Passivation is a key step in the post-processing of electroplating, which significantly improves the corrosion resistance, appearance stability and functionality of the plated parts by forming a dense protective film on the surface of the metal plating.
Author: Anna
Passivation is a key step in the post-processing of electroplating, which significantly improves the corrosion resistance, appearance stability and functionality of plated parts by forming a dense protective film on the surface of the metal plating. Below is the core role of passivation and its detailed description:
I. The core role of passivation
1. Improvement of corrosion resistance
Seal the micropores of the plating layer:
There are microscopic pores on the surface of plating layer (e.g. zinc, nickel, chromium), passivation solution (e.g. chromate, molybdate) can fill these pores and block the penetration of moisture, oxygen and corrosive media.
Formation of passivation film:
The passivation solution reacts with the plated metal to generate a chemically inert film (e.g. chromate passivation generates Cr₂O₃ or Cr(OH)₃), which delays the oxidation of the plated layer.
Effect: Salt spray test time can be extended by 50%-300% (e.g. galvanized layer is upgraded from 72 hours to more than 200 hours).
2. Preventing discoloration and white rust
Inhibits oxidation:
Zinc, copper and other active metals are prone to oxidation in humid environments (e.g. Zn₅(OH)₈Cl₂-H₂O for zinc), and passivation film can significantly slow down this process.
Maintaining Appearance:
Passivated plating is more uniform in color (e.g., zinc passivated appears blue-white, colored, or black) and avoids darkening or spotting caused by oxidation.
3. Enhances plating bonding
Priming for subsequent painting:
Passivation film can be used as a base for paint and powder coating to improve coating adhesion (e.g. automotive parts need to be passivated and then painted after galvanizing).
4. Environmentally friendly and functional
Alternative to harmful processes:
Trivalent Chromium passivation (Cr³⁺) can replace the traditional hexavalent chromium (Cr⁶⁺), which is compliant with RoHS and REACH regulations.
Special features:
Conductive passivation (for electronic components);
Self-repairing passivation (partial repair of damaged film layers).
II. Examples of application scenarios
Galvanized parts: guardrail, fasteners (chromate passivation against white rust).
Nickel-plated parts: electronic contacts (passivation against oxidation to maintain electrical conductivity).
Chrome plated parts: automotive trim (sealer passivation to enhance gloss).
Passivation is an indispensable part of the plating process as it significantly improves the corrosion resistance, appearance stability and functionality of plated parts through chemical film formation and pore closure. The choice of passivation type needs to be balanced between performance and environmental requirements (e.g. trivalent chromium or chromium-free processes are preferred), and the process parameters need to be strictly controlled to ensure quality.