Magnet Coatings and Surface Treatments: Complete Selection Guide

Why Coatings Matter

Sintered NdFeB magnets contain iron (approximately 64% by weight), making them inherently vulnerable to oxidation. Without surface protection, a bare NdFeB magnet will develop surface rust within days in humid conditions and lose magnetic performance within months.

The right coating choice directly impacts:

• Product lifetime — from months to decades
• Dimensional budget — coatings add 5–50 μm per side
• Cost — from $0.01 to $2+ per piece
• Compliance — some coatings enable medical or food-contact applications

Coating Comparison Table

Detailed Coating Profiles

NiCuNi (Nickel-Copper-Nickel)

The industry standard coating for NdFeB magnets. The three-layer structure provides:

• Nickel base layer: Adhesion to the magnet substrate
• Copper interlayer: Ductile barrier against micro-cracks
• Nickel top layer: Hard, bright surface finish

Advantages:

• Proven reliability with decades of field data
• Smooth, bright surface finish
• Good solderability with flux
• Temperature resistance up to 200°C

Limitations:

• Contains nickel (restricted in EU skin-contact applications under REACH)
• Can chip under impact, exposing substrate
• Not suitable for extended saltwater immersion

Typical thickness: 10–15 μm (standard), 15–25 μm (heavy duty)

Zinc

The most cost-effective coating option for indoor applications.

Advantages:

• 30% lower cost than NiCuNi
• Sacrificial protection (zinc corrodes before the magnet)
• No nickel allergen concern
• Simple plating process

Limitations:

• Lower salt spray resistance (48–96 hours)
• Dull grey appearance (can be chromate-passivated for blue/yellow finishes)
• Limited temperature resistance (120°C)

Best for: HVAC actuators, indoor sensors, cost-sensitive consumer products

Epoxy

A polymer coating applied by electrophoretic deposition (e-coating) or spray.

Advantages:

• Excellent chemical resistance
• High salt spray hours (500–1,000)
• Available in colors (black is most common)
• No metallic allergens
• Electrically insulating

Limitations:

• Softer than metallic coatings (can scratch)
• Thicker than NiCuNi (impacts dimensional budget)
• Temperature limited to 150°C
• UV degradation in prolonged outdoor exposure

Best for: Sensors in harsh environments, water treatment equipment, outdoor applications

Parylene C

A vapor-deposited conformal polymer coating. Applied at room temperature and molecular level, it provides the most uniform coverage of any coating type.

Advantages:

• Perfectly uniform thickness (no edge buildup or pooling)
• Biocompatible (USP Class VI, ISO 10993)
• Excellent chemical and moisture barrier
• Pinhole-free at just 5 μm thickness
• Transparent

Limitations:

• High cost (3–5× of NiCuNi)
• Specialized equipment required (vacuum chamber)
• Temperature limited to 125°C continuous
• Poor adhesion without primer on some substrates

Best for: Medical implants, precision sensors, semiconductor equipment

Gold (Au)

Thin gold plating over nickel or copper base layers.

Advantages:

• Excellent solderability without flux
• Chemically inert
• High conductivity
• Aesthetically premium

Limitations:

• Very expensive (gold material cost)
• Thin layer (typically 2–5 μm)
• Must be applied over NiCu base
• Soft, easily scratched

Best for: SMD magnet components, RF applications, connectors with integrated magnets

PTFE (Teflon)

A fluoropolymer coating with exceptional chemical resistance.

Advantages:

• Resistant to virtually all chemicals and solvents
• Low friction (useful in sliding applications)
• FDA food-contact compliant
• High temperature resistance (up to 260°C)

Limitations:

• Thick coating (15–40 μm)
• Poor adhesion without etching/primer
• Higher cost than standard coatings
• Limited availability from magnet suppliers

Best for: Food processing equipment, chemical industry, high-temperature chemical environments

Coating Selection Decision Guide

Answer these three questions to choose your coating:

1. What is the operating environment?

2. What is the temperature range?

3. What is the dimensional budget?

If your tolerance budget is tight (±0.02 mm), coating thickness matters:

Coating Specifications for Your RFQ

When specifying coatings in your RFQ, include:

1. Coating type (e.g., NiCuNi)
2. Thickness range (e.g., 10–15 μm per side)
3. Salt spray requirement (e.g., minimum 200 hours per ASTM B117)
4. Whether dimensions are pre- or post-coating
5. Color (for epoxy: black, grey, blue, etc.)
6. Compliance requirements (RoHS, REACH, biocompatibility)

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Need help selecting the right coating for your magnets? Submit your RFQ with your operating environment details and we'll recommend the optimal surface treatment.