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After galvanizing, the zinc surface is chemically reactive. During storage and transportation, moisture can react with the zinc to form "white rust"—a powdery corrosion product that damages appearance and performance.
Passivation is a surface treatment applied immediately after galvanizing to suppress this reaction. The passivation layer is extremely thin—typically less than 1 micron—and transparent, adhering to the zinc surface.
| Passivation Type | Chromium Content | Environmental Compliance | Corrosion Performance | Cost Level |
|---|---|---|---|---|
| Hexavalent chromium | Contains Cr(VI) | Restricted/banned in EU | Excellent | Low |
| Trivalent chromium | Contains Cr(III) | Mainstream compliant | Good | Moderate |
| Chromium-free | No chromium | Preferred for regulated markets | Good to very good (improving) | Higher |
Hexavalent chromium offered a unique combination of properties: excellent corrosion inhibition, self-healing behavior at scratches, and low cost. Replacing it required developing entirely new chemistries.
Chromium-free passivation systems typically use organic-inorganic hybrid formulations—often incorporating nano-scale materials, silane compounds, and corrosion inhibitors. The challenge is achieving comparable protection without the self-healing chemistry of chromium.
By 2026, chromium-free passivation has progressed from a niche option to a practical mainstream choice:
Major steel producers have developed and tested chromium-free passivation for galvanized flat steel
Green factory certification increasingly expects chromium-free as the default
Export-oriented producers in Europe have largely completed the transition
Performance gaps remain in some aggressive environments, but for most atmospheric exposure conditions, modern chromium-free systems deliver adequate protection.
When evaluating a supplier's "environmental" claim, ask specifically:
What passivation chemistry is used?
Can you provide a RoHS or REACH compliance declaration?
Is the chromium-free option available for the required coating weight?
Chromium-free passivation represents the current direction of the industry. Understanding the technology helps buyers ask the right questions and avoid accepting vague environmental claims.
