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Treatment method for surface coating of NdFeb
Time:08/21/2020
Neodymium iron boron is a kind of magnet, which is different from other magnets. It is called "Magnetic king" because of its excellent magnetic properties. Neodymium iron boron contains a large number of rare earth elements neodymium, iron and boron, its characteristics are hard and brittle. Because the surface is very easy to be oxidized corrosion, ndFeb must be surface coated. The following are the commonly used surface treatment methods for NdFeb in the magnetic industry: electroplating (electroless plating), conversion film, coating and gas phase coating.
Sintered Ndfeb
 
I. Electroplating (electroless plating)
 
The ndFeb electroplating is mainly nickel plating and galvanizing.
 
The nickel plating can be divided into single nickel, double nickel, nickel copper nickel and so on according to the coating structure. According to the appearance of different colors, the dark nickel, half bright nickel and light nickel. Bright nickel and semi-bright nickel are the most common nickel plating layers. The advantage of nickel plating is that the coating is wear-resistant, good environmental resistance, and so on. The nickel layer is a ferromagnetic material, which has a certain effect on the magnetic properties, especially obvious for thin small products, the improvement is to replace with part of the copper layer. The ferromagnetism of ni and Ni - P alloy is weak, but it is difficult to deplating, so it is not used as the main coating.
 
The chemical nickel layer is relatively more uniform than the electroplating nickel layer, but at present, it cannot be directly plated on the matrix of Neodymium iron boron. Moreover, chemical nickel USES a large number of complexing agents and reducing agents, and the plating solution life is short, the plating driving force is low, high energy consumption, so it cannot be used as the mainstream coating.
 
After nickel plating products, according to the coating requirements, can also be gold, silver, tin, chrome, imitation gold, black nickel coating.
 
Neodymium iron boron zinc plating is generally used to use chloride galvanized, from the domestic production, galvanized is the largest type of plating, especially the electric bicycle magnetic steel electroplating is more prominent. The advantages of the coating are cheap, convenient, zinc layer is not ferromagnetic. The disadvantage is that the wear resistance and weather resistance is not as good as nickel plating. After galvanized coating is generally passivated, because of the elimination of hexavalent chromium passivation, currently the commonly used passivation is trivalent chromium blue-white passivation and trivalent chromium color passivation. Of course, galvanized passivation can also be as rich as hardware; However, trivalent chromium blue - white passivation is the main trend at present.
 
Electroplating has been used zinc nickel alloy, but so far has not become a conventional ndFeb plating.
 
Ii. Conversion membrane
 
The conversion film of NdFeb mainly includes phosphating and passivation film. Since the conversion film is an interwork protective film, it is used for a long time and many products will have flash rust and other phenomena.
 
Three, coating
 
Coatings referred to herein are those coated by electrophoresis, spraying, brushing and dipping processes, excluding gaseous phase coatings. The most common coatings are epoxy coatings, followed by Everlube coatings, Teflon coatings and chrome-free Dacromet coatings.
 
Due to the different kinds of coatings, the salt spray resistance, hardness and color of epoxy coatings are different. Everlube coating is generally golden yellow with metallic luster. It is an improved solid lubrication film produced in the United States. The coating has excellent comprehensive performance and has been commercialized. Teflon coatings have also been commercialized. The advanced chromium-free Dacro coating is also a promising alternative to electroplating.
 
Iv. Gas phase coating
 
The vapor phase coating includes physical vapor deposition (PVD), which can be divided into evaporation plating, sputtering plating and ion plating, forming Al, Zn, Cr coatings, etc. Chemical vapor deposition (CVD) can form nitride and carbide coatings such as Ti and Cr. Chemical vapor deposition (CVD) polymerization coating pairin, etc.