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Protective Coatings/Surface Finish for Neodymium Magnets

A Neodymium magnet does not corrode and will retain its performance theoretically forever in a dry environment (if not subjected to excessive heat, radiation, or strong external magnetic fields). However, if it is placed in a wet environment, the result may be the opposite. The within-structure Iron can 'rust' and cause a permanent structural change in NdFeB, which will result in a permanent weakening of the magnetic performance; the worst-case scenario is a total loss of magnetism. Therefore, it is recommended to apply a coating on the magnet surface to protect the magnet from moisture (e.g. encasing, modified coatings such as zinc plus rubber, etc). The coating/surface finish should be for best corrosion protection; scratched or damaged surfaces may render the affected region more prone to corrosion. Marine environments (salt sprays, seawater) are particularly corrosive and far from ideal for NdFeB. It is the application and the overall design that determines how well the magnet will perform in damp environments.

Main Coating Types

Electroless Powder Spray E-Coating Nickel plating
Coating + Epoxy E-Coating
Homogeneity Excellent Good Poor Excellent Good Good
Effectiveness Versus Magnet Size Small (<20 grams) Excellent Good Fair Good Good
Large (>20 grams) Fair to Good Good Fair Good Good
Hours before coating is likely to fail Temp. & Humidity >2500 >500 >1500 >2500
(60°C, 95%RH)
Temp. & Humidity >500 >100 >300 >500
(85°C, 85%RH)
Salt Spray >48 <24 >100 >200
(35°C, 5% NaCl)
Coating Color Silver Silver Black Black Black
Heat Cycle Fair Fair Fair Fair Fair
Heat Resistance Poor Poor Poor Poor Poor
Collision Test Fair Fair Fair Fair Fair
Film to Material Adhesion test Fair Fair Fair Fair Fair
Glue Adhesion Test Fair Fair Fair Fair Fair
Tolerance Accuracy Excellent Excellent Fair Fair Fair to Poor
Additional Remarks 15-30 microns Ni-Cu-Ni Standard coating Epoxy resins are not hermetic Thickness buildup can be a problem
About the author

Cathy Marchio

Cathy Marchio is an expert at Stanford Magnets, where she shares her deep knowledge of magnets like Neodymium and Samarium Cobalt. With a background in materials science, Cathy writes articles and guides that make complex topics easier to understand. She helps people learn about magnets and their uses in different industries, making her a key part of the company's success.

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