Preparation method of sintered neodymium iron boron magnet free of heavy rare earth

Abstract

The invention discloses a preparation method of a sintered neodymium iron boron magnet free of heavy rare earth. The preparation method comprises the following steps of (a), configuring neodymium ironboron alloy and preparing a quick hardening sheet; (b), performing hydrogen demolish treatment on the quick hardening sheet to obtain rough powder; (c), adding a reagent to the rough powder, next performing grinding until the average grain diameter SMD is equal to 3.0-4.0[mu]m; (d), adding a reagent to the grinded powder, and performing re-grinding until the SMD is equal to 1.5-2.0[mu]m; (e), performing pressing and shaping in a magnetic field orientation condition, wherein the orientation magnetic field is 2.0-3.0T, and then carrying out an isostatic pressing mode to further enable the magnet to be sense; and (f), performing sintering on the green body obtained after isostatic pressing in a vacuum sintering furnace, performing cooling, and then carrying out first-stage aging tempering treatment and second-stage aging tempering treatment. According to the preparation method disclosed in the invention, in the air flow milling process, an additive is added and secondary grinding is performed, so that rough particles are reduced, and the mixed reagent can fully coat fine powder, powder oxidization is prevented, powder fluidity is improved, corrosion is eliminated, and powder consistency is improved.

Description

technical field [0001] The invention relates to the technical field of rare earth permanent magnet materials, in particular to a method for preparing a sintered NdFeB permanent magnet without heavy rare earth. Background technique [0002] With the rapid development of emerging industries such as new energy vehicles and wind power generation, the market demand for high-temperature-resistant sintered NdFeB has been greatly increased. Rare earth elements are used to prepare high coercive force NdFeB magnets, but the reserves of heavy rare earths are limited and the price is high. In order to reduce product costs and the consumption of heavy rare earth metals, low Dy or no Dy high coercive force sintered NdFe Boron magnets have become a research hotspot at present. [0003] It has been reported that the coercive force of sintered NdFeB can be improved by grain boundary diffusion technology, while avoiding a sharp drop in magnet remanence and magnetic energy product; Chinese pa...

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Problems solved by technology

[0002] With the rapid development of emerging industries such as new energy vehicles and wind power generation, the market demand for high-temperature-resistant sintered NdFeB has been greatly increased. Rare earth elements are used to prepare high coercive force NdFeB magnets, but the reserves of heavy rare earths are limited and the price is high. In order to reduce product costs and the consumption of heavy rare earth metals, low Dy or no Dy high coercive force sintered NdFe Boron magnets become the current research hotspot

[0003] It has been reported that the coercive force of sintered NdFeB can be improved by grain boundary diffusion technology, while avoiding a sharp drop in magnet remanence and magnetic energy product; Chinese patent (publication number CN105755441) mentions that Dy element The powder is sputtered onto the particle surface to prepare sintered NdFeB impregnated with heavy rare earth, but this method is difficult to control the content and distribution of Dy element in the magnet, and the operation is complicated and the cost is high

Therefore, the current market usually prepares non-heavy rare earth NdFeB magnets by means of grain refinement and process improvement to reduce production costs. The grain refinement technology mainly affects the powder by adjusting the average particle size of the powder. The uniformity of distribution, but due to the fine powder and its flammability, mixed reagents are required for protection and lubrication. However, during the grinding process of the jet mill, the high-speed airflow continuously impacts the surface of the particles to refine them. The mixed reagent on the surface of the particle is dispersed, and the newly generated section of the particle cannot be in contact with the reagent, resulting in a low coating rate of the mixed reagent, which affects the uniformity of distribution, fluidity and oxidation resistance of the powder. Considering safety Factors also limit the refinement of the particle size of the powder, thus affecting the performance of the subsequent magnet

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