Method for preparing high-coercivity sintered Nd-Fe-B permanent magnet

Abstract

The invention discloses a method for preparing a high-coercivity sintered Nd-Fe-B permanent magnet. The method includes the following steps that firstly, the vacuum rapid hardening technology is used for preparing Nd-Fe-B alloy magnetic material blank; secondly, chamfering, cleaning, washing, surface modifying and washing are sequentially performed on the blank; thirdly, a processed permanent magnet is placed to a nickel / heavy rare earth composite coating for being electroplated; fourthly, a sintered Nd-Fe-B magnetic material is placed into a vacuum heat treatment furnace to receive heat treatment. With the technology of compositing heavy rare earth on a nickel-plate, heavy rare earth solid matter can be effectively utilized, and maximum benefits of rare earth resources are achieved. Meanwhile, it is ensured that the proportion of the content of the heavy rare earth in the nickel-plate is stable, volatile matter which is prone to decomposition does not exist in the nickel-plate in subsequent heat treatment to pollute a vacuum heat treatment system, a production device with infiltration of the heavy rare earth can be stable continuously, the application range of a technology is wider, and the method can be popularized and applied in an enterprise more easily.

Description

technical field [0001] The invention relates to the field of magnetic materials, in particular to a method for preparing a sintered NdFeB permanent magnet with high coercive force. Background technique [0002] With the rise of the hybrid electric vehicle (HEV) industry, sintered NdFeB magnets for automobiles require magnets with high coercive force and high temperature resistance. The anisotropy field of sintered Nd-Fe-B compound, that is, the theoretical limit value of coercive force is 7.3T, but the actual coercive force of Nd-Fe-B permanent magnet alloy is usually only about 1 / 3 of its theoretical value. The coercive force of the magnet can be increased by adding alloying elements to refine the grains and improving the boundary structure by tempering heat treatment process. due to Dy 2 Fe 14 B and Tb 2 Fe 14 The anisotropy fields of B are 15 and 21T, respectively, much higher than that of Nd 2 Fe 14 7.3T of B, so the most effective way to increase the coercivity o...

AI Technical Summary

Problems solved by technology

The different ways of adding Dy have a great influence on the performance. One is direct alloying, that is, metal Dy is added when the master alloy is smelted. However, Dy 2 Fe 14 The saturation magnetization of B is only about 0.7T, less than Nd 2 Fe 14 Half of B's ​​1.60T, so adding Dy to increase the coercive force will lead to a decrease in magnetization

The second addition method - double alloy method, that is, Nd-Fe-B powder and Dy or Dy 2 o 3 The magnet is prepared by mixing the powder, Dy is mainly distributed on the boundary, the coercive force increases and the magnetization intensity does not change much, but the amount of precious metal Dy is large, which is uneconomical

However, this method has disadvantages such as low production efficiency, high cost, difficulty in mass production, and large investment in equipment.