KR920003638B1 - Permanent magnet and method of making the same - Google Patents

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Description

Permanent magnet and its manufacturing method

1 is a manufacturing process diagram of the R-Fe-B magnet of the present invention.

The present invention relates to a permanent magnet containing rare earth elements, transition metals, and boron as a main component and a method for producing the same.

Permanent magnets are one of the important electronic and electrical materials used in a wide range of fields, ranging from electrical appliances in general homes to peripheral terminals in large computers.

In accordance with the recent demand for miniaturization and high efficiency of electrical appliances, permanent magnets are also required to have higher performance. Representative permanent magnets currently used are alnico, light ferrite and rare earth-transition metal-based magnets. In particular, since R-Co permanent magnets and R-Fe-B permanent magnets, which are rare earth-transition metal magnets, have high magnetic performance, many researches and developments have been made.

Conventionally, there exists a method as shown in the following document regarding the manufacturing method of such R-Fe-B type permanent magnet.

(1) Method by sintering based on powder metallurgy method.

[Document 1, Document 2]

(2) Resin bonding method using quenching flakes by the melt spinning method which makes a quenching flake about 30 micrometers thick in a quenching strip manufacturing apparatus used for manufacturing an amorphous alloy, and makes the flakes the magnet by the resin bonding method.

[Document 3, Document 4]

(3) A method of mechanically orientating the quench flakes used in the method (2) above by a two-step hot pressing method.

[Document 4, Document 5]

From here,

Document 1: Japanese Patent Application Laid-Open No. 59046008.

Document 2: M., published March 15, 1984. Sagawa, S. Fujimura, Yen. Togawa, etch. Yamamoto, Y. Matsuura J.Appl, Phys, VoL, 55 (6). p2083.

Document 3: Japanese Patent Laid-Open No. 59-211549.

Document 4: Egg, published April 15, 1985. W. Lee's Apple, Phys, Lett, VoL 46 (8). p790.

Document 5: Japanese Patent Application Laid-Open No. 60-100420.

Hereinafter, the conventional method mentioned above is demonstrated.

First, in the sintering method of (1), an alloy ingot by melting and casting is produced, and pulverized to obtain a magnetic powder having an appropriate particle size (several µm). The magnet powder is kneaded with an adhesive, which is a molding aid, and press molded in a magnetic field to form a molded body. The molded body is sintered in argon at a temperature around 1100 ° C. for 1 hour and then quenched to room temperature. After sintering, the coercive force is improved by heat treatment at a temperature of around 600 ° C.

In the resin bonding method using the quenching flakes by the melt spinning method of (2), first, the quenching ribbon of the R-Fe-B alloy is made at the optimum rotational speed of the quenching ribbon manufacturing apparatus. The obtained ribbon-shaped thin ribbon having a thickness of 30 µm is an aggregate of crystals having a diameter of 1000 GPa or less, is easily broken off, and is magnetically isotropic because crystal grains are isotropically distributed. The thin ribbon is pulverized to an appropriate particle size, kneaded with a resin and molded into a press.

The manufacturing method of (3) obtains the dense and anisotropic R-Fe-B magnet by the method of calling the ribbon-shaped quenching ribbon or flake in (2) in a vacuum or inert atmosphere by a two-step hot pressing method.

In this press process, a single direction of pressure is applied, the easy magnetization axis is oriented parallel to the press direction, and the alloy is anisotropic.

In addition, the crystal grains of the ribbon-shaped thin ribbon produced by the first melt spinning method are made smaller than the particle diameter when it exhibits the maximum coercive force, so that coarsening of the crystal grains occurs during the subsequent hot pressing to obtain an optimum particle size.

The above-mentioned prior art has produced permanent magnets mainly composed of rare earth elements, iron, and boron, but their production methods have the following drawbacks.

In the sintering method of (1), it is essential that the alloy is powdered, but since the R-Fe-B alloy is very active against oxygen, the oxidation becomes more severe when powdered, and the oxygen concentration in the sintered body may be high. Also, when molding the powder, a molding aid such as zinc stearate must be used, which is removed in advance in the sintering process, but part of the molding aid remains in the form of carbon in the magnet body. This carbon is not preferable because it significantly lowers the magnetic performance of the R-Fe-B alloy.

The molded body after press molding with the addition of a molding aid is called a green body, which is very difficult to handle. Therefore, a significant drawback is that it takes considerable time to cleanly put the sinter plants side by side. Because of these drawbacks, generally speaking, the production of R-Fe-B permanent magnets requires not only expensive equipment but also low production efficiency and high magnet production costs. Therefore, it is difficult to say that the raw material cost is a method that can take advantage of the acid R-Fe-B magnet.

Next, the methods of (2) and (3) use a vacuum melt spinning apparatus, but this apparatus is very low in productivity and expensive.

Since the method of the resin bonding of (2) is essentially isotropic, it is low in energy and poor in forming each of the hysteresis loops, which is inappropriate in terms of temperature characteristics and use.

The method of (3) is a unique method of using a hot press in two stages, but in fact, it cannot be denied that it is very inefficient considering mass production. Moreover, in this method, coarsening of crystal grains is remarkable at high temperature, for example, 800 degreeC or more, by which the coercive force (iHc) falls extremely and it does not become a practical permanent magnet.

The present invention has been made to solve the above-mentioned drawbacks of the prior art, and an object thereof is to provide a high performance, inexpensive rare earth-iron permanent magnet and a method of manufacturing the same.

The permanent magnet of the present invention is a magnet composed mainly of rare earth elements (including Y), transition metals, and boron, wherein the macrostructure (casting structure) of the magnet is columnar, and is anisotropic. It is a permanent magnet.

The first method of manufacturing a permanent magnet according to the present invention is a method of manufacturing a magnet mainly composed of rare earth elements (including Y), transition metals and boron, which is melted and cast to form a magnet into the mat. Is a columnar tablet, heat treated at a temperature of 250 ° C. or more, and then the macrostructure of the magnet is a columnar tablet, and is a method of producing a permanent magnet, characterized in that it is cured magnetically; The second method for producing a permanent magnet according to the present invention is to melt and cast, orient the crystal axes of the crystal grains in a specific direction by hot working at a temperature of at least 500 ° C, and then hot working at a temperature of at least 500 ° C. The magnet is anisotropically manufactured. The third method of manufacturing a permanent magnet according to the present invention is to heat-treat at a temperature of 250 ° C. or higher after hot processing of the second manufacturing method described above. It is a method of producing a permanent magnet, characterized in that it is cured magnetically.

As described above, the sintering method and the quenching method, which are methods for producing rare earth-iron magnets, are difficult to manage powders by grinding. It has the big drawback of falling productivity.

In order to remedy these drawbacks, the present inventors began to study the magnetization in the volume state, and found that sufficient coercive force is obtained by first anisotropically treating the rare earth element, transition metal and boron as basic components and then performing heat treatment. In other words,

(1) By making the macrostructure at the time of casting into a fine columnar tablet, the magnet of in-plane anisotropy (about 70% of the orientation of an easy magnetization axis) is manufactured only by heat-processing as it is in a casting state.

(2) By making the cast macrostructure fine columnar crystals, unidirectional anisotropy by hot working is promoted, and the orientation of the axis of easy magnetization becomes considerably high.

(3) As a result of (1) and (2), since a high-performance magnet is produced even if the powder state is difficult to manage, no strict atmosphere management is required for heat treatment, the productivity of the magnet is high, and the equipment cost is greatly reduced.

As for the composition of the conventional R-Fe-B magnet, it is assumed that R ₁₅ Fe ₇₇ B ₈ as shown in Document 2 is optimal.

This composition is shifted toward R and B richer than the composition R _11.2 Fe _82.4 B _5.9 having the columnar R ₂ Fe ₁₄ B compound as an atomic percentage. This is explained by the fact that in order to obtain coercive force, not only a main phase but also a non-magnetic phase called an R-rich phase and a B-rich phase is required.

However, in the proper composition according to the present invention, there is a maximum coercive force at the place where B is reversely shifted. In this composition range, since the coercive force in the sintering method is greatly reduced, it has not been such a problem until now. However, when the casting method is used, the B side lower than the stoichiometric composition tends to obtain coercive force, and the high B side hardly.

This is considered as follows. First, the sintering method, the casting method, or the coercive force mechanism itself follows the nucleation model. This can be seen from the fact that the initial magnetization curves of both show a sharp increase such as SmCo ₅ .

For this type of magnet the coercive force basically depends on the terminal model. That is, in this case, if the R ₂ Fe ₁₄ B compound having large crystal magnetic anisotropy is too large, it will have a magnetic wall in the crystal grains, so that reversal of magnetization occurs easily due to the movement of the magnetic wall, and the coercive force is small.

On the other hand, when the particles become small and become smaller than a predetermined size, the particles do not have a magnetic wall, and the coercive force becomes large because reversal of magnetization proceeds only by rotation.

That is, in order to obtain an appropriate coercive force, it is necessary for the R ₂ Fe ₁₄ B phase to have an appropriate particle size. As this particle size, 10 micrometers is suitable, and in the case of a sintering type, a particle size can be made suitable by adjusting the powder particle size before sintering.

However, in the casting method, since the grain size of the R ₂ Fe ₁₄ B compound is determined in the solidification step from the molten metal, attention should be paid to the composition and the solidification process.

In particular, the meaning of the composition is large, and when B is contained by 8 atomic% or more, the size of the R ₂ Fe ₁₄ B phase after casting is easily coarse, and it is difficult to obtain the coercive force unless the cooling rate is faster than usual.

On the other hand, in the region with less boron, the crystal can be easily refined by studying the mold, the injection temperature, and the like. In other words, this region is also referred to as a phase richer in Fe than in R ₂ Fe ₁₄ B. In the solidification step, Fe first appears as a primary, and then a R ₂ Fe ₁₄ B phase appears by a clath reaction. At this time, since the cooling rate is very fast compared to the equilibrium reaction, the R ₂ Fe ₁₄ B phase solidifies around the primary Fe in the same form. In this composition range, since B is a smaller range, it is natural, but B-rich phases such as R ₁₅ Fe ₇₇ B ₈ , which is a representative composition of the sintered type, are almost ignored in quantity. The heat treatment is intended to reach the equilibrium state by diffusing primary Fe, and the coercive force is highly dependent on the diffusion of the Fe phase.

Next, in the present invention, the meaning of using columnar tablets in the macrostructure will be described.

As described above, there are two effects of using columnarity, one of which is in-plane anisotropy during casting, and the other is high performance during hot working.

First, in the former, the intermetallic compound R ₂ Fe ₁₄ B (R is rare earth), which is the source of the magnetism of the main magnet, is a plane in which the biaxial C axis for magnetization is perpendicular to the columnar crystal when developing the columnar crystal. It has a property to distribute inside. That is, in-plane anisotropy is distributed only in the plane perpendicular to the C-axis columnar development direction. This magnet is a natural one, but it is higher in performance than the one used in which the isotropic isotropic axis is used as a macrostructure, which is very advantageous. However, even when columnar crystals are used, the particle size must be made fine from the relation of the coercive force, and the same is true for the low B side.

×100%(Bx,By,Bz는 각각 x,y,z방향의 잔류자속밀도)로 정의하면, 등방성은 약 60%면내 이방성은 70%로 된다. 열간 가공성에 의한 이방성화 효과(배향도 상승효과)는 가공재의 배향도에 관계없이 존재하지만, 원재의 배향도가 높을수록 최종 가공재의 배향도도 높게 된다. 따라서, 주상정을 사용함으로써 원재의 배향도를 놓여 놓은 것은 최종적으로 고성능한 이방성자석을 얻는다는 점에서 효과가 있다.The latter, however, is to further enhance the effect of the anisotropy of hot working. The degree of orientation of the anisotropic magnet is MA = B × 1

When defined as x100% (Bx, By and Bz are residual magnetic flux densities in the x, y and z directions, respectively), the isotropic property is about 60% and the in-plane anisotropy is 70%. The anisotropic effect (orientation synergistic effect) due to hot workability exists regardless of the degree of orientation of the workpiece, but the higher the degree of orientation of the raw material, the higher the degree of orientation of the final workpiece. Therefore, placing the orientation of the raw material by using columnar crystals is effective in that a high performance anisotropic magnet is finally obtained.

Hereinafter, the preferable composition range of the permanent magnet by this invention is demonstrated.

Rare earths include Y, La, Cl, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Mo, Er, Tm, Yb, and Lu as candidates. use. The highest magnetic performance is obtained as Pr.

Therefore, Pr, Pr-Nd alloy, Ce-Pr-Nd alloy, etc. are used practically. In addition, small amounts of additive elements such as heavy rare earth elements such as Dy, Tb and Al, Mo, Si, etc., are effective in improving the coercive force.

철과 동일 구조의 입방정조직으로 되기 때문에 높은 자기 특성은 얻어지지 않는다.The main phase of the R-Fe-B magnet is R ₂ Fe ₁₄ B. Therefore, when R is less than 8 atomic%, the compound is not formed.

Since it becomes a cubic crystal structure having the same structure as iron, high magnetic properties are not obtained.

On the other hand, when R exceeds 30 atomic%, many R-rich phases of the nonmagnetic phase become remarkably degraded in magnetic properties. Therefore, the range of R is suitable for 8 to 30 atomic%. However, in order to make a cast magnet, 8-25 atomic% is preferable.

B is an essential element for forming the R ₂ Fe ₁₄ B phase, and the coercive force cannot be desired since it becomes the R-Fe system of the rhombohedron at less than 2 atomic%. In addition, if it exceeds 28 atomic%, the B-rich nonmagnetic phase increases, and the residual magnetic flux density is remarkably lowered. However, as a cast magnet, B is preferably 8 atomic% or less, and finer R ₂ Fe ₁₄ B is difficult and the coercive force becomes small.

Co is an effective element to increase the Curie point of the main magnet, and basically replaces the Fe site to form R ₂ Fe ₁₄ B, but this compound has a small crystal anisotropy magnetic field and the coercive force as a whole magnet as the amount increases Becomes small. Because of this, less than 50 atomic percent is desirable to give a coercive force of 1 KOe or more, which is considered to be a permanent magnet.

Al has the effect of increasing the coercive force. (7; Proceedings of the 8th International Workshop on Rate-Farth Magents, 1985, p514, Zhnag Maocai et al.)

This document 7 shows the effect on the sintered magnet, but the effect also exists in the cast magnet. However, since Al is a nonmagnetic phase element, increasing the amount of addition decreases the residual magnetic flux density, and when it exceeds 15 atomic%, it becomes the residual magnetic flux density below light ferrite, and thus cannot serve the purpose as a rare earth magnet. Therefore, the amount of Al added is preferably 15 atomic% or less.

The following describes an embodiment of the present invention.

EXAMPLE

The process chart of the manufacturing method by this invention is shown in FIG.

First, according to the process diagram of FIG. 1, an alloy having a composition as shown in Table 1 is dissolved in an induction furnace and cast into an iron mold to form columnar tablets.

Next, in order to harden an ingot magnetically, it annealed at 1000 degreeCx24 hours.

In the case of a casting mold, when these steps are cut and ground, it becomes an in-plane anisotropic magnet using the anisotropy of columnar crystals.

In the case of anisotropic molding, hot working is performed before annealing, followed by annealing.

In this embodiment, a hot press was used as the hot working method.

Processing temperature was 1000 degreeC. Next, columnar crystals were formed using iron molds for Pr ₁₄ Fe ₈₂ B ₄ and Nd ₁₅ Fe ₇₇ B _{8, which} are the optimum compositions of the sintering method of Document 2, and isotropic using vibration molds. Three types of shafts were formed and coarse grains were formed using a ceramic mold. The results are shown in Table 3.

TABLE 1

TABLE 2

TABLE 3

It is clear from Table 3 that less B shows higher magnetic performance.

It can be seen that the columnar crystals formed in the present invention are excellent in all magnetic properties such as casting, hot working, coercive force (iHc), maximum energy [(BH) max], and degree of orientation.

As described above, according to the permanent magnet of the present invention and its manufacturing method, it is possible to obtain a high-performance magnet and increase the productivity by only heat treatment without grinding the casting ingot.

Claims (4)

A permanent magnet composed mainly of rare earth elements (including Y), transition metals, and boron, wherein the cast structure of the magnet is columnar crystals and is anisotropically formed. In the method for producing a permanent magnet composed mainly of rare earth elements (including Y), transition metals, and boron, melting and casting are carried out, and the cast structure of the magnet is columnar and heat-treated at a temperature of 250 ° C. Method for producing a permanent magnet, characterized in that it is cured magnetically. In the manufacturing method of a permanent magnet composed mainly of rare earth elements (including Y), transition metals, and boron, after melting and casting, hot working at a temperature of 500 ° C. or higher to orient the crystal axis of the crystal grains in a specific direction. A method for producing a permanent magnet, characterized in that the magnet is anisotropically magnetically. In the method for producing a permanent magnet having a rare earth element (including Y) and boron as a main component, after melting and casting, hot working at a temperature of 500 ° C. or higher, followed by heat treatment at a temperature of 250 ° C. or higher, to harden magnetically Method for producing a permanent magnet, characterized in that.

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