JPH04293206A - Pare earth elements-fe-b based anisotropic permanent magnet - Google Patents

Abstract

PURPOSE:To obtain a rare earth elements-Fe-B based magnet which has both performances of thin configuration and high quality and is most suitable to a permanent magnet for, e.g. a voice coil motor. CONSTITUTION:In order to micronize crystal, a specified amount of one or more kinds of element selected out of a group composed of Ag, Au, Pt, Sn and Zn is added to the rare earth elements-Fe-B based basic component. Hence the crystal in an ingot stage or after an anisotropic state is obtained has an average grain diameter smaller than or equal to 30mum, and a permanent magnet whose maximum energy product is 35MGOe and whose coercive force is 14KOe can be obtained even in the configuration thinner than or equal to 3mum.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to rare earth element-Fe-B anisotropic permanent magnets, and more specifically, rare earth element magnets that are thin-walled yet high-performance, and that exhibit optimal characteristics for use in, for example, voice coil motors. The present invention relates to an anisotropic permanent magnet based on element-Fe-B.

0002

2. Description of the Related Art Magnetic materials, including permanent magnets, are used in a wide range of fields, from various household appliances to peripheral end devices for large computers, and are important electrical and electronic materials. Recently, the miniaturization of motors, etc.
As performance continues to improve, permanent magnets are becoming thinner and thinner.
High performance is required. In particular, thinner, higher-performance permanent magnets are required for voice coil motors used in head actuator mechanisms for positioning magnetic heads on arbitrary information tracks on magnetic disks.

[0003] In recent years, rare earth magnets have attracted attention as the third type of permanent magnet after ferrite magnets and alnico magnets. This rare earth magnet is expected to exhibit excellent magnetic properties that can contribute to the miniaturization and higher precision of electrical products and precision instruments, and active progress is being made in both physical property research and production technology. Among them, the rare earth element-transition element-B system, such as Nd-F, has been particularly expected in recent years.
It is a permanent magnet such as e-B or Pr-Fe-B. The permanent magnet composition of the present invention has a rare earth element -Fe-B as a basic component, and also contains one or more elements selected from the group consisting of Ag, Au, Pt, Sn and Zn as an essential component. Although the evaluation will be explained in detail later, in the following explanation, for convenience, we will use a rare earth element-Fe-B system (hereinafter sometimes abbreviated as R-Fe-B system magnet) ternary system magnet as a representative. I would like to discuss this topic.

By the way, the following two methods were initially considered as methods for manufacturing R--Fe--B magnets. The first method is a sintering method based on powder metallurgy as seen in, for example, JP-A No. 59-46008; (2) Oxygen brought in during sintering has a negative effect on magnetic performance. (2) Magnetic performance may be degraded due to carbon content from forming aids added during sintering. , ■ The formed body (green body) before sintering has low strength,
Due to several drawbacks such as poor handling, the characteristics expected of R-Fe-B magnets have not been fully demonstrated.

The second method is to make a quenched flake and then use a thermoplastic resin or the like to make a bonded magnet.It does not have the above drawbacks, but has the following disadvantages: (1) low productivity, and (2) isotropic in principle. Only magnets can be obtained, and therefore the maximum energy product [hereinafter (
BH) max] is low, and the squareness is also poor. Therefore, as a means to actively make the anisotropy, it has been considered to subject the rapidly cooled flakes to a two-step hot press treatment (mechanical orientation treatment) (for example, Japanese Patent Application Laid-open Nos. 59-211549 and 60-1004).
No. 02, etc.). However, this is not a realistic method considering the need for mass production since the productivity is even lower.

[0006] Therefore, as a third method, for example,
As seen in No. 2-276803, hot rolling is applied to cast alloys to refine the grains and increase the coercive force. A means of sexualization was developed. However, in the normal rolling method, there is no restraint from both sides in the plate width direction, so the central part of the rolled ingot is rolled out in the plate width direction.
Sufficient density cannot be obtained on the edge side of the plate width, and the orientation of the crystal axes is incomplete. Therefore, even if this method is adopted, it does not mean that magnetic anisotropy can be immediately obtained over the entire width direction of the plate. Moreover, in order to form the desired degree of axial orientation across the entire width of the sheet under the normal hot rolling conditions described above, it is necessary to carry out considerably strong working, and therefore it is necessary to have sufficient workability to cope with this. There was also a problem in that the alloy composition of rare earth magnets was greatly restricted due to the requirement for materials with a high degree of compatibility.

[0007] The present inventors therefore proposed a method that can overcome the drawbacks of the third method described above, by enclosing an alloy ingot in a metal capsule and applying hot plasticity to the metal capsule while constraining it from the width direction. We have proposed a series of methods for processing (rolling, casting) and, if necessary, heat treatment after hot working, and have previously filed an application (Japanese Patent Laid-Open No. 2-250918-23). With the development of the above-mentioned technology, it has become possible to obtain anisotropic permanent magnets with excellent magnetic properties relatively easily and freed from restrictions in terms of materials due to processing reasons.

[0008]

[Problems to be Solved by the Invention] As mentioned above, for products such as voice coil motors that require particularly small size and high performance, the permanent magnets used must be thinner and have higher performance. It is necessary to satisfy the characteristics. However, in general, the thinner the magnet, the lower its performance tends to be, and the important point is how to satisfy both of these contradictory characteristics.

For example, thin-walled permanent magnets of 1 mm or less can be manufactured using bonded magnets, but as mentioned above, there are difficulties in terms of magnetic properties, and even more so for permanent magnets for voice coil motors, which require thinner walls and higher performance. It is not usable as such. On the other hand, in the sintering method, it is difficult to sinter the thin wall. For example, if you want to obtain a thin magnet of 3 mm or less,
Although it is machined from a large block, the performance decreases due to thinning, and as shown in Examples below, when the thickness is about 1 mm, the desired magnetic properties cannot be obtained. Regarding thin-walled anisotropic magnets, for example, JP-A-62-19256
As shown in No. 6, a method of mechanically polishing a magnet to make it thinner has been proposed. However, a decline in productivity cannot be avoided.

[0010] The present invention was made to solve the above-mentioned technical problems, and its purpose is to provide a thin-walled magnet with magnetic properties superior to those of a sintered magnet, which also has the characteristics of high performance. An object of the present invention is to provide a rare earth element-Fe-B magnet.

[0011]

[Means for Solving the Problems] The present invention, which has achieved the above object, is a method in which a columnar crystal structure having an average grain size of 30 μm or less and having the following compositions (A) to (D) is subjected to hot plastic working and heat treatment. It is a rare earth element-Fe-B magnet having an average grain size of 30 μm or less. (A) Two or more rare earth elements including Y (however, 50
% by weight or more is Pr): 12 to 18 atomic % (B)
B: 4 to 6 atomic% (C) One or more elements selected from the group consisting of Ag, Au, Pt, Sn and Zn: 0.2 to 2 atomic% (
D) Remainder: Fe and inevitable impurities

0012

[Operation] The present inventors manufactured a magnet according to the manufacturing method proposed and disclosed above, and studied from various angles a permanent magnet that has both characteristics of being thin and having high performance. As a result, in order to improve the performance of R-Fe-B magnets, it is effective to refine the average grain size of the columnar crystal structure (ingot grain size) at the ingot stage, which is the raw material, as shown in Figure 1. It turned out to be. Although the above-mentioned refinement can be achieved to some extent by increasing the amount of heat removed during casting, the equipment becomes large-scale, leading to a decrease in productivity. Therefore, the inventors of the present invention repeatedly investigated the refinement using additive elements, and found that R-Fe
-As the fourth element for the B system, Ag, Au, Pt,
It has been found that Sn, Zn, etc. are effective, and by adding one or more of them in combination, the crystal grains of the magnetic alloy can be made finer. Furthermore, the above additive elements exist in the grain boundary phase of the alloy, suppressing the formation of a surface deterioration layer due to processing, and even when the thickness is made as thin as 0.5 mm, the magnetic properties surpass those of sintered magnets. [(BH)max=35
MGOe or more, iHc = 14KOe or more], and completed the present invention.

Next, the alloy composition constituting the R-Fe-B magnet of the present invention will be explained. First of all, as a rare earth element,
Until now, lanthanoid rare earth elements containing Y have been widely used, but in the present invention, it has been concluded that it is useful to use two or more rare earth elements containing at least half of Pr. The type of rare earth element used in combination with Pr is not particularly limited, but among them Nd, Ce, La, Tb
, Dy, Ho, Y, etc. are particularly preferred. The reason why 50% by weight or more of the rare earth elements used in the magnet of the present invention is Pr is because Pr exhibits the most excellent magnetic properties. Regarding rare earth elements other than Pr, one type or a combination of two or more of the rare earth elements other than Pr may be used, but Pr--Nd alloy is most advantageously used practically. Note that the rare earth elements in the magnet of the present invention may contain a small amount of rare earth elements other than the above, but 1
It should be kept below % by weight.

In the R-Fe-B magnet of the present invention, R
If it is too small, the main phase R2-Fe14-B (atomic ratio, e.g. Pr2Fe14B) cannot be formed, and the amount of liquid phase (main phase amount) necessary for anisotropy during hot working cannot be formed.
cannot be obtained, and the high performance of the magnet cannot be achieved. From this point of view, the proportion of rare earth elements needs to be 12 atomic % or more. On the other hand, if the upper limit exceeds 18 at %, the R-rich phase, which is a non-magnetic phase, will be excessive, and this will appear as a decrease in magnetic flux density, making it impossible to exhibit good magnetic properties.

B must be contained in an amount of 4 to 6 atomic %; if it is less than 4 atomic %, the volume fraction of the main phase will be insufficient, leading to a decrease in magnetic flux density. On the other hand, regarding the upper limit, R2 does not have magnetic properties.
From the viewpoint of preventing a decrease in iHc due to the appearance of the Fe4B4 phase, it is necessary to keep it at 6 atomic % or less.

Additive elements such as Ag, Au, Pt, Sn, and Zn achieve the refinement of the columnar structure and the suppression of the formation of a surface deterioration layer that accompanies the grinding process, as described above, thereby making it possible to achieve thin walls. It is designed to achieve high performance even when In order to achieve the above effect, it is necessary to use 0 individually or in total.
．． It is necessary to set it to 2 at%, but if it is too large, the non-magnetic grain boundary phase will increase and the properties will deteriorate, so it should be set at 2 at%.
It should be:

In addition to the above-mentioned essential components, the magnet of the present invention basically consists of Fe and inevitable impurities. Although Fe is an essential element for forming a magnetic phase, a portion (for example, about 20% by weight) of Fe may be replaced with Co.

In the magnet of the present invention, the average grain size of both the columnar crystal structure and the crystal structure after anisotropy is specified to be 30 μm or less, and the reason for this is as follows. It is. First, as shown in FIG. 1, in order to obtain properties equivalent to or better than those of a sintered magnet, the average grain size of the columnar crystal structure after casting must be 30 μm or less. In addition, hot plastic working and heat treatment of the ingot improves the coercive force, but excessive heat treatment will coarsen the crystal grains and cause a decrease in the coercive force. Even in crystals, the average grain size is 30μ
It must be less than m.

[0019] The present invention will be explained in more detail with reference to examples below, but the following examples are not intended to limit the present invention, and any design changes in accordance with the spirit of the preceding and following descriptions are within the scope of the present invention. It is included in the technical scope.

[0020]

[Example] Alloy ingots having the compositions shown in Table 1 (No. 1 to
20) was produced by high frequency melting. The starting materials at this time were electrolytic iron with a purity of 99.9% by weight for Fe, ferroboron alloy for B, and 99.9% by weight of rare earth elements and other additive elements. Then, it was cast using a copper mold to form fine columnar crystals with an average grain size of 30 μm or less.

[0021]

[Table 1]

Next, the alloy ingot was cut and sealed in an iron capsule, and hot rolled at 950° C. with a total reduction of 76% while being restrained from the width direction. Continue to 1000℃
Heat treatment was performed at 480°C for 6 hours (first stage) and at 480°C for 2 hours (second stage), and the magnetic properties and average grain size of the obtained magnet alloy were investigated. The results are shown in Table 2.Ag,
It can be seen that those to which Au, Pt, Sn, Zn, etc. are added can make the crystals finer and obtain good magnetic properties.

[0023]

[Table 2]

Next, an alloy powder having a composition (atomic ratio) of Nd13Dy1Fe79B7 and an average particle size of 3 μm was pressure-molded in a 10 KOe magnetic field at a pressure of 1.5 ton/cm2, and then the powder had a purity of 99.999%. The magnet was sintered in Ar gas (250 Torr) at 1070°C for 2 hours, and further subjected to aging heat treatment at 530°C for 1 hour to obtain a sintered magnet. The obtained sintered magnet and No. 1 shown in Table 2. 11
, 14, 17, 19, and 20 magnets with a thickness of 3
,1 ,0.5 ,0.3 ,1.0 ,0.05(
mm), and the magnetic properties of each were investigated. The results are shown in Table 3, and the one of the present invention is 0.5
It can be seen that even with a thickness as thin as mm 2 , it exhibits good magnetic properties that can be used as a permanent magnet for a voice coil motor, for example.

[0025]

[Table 3]

[0026]

Effects of the Invention As described above, according to the present invention, Ag, Au, and Pt are added as the fourth element to the rare earth element-Fe-B system.
By adding . Further, the permanent magnet according to the present invention is most suitable as a permanent magnet for a voice coil motor due to its characteristics.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between ingot particle size and magnetic properties.

Claims (2)

[Claims] [Claim 1] Containing the following components (A) to (D), a columnar crystal structure with an average grain size of 30 μm or less is made anisotropic by hot plastic working and heat treatment,
A rare earth element-Fe-B anisotropic permanent magnet having an average particle size of 30 μm or less. (A) Two or more rare earth elements including Y (however, 50
% by weight or more is Pr): 12 to 18 atomic % (B)
B: 4 to 6 atomic% (C) One or more elements selected from the group consisting of Ag, Au, Pt, Sn and Zn: 0.2 to 2 atomic% (
D) Remainder: Fe and inevitable impurities [Claim 2]
The thickness in the anisotropy direction is 0.5 to 3 mm, the maximum energy product is 35 MGOe or more, and the coercive force is 14 KOe.
The anisotropic permanent magnet according to claim 1, which is the above.