Why do neodymium magnets rust?
Short answer: yes, neodymium magnets can rust. They contain iron and are therefore sensitive to moisture and oxygen. That is why almost all neodymium magnets have a protective coating. As long as that coating remains intact, the risk is small; it increases if it is damaged, exposed to moisture, or used outdoors.
Neodymium magnets are the most powerful permanent magnets commercially available. They are used in machines, electric motors, electronics, and magnetic closures. Yet they have a characteristic that surprises many users: without protection, they rust. This is not a manufacturing defect, but a property of the material.
What is a neodymium magnet made of?
A neodymium magnet does not consist solely of neodymium. The material is an alloy of:
- Neodymium (Nd)
- Iron (Fe)
- Boron (B)
This combination is called NdFeB. It is the iron that reacts easily with moisture and oxygen, similar to the rusting of ordinary steel. You can read more about the material in What is neodymium and where does it come from?
How does corrosion occur?
Corrosion begins when moisture and oxygen reach the magnetic material. As long as the coating is intact, the material underneath is largely protected. If the coating is damaged by an impact, scratch, or break, moisture can penetrate and oxidation begins. You will often see small discolorations first; later, the degradation can spread, even underneath the protective layer.
Why are neodymium magnets sensitive to damage?
Neodymium magnets are very hard but also brittle. If two strong magnets slam together, small pieces of the coating can chip off. Damage can also occur during assembly or transport. As soon as the protective layer is broken, the risk of corrosion increases. You can find useful tips in How do you mount a magnet?
In which environments do magnets rust faster?
Dry indoor spaces are generally not a problem. The risk of corrosion increases with:
- high humidity and condensation
- outdoor use
- salt water and maritime applications
- bathrooms and damp rooms
- industrial environments
- damaged coatings
What happens when a magnet rusts?
Rust does not just affect the appearance. If the corrosion penetrates deeper into the material, the material can crumble, crack, or weaken, and the magnetic properties may diminish.
Can a rusted magnet still work?
A slightly corroded magnet often retains its magnetic properties because corrosion first affects the surface. If the degradation spreads further, performance and mechanical strength may decrease. Replace a magnet with visible cracks or crumbling material.
Which coatings are available?
| Coating | Characteristics | Suitable for |
|---|---|---|
| Ni-Cu-Ni (nickel-copper-nickel) | Most common finish: good corrosion protection, shiny metal, wear-resistant | Dry indoor spaces |
| Epoxy | Extra protective plastic layer, often black; better protection against moisture | Harsher conditions, outdoors |
| Rubber | Protects both the magnet and the contact surface | Vehicles, displays, sensitive surfaces |
| Plastic housing | Magnet completely encased in plastic | Maximum protection against moisture and damage |
In addition, there are decorative finishes such as gold, rose gold, and gunmetal. These are primarily chosen for their appearance in visible applications; the magnet underneath remains the same. A detailed comparison can be found in Which coating or finish should you choose? and Why do neodymium magnets have a coating?
Can neodymium magnets be used outdoors?
Yes, provided you choose the right version. Generally suitable for outdoor use are:
A standard nickel-plated magnet can function outdoors, but typically has a shorter lifespan when exposed to moisture for long periods. See also Can magnets be used outdoors?
How do you prevent corrosion?
- Prevent damage to the coating and do not let strong magnets slam together.
- Store magnets in a dry place.
- Avoid prolonged contact with water.
- Choose the right coating for the environment.
Conclusion
Neodymium magnets contain iron and are therefore sensitive to corrosion when moisture and oxygen reach the material. To prevent this, almost all neodymium magnets receive a protective coating such as nickel, epoxy, rubber, or plastic. With the right coating and careful use, they remain reliable for years.
Not sure which version you need? View our neodymium magnets or ask the Magnet Specialist via the Magnet Advisor.
