Knowledge of NdFeB surface treatment

 

NdFeB contains a large number of rare earth elements neodymium, iron and boron, its characteristics of hard and brittle. At the same time, neodymium and other rare earth metals are very lively, so that the material is easy to powder corrosion, must be taken by surface treatment or adjust its chemical composition to be improved in order to achieve practical application requirements. As the adjustment of components will change its performance, so the surface treatment is more important.

 

At present, the NdFeB magnets surface treatment mainly electroplating (chemical plating), conversion film, coating and gas coating and other aspects.

 

 

1. plating

The normal plating for NdFeB magnet is Nickel and Zn.

Nickel according to the different coating structure, divided into single nickel, double nickel, nickel copper and nickel; according to the appearance of different color, sub-dark nickel, semi-bright nickel and light nickel. General nickel-plated nickel-nickel-nickel-nickel and semi-bright nickel mostly. The advantages of nickel plating is more wear-resistant, good resistance to environmental, etc., is relatively poor nickel layer is a ferromagnetic material, the magnetic properties have a certain impact on the thin product is particularly evident, the improvement is to replace part of the copper The Chemical nickel and electroplated nickel-phosphorus alloy ferromagnetism is weak, but the layout is too much trouble, generally not as a mainstream coating for use.

Chemical nickel is relatively uniform compared with the electroplated nickel-nickel layer, but it is not currently available on the substrate of NdFeB directly, and the chemical nickel uses a large amount of complexing agent, reducing agent and the bath life is short, the plating driving force is low , High energy consumption, and therefore can not be the mainstream coating.

After nickel plating products, according to the requirements of the coating, but also gold, silver, tin, chrome, imitation gold, black nickel and other coatings.

 

Zn generally used chloride galvanized, from the domestic production point of view, galvanized is the largest plating species, especially electric bike magnet plating more prominent. The advantages of the coating are cheap and convenient, the zinc layer is not ferromagnetic. The disadvantage is wear resistance, weatherability is better than nickel plating. Zn coating after the general passivation treatment, due to the elimination of hexavalent chromium passivation, the current passivation is trivalent chromium blue and white passivation and trivalent chromium color passivation.Of course, zn layer passivation can also be as richer as hardware; however, the current mainstream is trivalent chromium blue and white passivation.

Electroplating layer is also used zinc nickel alloy, etc., however, to the present has not yet become a conventional NdFeB plating.

 

 

2. Conversion film

  NdFeB conversion film is mainly phosphating and passivation film, because the conversion film is a protective film between the workers, for long-term, many products will flash rust and so on.

 

3. Coating

The coating referred to herein refers to a coating process such as electrophoresis, spraying, brushing and dipping, and does not include a gas phase coating. At present the more common coating with epoxy paint coating, followed by Everlube coating, Teflon coating, chrome-free Dacromet coating.

 

Epoxy coating due to different varieties of paint, salt spray test, hardness, color and so on are different. Everlube coating is generally metallic luster of the golden yellow, is the United States produced a solid lubricating film improved over the coating comprehensive performance is very good, has been commercialized. Teflon coating has also been commercialized. Advanced chrome-free dacromet is also a kind of coating that is expected to replace electroplating.

The vapor-phase coating includes physical vapor deposition (PVD) method, physical vapor deposition and evaporation, sputtering and ion plating. It can form Al, Zn and Cr plating. Chemical vapor deposition (CVD) Cr ethers, carbide coatings, and chemical vapor deposition (CVD) polymer coatings.