Why do neodymium magnets rust?

Many people assume that a magnet consists of solid metal that remains unchanged for years. When a neodymium magnet shows rust spots or when the coating starts to peel after some time, it often leads to confusion.

Nevertheless, corrosion is a known phenomenon with neodymium magnets. It is not due to a manufacturing defect, but to the properties of the material itself.

To understand why neodymium magnets can rust, we must first look at their composition.

What is a neodymium magnet made of?

A neodymium magnet is manufactured from an alloy of neodymium, iron, and boron. This combination is known as NdFeB.

The exceptional magnetic properties of this material make it possible to produce very powerful magnets. At the same time, the alloy has a disadvantage: it is susceptible to corrosion.

Particularly the iron in the material reacts easily with moisture and oxygen from the environment.

If the magnetic material were used unprotected, corrosion could occur relatively quickly.

Why do neodymium magnets have a coating?

Virtually all neodymium magnets are provided with a protective coating.

This coating forms a barrier between the magnetic material and the environment.

The most common coating is a combination of nickel, copper, and nickel. This three-layer finish is often referred to as Ni-Cu-Ni.

In addition to protection against corrosion, the coating provides a smooth surface and an attractive finish.

Without a coating, many neodymium magnets would last significantly less long.

How does corrosion occur?

Corrosion occurs when moisture and oxygen reach the magnetic material.

As long as the coating remains intact, the underlying material is largely protected.

However, if the coating is damaged by an impact, scratch, or break, moisture can penetrate. At that moment, oxidation can begin.

Initially, small discolourations are often visible. Over time, the damage can spread further.

Why are neodymium magnets susceptible to damage?

Neodymium magnets are very hard, but at the same time relatively brittle.

When two strong magnets strike each other, 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.

Influence of humid environments

Not every environment poses the same risk.

In dry indoor areas, neodymium magnets generally remain in excellent condition for years.

Humid conditions significantly increase the risk of corrosion.

For example, consider:

• outdoor use
• marine applications
• bathrooms
• production areas with high humidity
• applications near salt water

In such situations, extra protective coatings are often chosen.

What coatings exist?

In addition to the standard nickel-plated version, various alternatives exist.

Epoxy coatings generally offer better protection against moisture.

Rubber coatings protect not only against corrosion but also against damage to vulnerable surfaces.

For specific applications, zinc, gold, and plastic coatings are also used, among others.

The choice of coating depends on the environment in which the magnet is used.

Can a rusted magnet still work?

In many cases, a slightly corroded magnet still retains its magnetic properties.

Corrosion initially affects primarily the surface.

However, if the damage spreads further, the internal structure of the material can also be affected. At that point, performance may decrease, and the mechanical strength of the magnet may be reduced.

How to prevent corrosion?

The lifespan of a neodymium magnet can be significantly extended by:

• preventing damage to the coating
• limiting contact with moisture
• choosing the right coating
• storage in dry conditions
• careful handling of powerful magnets

Especially for outdoor applications, the choice of coating requires extra attention.

Conclusion

Neodymium magnets owe their exceptional strength to an alloy of neodymium, iron, and boron. However, this alloy is susceptible to corrosion when exposed to moisture and oxygen.

For this reason, almost all neodymium magnets are provided with a protective coating. As long as this coating remains intact, the risk of corrosion is limited. However, damage, humid conditions, and prolonged exposure to water can shorten the lifespan of a magnet.

The correct coating and careful application are therefore important factors for a long lifespan.