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Development of a Composite Coating for Pre-Coated Automotive Sheet Metal
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English
Abstract
The development of a new corrosion-resistant coating composite for automotive sheet metal is described. The three-layer coating combines the galvanic properties of a thin electroplating with the passivating and barrier protection of an inorganic intermediate layer and an organic outer layer. The combined effect of the composite is to act as three lines of defense against corrosion. The organic top layer provides barrier protection, while the inorganic intermediate layer provides passivation to slow down corrosive reactions once the barrier is breached. The plating layer provides galvanic action as the last line of defense, being called into play only after the initial two coatings are exhausted. The zinc coating then corrodes galvanically to protect the underlying steel.
Corrosion tests indicate that this combined coating is more effective than the individual coatings alone. This composite thus allows a relatively thin zinc electroplating to be used, and welding and forming problems are minimized. Incorporation of internal lubricants in the topcoat allows deliberate control of the lubricity of the coating to permit maximum latitude in forming operations. Metallic pigments in both the inorganic and organic layers form electrically conductive pathways necessary for welding. The baked-on organic surface is compatible with adhesives, thus allowing further freedom in manufacturing.
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Citation
Dorsett, T., "Development of a Composite Coating for Pre-Coated Automotive Sheet Metal," SAE Technical Paper 862027, 1986, https://doi.org/10.4271/862027.Also In
References
- Dorsett T. Brady R. Rininger D. Van de Streek G. “Anti-Corrosion Performance of Coating Systems over Electrogalvanized Steel: Effects of Cyclic Test Variables and Comparative Cyclic Corrosion Resistance of Coated Steels 1986 SAE Congress Detroit
- Riffe W. J. “Solutions to Manufacturing Problems Using Galvanized Steel,” Report SG 85-2 American Society for Metals Detroit 1985
- Gosselin C. A. “The Durability of Lap-Shear Adhesive Bonds Following Accelerated Environmental Testing 1985 SAE Congress Detroit