Preparation method for sintered neodymium iron boron permanent magnet free of heavy rare earths

Abstract

The invention discloses a preparation method for a sintered neodymium iron boron permanent magnet free of heavy rare earths. By virtue of the preparation method, the content of a B element is reduced,the volume fraction of a neodymium iron boron main phase is reduced, the volume fraction of a grain boundary phase is improved, and the content of a Ga element is increased. After the normal temperature is quickly heated to 300-350 DEG C, heat preservation is not performed, and instead, slow heating is performed to 1,050-1,070 DEG C, then short-term densifying is carried out, and then the temperature is cooled to 1,000-1,040 DEG C, and low-temperature sintering is carried out. By adopting the sintering process, the stage type heating and heat preservation and degassing processes in the conventional sintering process are avoided, the permanent magnet sintering time is shortened, the production efficiency is improved, and electric energy is saved; and meanwhile, by virtue of the sintering process, continuous degassing is facilitated, formation of tiny pores in the permanent magnet can be prevented, the magnet density is increased, and the sintered neodymium iron boron permanent magnet free of any heavy rare earths can be produced stably without adding the rare earth elements of Dy, Tb, Ho and the like and without lowering the permanent magnet residual magnetism.

Description

technical field [0001] The invention relates to the technical field of rare earth permanent magnet materials, in particular to a preparation method of a heavy rare earth-free sintered NdFeB permanent magnet. Background technique [0002] Neodymium iron boron (Nd2Fe14B) permanent magnet has high remanence, high coercive force and high magnetic energy product. It is the rare earth permanent magnet material with the highest comprehensive performance known today, which promotes the development of miniaturization and light weight of magnetic devices. It has been widely used in high-end popular fields such as wind power generation, inverter compressors and new energy passenger vehicles. [0003] In the existing technology, in order to obtain high-performance sintered NdFeB permanent magnets, heavy rare earth (Dy, Tb, Ho) and other elements are mainly added, but the price of heavy rare earth elements is high and the proven reserves are very limited. Therefore, The research and dev...

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Problems solved by technology

[0003] In the existing technology, in order to obtain high-performance sintered NdFeB permanent magnets, heavy rare earth (Dy, Tb, Ho) and other elements are mainly added, but the price of heavy rare earth elements is high and the proven reserves are very limited. Therefore, The research and development of sintered NdFeB permanent magnet technology without heavy rare earth elements can not only greatly reduce product costs, but also is required by the national rare earth strategy

[0004] Currently on the market, the double alloy process and grain refinement are usually used to increase the coercive force of the magnet to realize the preparation of heavy rare earth permanent magnets; in the research of non-heavy rare earth sintered NdFeB permanent magnets: Chinese patent (publication number CN105304252A) discloses a heavy rare earth high-performance NdFeB permanent magnet and its preparation method. The heavy rare earth permanent magnet in the patent adopts a double alloy process, wherein the auxiliary alloy is Nd hydride or PrNd alloy hydride , in the airflow milling of the auxiliary alloy, it is very easy to oxidize and affect the magnetic properties, and during the sintering process, the grain boundary phase formed by the auxiliary alloy entering the magnet cannot be uniformly distributed, and the magnetic properties are poorly consistent; Chinese patent (public number CN106158207A), mentioned A preparation method of NdFeB that does not contain heavy rare earths based on the principle of fine grains. In the sintering process of this method, the sintered body is obtained by step-wise heating and heat preservation in four stages. The sintering time is too long, which consumes electric energy and controls the operation. Complicated, manual real-time monitoring is required during each stage of temperature rise, which increases labor intensity and labor costs, which is not conducive to automated production. At the same time, the distribution uniformity of the Nd-rich grain boundary phase in the sintered body is not high, and the coercive force of the products involved needs to be improved.

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