Method for rapidly sintering Nd-Fe-B ferromagnet

Abstract

The method for sintering NdFeB magnets at low temperature and rapidly using an electric field disclosed by the present invention is to crush NdFeB alloys containing Nd 12.4 to 15.5, Fe 77.7 to 81.4, and B 6.0 to 6.8 in atomic percentages, after vacuum melting, crushing and ball milling. 3-5μm Nd-Fe-B alloy fine powder is put into the mold, pressed into a green body after being oriented by a magnetic field, and then the green body is placed in an electric heating device, with an output voltage of 3-10 volts and an output current of 800-5000 A , Under the vacuum condition of 10-3Pa, use the current to directly pass through the green body to rapidly heat it, so that the components in the green body can be continuously sintered at 500-900 °C for 5-8 minutes to complete the densification process of the green body. The invention has low sintering temperature and short sintering time, which not only shortens the manufacturing cycle of the magnet, improves the efficiency, and greatly reduces energy consumption, but also obtains ultra-fine grain structure, which is very beneficial to improving the performance of the magnet; it can also be conveniently passed Adjust the heating rate, sintering temperature and current to control the magnet to achieve sintering density.

Description

1. Technical field [0001] The invention belongs to the technical field of sintering NdFeB magnets, and in particular relates to a method for rapidly sintering NdFeB magnets at low temperature using an electric field. 2. Background technology [0002] At present, the vast majority of neodymium iron boron (NdFeB) magnets are made by traditional powder metallurgy. The process of this method is as follows: the smelted NdFeB alloy ingot is broken into fine powder of 3-5 μm, pressed into a green body with a relative density of 50-70% in a magnetic field, and then sintered at a temperature of Sintering is carried out in a vacuum sintering furnace at about 1050°C to 1120°C. The specific sintering temperature is related to the content of Nd in the NdFeB alloy. The lower the Nd content, the higher the sintering temperature, and when the green body is heated from room temperature to the sintering temperature in this method, the heating time takes about 2 hours, and the sintering time...

AI Technical Summary

Problems solved by technology

However, when the sintering temperature is lower than 780 ° C, the pressure is small, and the holding time is less than 10 minutes, denser sintered NdFeB magnets cannot be obtained.

Since the SPS technology uses the instantaneous high-temperature field generated by pulse energy, discharge pulse pressure and Joule heat to realize the sintering process, it greatly shortens the heating time and sintering time compared with the traditional process of preparing sintered NdFeB magnets, and reduces Sintering temperature, but because the heating time of SPS technology is limited by the plasma generated between the magnetic powders during sintering, it cannot be greatly shortened; at the same time, when the sintering temperature and sintering time are continued to be reduced, dense sintered NdFeB magnets will not be obtained ; Moreover, the use of SPS technology for sintering requires a low density of the green body, generally below 50%, otherwise, too dense a green body is not conducive to the generation of plasma under the action of current, and it cannot generate high temperature

In addition, since SPS sintering is a system pressure sintering method, during the sintering process, on the one hand, the system needs to provide a strong external pressure to make the sintered compact, so as to improve the magnetic properties of the sintered NdFeB magnet; The huge pressure applied will inevitably seriously reduce the degree of orientation of the magnet, which will greatly reduce the performance of the magnet.

Therefore, when SPS technology is used for sintering, there is always a contradiction between increasing the density of magnets and reducing the magnetic properties of magnets, which also leads to the problem that the magnetic properties of sintered NdFeB magnets prepared by SPS method are all low.

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