When a box of plated fasteners looks shiny on arrival but the coating starts to flake off during assembly or on site, everyone is unhappy. Plating peeling is more than a cosmetic problem. Once the zinc or other coating lifts, the base steel is exposed, corrosion speeds up, and your customer loses confidence in both the product and the supplier. In severe cases, loose flakes can also interfere with threads and torque control.
Good news: most plating peeling problems are preventable if buyers, engineers and suppliers cooperate on design, surface preparation and quality control. This article explains what causes plating to peel on fasteners, how to spot early warning signs, and what purchasing and QC teams can do to reduce the risk before parts leave the factory.
1. What “plating peeling” looks like on fasteners
Plating peeling usually appears in one or more of these ways:
- Flakes of zinc or other coating coming off when the fastener is bent slightly or tightened.
- Blisters or bubbles in the coating that burst and reveal bare steel.
- Large regions where the plating lifts at the edges and can be scraped away with a fingernail.
- Ring-shaped peeling around the head-to-shank transition or around thread roots.
- Coating loss after simple handling tests, such as running the bolt through a nut a few times.
It is important to distinguish peeling (poor adhesion between coating and substrate) from wear or damage caused by rough handling. Normal light scratches on packed fasteners are expected; whole areas of coating coming away in sheets are not.
2. Why plating peels: main technical causes
Plating systems for fasteners are well-studied in standards such as ISO 4042 and ASTM B633, which describe zinc coatings for threaded parts and their performance requirements. Behind these standards, several repeatable technical causes are responsible for most peeling cases:
2.1 Poor surface preparation
Good adhesion starts with a clean surface. Common problems include:
- Oil and grease not removed – Cutting fluids or rust inhibitors left on the part can block the plating solution from reaching the steel.
- Incomplete pickling – Remaining oxides or scale create “islands” where the coating cannot bond.
- Smearing from machining – Cold work on the surface can roll oxides into the metal, making them hard to remove.
If pre-treatment is rushed or baths are overloaded, the plating may look complete but have low adhesion, especially at corners and thread roots.
2.2 Incorrect chemistry or process control
Electroplating and mechanical plating lines require tight control of:
- Solution composition and pH
- Temperature and agitation
- Current density and time (for electroplating)
- Impact media and additives (for mechanical plating)
If these parameters drift out of range, the coating may become brittle, porous or poorly bonded. For example, too high a current density can create burned, flaky deposits on edges, while contamination by organics can trap gas at the interface.
2.3 Base metal defects and heat treatment
Fasteners made from poor-quality steel or with surface decarburization, laps and seams can have reduced adhesion. Heat treatment steps (quenching and tempering) may also create oxides or microcracks if not controlled, making it harder for the coating to grip the surface.
High-strength fasteners are often de-embrittled after plating to reduce hydrogen embrittlement risk. If this bake process is not suitable, it may also affect coating properties.
2.4 Over-thick or multi-layer coatings
Very thick zinc coatings, multiple passivations or additional paint layers can generate high internal stress. When the fastener is tightened or flexed, the stressed coating can crack and peel away from the substrate or from an underlying layer.
This is sometimes seen when parts receive both mechanical plating and a heavy paint system, or when galvanizing is followed by thick secondary coatings.
2.5 Mechanical damage during handling
Coating that is well adhered can still be damaged if parts are over-tumbled, dropped or roughly mixed with sharp components. In some cases, what looks like “peeling” is actually severe gouging where the plating is torn off by impact.
Good packing design helps reduce this type of damage, especially during long sea shipments.
3. Why plating peeling matters to buyers and engineers
Plating peeling is a red flag for several reasons:
- Corrosion protection drops sharply – Once the sacrificial layer is gone, bare steel corrodes faster, especially in coastal and industrial environments.
- Appearance and brand value suffer – Visible flakes and patches of bare metal make products look cheap and unreliable.
- Function can be affected – Flakes can jam threads, change friction during tightening and make torque values inconsistent.
- Customer complaints escalate costs – Sorting, rework, replacements and site visits quickly consume any price advantage.
From a procurement point of view, every peeling case is an avoidable cost. Putting some quality focus on plating before shipment is much cheaper than handling returns after installation.
4. How to build plating requirements into your specifications
Many problems start because the plating requirement in a purchase order says only “zinc plated” or “galvanized”. That leaves too much room for interpretation. A clearer specification should cover at least the following points.
4.1 Define coating type and standard
Where possible, refer to recognized standards rather than generic words:
- Electroplated zinc to a specific thickness, referring to standards such as ISO 4042 or ASTM B633.
- Mechanical zinc plating for certain high-strength fasteners if required.
- Zinc flake coatings where higher corrosion resistance and good thread fit are needed.
- Hot dip galvanizing for structural or outdoor applications.
You can list coating types differently for each product family, for example:
- General bolts and nuts: electroplated zinc.
- Structural bolts and washers: hot dip galvanized.
- Decking screws: zinc flake or similar high-performance system.
4.2 Specify thickness and performance level
Instead of saying “zinc plated”, specify a thickness range (for example 8–12 μm) or performance requirement (for example neutral salt spray hours) that suits the environment. Standards and technical articles from organisations such as ASTM and ISO provide guidance on coating classes for different service conditions.
Useful general resources include:
https://www.astm.org/
https://www.iso.org/
4.3 Clarify chromate / passivation and topcoats
Passivation (trivalent chromate or similar) and sealers greatly influence corrosion resistance and colour. Make clear whether you require:
- Clear, yellow, black or other passivation appearance.
- Additional topcoats (for example organic sealers) for higher performance.
- Restrictions on hexavalent chromium for environmental compliance.
4.4 Address hydrogen embrittlement risk
For high-strength parts (typically above property class 10.9 or Rockwell C 39), electroplating can introduce hydrogen embrittlement risk. If you are buying such fasteners, consider specifying:
- Mechanical or zinc flake coating instead of standard electroplated zinc.
- Post-plating baking conditions (temperature and time).
- Any testing requirements, such as sustained load tests on representative samples.
5. Incoming inspection focused on plating adhesion
A simple incoming inspection routine can catch many plating peeling issues before fasteners reach your customer.
5.1 Visual inspection
On a representative sample from each lot:
- Check for blisters, bubbles, cracks and flaking on heads and threads.
- Look at edges, under the head and in thread roots where adhesion is often weakest.
- Compare colour and gloss between cartons to find process variation.
Any large-area peeling or widespread blistering should trigger a hold or rejection decision.
5.2 Simple adhesion tests
Production plating lines often use basic adhesion tests such as:
- Bending a coated metal strip around a mandrel.
- Cross-hatch scribe with tape pull.
- Moderate deformation (for example compressing a spring washer) to see whether coating stays attached.
For fasteners, practical warehouse tests include:
- Running a bolt repeatedly through a nut and inspecting for flaking.
- Lightly hammering or pressing a screw head and checking edges.
- Scratching a small area with a sharp tool (without cutting into base metal) to see how the coating behaves.
These simple tests are not a replacement for laboratory methods, but they give quick feedback on adhesion quality.
5.3 Coating thickness checks
Use a coating thickness gauge to confirm that the layer is within your specified range. Too thin a layer may corrode quickly; too thick a layer can crack or jam threads, especially on fine pitches.
Recording thickness measurements over time helps you spot processes that drift.
5.4 Documentation review
Ask for plating certificates or process reports from your supplier, especially for critical items. Check that:
- The coating system and thickness match the standard you requested.
- De-embrittlement bake records are present for high-strength parts where required.
- Any salt spray or performance tests have been run on representative samples.
If documentation is missing or inconsistent, treat that as a quality risk alongside physical defects.
6. Working with your supplier to prevent plating peeling
Plating quality is a shared responsibility. Buyers do not control the plating line, but they can strongly influence process stability through clear requirements and cooperation.
6.1 Choose suppliers with plating and QC capability
A fastener supplier who has its own cold forming and in-house or closely controlled plating resources, plus an inspection room, can respond faster to adhesion issues. They can:
- Adjust pre-treatment, bath chemistry and baking schedules.
- Run adhesion and thickness tests during production.
- Isolate and rework suspect batches before shipment.
Linkworld, for example, focuses on cold formed fasteners such as bolts, nuts, washers and screws, and also integrates stamping, machining and rigging parts from partner factories. The team uses internal QC and inspection facilities to check dimensions, coatings and packing before exporting to markets like Australia and New Zealand.
You can learn more about their background here:
https://linkworldfast.com/about-us/
6.2 Share problem samples and photos
When you see plating peeling, good communication helps:
- Keep failed samples and take clear photos of how and where the coating is lifting.
- Describe the environment and how the customer used the product.
- Share installation torque values, tools and any cleaning or chemical exposure on site.
This information allows the supplier’s plating team to trace root causes, whether they are pre-treatment, plating chemistry or mechanical damage.
6.3 Agree on control plans and trial lots
For high-risk applications (for example coastal outdoor projects, structural or safety-critical parts), consider:
- Trial lots with enhanced testing (adhesion tests, more frequent thickness checks, salt spray).
- Jointly defined control plans covering pre-treatment, plating, baking and packing.
- Clear acceptance criteria for incoming inspection at your warehouse.
Once a stable process is proven, you can gradually relax sampling intensity while still monitoring key indicators.
6.4 Improve packing to protect the coating
Even good plating can be damaged by bad packing. Talk with your supplier about:
- Using plastic bags or inner boxes inside master cartons.
- Limiting carton weight to reduce drop damage.
- Separating sharp components from softer ones.
- Selecting pallet and wrapping methods that keep cartons stable and dry.
You can see typical packing-related product groupings here:
https://linkworldfast.com/products/
7. Choosing coatings and fastener types to reduce peeling risk
Sometimes the best way to avoid plating peeling is to choose a different coating or fastener type in the design stage.
7.1 Consider zinc flake or mechanical plating for high-strength bolts
For very high-strength bolts and studs, mechanical zinc or zinc flake systems can reduce the risk of hydrogen embrittlement, and they generally have good adhesion and uniform thickness. They are often chosen for automotive and structural components where both performance and thread fit are critical.
7.2 Use hot dip galvanizing where heavy duty protection is needed
For structural steelwork, marine or highly corrosive environments, hot dip galvanizing remains a robust option. Although it can change thread dimensions and friction, proper design and nut over-tapping can handle this. The key from a peeling perspective is good surface preparation and smooth handling after galvanizing.
7.3 Match fastener material to the environment
Sometimes a better option than thick plating is stainless steel or other corrosion-resistant materials, especially for:
- Coastal decking screws
- Marine and rigging hardware
- Components in chemical plants
Rigging and marine fasteners, such as chains and shackles, often benefit from stainless or heavily galvanized finishes. You can explore related products here:
https://linkworldfast.com/product-category/riggings/
For general construction fasteners, see:
https://linkworldfast.com/product-category/bolts-nuts-washers/
https://linkworldfast.com/product-category/screws/
8. Procurement checklist to avoid plating peeling
Before you place your next fastener order, run through this short checklist:
- Have you defined the coating type and standard clearly?
- Electroplated zinc, mechanical plating, zinc flake, hot dip galvanized, etc.
- Did you specify thickness or performance class?
- For example, a target μm range or salt spray requirement suitable for the environment.
- Are hydrogen embrittlement risks addressed?
- Coating choice and de-embrittlement bake for high-strength parts.
- Do you have agreed adhesion and appearance criteria?
- Maximum allowable peeling, blistering, rust and colour variation.
- Is incoming inspection set up to check plating?
- Visual, simple adhesion tests, thickness checks and documentation review.
- Does your supplier have plating control and QC capability?
- Ability to adjust processes, test coatings and trace batches.
- Is packing suitable for long transport and handling?
- Inner bags, strong cartons, stable pallets and moisture protection.
- Are you keeping good records of issues and feedback?
- Photos, batch numbers and corrective actions shared with the supplier.
If you can answer “yes” to most of these questions, your risk of plating peeling will be much lower.
9. Conclusion
Plating peeling on fasteners is frustrating, but it is rarely random. In most cases, the root causes sit in a small set of familiar problems: surface preparation, process control, coating choice and handling. As a buyer or engineer, you do not need to become a plating chemist, but you can greatly reduce risk by tightening specifications, running smart incoming inspections and working closely with your fastener manufacturer.
If you are reviewing your current plating requirements or planning a new project, you are welcome to discuss your fastener list, coating preferences and packing ideas with a supplier like Linkworld. With in-house cold forming, integrated partner workshops and a dedicated QC team, they can help you choose coating systems and inspection methods that match your environment and quality expectations.
For more information or to send your drawings and BOM, you can visit:
https://linkworldfast.com/about-us/
https://linkworldfast.com/products/
https://linkworldfast.com/contact/
They can work with you to reduce plating peeling problems and deliver fasteners that stay protected and presentable throughout their service life.