The sintered neodymium iron boron permanent magnet material 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. After the magnetic material is corroded or damaged by the components, the magnetic properties will be attenuated or even lost over time, which will affect the performance and life of the whole machine. Therefore, strict anti-corrosion treatment must be carried out before use.
At present, the anti-corrosion treatment of neodymium/Ndfeb magnets generally uses 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 links: pretreatment and electroplating.
The quality of Neodymium magnet electroplating is closely related to its pre-treatment effect. The pre-treatment generally includes abrasive grinding chamfering-soaking chemical degreasing- pickling oxide film-weak acid activation, etc., interspersed with ultrasonic cleaning during the process, and after the above treatment, The neodymium iron boron magnet is exposed to the basic surface that is clean and suitable for electroplating, and then it can be electroplated. If there is a link in the pre-treatment process that is not cleanly handled, it will bring latent defects to the final electroplated product, causing problems such as blistering and peeling of the electroplated layer.
NdFeB strong magnetic electroplating can use 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, epoxy resin, etc., generally zinc plating, nickel plating The three processes of +copper + nickel, nickel plating + 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. Such a coating design is more conducive to the thermal demagnetization index of NdFeB components to meet customer needs.
The characteristics of different coatings and the description of the use environment
The details please check follow PDF documents, it will helpful for you to chose right neodymium magnet coating neodymium-magnet-different-coating.pdf
The most commonly used coatings for NdFeB/neodymium magnets are Znic and nickel-plated. They have obvious differences in appearance, corrosion resistance, service life, and price:
Polishing difference: Nickel plating is superior to zinc plating in 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-plated surface treatment, its corrosion resistance is higher.
Difference in service life: Due to the difference in corrosion resistance, the service life of zinc plating is lower than that of nickel plating. The main manifestation is that the surface coating is easy to fall off after a long time of use, causing the magnet to oxidize, which affects the magnetic performance.
Hardness difference: Nickel plating is higher than zinc plating, which can greatly avoid corners and chipping of the powerful neodymium iron boron magnets caused by collisions during use.
Price difference: Zinc plating is very advantageous in terms of price. The prices of NdFeB coatings from low to high are: zinc plating, nickel plating, and epoxy resin.
When using neodymium iron boron strong magnets, it is necessary to consider which coating to choose according to the use temperature, environmental impact, corrosion resistance characteristics, product appearance, coating adhesion, adhesive effect and other factors.