from directly reacting with air and moisture, reducing the formation of white rust; and improve the corrosion resistance and adhesion of the zinc coating (preventing paint from peeling later).
What is the difference between "chromium-free passivation" and "chromium-containing passivation"? A: The key lies in environmental friendliness and corrosion resistance. Chromium passivation (containing hexavalent chromium) offers strong corrosion resistance, but hexavalent chromium is toxic and does not comply with environmental standards (such as EU RoHS). Chromium-free passivation (using zirconium, titanium, etc.) is environmentally friendly and pollution-free, but its corrosion resistance is slightly lower than that of chromium passivation and is currently the mainstream process.
What is the role of "plating flux" in galvanized sheet production?
A: Plating flux (such as ammonium chloride and zinc chloride solution) is used to treat the substrate before hot-dip galvanizing. Its functions are to: remove residual scale and oil stains on the substrate surface, ensuring a clean substrate; and to form a "protective film" on the substrate surface to prevent secondary oxidation before entering the zinc bath, ensuring uniform zinc adhesion.