2019-08-26 09:34:53

Joint Development of Dysprosium-free Magnets for HEV by Datong Special Steel and Honda

Japan Datong Special Steel and Honda announced on July 12, 2016 that they have developed Nd-Fe-B (Nd-Fe-B) magnets (Nd magnets) which do not use heavy rare earth dysprosium (Dy) and so on, and intend to use them in the motor of Honda Hybrid Electric Vehicle (HEV). The two companies said it was the first time in the world that dysprosium-free neodymium magnets would be installed on HEV motors.


The developed magnet will be used in the MPV "Freed" single motor hybrid mechanism "i-DCD" scheduled to be launched in autumn 2016. Honda intends to extend this magnet to other HEVs equipped with i-DCD in the future. EVs equipped with i-DCD include small car "flying" and small SUV "Vezel" and so on.


Datong Special Steel has developed a technology that can maintain the magnetic strength of Nd magnet without Dy and improve its heat resistance. At the same time, Honda has improved the heat resistance of the motor so that the technology can be used in HEV motor. The maximum torque and output power of the motor are 160 N. m and 22 kW, respectively, which are the same as the original.


The residual flux density of neodymium magnet (the index of magnetic strength) is larger, which can improve the torque of motor, but the heat resistance index - coercivity is smaller. Therefore, it is necessary to mix heavy rare earth dysprosium or terbium (Tb) to improve the coercivity. But dysprosium and terbium are not only expensive, but basically only produced in China. The policy changes of the Chinese government will lead to the purchase of these rare earth elements, and the "dysprosium-free" magnets will be able to purchase magnet materials steadily and easily regardless of the intention of the Chinese government.


In order to improve the coercivity without adding dysprosium, the manufacturing technology of magnet powder with very small diameter was developed for Datong special steel pipe. The smaller the size of the magnet crystal, the more difficult it is to demagnetize when the temperature rises. The size of the developed magnet crystal is only 100-500 nm. The crystal size of ordinary Nd magnets is 5-10 micron, which is nearly 10 times as large as that of the developed products.


Datong special steel has developed a hot forming technology that heates the die to a lower temperature, then fills the die with magnet powder and extrudes it by force. Normal neodymium magnets are filled with larger powders of magnets and sintered at high temperatures of about 1000 C.


The cost of production can be greatly reduced by adopting the newly developed production technology because the sintering process, which sometimes takes tens of hours, can be saved. Compared with the production of sintered magnets, the production time can be reduced to about 1/10-1/5. Another reason for significantly shortening production time is that Near Net-Shape (Near Net-Shape) is achieved, in which most of the magnets can be transformed into target shapes. The sintered magnets need to be machined in the target shape after the bulk sintering.


However, although the coercivity of dysprosium-free magnets has been increased this time, the level is only about half of that of dysprosium-containing magnets. Honda has improved the motor rotor embedded in magnets to achieve a structure that can also be used with a slightly lower coercivity.


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