Galvanizing Process And The Trend Of Choosing Modern Passive Chemicals

In the metal processing and surface treatment industry, galvanizing has long been considered an effective solution for protecting steel from corrosion, extending product lifespan, and enhancing commercial value. However, in reality, many galvanized products still develop white rust after only a short period of use or storage. The cause lies not only in the quality of the galvanizing layer but also depends on the passivation process – the final treatment step that determines the product’s corrosion resistance.

So what are the steps in a standard galvanizing process? Should businesses choose Cr6+, Cr3+ passivation chemicals, or chrome-free technology? These are questions that many manufacturers of steel, mechanical components, and metal accessories are interested in.

Industrial Standard Galvanizing and Passivation Process

To create a durable protective coating, the post-plating process needs to be tightly controlled from cleaning to drying.

Step 1: Rinse After Plating

After the galvanizing process is complete, the product surface still retains residual chemicals and additives from the galvanizing solution.

The goal of this step is to completely remove impurities to prevent contamination of the passivation tank and ensure the quality of the protective film.

Multi-tank backwashing systems are now considered the optimal solution for improving cleaning efficiency and saving water.

Step 2: Surface Activation

After exposure to air, zinc surfaces form a thin oxide layer that reduces the reactivity of passivating chemicals.

Therefore, the product is often immersed in a dilute acid solution for a short time to remove this oxide layer, creating a “fresh” and uniform zinc surface.

Step 3: Passivation – The Heart of the Process

This is the most important step.

The product is immersed in a passivation solution to create an ultra-thin chemically converted film on the zinc surface. This film acts as a protective barrier against moisture, oxygen, and corrosive agents.

The parameters that need to be strictly controlled include:

• Chemical concentration.
• pH value.
• Solution temperature.
• Soaking time.
• Level of stirring.

Even a single parameter exceeding the permissible limit can significantly reduce the corrosion resistance of the coating.

Step 4: Post-Passive Washing

The purpose is to remove any excess chemicals that remain on the surface.

For high-quality products, demineralized water (DI water) is often used in the final stage to minimize blemishes and improve coating uniformity.

Step 5: Drying

The newly formed passive film has a gel-like structure and is quite sensitive to temperature.

Therefore, the drying temperature is usually maintained at 60–70°C to ensure the film is stable and achieves maximum corrosion resistance.

In the context of increasingly stringent environmental standards, Chromium 3+ and Chrome-Free are emerging as optimal alternatives to traditional Chromium 6+.

Factors Determining the Quality of Passive Classes

Many businesses invest in high-quality chemicals but still experience coating instability. The causes often stem from the following factors:

Chemical and Water Quality

Iron impurities, chloride ions, or substandard water can reduce the passivation efficiency and cause black spots or discoloration on the product surface.

Process Control

pH, temperature, and immersion time are three factors that directly affect the color and corrosion resistance of the coating.

Inadequate controls during galvanizing can lead to defects.

Filtration Equipment and Systems

The passivation solution needs to be continuously filtered to remove metal dust and precipitated particles that could cause surface defects.

Operational Skills

Inconsistent control of drip time between tanks, product hanging methods, or operating procedures can all cause variations in product quality between batches.

Environmental Conditions

Metal dust, oil vapors, or other air pollutants in the factory can also affect the adhesion and quality of the coating.

Should you choose a Chromium 6+ , Chromium 3+  , or Chrome-Free passivation chemical ?

The development of international environmental standards has led the surface treatment industry to enter a major transition phase from Cr 6+ to Cr 3+ and non-chromium technologies.

Chromium 6+ is highly effective but is gradually being phased out.

For decades, hexavalent chromium (Chromium 6+) was considered the gold standard due to its superior corrosion resistance and self-healing properties when the coating is scratched.

However, Chromium 6+ is classified as a hazardous chemical, posing a risk to human health and the environment. Therefore, many major markets such as Europe, the US, and Japan have restricted or eliminated the use of this technology.

Chrome 3+: A Solution That Balances Performance and the Environment

Currently, Chromium III (Chromium 3+) technology is becoming the most popular choice in the galvanized steel industry.

Modern Chromium 3+ passive systems offer:

• High corrosion resistance.
• Does not contain harmful Chromium 6+.
• Complies with international environmental standards.
• Maintain consistent aesthetic color.
• Easily integrated into existing production lines.

This is considered the optimal solution for most businesses seeking a balance between technical efficiency and sustainable development requirements.

Chrome-Free – The Trend of the Future

Completely chromium-free passivation systems are gaining increasing attention.

Key advantages include:

• Does not contain Chromium 3+ and Chromium 6+
• Environmentally safe.
• To meet the increasingly stringent RoHS and REACH regulations.
• Suitable for green production strategies.

Although the initial investment cost may be higher, Chrome-Free is predicted to become the mainstream trend in the surface treatment industry in the coming years.

Which Solution Should Businesses Choose?

For export businesses or those aiming for international standards, Cr6+ is no longer a suitable long-term option.

Meanwhile:

• Chromium 3+ is suitable for most current industrial applications, offering high corrosion resistance and meeting environmental requirements.
• Chrome-Free is an ideal choice for businesses pursuing ESG strategies, green manufacturing, and sustainable development.

Current market trends indicate that Chrome 3+ and Chrome-Free are gradually replacing traditional passive Chrome 6+ coatings entirely.

Related Articles

• Flux in Hot-Dip Galvanizing: Role, Composition, and Optimization of Flux Baths to Enhance Coating Quality
• Why Does Galvanized Steel Still Rust? Effective Passivation Solutions for the Metal Industry
• Zinc Plating Chemicals and Common “Problems” of the Plating Layer

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