Q:What are the core factors affecting the corrosion resistance of electrogalvanized steel?
A:1. Coating thickness
Basic protection mechanism: The zinc layer acts as a "sacrificial anode" to protect the steel substrate by self-oxidation (forming ZnO/Zn (OH)₂). The thicker the thickness, the longer the corrosion time.
2. Passivation process
No passivation (bare zinc layer): poor corrosion resistance, easy to white rust (zinc oxide), only used for temporary protection.
3. Use environment
Neutral atmospheric environment (such as indoors, dry areas): The zinc layer has a low corrosion rate, and a 10 μm coating can protect for 5-10 years.
Q:What are the common thickness standards for electrogalvanizing?
A:Decorative galvanizing: 3–8 μm, salt spray resistance test is about 24–72 hours (such as furniture hardware);
Protective galvanizing: 8–25 μm, salt spray resistance can reach 100–1000 hours (such as automobile bolts need 8–12 μm, salt spray resistance for more than 200 hours).
Q:How does a special environment affect the corrosion resistance of electrogalvanized steel?
A:Salt spray environment (ocean, northern snow-melting agent road sections): Chloride ions accelerate the corrosion of the zinc layer, requiring a coating ≥ 20 μm + trivalent chromium passivation (salt spray resistance ≥ 500 hours); ◦ Acidic/alkaline environment (industrial areas, agricultural areas): Sulfur dioxide (SO₂), ammonia (NH₃), etc. accelerate corrosion, requiring an increased coating thickness or a closed coating.
Q:What is the effect of passivation process on the corrosion resistance of electrogalvanized products?
A:No passivation (bare zinc layer): poor corrosion resistance, easy to white rust (zinc oxide), only used for temporary protection.
Chromate passivation (traditional process, gradually eliminated):
Hexavalent chromium passivation: forms a passivation film containing Cr⁶⁺, which can withstand salt spray for 500-1000 hours, but is restricted by regulations such as RoHS due to toxicity.
Chromium-free/low-chromium passivation (mainstream process):
Trivalent chromium passivation: forms a Cr³⁺ composite film, which can withstand salt spray for 200-500 hours, and significantly improves environmental protection;
Silane/organic sealant: seals the micropores of the zinc layer through a molecular membrane, which can withstand salt spray for 100-300 hours, and is suitable for scenes with high environmental protection requirements.
Q:What is the corrosion resistance performance in typical application scenarios?
A:1. Automobile bolts:
Salt spray resistance test 200–500 hours, service life of about 5–8 years in urban road environment.
2. Outdoor clothes drying rack: service life of about 3–5 years in coastal areas, 8–10 years in inland areas. 3. Electronic component housing: long-term protection in indoor environment (more than 10 years), but easy to rust when exposed to sweat or humid air.