Green coating technology makes NdFeB magnet materials shine brilliantly.

At the end of the year, it was reported from Baotou Zhongketai Magnetic coating Technology Co., Ltd. (hereinafter referred to as "Zhongketai Magnetic") that the design of the company's fully automatic magnetron sputtering coating equipment has been completed and the equipment is being customized in other provinces. Installation is expected to be completed in April 2021. "at present, our production line handles 100 tons of NdFeB magnet materials per year. After installing the new equipment, we can handle 300-400 tons of NdFeB magnet materials annually. The production efficiency is increased by 4 times and the number of personnel is reduced by 30%." Zhang Yanjie, chairman of China Ketai Magnetics, said.

In recent years, with the increasing awareness of environmental protection from all walks of life, the development of green coating technology adapted to the protection of rare earth permanent magnet materials is related to the healthy development of the industry in the future. "it is a common concern for the domestic NdFeB industry to study the electroplating technology, process and equipment to improve its performance and reduce emissions. The research and application of physical vapor deposition magnetron sputtering technology is aimed at improving the equipment manufacturing capability of magnet protection technology and large rare earth permanent magnet surface protection equipment in our country. " Xia Yuan, researcher and doctoral supervisor of the Chinese Academy of Sciences, said.

The surface protection of NdFeB material needs to be upgraded urgently.

As we all know, NdFeB permanent magnet materials have outstanding magnetic properties, such as high remanence, high coercivity, high magnetic energy product and so on. NdFeB permanent magnet materials are widely used in wind power, electric vehicles, energy-saving motors, smart phones, intelligent manufacturing equipment (industrial robots), aerospace and other high-tech fields, and have become one of the important material bases for high and new technology, emerging industries and social progress. Therefore, the permanent magnet material industry has become an industry of important strategic significance.

Relevant statistics show that China is rich in rare earth resources, especially the proved reserves of metal neodymium, which is the main raw material in NdFeB magnetic powder, accounts for 48% of the world's reserves. In terms of NdFeB permanent magnet products, China is also the largest producer in the world, but it is worth noting that there is still a certain gap between domestic NdFeB magnet related technical indicators and foreign high-performance NdFeB permanent magnet products.

"in recent years, permanent magnet materials represented by sintered NdFeB have made great progress in the preparation process and the improvement of magnetic properties. Due to the introduction and digestion of new equipment, a number of enterprises can be on a par with Japan's Sumitomo, Shinyue and other enterprises in improving their magnetic properties." Wang Qiang, technical vice president of Baotou Jinmenghui Magnetic Materials Co., Ltd., said that due to the structure of NdFeB, its corrosion resistance is poor, and it must be applied through protective treatment. More than 95% of domestic sintered NdFeB products use electroplating protection technology, while generally more than 65% of NdFeB magnets are electroplated in the form of "foreign cooperation".

According to Xia Yuan, the structure and chemical properties of NdFeB make it react with pickling solution and electroplating solution in the electroplating process. When the protective coating does not cover the magnet workpiece, the magnet has already been corroded, resulting in defects such as looseness, electrolyte residue and cracks on the magnet surface. NdFeB enterprises own electroplating processing and through "outsourcing" processing, the pressure of environmental protection and emission control is increasing day by day, and the management level and product consistency are also uneven.

Zhang Yanjie said frankly that the magnet of power motor is an important application direction of NdFeB in the future, and electroplating is difficult to meet the protection requirements, because the frequent start of the motor leads to the fluctuation of plating stress under the action of alternating temperature field. it eventually leads to the peeling of the coating.

Put a green coat on NdFeB material

Wang Qiang told the reporter a fact: at present, the main problems existing in China's NdFeB industry are the low grade and poor quality of NdFeB products, and the average price of foreign products is 3 to 4 times that of domestic products, while improving the surface protection level of NdFeB and meeting the requirements of various application environments is one of the keys to improve the quality and performance of NdFeB products.

"because of the market prospect and important position of NdFeB, foreign manufacturers regard the surface protection technology of NdFeB as an important technical secret. therefore, in order to improve the competitiveness of products, occupy the international market and give full play to the resource advantages of large rare earth countries, it is necessary to develop NdFeB protection technology with independent intellectual property rights in China." Xia Yuan said.

According to Li Guang, associate researcher and postdoctoral fellow of the Chinese Academy of Sciences, physical vapor deposition thin film technology (PVD), such as magnetron sputtering, ion plating, evaporation plating, is a good means of depositing thin films, and protective coatings can be obtained. The metal film deposited on the surface of NdFeB by this technology has high stability, coating / substrate adhesion, high density and strong anti-corrosion ability in hot and cold alternating environment. Previous studies have shown that if the energy of sputtered particles in the deposition process is high enough, the coercivity of magnets can be improved. In addition, in the process of physical vapor deposition, the effect of the edge of magnet workpiece on the coating thickness is much lower than that of electroplating and electroless plating, and there is no pollution in the preparation process.

"the physical vapor deposition magnetron sputtering technology is that the orthogonal electric field and magnetic field are applied between the anode (substrate) and the cathode (heavy rare earth target), so that the argon gas is excited to produce high energy argon ions between the electric field and the magnetic field. Argon ions are deposited on the surface of the substrate in the form of atoms through the Tackle heavy rare earth target, so that the excited atoms of the high energy heavy rare earth target are uniformly and firmly attached to the surface of the substrate. It is beneficial to the subsequent thermal diffusion process of heavy rare earth atoms in high vacuum. " Zhang Yanjie said: at present, 15 patents have been applied for, including 1 patent for invention, 6 patents for utility model and 4 trademarks.

The use of green and pollution-free physical vapor deposition technology is the development direction of NdFeB protection in the future. The first industrial demonstration production line of continuous green pollution-free physical vapor deposition with an annual output of 100 tons has been built in China. The products can not only meet the requirements of new application fields such as wind power and electric vehicles, but also meet the needs of high-tech fields with high-temperature samarium cobalt permanent magnets protected by physical vapor deposition. It is of great significance to promote the industrialization of green coating and to improve the product quality of rare earth permanent magnet materials in China.