What is neodymium magnet rust?

Neodymium magnet rust is a big problem during the production process. People have to add a magnet coating to the magnet to protect it

Neodymium magnets are the 3rd generation of rare earth permanent magnets. They have excellent magnetic performance, mechanical processing characteristics, and high cost-effectiveness. For these reasons, they have wide applications in various fields and industries – computers, home appliances, automobiles, etc.

However, the materials of neodymium magnets are unstable. They can have negative chemical reactions – corrosion (rust) – under hot and humid working conditions. This will weaken the magnetic performance and even shorten their life spans.

In order to prevent neodymium magnet rust, engineers have found 3 different solutions. Below, Osenc will explain them in detail, based on our knowledge and experience as a custom neodymium magnet supplier for more than 20 years.

1. Improve the rust resistance of the neodymium magnets. Using the hot-pressing technique, we can optimize their microstructure. In this way, we will be able to obtain magnets with higher densities and ultra-fine grains. This can greatly enhance the corrosion resistance of magnets themselves.

2. Add appropriate alloy elements to neodymium magnets’ properties. This is also an effective way to improve their corrosion resistance. However, this solution has a negative side. That is, sometimes the additional elements can reduce magnetic performance, and also increase production costs. These 2 factors limit the adoption of this solution.

3. Use proper coatings. Applying a layer or multiple layers of coating to the surfaces of neodymium magnets, we can avoid the direct touch between the magnet materials and their working environments. This is a fundamental, and widely adopted solution. All of the magnets that Osenc offer will be covered with a layer of coating, depending on the customers’ applications and expectations.

Now that Osenc focuses on offering neodymium magnets with coatings, we will explain the different types of coating techniques below. The notes below will help you better understand what to look for when you purchase magnets.

Electroplating coating

Electroplating is a kind of technique that use electricity to make metal ions adhere to the surfaces of neodymium magnets, generating a protective layer of coating. This coating technique began to use on neodymium magnets during the years 1985 – 1995. After years of development and optimization, it has been an optimum choice for neodymium magnets. Now it is time for continuous innovation of this coating technique.

Currently, the major options available in the market include zinc plating, nickel plating, nickel-zinc alloy plating, and other composite coating layers of different alloys.

Chemical plating coating

The chemical plating technique doesn’t use electricity to generate coatings for neodymium magnets. It generates a layer of coating for the magnets by accumulating metal ions in the chemical solution on the surface of the substrate, based on the redox reaction.

This technique has some important features, which include: the autocatalytic phenomenon of the substrate itself, the densities and uniformities of the coating layers, low porosities, and relatively simple application facilities.

Thanks to these features, chemical plating has become the most widely adopted coating technique for neodymium magnets. It has been a fundamental production procedure to provide a protective film for neodymium magnets against corrosion and wear.

Nowadays, the main chemical coatings for neodymium magnets include:

nickel-phosphorus, nickel-copper-phosphorus, nickel-tungsten-phosphorus, nickel-copper-phosphorus, etc.

The plating solution used for chemical plating can be divided into 2 types – acidic and alkaline.

In an acidic environment, it tends to produce high phosphorus non-magnetic coating; in an alkaline environment, it tends to produce low phosphorus magnetic coating and has certain magnetic shielding properties.

However, the acidic plating solution has an obvious hydrogen absorbing effect, which seriously affects the surface quality of the neodymium magnets. Therefore, the alkaline plating solution is mostly used in production.

Organic coating

This technique is one of the most widely used methods for protecting metals. Resin and organic polymer materials are the main organic coatings for sintered neodymium magnets, and epoxy resin is used more often. This is because epoxy resin has excellent water resistance, chemical corrosion resistance, bonding capability, and enough hardness.

Add an additional layer of epoxy resin coating to the neodymium magnets that already have a layer of zinc or nickel coating. The magnets will have enhanced antirust performance, which greatly exceeds that of conventional zinc and nickel plating.

In addition to epoxy resin, other resin materials – polyacrylate, polyamide, polyimide, etc. – also use mixtures of two or more of these resins as coatings. Meanwhile, we can also add rust-proof coatings, such as minium, chromium oxide, etc.

Physical vapor deposition coating

Physical vapor deposition is a new coating technology that is different from electroplating and chemical plating.

The coating applied by this method has better bonding quality with the substrates. Such coating layers have higher densities, better smoothness, and fewer porosities.

Meanwhile, this technique can eliminate the residue of electrolytes in the coating layer during electroplating, avoiding secondary damage to the coating layer caused by the residual liquid. And it can reduce the possibility of brittle cracking of the coating, which is caused by the hydrogen gas generated by the magnetic field reaction during chemical plating.

Common physical vapor deposition methods include vacuum evaporation coating, magnetron sputtering coating, multi-arc ion coating, etc.

Common materials include Al, Ti/Al, Al/Al2O3, TiN, Ti, etc.

The coatings generated with this technique has excellent bonding quality with substrates, excellent anti-corrosion performance, and have no waste liquid and other pollution.

For these reasons, this technique is the development direction for neodymium magnets’ anti-corrosion technologies.

So far, we have introduced the 4 industrial methods that we can prevent neodymium magnet rust.  Through these coatings, we can achieve a high-strength protection of salt spray test (SST) 720 hours.You can keep them in mind when you look for custom neodymium magnets.

In case you are not sure, contact Osenc. We can help you make it simpler for you to choose the right custom neodymium magnets.