How to choose the coating of NdFeB magnets

-Why does sintered NdFeB need coating?

-How to choose coating material? Zinc plating, nickel plating or other materials? What are the differences between different coatings?

Today, this article will tell you about the issues related to the coating of NdFeB magnets.

NdFeB magnets are produced using powder metallurgy technology. They are a very chemically active powder material with tiny pores and cavities inside, making them easily corroded and oxidized in the air. After the material is corroded or the components are damaged, the magnetic properties will be attenuated or even lost over time, thus affecting the performance and life of the entire machine. Therefore, strict anti-corrosion treatment must be carried out before use.

At present, the anti-corrosion treatment of NdFeB generally adopts electroplating, chemical plating, electrophoresis, phosphating and other methods. Among them, electroplating, as a mature metal surface treatment method, is the most widely used.

The electroplating quality of NdFeB magnets is closely related to pre-treatment

The NdFeB electroplating process includes pre-treatment and electroplating. The quality of NdFeB electroplating is closely related to its pre-treatment. This pre-treatment process generally includes abrasive grinding and chamfering-immersion chemical degreasing-pickling oxide film-weak acid activation and other processes, during which ultrasonic cleaning is interspersed. After the above-mentioned treatment , so that the NdFeB magnet exposes a clean basic surface suitable for electroplating, and then it can be electroplated. If any part of the pre-treatment process is not handled cleanly, it will bring latent defects to the final electroplated product, causing problems such as blistering and peeling of the electroplated layer.

Compared with ordinary steel parts, the pre-plating treatment of NdFeB products is more difficult. The reason is that its rough, loose and porous surface easily "harbors dirt". If these "dirt" are not completely removed, it will cause damage to the NdFeB products. The bonding force between the NdFeB coating and the substrate has adverse effects. At present, multi-channel ultrasonic cleaning is generally used for pre-treatment of NdFeB plating. The cavitation effect of ultrasonic waves completely removes oil, acid and alkali and other substances in the micropores of NdFeB. In addition, ultrasonic cleaning also helps to remove the acid in NdFeB. The boron dust produced on the surface during washing further eliminates the hidden danger of bonding.

Coating types and characteristics of NdFeB magnets

NdFeB electroplating adopts different electroplating processes according to the different use environments of the products, and the surface plating is also different, such as zinc plating, nickel plating, copper plating, tin plating, precious metal plating, etc. Generally, zinc plating, nickel plating + copper plating + nickel, nickel plating + copper + electroless nickel plating are the three processes that are mainstream. Only zinc and nickel are suitable for direct plating on the surface of NdFeB magnets, so multi-layer plating technology is generally implemented after nickel plating. Nowadays, the technical difficulty of direct copper plating of NdFeB has been broken through. Direct copper plating and then nickel plating is the development trend. This kind of plating design is more conducive to achieving the thermal demagnetization index of NdFeB components to meet customer needs.

There are certain differences in the corrosion resistance between different coatings, as follows:

Galvanized vs Nickel Plated

The most commonly used coatings for NdFeB powerful magnets are zinc plating and nickel plating. They have obvious differences in appearance, corrosion resistance, service life, price, etc.:

Difference in polishability: Nickel plating is superior to zinc plating in terms of polishing, and the appearance is brighter. Those with high requirements on product appearance generally choose nickel plating, while some magnets are not exposed, and those with relatively low requirements on product appearance are generally galvanized.

Difference in corrosion resistance: Zinc is an active metal and can react with acid, so its corrosion resistance is poor; after nickel plating surface treatment, its corrosion resistance is higher.

Difference in service life: Due to different corrosion resistance, the service life of zinc plating is lower than that of nickel plating. The main reason is that the surface coating easily falls off after a long time of use, causing the magnet to oxidize, thereby affecting the magnetic performance.

Difference in hardness: Nickel plating is higher than zinc plating. During use, it can greatly avoid collisions and other situations, which may cause the NdFeB powerful magnets to fall off, break, etc.

Price difference: Galvanizing is extremely advantageous in this regard. The prices from low to high are galvanizing, nickel plating, epoxy resin, etc.

When choosing NdFeB magnets, you need to consider which coating to use based on factors such as operating temperature, environmental impact, corrosion resistance, product appearance, coating bonding strength, and adhesive effect.