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What are Coating and Plating Options for Neodymium Magnets?

Posted on April 20, 2017

Armstrong Neodymium Magnets

Neodymium magnets are much more susceptible to corrosion than Ceramic, Samarium Cobalt and Alnico, and would need to be coated and protected, particularly in harsh settings. They can be easily oxidized if exposed to air and moisture in atmosphere, and would become structurally vulnerable leading to breakage. To prevent this, there are several types of coatings available for custom magnets and selection should be dependable on their tolerance to the operating environment, especially the ones with high acidity and humidity. To reinforce their durability and resistance to abrasion, the coatings are often multi-layered. However, when their coating wears down or chips off, the Neodymium magnets cannot be re-plated and the exposed area will rust, breaks down into powder and lose their magnetic performance. Let’s take a look at the variety of surface finishes available in the market.

  • Nickel (Ni-Cu-Ni): Most commonly used, multi-layer plating, ~12-18 microns, shiny metallic color
    Pros: durable, suitable for indoor use and can withstand moderate amount of abrasion and humidity, low cost to performance ratio
    Cons: cannot resist acidity or salty environment
  • Zinc (Zn): turns white creating a durable layer of protection when exposed to corrosiveness, single layer, ~8-10 microns, shiny silver metallic color
    Pros: high resistance against abrasion and humidity, can withstand moderate acidity and salty environment, low cost to performance ratio
    Cons: cannot survive in salt water
  • Gold (Ni-Cu-Ni-Au) or Silver (Ni-Cu-Ni-Ag): gold or silver layer thickness is ~0.05 microns, entire layer is ~12-18 microns, shiny golden or silver metallic color
    Pros: similar features as Ni-Cu-Ni but more chemically inert
    Cons: high cost to performance ratio making this expensive fourth layer
  • Epoxy (Ni-Cu-Ni-Epoxy or Epoxy alone): ~10-12 microns, black color
    Pros: Non-corrosive, good for outdoor application
    Cons: not resistant to impact, prone to scratch, can be easily damaged to expose the magnet, medium cost to performance ratio
  • Chrome (Ni-Cu-Ni-Cr): ~18 microns, dull grey metallic color
    Pros: resilient against rubbing
    Cons: cannot resist acidity or salty environment
  • Titanium Nitride (TiN): ~12-15 microns, dull golden metallic
    Pros: good chemical stability and corrosion resistance, frequently used dental and medical applications
    Cons: high cost to performance ratio, not suitable for acidic solution
  • Teflon: ~15-25 microns, light grey color
    Pros: waterproof or repel moisture, resilient to scratch
    Cons: medium cost to performance ratio
  • Plastic or Rubber: >250 microns, various color, need to create mold for plastic shell
    Pros: highly corrosion resistant, increase friction
    Cons: medium cost to performance ratio, weaken magnetic pull strengths
  • Naked:Black/grey must be isolated from air or oxygen and should be vacuum packed.
Besides the above choices, there are a few other commonly requested platings, like Tin (Sn), Titanium (Ti), Parylene, Zinc Chromate and Phosphate Passivation.

During plating process, magnets must be thoroughly cleaned and dried to avoid moisture trapped in between magnets and coating. Besides properly preparing the magnet material and carrying out the plating process, chamfering magnets’ edges are also crucial for successful and durable plating. Every application can be complex with multiple elements to be considered. It is recommended to test a small number of magnets first to verify their compatibility with the application and effectiveness of their coating, especially in prolonged exposure to harsh chemicals and abrasion in a controlled environment. Our Neodymium magnet assemblies mostly use Ni-Cu-Ni plating with additional rubber cover or mild steel cups.