Factors and methods affecting the performance of NdFeB

- Nov 16, 2019-

Ndfeb permanent magnet material since the advent of its superior magnetic properties and attention, known as the "The King of Magnet", in the market demand continues to grow, ndfeb production technology and magnet performance also continue to develop and improve. Remanence, coercivity and maximum magnetic energy product are used to measure the properties of magnetic materials.


Remanence Br


If you compare a magnet to a sponge, the remanence is like a sponge absorbing water and saturated, at which time the magnetic force of the magnet is displayed. It refers to the magnetic induction intensity of a magnet when it is magnetized by the external magnetic field in a closed-circuit environment until the technology is saturated and the external magnetic field is cancelled.


Coercivity Hcb and intrinsic coercivity Hcj


The water in the sponge is sucked up to its maximum, and then the pressure is pushed out until there is no water in the sponge. It is the value of the strength of the reverse magnetic field needed to reduce the magnetic induction intensity to zero when the magnet is negatively charged. However, in this case, the magnetization intensity of the magnet is not zero, but the added reverse magnetic field and the magnetization intensity of the magnet cancel each other. In this case, if the external magnetic field is cancelled, the magnet still has certain magnetic properties. The intrinsic coercivity is the strength of the reverse magnetic field required to reduce the magnetization of the magnet to zero.


Maximum magnetic energy product (BH) Max


Sponge water absorption saturation, the total amount of water can be understood as the maximum magnetic energy product. It represents the magnetic energy density established by the space of two magnetic poles of the magnet, that is, the magnetostatic energy per unit volume of air gap. It is the maximum value of the product of Br and Hcj, and its size directly indicates the performance of the magnet.




What determines the above performance of ndfeb strong magnetic, how to improve the performance of magnetic material through technical means, and how to avoid the use of magnetic material performance without loss.


Ndfeb strong magnetic raw material composition and production process determine its innate magnetic properties, and after becoming a strong magnetic product, its working environment (including temperature, humidity and other factors) will affect the play of its innate magnetic properties, improper use, there will be permanent demagnetization.


1. Effect of raw material composition on ndfeb strong magnetic properties



Strong ndfeb magnetic as the name suggests is made from rare earth neodymium metal, pure iron and boron powder metallurgy process made of magnetic material, in order to further enhance ndfeb magnetic, can in a Nd - Fe - B ternary material on the basis of further add other elements, but the element to add effect on the properties of magnets is likely to be a two-way street, should according to the using situation of the strong ndfeb magnetic specific requirements to determine the add elements on the properties of magnets.


2. Effect of production process on nd-fe-b strong magnetic properties


In order to obtain high performance ndfeb permanent magnets, new technologies and new processes keep emerging. In the sintering NdFeB production process, the main problem is to prevent the precipitation of alpha-fe phase and alloy oxidation, difficult to get the ideal microstructure, in order to solve the problems in these aspects, the practice of the continuous emergence of new methods and processes, such as: add antioxidant, lubricant, and using fast quenching zapping method to prepare magnets; Ingot homogenization treatment and sheet casting process; Preparation process by two-phase method; Wet molding process.


The biggest advantage of adding anti-oxidant is to reduce the oxygen content of the final magnet, while the magnetic powder can be ground more finely, which is conducive to improving coercivity. In addition, the reduction of oxygen content is also conducive to improving coercivity. Compared with the traditional process, the intrinsic coercivity of the magnet with anti-oxidant can be increased by about 160kA/m.


After adding lubricant, the friction between magnetic particles decreases, the fluidity of magnetic particles is improved, the orientation is improved, and the remanence is improved.


A -Fe phase can be eliminated completely with a thickness of 0.25 ~ 0.35mm. As the anti-oxidation ability of the powder obtained by the strip swing method is enhanced, the size of the magnet grain becomes smaller and the coercing force is greatly improved.


3. Effect of working environment on ndfeb strong magnetic properties


Temperature: ndfeb strong magnetic has a strict working temperature limit, higher than the working temperature magnet may appear demagnetization phenomenon, and higher than the currie temperature, magnet demagnetization will be irreversible.

Humidity: sintered ndfeb is a powder metallurgy process to suppress the formation of magnetic material, its internal structure is void, very easy to oxidation, so sintered ndfeb coating for corrosion treatment. However, the coating can not fundamentally deal with the effect of environmental humidity on the magnet. The drier the environment, the more permanent the magnetic properties of the magnet.