Hot-Dip Galvanized Steel Surface Treatments: Passivation, Oiling and Anti-Fingerprint Coatings

Hot-dip galvanizing provides steel with a protective zinc coating, but zinc coating weight is not the only factor affecting product performance. The post-treatment applied after galvanizing can significantly influence storage stability, forming behavior, surface appearance, paint adhesion and electrical conductivity.

Passivation, oiling and anti-fingerprint coating are three common surface treatment options for hot-dip galvanized steel coil. Although they are sometimes treated as interchangeable, each serves a different purpose. Buyers should select the treatment according to transportation conditions, downstream processing and the final application.

Why Does Hot-Dip Galvanized Steel Need Surface Treatment?

Freshly galvanized steel can react with moisture, especially when sheets or coil laps are tightly stacked and cannot dry properly. This reaction may create white corrosion products, commonly called white rust or wet-storage stain.

A post-treatment adds temporary protection or additional functionality to the zinc surface. Depending on the selected treatment, it can:

• Reduce the risk of white rust during transportation and storage

• Improve lubrication during stamping and roll forming

• Reduce visible fingerprints and handling marks

• Improve scratch resistance

• Support paint adhesion or direct coating

• Control electrical conductivity

• Help maintain a more consistent surface appearance

Surface treatment does not replace the zinc coating. The zinc coating provides the main corrosion protection, while the post-treatment protects or modifies the zinc surface. Buyers therefore need to specify both coating weight, such as Z120 or Z275, and the required surface treatment.

What Is Passivation?

Passivation is a chemical treatment that creates a very thin protective film on the galvanized surface. Its main purpose is to slow the reaction between zinc, oxygen and moisture, reducing the risk of white rust during shipping and storage.

The passivation layer is normally dry and almost invisible. It does not significantly change the dimensions of the steel sheet or coil.

Main Benefits of Passivation

Passivation is commonly selected because it provides:

• Better resistance to wet-storage stain

• Cleaner coil surfaces during transportation

• Less oil contamination in the workshop

• Easier handling than heavily oiled steel

• Additional temporary protection in humid conditions

It is suitable for coils that may remain in warehouses for extended periods or travel long distances by sea.

Chromium-Containing and Chromium-Free Passivation

Passivation formulations may contain chromium or use chromium-free chemical systems. Because environmental and material restrictions vary between markets and applications, buyers should not simply write “passivated” in a purchase order.

The order should clearly identify whether chromium-free treatment is required. Buyers may also request the relevant material declaration, test report or compliance document from the supplier.

Chromium-free treatments are increasingly used for household appliances, construction products and components supplied to environmentally controlled manufacturing chains. However, their corrosion resistance, paintability and conductivity may differ between formulations. Sample testing is recommended before mass production.

Limitations of Passivation

Passivation mainly provides temporary surface protection. It should not be considered a substitute for a suitable zinc coating weight or a properly designed paint system in severe outdoor environments.

The treatment may also affect painting, adhesive bonding, welding or electrical contact resistance. If the galvanized steel will be painted, bonded or electrically grounded, the buyer should confirm compatibility with the supplier before ordering.

What Is Oiling?

Oiling applies a thin layer of protective oil to the galvanized surface. Unlike passivation, it does not create a chemical conversion layer. The oil forms a physical barrier between the zinc surface and the surrounding moisture.

Oiling can also provide lubrication during subsequent processing.

Main Benefits of Oiling

Oiled hot-dip galvanized steel offers several practical advantages:

• Temporary protection against moisture and white rust

• Reduced friction during stamping and bending

• Lower risk of surface scratches during handling

• Improved coil unwinding and sheet separation

• Reduced zinc pickup on forming tools

• Better protection during transportation

Oiling is often selected for galvanized steel used in stamping, profiling, tube production and general sheet-metal fabrication.

Oil Quantity Matters

Too little oil may not provide sufficient protection or lubrication. Too much oil can create other problems, including:

• Oil leakage from coils

• Dirty packaging and work areas

• Uneven feeding during processing

• Difficulty during welding

• Extra cleaning before painting or bonding

• Surface stains caused by irregular oil distribution

Buyers should specify the oil type and, where necessary, the target oil quantity. The selected oil must also be compatible with the customer’s cleaning system and forming process.

Does Oiled Galvanized Steel Need Cleaning?

If the steel will be painted, powder coated, bonded or sealed, the oil normally needs to be removed. Alkaline cleaning or another approved degreasing method may be used, depending on the oil and subsequent process.

For simple bending or roll forming, the existing oil may be beneficial. For precision stamping, however, the customer should confirm whether additional press lubricant is required.

Passivation Plus Oiling

Passivation and oiling can be combined. In this case, the galvanized surface receives a chemical passivation layer followed by a protective oil film.

This combined treatment offers stronger temporary storage protection than either treatment may provide alone. The oil can also improve lubrication during forming.

Passivation plus oiling is useful when:

• The coil will be transported by sea

• Storage conditions are humid

• The material will be stamped or roll formed

• A longer storage period is expected

• Additional protection is required between production stages

The disadvantage is that cleaning may be required before painting, bonding or applying other surface coatings.

What Is an Anti-Fingerprint Coating?

An anti-fingerprint coating is a thin functional film applied over the galvanized surface. Depending on the formulation, it may be organic, inorganic or a hybrid system.

Its purpose is not to prevent people from touching the steel. Instead, it reduces the visibility of fingerprints, oil marks and handling stains. It can also make the surface easier to clean.

Modern anti-fingerprint treatments may provide several additional properties:

• Improved resistance to white rust

• Better scratch and abrasion resistance

• More consistent surface appearance

• Reduced surface staining during handling

• Improved formability

• Controlled electrical conductivity

• Protection without visible oil

These properties make anti-fingerprint galvanized steel particularly suitable for products where the metal surface remains exposed.

Common Applications

Anti-fingerprint coated galvanized steel is frequently used for:

• Electrical cabinets

• Appliance components

• HVAC equipment

• Computer and electronic housings

• Metal furniture

• Interior building panels

• Cable trays

• Equipment covers

• Control boxes and enclosures

For visible components, buyers should evaluate color consistency, gloss, fingerprint resistance and scratch resistance. A treatment that performs well on an internal electrical part may not provide the appearance required for a decorative appliance panel.

Conductive Anti-Fingerprint Coatings

Some electrical enclosures require both fingerprint resistance and electrical conductivity. A conventional organic film may increase surface electrical resistance, which can affect grounding, electromagnetic shielding or resistance welding.

In these applications, buyers should request a conductive anti-fingerprint treatment and define the required contact resistance. Rosen’s available treatment options include chrome-free fingerprint-resistant N5 and highly conductive fingerprint-resistant NE.

Passivation vs Oiling vs Anti-Fingerprint Coating

How to Choose the Correct Treatment

The best option depends on what happens to the steel after delivery.

For Long-Distance Transportation

Passivation or passivation plus oiling is generally preferred. Coils transported by sea face humidity, condensation and temperature changes, so packaging and dry storage are also important.

For Stamping and Roll Forming

Oiling or passivation plus oiling can reduce friction and protect the zinc coating from tool damage. The oil should be compatible with the forming lubricant and cleaning system.

For Visible Appliance and Equipment Parts

Anti-fingerprint treatment provides a cleaner appearance and reduces visible handling marks. Scratch resistance, gloss and color consistency should be tested using production samples.

For Painting or Powder Coating

Confirm that the treatment is compatible with the cleaning, pretreatment and coating system. Untreated or specially passivated material may be preferred, depending on the production line.

For Welding and Electrical Enclosures

Ask the supplier about weldability and surface resistance. A conductive anti-fingerprint treatment may be required for grounding or electromagnetic shielding applications.

What Buyers Should Include in the Purchase Order

A complete specification should state:

1. Steel grade, such as DX51D+Z or DX53D+Z

2. Steel thickness and width

3. Zinc coating weight

4. Surface quality and spangle requirement

5. Surface treatment code

6. Chromium-free requirement, if applicable

7. Oil type or oil quantity

8. Painting, welding, bonding or forming requirements

9. Electrical conductivity requirements

10. Packaging and storage conditions

Buyers should also request samples when changing suppliers or surface treatment systems. A sample can be used to test forming, cleaning, paint adhesion, welding, conductivity and surface appearance before placing a large order.

Available Hot-Dip Galvanized Steel Treatments

Rosen supplies hot-dip galvanized steel in multiple grades, dimensions, zinc coating weights and surface treatment conditions.

Available options include untreated, oiling, passivation, passivation plus oiling, chromium-free passivation, self-lubricating treatments and fingerprint-resistant coatings. This allows buyers to select the treatment according to storage conditions, processing requirements and final product performance.

Match the Surface Treatment to the Next Process

Passivation is primarily selected for temporary protection against white rust, while oiling adds lubrication and handling protection. Anti-fingerprint coatings are more suitable when appearance, cleanliness or additional functional properties are important. Before ordering, buyers should consider every downstream operation—not only corrosion resistance. Clearly defining forming, painting, welding, bonding and conductivity requirements helps prevent processing problems and ensures that the delivered hot-dip galvanized steel is ready for its intended application.