Introduction
Permanent magnets—especially high-performance NdFeB—are inherently susceptible to corrosion, oxidation, and surface degradation when exposed to moisture, salt spray, or mechanical abrasion.
To ensure long service life and stable magnetic performance, selecting the correct protective coating is essential.
This guide provides a detailed comparison of mainstream magnet coatings, selection criteria for industrial customers, and how manufacturers—including suppliers like Magnetstek—tailor coating solutions for demanding applications such as robotics, motors, sensors, and outdoor equipment.
Why Magnet Coatings Matter
Corrosion Protection
NdFeB magnets contain iron and rare-earth elements that oxidize rapidly in humid or salt-rich environments.
Coatings prevent surface reactions and extend operational lifetime.
Wear & Abrasion Resistance
Many assemblies involve sliding, rotating, or repeated mechanical contact.
Surface coatings protect the magnet from chipping and micro-fractures.
Chemical Resistance
Coatings must resist acids, alkalis, oils, cleaning chemicals, and sterilization processes.
Biocompatibility
Medical, wearable, and implantable devices require coatings safe for skin or biological contact.
Common Magnet Coatings and Their Performance Profiles
1. Nickel–Copper–Nickel (NiCuNi): The Industry Standard
Overview
- Most widely used coating for sintered NdFeB.
- Provides bright metallic finish.
- Typical thickness: 12–25 μm.
Strengths
- Good corrosion resistance
- Good wear resistance
- Rigid and strong adhesion
- Cost-effective
Limitations
- Not suitable for high salt-spray environments
- Can crack under mechanical shock
Best For
Motors, sensors, general industrial assemblies, robotics.
2. Epoxy Coating (Black / Gray / Color)
Overview
Epoxy provides a polymer-based, highly corrosion-resistant coating.
Strengths
- Excellent resistance to moisture and salt spray
- Good chemical resistance
- Custom colors possible
Limitations
- Lower wear resistance
- Can be damaged by sharp edges or impacts
Best For
Outdoor applications, corrosive environments, security devices, encapsulated assemblies.
3. Zinc (Zn) Coating
Overview
Economical metallic coating.
Strengths
- Low cost
- Good initial corrosion protection
- Matte finish
Limitations
- Weaker corrosion resistance compared to NiCuNi & epoxy
- Less durable under abrasion
Best For
Low-cost consumer electronics and non-harsh environments.
4. Phosphate Coating
Overview
Conversion coating primarily for bonded magnets.
Strengths
- Improves adhesion for bonding
- Low cost
- Provides minimal corrosion resistance
Limitations
- Not suitable as a sole corrosion barrier
Best For
Bonded/epoxy-bonded NdFeB or ferrite magnets.
5. Everlube or PTFE (Teflon) Coating
Overview
Provides a friction-reducing, non-stick surface.
Strengths
- Excellent wear and sliding resistance
- Good chemical stability
- Very low friction coefficient
Limitations
- Higher cost
- Moderate corrosion protection
Best For
Precision actuators, linear drives, valve systems.
6. Gold (Au) Coating
Overview
Electroplated thin gold layer.
Strengths
- Exceptional corrosion resistance
- Biocompatible and hypoallergenic
- Suitable for sensitive environments
Limitations
- High cost
- Thin, susceptible to wear
Best For
Medical sensors, implants, laboratory devices.
7. Parylene Coating (Parylene C / N / F)
Overview
Chemical Vapor Deposition (CVD) polymer coating providing a uniform, pinhole-free protective layer.
Strengths
- Excellent moisture barrier
- Biocompatible
- Uniform thickness even on complex shapes
- High dielectric strength
Limitations
- Higher cost
- Longer production cycle
Best For
Medical devices, underwater sensors, hermetically sealed magnet components.
Selecting the Right Coating for Real Applications
A. High Humidity or Outdoor Environments
Recommended coatings:
- Epoxy
- Parylene
- NiCuNi + Epoxy hybrid
Use cases: drones, outdoor motors, renewable energy equipment.
B. High Wear or Repeated Mechanical Contact
Recommended coatings:
- NiCuNi
- PTFE (Teflon)
- Hard nickel variants
Use cases: robotics joints, high-speed rotors, sliding assemblies.
C. Salt Spray / Marine Conditions
Recommended coatings:
- Epoxy (best economy choice)
- Parylene C (premium option)
- NiCuNi + Epoxy double coating
Use cases: marine instruments, offshore sensors.
D. Medical / Skin Contact / Wearables
Recommended coatings:
- Parylene C
- Gold plating
- Biocompatible epoxy
Use cases: medical device magnets, wearable locking systems.
E. High Temperature Environments
Coating is secondary; material grade is primary (SmCo, NdFeB SH–AH).
Best paired coatings:
- NiCuNi
- Phosphate (for bonded magnets)
Use cases: EV motors, aerospace actuators, industrial servo motors.
xHow Manufacturers Validate Coating Quality
Salt Spray Test (ASTM B117)
Measures corrosion resistance under accelerated conditions.
Cross-Cut Adhesion Test
Evaluates bonding strength of coatings.
Coating Thickness Measurement
Performed via XRF or magnetic induction.
Environmental Cycling
Heat–cold–humidity cycling simulates real product lifecycle.
Why Coating Quality Matters in Custom Assemblies
Magnet assemblies—especially Halbach arrays, multi-pole rings, or rotor magnets—often involve:
- Tight tolerances
- Close mechanical interfaces
- High rotational stress
- Exposure to lubricants or cooling fluids
A failed coating can lead to:
- Surface pitting
- Loss of magnetic strength
- Rotor imbalance
- Catastrophic mechanical failure
Manufacturers and integrators typically specify:
- Coating type
- Thickness range
- Salt spray duration
- Adhesion grade
- Edge protection requirements
Conclusion
Choosing the right magnet coating is essential for ensuring durability, reliability, and long-term performance in demanding industrial environments.
By understanding application requirements—humidity, temperature, mechanical stress, and chemical exposure—engineers can select the ideal coating to maximize magnet lifespan and protect equipment performance.
Magnetstek supports OEM and engineering customers with a wide range of magnet materials, coatings, and fully custom magnetic assemblies designed for long-term operation in harsh environments.