In many metalworking factories, a significant number of businesses encounter a situation where newly finished galvanized parts, with their bright, attractive surfaces, develop white rust spots after only a few weeks of storage or transportation.
This phenomenon of galvanized steel rusting not only reduces its aesthetic appeal but also results in costly warranty and reprocessing expenses, and negatively impacts the company’s reputation.
According to metal surface treatment experts, the main cause is not the quality of the plating but rather the fact that the passivation process for galvanized steel has not been properly implemented or has been omitted in the production process. An effective passivation solution needs to be applied to improve this situation.
What Is White Rust?
White rust is the formation of a white layer of zinc oxide or hydroxide on the surface of galvanized steel when exposed to a high-humidity environment.
Causes of white rust formation
After plating, the new zinc layer is highly chemically active and readily reacts with:
- Oxygen in the air
- Steam
- Salt and other corrosive agents
In Vietnam’s hot and humid climate, these reactions occur rapidly, forming a white, corroded layer on the metal surface.
Why does galvanized steel rust despite its shiny surface after finishing?
This is because the zinc coating protects the underlying steel through a sacrificial corrosion protection mechanism.
The zinc will corrode first to protect the steel inside.
However, if the zinc surface is not protected by a passivation film, the rate of zinc corrosion will increase significantly, especially in the following environments:
- High humidity
- Coastal air
- Closed storage
- Sea transport process
In reality, many products such as:
- Zinc-plated bolts
- Hinge
- Metal accessories
- Mechanical components
White rust may appear within just a few weeks if not properly passivated.
What is Passivity?
Passivation is a post-plating chemical treatment process that creates an extremely thin conversion film on the metal surface.
This film acts as an “invisible shield,” separating the galvanized coating from the external environment.
The passive membrane helps to:
- Prevent moisture from coming into contact with the metal.
- Limit oxidation reactions
- Reduces the formation of white rust.
- Increase the lifespan of the plating layer.
- Maintain surface shine.
- Improve corrosion resistance
As a result, the product’s protection time can be increased many times compared to conventional plating.
Benefits of Chemical Passivation
Today, passivity has become an almost mandatory requirement for many industries:
- Construction steel
- Household electrical appliances
- Precision engineering
- Car
- Metal structure
- Industrial equipment
Enhance Corrosion Resistance
The protective film helps increase the resistance time in the tests:
- Salt Spray Test (NSS)
- Humidity Test
- Corrosion Resistance Test
Increase Product Value
- Reduce the rate of defective goods.
- Reduce warranty costs.
- Keeps surfaces shiny and beautiful for longer.
- Enhance brand image
Improving Machining Efficiency
Some modern passivation technologies also help:
- Reduce friction during stamping.
- Dry shaping support
- Increase paint adhesion
- Increases adhesion of the next coat.
Meets Environmental Standards
New chemical systems used:
- Chromium III (Cr3+)
- Chrome-Free
This helps meet international environmental standards such as RoHS and REACH.
PRIMECOAT® Z838 – High-Performance Chromium III Passivation Solution
PRIMECOAT® Z838 – 4P is a Chromium III passivation chemical developed by AD International BV (Netherlands).
Outstanding Advantages
- Does not contain harmful Chromium VI.
- Fluoride-free
- Increased corrosion resistance
- Reduce friction during shaping.
- Improve paint adhesion.
- Anti-fingerprint
- Supports Passivation and TOC
- Suitable for galvanized steel, cold-rolled steel, and ZAM steel.
Find out more product details here ⇓
PRIMECOAT® Z908 VH – Chromium-Free Passivation Technology
PRIMECOAT® Z908 VH is an advanced phosphate-based chrome-free solution.
Key Benefits
- Completely chromium-free.
- High corrosion resistance
- Environmentally friendly
- An effective replacement for traditional chromium systems.
- Maintain surface aesthetics
Applications for Galvanized Steel
- Galvanized steel (Z)
- Zinc Magnesium (ZM)
- Galvannealed (GA)
- Aluzinc (AZ)
- Electro Galvanized (EG)
Find out more product details here ⇓
DK-Chemicals: Metal surface pretreatment solutions for industry
DK-Chemicals provides chemical surface treatment solutions for metals serving the aluminum, galvanized sheet, color-coated steel, coil-coating, and related industrial applications.
With a focus on providing advanced, environmentally friendly technologies that meet modern production requirements, DK-Chemicals partners with customers in selecting suitable pre-treatment solutions, optimizing surface quality, and enhancing product durability after coating.
Contact DK Chemicals’ technical team today for detailed advice: .
DK Chemical Company Limited
Address: 50 Street No. 12, Cityland Park Hills Residential Area, Go Vap Ward, Ho Chi Minh City
Hotline: 0909678599
Email: de@dk-chemicals.vn
