How to Protect Magnets from Corrosion
Most magnets contain some amount of iron. In fact, the strongest permanent magnet material, Neodymium, is more than 60% iron. Unfortunately, this iron can make magnets susceptible to corrosion when uncoated. For example, Neodymium magnets may rust in humid conditions, inhibiting their magnetic performance over time.
Magnets should have rounded corners with 0.015” to 0.020” radius to facilitate coating optimization.
To prevent this loss of functionality and strength, we recommend a multi-layer plating of nickel, copper, and nickel (Ni-Cu-Ni). This coating offers a high level of corrosion protection for the value.
In addition, it has a maximum working temperature of approximately 220-240°C (higher than the magnet’s operating temperature). Ni-Cu-Ni coating is used in many applications, including sensors, motors, generators, medical devices, pumps, and more.
Other coatings with different properties make them more or less suited to a particular working environment. The table below outlines these coatings/platings and their respective performance under commonly seen conditions. Our applications experts can also answer any questions you might have about the right plating or coating for your specific needs.
Other reasons to coat magnets
Samarium Cobalt magnets are inherently corrosion-resistant, so coating for increased corrosion protection is not common. However, smaller SmCo magnets are sometimes coated to prevent chipping or cracking. Likewise, un-ground sintered SmCo material can have rough surfaces, so a coating or plating might make sense to make it easier to clean these magnets if necessary. The most common coating is Nickel (not Ni-Cu-Ni) although others are available.
Like Samarium Cobalt, Alnico is also intrinsically corrosion resistant. However, it does contain some free iron, and, over time, surface corrosion may propagate. Although not commonly required, red epoxy paint can prevent this corrosion and is most often seen on horseshoe magnets.
Made from iron oxides, Ceramic magnets are the most naturally corrosion-resistant sintered magnets available. As a result, exposure to water, saltwater, solvents, oils, and even weak acids will have a negligible impact on their performance. Coatings are most commonly applied to Ceramic magnets for cosmetic reasons or to help prevent the transfer of ferrite dust. Because Ceramic magnets are non-conductive, they can’t be electroplated like NdFeB, SmCo, and Alnico materials, but there are many electroless coatings available. Common surface treatments for Ceramic ferrite magnets include paint, powder coat, parylene, phenolic resin, Teflon, silicone, and EPDM rubber.
Contact us for more details about coating options!
|Coating||Color||Approx. Thickness (µ m)||Salt fog||Salt Water||Humidity||Water||Abrasion Resistance||Relative Cost|
|Nickel Copper Nickel||Bright||10-20||Poor||Poor||Fair||Fair||Excellent||Lowest|
|Zinc W/ Chromate||Multi-color||8-10||Fair||Poor||Good||Fair||Good||Low|
|Nickel Tin||Silver White||12||Good||Fair||Good||Good||Good||Medium|
|Nickel Copper Everlube||Gold Metallic||15-25||Excellent||Excellent||Excellent||Excellent||Good||High|
|Parylene C||Clear||10 – 25||Excellent||Excellent||Excellent||Excellent||Poor||Highest|
|AL (PVD)||Silver, Grey||2||Poor||Poor||Fair||Poor||Excellent||Highest|