NdFeB Magnet Coating Selection Guide
Neodymium (NdFeB) magnets contain iron and oxidize and rust easily, so almost every application requires a protective coating. A coating does more than prevent rust—it also affects appearance, conductivity, solderability, and biocompatibility. This article summarizes the characteristics and suitable environments of common coatings to help you choose quickly.
Why do NdFeB magnets always need a coating?
NdFeB is currently the strongest permanent magnet, but its main constituents are quite sensitive to moisture and oxygen. Uncoated material gradually oxidizes and powders in humid environments, degrading magnetic performance and even breaking down. Therefore, except for a few cases involving further encapsulation or secondary processing, magnets receive a protective layer before leaving the factory. When choosing a coating, there are four main considerations: the operating environment (humidity, indoor or outdoor), whether conductivity or soldering is needed, appearance requirements, and cost.
Comparison of common coatings
| Coating | Color | Corrosion resistance | Conductive | Application / Notes |
|---|---|---|---|---|
| Nickel-Copper-Nickel (Ni-Cu-Ni) | Bright silver | Good | Yes | Most common, good value, general indoor use; hard, not suited to prolonged humidity |
| Zinc (Zn) | Blue-gray / silver-gray | Medium | Yes | Low cost, suited to applications needing grounding; surface oxidizes and discolors easily |
| Epoxy | Black | Excellent (humid) | No | Humid, outdoor, high rust-resistance needs; softer, edges chip easily |
| Gold (Au) | Gold | Good | Excellent | Electronics, decorative, conductivity needs; high cost, usually plated over a nickel base |
| Silver (Ag) | Silver | Medium | Excellent | High conductivity needs; oxidizes and discolors easily |
| Tin (Sn) | Silver | Medium | Solderable | Applications requiring soldered assembly; good solderability |
| Parylene | Transparent | Excellent (chemical / medical) | No | Medical, chemical environments; extremely thin, uniform coating with good biocompatibility |
| Uncoated | Gray-black | Poor (rusts easily) | — | For further processing or low-cost use; requires subsequent coating or encapsulation |
How to choose by application?
- General indoor, dry environments: Nickel-copper-nickel (Ni-Cu-Ni) is the first choice—bright silver, wear-resistant, and reasonably priced.
- Humid, outdoor, long-term rust resistance: Epoxy offers good weather resistance; if hardness is also needed, consider a nickel-plus-epoxy double layer.
- Conductivity required (grounding, signal): Zinc, gold, silver; among these, gold offers the best conductivity and oxidation resistance but at high cost.
- Soldered assembly required: Tin coating offers the best solderability.
- Medical, chemical, or food-contact environments: Parylene is thin, uniform, and biocompatible.
Common coating questions
Does the coating affect magnetic force?
The coating itself has almost no effect on the magnet's internal magnetic performance, but it does add a little to the outer dimensions (nickel about 0.01–0.02 mm, epoxy thicker) and creates a small gap between the magnet surface and the object being attracted, which has a very slight effect on pull force. If precise dimensions are needed, let us know when ordering and AHL will factor coating thickness into the tolerance.
Can the coating peel off?
Under normal use, nickel coating is quite durable; however, the instant impact of strong magnets snapping together, or edge collisions, can chip the coating at the corners. We recommend wearing gloves and avoiding hard impacts during handling.
Need help choosing a coating or a quote?
Inquiries are welcome even without a purchase. Provide your operating environment and specifications, and we'll offer fast, professional, pressure-free advice.
Contact AHL +886-2-2976-3000