Common Surface Treatments of Hot-Dip Galvanized Steel Coils & Their Properties

Byadmin
Introduction

In modern industrial manufacturing, hot-dip galvanized steel coils have become an indispensable structural material thanks to their excellent corrosion resistance and formability. Different applications, from home appliances and electronics to construction and automotive parts, impose distinct requirements on surface quality and service performance.

This article breaks down the most common surface treatment types for hot-dip galvanized steel coils, explains their core characteristics, advantages, and typical applications, to help you select the right surface finish for your project.

Common Surface Treatment Types & Properties of Hot-Dip Galvanized Steel Coils

1. No Surface Treatment (Bare Surface)

This means no chemical passivation, oiling, or anti-fingerprint coating is applied to the galvanized surface.
  • Characteristics:

    Prone to white rust, scratches, and friction marks during handling, storage, and transportation.

  • Advantages:

    Reduces cleaning and degreasing pressure in downstream processing, lowering energy consumption and carbon emissions.

  • Disadvantages:

    Extremely high requirements for logistics and storage management; high risk of surface quality disputes.

  • Applications:

    Used only when immediate in-house processing or post-treatment is planned.

2. Oiled Only

A basic and widely used surface treatment where a thin layer of anti-rust oil is applied.
  • Characteristics:

    Effectively prevents white rust during storage and transportation.

  • Advantages:

    Cost-effective, highly versatile, and compatible with most general processing.

  • Disadvantages:

    Lower protection compared to passivated or coated surfaces; the oil is typically not intended as stamping or drawing lubricant.

  • Applications:

    General fabrication, structural parts, components with follow-up cleaning or painting.

3. Chromate Passivation & Chromium-Free (Organic) Passivation

Passivation forms a thin protective film on the galvanized layer to enhance corrosion resistance.
  • Characteristics:

    Significantly reduces white rust; provides minor anti-friction and lubrication benefits.

  • Advantages:

    Strong anti-corrosion performance; chromium-free passivation complies with RoHS directives, eliminating harmful hexavalent chromium.

  • Applications:

    General industrial parts, electrical enclosures, and export products requiring environmental compliance.

4. Chromate Passivation + Oiling & Chromium-Free Passivation + Oiling

This combines passivation film with a thin anti-rust oil layer.
  • Characteristics:

    Dual protection for long-term corrosion resistance.

  • Advantages:

    Excellent resistance to humid and marine environments; ideal for long-distance sea transportation.

  • Applications:

    Overseas export orders, especially for Southeast Asia, Middle East, and other tropical or coastal regions.

5. Chromium-Free Anti-Fingerprint (AFP)

A functional coating designed to resist fingerprints and perspiration contamination.
  • Characteristics:

    Prevents white rust; resists stains and sweat marks from manual handling.

  • Advantages:

    Environmentally friendly (chromium-free, RoHS compliant); improves surface appearance; provides moderate stamping lubricity.

  • Applications:

    Home appliances, refrigerators, washing machines, air conditioners, and visible metal components.

6. Self-Lubricating Coating

A functional surface treatment that integrates anti-corrosion and lubricating properties.
  • Characteristics:

    Protects against white rust while greatly improving formability.

  • Advantages:

    Reduces die wear and scratching during stamping, bending, and deep drawing.

  • Applications:

    Complex stamped parts, automotive components, and precision metal forming.

7. Inorganic Solid Lubrication

Often referred to as a pre-phosphating treatment by many manufacturers.
  • Characteristics:

    Forms a hard inorganic film with exceptional lubricity.

  • Advantages:

    Excellent surface hardness, superior deep-drawing performance, and stable coating adhesion.

  • Disadvantages:

    Relatively weaker standalone corrosion resistance.

  • Applications:

    High-strength forming parts, components requiring painting or bonding.

8. Chromium-Free High-Conductivity Anti-Fingerprint

A high-performance coating for electrical and electronic applications.
  • Characteristics:

    Chromium-free, anti-fingerprint, and highly conductive.

  • Advantages:

    Improves electrical grounding performance and enhances EMC (Electromagnetic Compatibility).

  • Applications:

    Office automation equipment, copiers, printers, computers, and electronic enclosures.

Conclusion

In addition to the mainstream surface treatments above, many customized options are available on the market, such as chromium-free self-lubricating, inorganic self-lubricating, and easy-forming self-lubricating coatings.
With advances in chemical technology, global suppliers including Henkel, Nippon Paint, and PPG continue to develop new functional films to meet stricter environmental and performance demands. Essentially, all surface treatments for hot-dip galvanized steel coils work by applying functional coatings to the base metal, so their performance directly depends on film composition and application process.
When planning production, you can choose pre-treated galvanized steel coils or conduct surface treatment after part forming, based on your processing flow, cost budget, and end-use environment.

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