-- Do all sintered NdFeB magnets need coating?

Sintered NdFeB permanent magnet materials are produced by powder metallurgy process. It is a 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 when placed in air at 150°C for 51 days. After the magnetic material is corroded or the components are damaged, the magnetism will attenuate or even lose as time goes by, which will affect the performance and life of the whole machine, so strict anti-corrosion treatment must be carried out before use.

--- The NdFeB electroplating process

At present, electroplating, electroless plating, electrophoretic coating, phosphating treatment and other methods are commonly used for NdFeB anti-corrosion treatment, among which electroplating is widely used as a mature metal surface treatment method. The NdFeB electroplating process includes two important steps: pretreatment and electroplating.

Pre-processing

The quality of NdFeB electroplating is closely related to its pretreatment effect. Pre-treatment generally includes abrasive grinding and chamfering—soaking chemical degreasing—pickling oxide film—weak acid activation and other processes, interspersed with ultrasonic cleaning. After the above treatment, the NdFeB magnet exposes a clean base surface suitable for electroplating, and can be electroplated. If there is a link in the pre-treatment process that is not cleaned, it will bring potential defects to the final electroplating product, resulting in problems such as blistering and peeling of the electroplating layer.
Compared with ordinary steel parts, the pre-plating treatment of NdFeB products is more difficult. The reason is that the surface is rough, loose and porous, and the dirt is difficult to completely remove, which will have an adverse effect on the bonding force between the NdFeB coating and the substrate. At present, the pretreatment of NdFeB plating generally adopts multi-channel ultrasonic cleaning. Ultrasonic cavitation can completely remove oil, acid and alkali in the micropores of NdFeB; in addition, ultrasonic cleaning is also beneficial to remove boron ash produced on the surface of NdFeB during pickling, and further eliminate the hidden danger of bonding force.

Plating

NdFeB strong magnetic electroplating can adopt different electroplating processes according to different use environments of the products, and the surface coatings are also different, such as galvanized, nickel-plated, copper-plated, tin-plated, precious metal-plated, epoxy resin, etc., generally galvanized, The three processes of nickel + copper + nickel, nickel + copper + electroless nickel plating are the mainstream.

Only zinc and nickel are suitable for direct electroplating on the surface of NdFeB magnets, so multi-layer electroplating technology is generally implemented after nickel plating. At present, the technical problem of direct copper plating of NdFeB has been broken through. Nickel plating after direct copper plating is a development trend. Such a coating design is more conducive to the thermal demagnetization index of NdFeB components to meet customer needs.

-- What is the difference between the different coatings? how to choose?

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.:

The difference in polishing: The polishing of nickel plating is better than that of galvanizing, and the appearance is brighter. Nickel plating is generally selected for high requirements on product appearance, while some magnets are not exposed, and zinc plating is generally selected for relatively low product appearance requirements.

The difference in corrosion resistance: Zinc is an active metal that 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 the difference in corrosion resistance, the service life of galvanized plating is lower than that of nickel plating, mainly because the surface coating is easy to fall off after long-term use, resulting in oxidation of the coating. magnets and affect magnetic properties.
Difference in hardness: Nickel plating is higher than zinc plating, which can largely avoid the phenomenon of falling corners and fragmentation of NdFeB powerful magnets due to collisions during use.

Price difference: In terms of price, galvanized is extremely advantageous. The prices of NdFeB coatings are ranked from low to high: galvanized, nickel-plated, epoxy resin.