Failure analysis
Magnet Coating Peeling or Blistering: Root Causes to Check
A peeling magnet coating is a symptom, not a complete root cause. Separate coating lift or blistering from brittle-part chipping, impact, edge damage, contamination, corrosion beneath the coating, incompatible cleaning or adhesive chemistry, press-fit stress, trapped moisture, and storage or handling history. Preserve the part and compare location, layers, interfaces, environment, and reference samples before changing the coating.
First identify what is actually peeling
A visible flap or flake may be one coating layer, several layers, corrosion product, adhesive, residue, packaging material, or a fragment attached to a chipped magnet edge. Record the full part, exact location, affected area, layer colour and texture, substrate appearance, and nearby mechanical or chemical interfaces before cleaning or scraping.
Compare affected parts with retained or unaffected parts from the same delivery when available. The useful question is not only “which coating was ordered?” but “where did separation begin, what condition reached that location, and what evidence distinguishes coating failure from mechanical or corrosion damage?”
Coating-failure cause tree
| Observed condition | First separation | Evidence to preserve | Controlled next step |
|---|---|---|---|
| Blister or local lift | Coating separation versus residue or trapped fluid. | Location map, intact reference area, environment, cleaning, storage, and assembly history. | Inspect layer boundary and underlying surface without destroying all evidence. |
| Flake or peel | Adhesion/cohesion issue versus impact, bending, press-fit, or edge damage. | Flake surfaces, edge condition, mating parts, loads, handling, and coating definition. | Identify whether failure began at substrate, within a layer, or from mechanical damage. |
| Crack or chip | Brittle magnet fracture versus coating-only damage. | Magnified images, geometry, corners, holes, impacts, fixture contacts, and assembly sequence. | Contain parts and review mechanical cause plus protection route. |
| Discoloration or powder beneath coating | Contamination versus corrosion through a breach. | Moisture or chemical history, mating metals, deposits, dimensions, magnetic and functional comparison. | Route to corrosion analysis before cleaning, reuse, recoating, or material change. |
| Recurring field failure | Design or process mismatch versus isolated damage. | Lot pattern, position pattern, packaging, cleaning, assembly, exposure, and acceptance records. | Update drawing, surface route, handling, assembly, inspection, and validation together. |
Mechanical damage can look like coating adhesion failure
Sintered magnets are brittle. An impact, sharp edge, countersink, hole, uncontrolled clamp, press fit, assembly interference, fixture contact, abrasive handling, or part-to-part collision can chip the substrate and carry coating away with it. If magnetic material is attached to the flake or the edge is fractured, investigate mechanical loading and geometry as well as the surface route.
Cleaning, adhesive, and assembly chemistry can change the interface
Cleaners, residues, oils, release agents, adhesives, primers, curing conditions, heat, moisture, and chemical exposure may affect coating, bond, or the interface beneath it. Record the actual products, concentrations, contact time, temperature, cure, rinse, drying, and delay before assembly. A compatible coating name does not guarantee compatibility with an uncontrolled process.
Check for corrosion beneath or beside the coating
Blistering, dark deposits, powder, pitting, swelling, or material loss can indicate an exposure path beneath a lifted area or through a chip, pore, edge, hole, masked region, or trapped-fluid interface. Use the NdFeB corrosion-path guide to keep contamination, coating breach, substrate attack, material loss, and functional consequences separate.
Preserve evidence before destructive examination
- Contain affected and unaffected parts and record delivery, lot, position, and assembly context.
- Photograph the full part, defect, edges, interfaces, loose flakes, and reference parts with scale and consistent lighting.
- Record coating specification, finished dimensions, masking, handling, packaging, storage, cleaning, adhesive, cure, assembly loads, and service exposure.
- Map whether the condition repeats by face, edge, cavity, contact point, assembly position, or lot.
- Compare dimensions, magnetic or functional output, and retention using the same method and condition.
- Retain representative evidence before sectioning, cleaning, scraping, or other destructive analysis.
Do not change only the coating name
The coating selection guide helps compare protection routes around environment, dimensional build, bonding, and handling. A recurrence-prevention decision may also require geometry changes, edge controls, press or clamp limits, drainage, sealing, cleaning controls, assembly sequence, packaging, inspection, and representative environmental or functional validation.
What to send for coating-failure review or an RFQ
Provide the controlled drawing, material and coating definition, finished dimensions and edge condition, defect photographs and location map, loose flakes where available, mating materials, adhesive and cleaning process, assembly method and loads, environment and temperature history, packaging and storage, affected quantity, reference parts, and comparable dimensional, magnetic, retention, or functional results. Review the NdFeB product route, Custom Capabilities, Quality and inspection planning, and the existing RFQ path.
Sources and evidence boundary
- Arnold Magnetic Technologies: Neodymium Iron Boron Magnets supports the relationship among NdFeB, surface protection, geometry, and application conditions; publisher values and capabilities are not Elite specifications.
- K&J Magnetics: What Magnet Coating Should I Use? supports application-led coating selection and the absence of one universal coating; seller claims are not transferred.
- The dated Google US SERP research was used only for symptom vocabulary, result types, repeated questions, and the diagnostic coverage gap.
EM-FAIL-04 is an original Elite Magnets framework. No visible symptom alone establishes a plating-process defect, coating life, root cause, rework, or reuse decision.
Engineering note: Final disposition depends on the actual layer boundary, substrate, part geometry, mechanical and chemical history, environment, assembly, inspection method, product risk, and approved acceptance evidence.
Frequently asked questions
Why does a magnet coating peel?
Possible paths include coating separation, substrate or edge chipping, impact, press-fit or assembly stress, contamination, corrosion beneath a breach, incompatible cleaning or adhesive chemistry, moisture, and handling history.
Is peeling always a plating adhesion problem?
No. Preserve the flake and inspect the layer boundary and substrate. A brittle-part fracture, mechanical damage, residue, corrosion product, or assembly interference can look like coating adhesion failure.
Can a peeling coating cause magnet corrosion?
A breach can create an exposure path, but corrosion depends on the susceptible material, moisture or chemicals, edge and pore condition, trapped fluid, mating materials, storage, and service environment.
Can the magnet simply be recoated?
There is no universal recoat answer. Rework can change dimensions, cleanliness, edges, bonding, magnetized-part handling, traceability, and product risk. Disposition needs controlled evidence and approval.
What evidence should be sent for a coating-failure review?
Send the drawing, material and coating definition, defect map and photographs, loose flakes, edges and interfaces, cleaning and adhesive process, assembly loads, environment, packaging, affected quantity, reference parts, and comparable results.