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Method producing rare earth magnet

a rare earth magnet and magnet technology, applied in the direction of magnetic materials, inductance/transformer/magnet manufacture, magnetic bodies, etc., can solve the problems of limiting the improvement of magnetization, the inability to obtain high magnetization, and the degree of crystal orientation, so as to improve the degree of orientation, improve the effect of crystal grain strain deformation and improve the effect of magnetization

Active Publication Date: 2015-06-30
TOYOTA JIDOSHA KK
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0008]The invention provides a method of producing a rare earth magnet that provides the resulting rare earth magnet with high magnetization and ensures its high coercivity by hot working.
[0021]First, as shown in FIG. 1A, when the reduction ratio in the hot working is 60% or higher, alignment levels off and improvement in magnetization also levels off accordingly. In addition, as shown in FIG. 1B, when hot working is performed, the degree of orientation is improved and the magnetization increases, whereas the coercivity significantly decreases.<Analysis of Problems of Prior Arts>
[0026]Magnets for hybrid vehicle (HV) motors are required to have a magnetization (residual magnetization) of 1.2 T or higher, preferably 1.35 T or higher. To achieve the magnetization, a reduction ratio of 60% or higher in hot working is necessary. A microstructure after hot working with a reduction ratio of 60% has a very high crystal grain flatness as shown in a transmission electron microscope (TEM) photograph of FIG. 5. Thus, the demagnetizing field that is created by the crystal itself is so strong that magnetization reversal tends to occur as compared to isotropic crystal grains (with an aspect ratio of 1), resulting in lower coercivity.
[0027]In addition, the fact that the magnetic decoupling effect of the crystal grain boundaries is reduced because adjacent crystal grains are apparently bound to each other during the hot working and the effect of the interfaces between the particles as domain walls is lowered, is another factor for decrease in coercivity.
[0029]According to the method of the invention, because hot working is performed in a direction that is different from the forming direction, the mechanism that is described in detail later (1) prevents the quench flakes from gliding along their surfaces and enables the energy that is applied by hot working to contribute to strain deformation of crystal grains effectively, whereby the degree of orientation improves in proportion to the reduction ratio in the hot working, and especially, the magnetization is improved even when reduction ratio is 60% or higher, and (2) prevents flattening of crystal grains and reduces apparent binding between crystal grains, thereby ensuring high coercivity.

Problems solved by technology

In this state, however, the individual nano-crystal grains are randomly oriented and high magnetization cannot be obtained.
However, there is a limit to the improvement of magnetization because there is a limit to the resulting degree of crystal orientation.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

example 1

[0073]Rare earth magnets were produced according to the following procedure and under the following conditions based on the method of the invention, and their magnetic properties were evaluated.

[0074]Raw materials of a rare earth magnet were mixed in amounts that provided an alloy composition (% by mass) 31Nd-3Co-1B-0.4Ga-bal.Fe, and the mixture was melted in an Ar atmosphere. The melt was quenched by injecting it from an orifice onto a rotating roll (chromium-plated copper roll) to form alloy flakes. The alloy flakes were pulverized with a cutter mill and sieved in an Ar atmosphere to obtain a rare earth alloy powder W with a particle size of 2 mm or less (average particle size: 100 μm). The powder particles had an average crystal grain diameter of approximately 100 to 200 nm and an oxygen content of 800 ppm.

[0075]Description is hereinafter made with reference to the FIG. 10.

[0076]The powder W was filled into a cemented carbide alloy die D1 with a 10×10×30 (H) mm capacity, and the ...

example 2

[0086]Rare earth magnets were produced according to the following procedure and under the following conditions based on the method according to a preferred embodiment of the invention, and their magnetic properties were evaluated.

[0087]The same procedure from to as in Example 1 was followed to obtain a bulk body.

[0088]Description is hereinafter made with reference to FIG. 12.

[0089]The bulk body M0, which was formed as described above and as shown in FIG. 12(1), was set between φ30 mm cemented carbide alloy punches P2 with its orientation unchanged as shown in FIG. 12(2). The die / punch assembly was placed in the chamber, and the chamber was decompressed to 10−2 Pa. The die / punch assembly was heated with the high-frequency coils, and hot upsetting F was performed with a reduction ratio of 10, 30, 45, 60, or 80% immediately after the temperature reached 700° C. to obtain a preliminarily compact M1 (FIG. 12(3)).

[0090]As shown in FIGS. 12(4) to 2(5), the preliminarily compact M1 was ma...

example 3

[0094]A rare earth magnet was produced in the same manner as in Example 2 based on the method according to a preferred embodiment of the invention, and its magnetic properties were evaluated.

[0095]However, the preliminary hot working and hot working were performed as described below. Description is made with reference to FIG. 13.

[0096]The bulk body M0, which was formed in the same manner as in Example 2 and as shown in FIG. 13(1), was set with its orientation unchanged at the center of a cemented carbide alloy die D2 with a volume of 13×13×20 mm, using cemented carbide alloy punches P2 as shown in FIG. 13(2). The die / punch assembly was placed in the chamber, and the chamber was decompressed to 10−2 Pa. The die / punch assembly was heated with the high-frequency coils, and hot upsetting F1 was performed until the space in the die D2 was filled immediately after the temperature reached 750° C. to obtain a preliminarily compact M1 (13×13×8.8 (II) mm) (FIG. 13(3)). At this time, the reduc...

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Abstract

A method of producing an R-T-B rare earth magnet that include forming an R-T-B (R: rare-earth element, T: Fe, or Fe and partially Co that substitutes for part of Fe) rare earth alloy powder into a compact and performing hot working on the compact, wherein the hot working is performed in a direction that is different from the direction in which the forming was performed.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is a national phase application of International Application No. PCT / IB2012 / 000321, filed Feb. 22, 2012, and claims the priority of Japanese Application No. 2011-037320, filed Feb. 23, 2011, the content of both of which is incorporated herein by reference.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The invention relates to a method of producing a rare earth magnet using hot working. “Hot working” has substantially the same meaning as “hot plastic working”.[0004]2. Description of Related Art[0005]Rare earth magnets, as typified by neodymium magnet (Nd2Fe14B), have a very high magnetic flux density and are used for various applications as strong permanent magnets.[0006]It is known that a neodymium magnet has higher coercivity as its crystal grain size is smaller. Thus, a magnetic powder (powder particle size: approximately 100 μm), which is a nano-polycrystalline material with a crystal grain size of app...

Claims

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Application Information

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Patent Type & Authority Patents(United States)
IPC IPC(8): H01F7/02H01F41/02H01F1/057C22C38/00C22C38/10C22C1/00B22F3/14
CPCH01F41/0253H01F1/0576H01F41/0266C22C38/002C22C38/005C22C38/10C22C1/00B22F3/14C22C2202/02H01F7/02
Inventor MIYAMOTO, NORITAKAMANABE, AKIRASHOJI, TETSUYAICHIGOZAKI, DAISUKE
Owner TOYOTA JIDOSHA KK