Many of our customers will have such questions: Do sintered NdFeB magnets need coating? What are the coating materials of the sintered NdFeB magnets? What are the differences between different coatings? In this article, we will take a closer look at the coatings for sintered NdFeB magnets and try to answer the above questions.
Sintered NdFeB magnet is produced by powder metallurgy technology. It is a kind of powder material with very strong chemical activity. There are tiny pores and cavities inside, which are easily corroded and oxidized in the air. The experimental results show that a 1cm³ sintered NdFeB permanent magnet will be completely oxidized and corroded if placed in the air at 150°C for 51 days. Therefore, strict anti-corrosion treatment must be carried out before use.
At present, NdFeB anti-corrosion treatment generally adopts electroplating, electroless plating, electrophoretic coating, phosphating treatment, and other methods. Among them, electroplating is widely used as a mature metal surface treatment method.
The NdFeB electroplating process includes two important steps: pretreatment and electroplating.
The quality of NdFeB electroplating is closely related to the effect of its pretreatment. Pretreatment generally includes abrasive grinding and chamfering-soaking chemical degreasing-pickling oxide film-weak acid activation, etc., interspersed with ultrasonic cleaning during the process. After the above treatment, the surface of the neodymium magnet is clean and suitable for electroplating, and then the electroplating treatment can be carried out.
If the pretreatment process is not handled well and the surface of the magnet is not clean, it will bring latent defects to the final electroplated product, causing problems such as blistering and peeling of the electroplated layer.
The electroplating of neodymium magnets can adopt different electroplating processes according to the different use environment of the product, and the surface coating is also different, such as zinc plating, nickel plating, copper plating, tin plating, precious metal plating, epoxy resin, etc. In general, zinc plating, nickel-copper – nickel plating, nickel-copper – electroless nickel plating are the mainstream.
Only zinc and nickel are suitable for direct plating on the surface of neodymium iron boron magnets, so multi-layer electroplating technology is generally implemented after nickel plating. At present, the technical difficulty of direct copper plating of NdFeB has been broken. Direct copper plating and then nickel plating is a development trend.
The corrosion resistance of different coatings has certain differences, as follows:
The most commonly used coatings for NdFeB magnets are zinc plating and nickel plating. They have obvious differences in appearance, corrosion resistance, service life, price, etc.
Polishing difference: nickel plating is superior to zinc plating on polishing, and the appearance is brighter. Those with high product appearance requirements generally choose nickel plating, while some magnets are not exposed, and those with relatively low product appearance requirements generally choose zinc plating.
Corrosion resistance difference: zinc is an active metal and can react with acid, so it has poor corrosion resistance. After nickel plating surface treatment, its corrosion resistance is higher.
Service life difference: due to different corrosion resistance, the service life of zinc plating is lower than that of nickel plating, which is mainly manifested in that the surface coating is easy to fall off after a long time of use, causing the magnet to oxidize, thereby affecting the magnetic properties.
Hardness difference: Nickel plating has a higher hardness than zinc plating, and it can largely avoid chipping of neodymium magnets caused by collisions during use.
Price difference: Zinc plating is very advantageous in terms of price. The prices of NdFeB coatings are arranged from low to high: zinc plating, nickel plating, and epoxy resin.
When choosing a neodymium magnet, it is necessary to consider which coating to choose according to the use temperature, environmental influence, corrosion resistance characteristics, product appearance, and other factors.
Thank you for reading our article and we hope it can help you to have a better understanding of the coatings for sintered NdFeB magnets. If you want to learn more about sintered NdFeB magnets or other types of magnets, we would like to advise you to visit Stanford Magnets for more information.