Properties of hot-pressed and hot-deformed NdFeB magnets

Hot-pressed and hot-deformed NdFeB magnets were successfully researched and developed almost simultaneously with sintered NdFeB magnets. In 1985, the General Motors Corporation (GM) Research Center of the United States reported that using hot pressing technology to press the quenched NdFeB magnetic powder in an argon environment at 700 ° C, a solid-density isotropic magnet can be obtained, which was later called MQ-II magnet. ; If the isotropic solid density magnet is thermally deformed, that is, the MQ-II magnet is thermally upset to less than 50% of the original height at a temperature above 700 ° C, the easy magnetization axis can reach more than 75% in the direction of the upset pressure. The degree of orientation is made into solid-density anisotropic heat-deformable magnets, and these three magnets are called MQ-Ⅲ.

The figure below shows the demagnetization curves of high quenching rate (overquenching) Nd0.13(Fe0.95B0.05)0.87 quenching powder, MQ-Ⅱ magnet, MQ-Ⅲ magnet, in which the pressing direction (∥) and perpendicular to the pressing direction (⊥) The difference between the measured curves can reflect the degree of orientation of the magnet. Obviously, the difference measured by MQ-Ⅱ in the two directions is not large, but there are still some orientations, while MQ-Ⅲ shows a strong orientation Features, the demagnetization curve in the pressing direction (∥) is very close to the square shape of the sintered NdFeB magnet, and the large remanence perpendicular to the pressing direction (⊥) indicates that the orientation is not sufficient.

Properties of hot-pressed and hot-deformed NdFeB magnets

Properties of hot-pressed and hot-deformed NdFeB magnets

Since the temperature of hot pressing and heat deformation is not high and the action time is not long, the fine grain (nanometer or submicron) structure of the rapidly quenched NdFeB magnetic powder is basically maintained, so MQ-II and MQ-III magnets still have high HcJ, especially the HcJ of MQ-Ⅱ is only 1~2kOe lower than the original powder. After a long period of time, GM company was producing MQ-Ⅱ and MQ-Ⅲ magnets. Until the beginning of the 21st century, they transferred the production of fast-quenched NdFeB magnetic powder to Tianjin, and the production line of MQ-Ⅱ and MQ-Ⅲ magnets moved to Production was discontinued shortly thereafter in Mexico.

In the research and development process of hot pressing and hot deformation technology, Daido Electronics, a subsidiary of Japan’s Daido Steel Works, and Magnequench Inc. (MQI), a subsidiary of GM, maintain a close cooperative relationship. This relationship has not changed owners several times because of MQI. However, in 1991, they launched their own brand NEOQUENCH-H and NEOQUENCH-D products to the market, corresponding to MQ-Ⅱ and MQ-Ⅲ respectively, and they are still in mass production. In 1992, they introduced hot pressing-back extrusion The radiation-oriented magnetic ring produced by this method is commercialized, and the product name is NEOQUENCH-RD. This is a key component that is very much needed for precision permanent magnet motors and has broad development prospects.

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