NdFeB is a (new) member of the large family of magnetic materials. Magnetic materials from the application function can be divided into soft magnetic materials, permanent magnetic materials, magnetic recording - moment magnetic materials, magnetic materials, etc., collectively referred to as magnetic functional materials. The permanent magnetic material refers to a kind of magnetic material that can not demagnetize easily after magnetization and can retain magnetic property for a long time, also called hard magnetic material or constant magnetic material. Permanent magnet materials are Alnico, ferrite and rare earth permanent magnet materials and other varieties. The rare earth permanent magnet material refers to the rare earth element samarium, neodymium, cerium, praseodymium and transition elements such as iron, cobalt and other alloys, its magnetic properties greatly exceeded AlNiCo and ferrite system, it is obtained in modern electronic communication technology Wide range of applications. The development of rare earth permanent magnetic materials has gone through three generations so far. The first and the second generation are samarium-cobalt series. Although their magnetic properties are good, the development of rare earth permanent magnet materials is limited due to the scarce reserves of samarium and the scarce and expensive strategic metallic cobalt. The third generation that is, NdFeB, was first born in 1983 in Japan's Sumitomo special metals company, its energy product is AlNiCo 5 to 6 times, ferrite system about 10 times, about 2 times samarium cobalt series, Is by far the strongest magnetic permanent magnet material, known as the "permanent magnet king." Moreover, NdFeB (relative to samarium-cobalt series) is cheap and has abundant resource reserves. Therefore, NdFeB has been widely used as an electronic information, automobile manufacturing, general machinery, petrochemical and cutting-edge technology sectors The lack of magnetic functional materials, is the sunrise industry in the 21st century.
However, compared with other permanent magnetic materials (such as ferrite), NdFeB is highly susceptible to corrosion. Because: (1) The material contains about 1/3 of highly active neodymium (standard potential -2.431V), then (especially in warm and humid and high temperature environment) surface easily oxidized, resulting in grain boundary corrosion; (2) Neodymium-rich phase in the material, boron-rich phase with the main phase Nd2Fe14B form the primary battery, so that corrosion accelerated. Therefore, neodymium iron boron products must be strictly anticorrosive treatment before use, or material corrosion greatly reduced magnetic properties, will directly affect the overall performance and life of the machine.
Plating as a mature means of metal surface treatment, anti-corrosion in the field of NdFeB magnets is widely used. NdFeB magnets according to different production methods are divided into sintered and bonded two. NdFeB plating is generally used for sintering rather than bonding, because the bonded NdFeB volatile in the production process easy to form a hole in the solvent, holes and adhesives can not constitute a conductive loop, making it difficult to metal Electrochemical deposition on the part surface. NdFeB products wafer, ring, cylinder, pipe, fan, square, box, tile and other shapes, but mostly small parts, it is widely used barrel plating. And, even if slightly larger parts (such as boxes, tiles, etc.) through process or equipment improvements, the current use of a lot of barrel plating. But NdFeB parts barrel plating can be described as difficult, far less than the ordinary steel parts, which is mainly due to the special nature of NdFeB material caused by: affect the pre-plating treatment with acid, alkali should not be too strong , And avoid the use of hydrochloric acid; ② pre-plating (or direct plating), if you choose a simple type of salt bath, can easily cause oxidation of the parts and the coating adhesion to the substrate, and the parts are corroded and plating bath contamination; ③ difficult to choose Large-size rollers, or mixed cycle of greater impact, serious oxidation parts. (2) NdFeB products for the magnetic functional materials, any surface coating may have an impact on its magnetic properties, so how to coordinate the type of coating, the combination of thickness and the magnetic properties of the product is a NdFeB plating Difficulties. (3) The surface of NdFeB is porous and rough, which not only imposes a great burden on the pre-plating process, but more importantly, the choice of the pre-plating (or direct plating) process is greatly restricted, that is, the bonding strength of the coating can not be selected Good, corrosion resistance but low current efficiency complex plating solution (such as alkali copper, nickel citrate, alkali zinc, etc.). (4) Neodymium iron boron material brittle, vulnerable to bump and damage, which not only increase the operational difficulties of workers, more important is difficult to choose a large size of the drum, thus affecting the improvement of labor and production efficiency.
Article from NdFeB Industry Network