JP7435134B2 - Manufacturing method of RTB based sintered magnet - Google Patents

Description

The present disclosure relates to a method for manufacturing an RTB-based sintered magnet.

The RTB system sintered magnet (R is at least one rare earth element, T is Fe or Fe and Co, and 90% by mass or more of T is Fe) has an R ₂ T ₁₄ B type crystal structure. It consists of a main phase consisting of a compound having the following properties and a grain boundary phase located at the grain boundaries of this main phase, and is known as the highest performance magnet among permanent magnets. Therefore, they are used in a wide variety of applications, including voice coil motors (VCMs) for hard disk drives, motors for electric vehicles (EV, HV, PHV), motors for industrial equipment, and home appliances.

Patent Document 1 discloses that the amount of precipitated R ₂ T ₁₇ phase is adjusted by adjusting the amount of R and the amount of B to appropriate ranges, and the amount of Ga is adjusted to the optimal range according to the amount of precipitated R ₂ T ₁₇ phase. By doing so, the RTB has a high residual magnetic flux density B _r (hereinafter sometimes simply referred to as "B _r ") and a high coercive force H _cJ (hereinafter sometimes simply referred to as "H _cJ "). It is described that a system sintered magnet can be obtained.

The RTB system sintered magnet described in Patent Document 1 is a sintered magnet in which the component in R is mainly Nd (hereinafter sometimes referred to as Nd magnet), and has a high B _r at room temperature. It has a high H _cJ . On the other hand, there is a sintered magnet (hereinafter sometimes referred to as a Pr magnet) in which the component in R is mainly Pr as a magnet that exhibits higher _Br at a lower temperature than a Nd magnet.

International Publication No. 2014/157448

Pr magnets are used for applications such as undulators because they can obtain high _Br at low temperatures. Further, particularly in applications such as undulators, a high squareness ratio H _k /H _cJ (hereinafter sometimes simply referred to as H _k /H _cJ ) is required at room temperature. This is because when H _k /H _cJ at room temperature is low, demagnetization tends to occur when a magnet is assembled to an undulator (especially when a magnet is assembled to form a magnetic circuit), and this causes high B _r at low temperatures. This is because it may cause a problem of not being able to obtain the required amount. Therefore, Pr magnets are required to have high B _r at low temperatures and high H _k /H _cJ at room temperature. However, according to studies conducted by the present inventors, it has been found that RTB-based sintered magnets have a problem in that H _k /H _cJ at room temperature decreases when the Pr content increases.

Therefore, the present disclosure provides a method for manufacturing an RTB-based sintered magnet that has high B _r at low temperatures and high H _k /H _cJ at room temperature.

In a non-limiting embodiment, the method for manufacturing an RTB-based sintered magnet of the present disclosure includes an RTB-based sintered magnet (R is at least one kind of rare earth element and always includes Pr, T is (Fe or Fe and Co, and the content of Fe is 90% by mass or more based on the total T), comprising the steps of preparing an RTB alloy powder, and the step of preparing an RTB alloy powder; The content of Pr in the R-T-B-based sintered magnet includes a step of molding a system alloy powder to prepare a molded body, and a step of sintering the molded body to produce a sintered body. is 75% by mass or more of the entire R, and in the step of preparing the sintered body, the molded body is heated at a temperature of 950° C. or more and 1100° C. or less, and the heating time is 10 hours or more and 56 hours or less, and When the heating time is t (hour), the Pr content (mass%) of the RTB sintered magnet is [Pr], and the R content (mass%) is [R], t ≧0.859×e ^{(3.26×[Pr]/[R])} (e is Napier's number).

In one embodiment, the content of Pr in the RTB sintered magnet is 80% by mass or more of the total R.

According to embodiments of the present disclosure, it is possible to provide a method for manufacturing an RTB-based sintered magnet that has high B _r at low temperatures and high H _k /H _cJ at room temperature.

As a result of studies, the present inventors found that when the Pr content in the RTB-based sintered magnet increases, high _Br can be obtained at low temperatures, but H _k /H _cJ at room temperature decreases. As a result of further investigation, it was found that in order to obtain high H _k /H _cJ at room temperature, it was necessary to appropriately manage the sintering heating time according to the Pr content. As a result of further experiments, the heating time was t (hour), the Pr content (mass%) of the RTB sintered magnet was [Pr], and the R content (mass%) was [R]. It has been found that a high H _k /H _cJ can be obtained if t≧0.859×e ^{(3.26×[Pr]/[R])} (e is Napier's number). This makes it possible to obtain an RTB-based sintered magnet that has high B _r at low temperatures and high H _k /H _cJ at room temperature.
In the field of RTB sintered magnets, H _k , which is a parameter measured to obtain H _k /H _cJ , is generally calculated as J (strength of magnetization) - H (strength of magnetic field). ) In the second quadrant of the curve, the H-axis reading at the position where J has a value of 0.9×J _r (J _r is residual magnetization, J _r =B _r ) is used. The ratio of H _k to H _cJ of the demagnetization curve H _k /H _cJ (=H _k (kA/m)/H _cJ (kA/m)×100 (%)) is defined as the squareness ratio. The same definition is given in this disclosure.
Furthermore, in the present disclosure, low temperature refers to -180°C±20°C, and room temperature refers to 25°C±10°C.

[RTB-based sintered magnet]
First, an RTB-based sintered magnet obtained by the manufacturing method of the present disclosure will be described.
[Composition of RTB sintered magnet]
The RTB-based sintered magnet of the present disclosure has, for example, the following composition.
R: 28.5% by mass or more and 33.0% by mass or less B: 0.80% by mass or more and 1.50% by mass or less,
Cu: 0.05% by mass or more and 0.50% by mass or less,
T: Contains 61.5% by mass or more and 70.0% by mass or less.
Each composition will be explained in detail below.

(R: 28.5-33.0% by mass)
In the RTB-based sintered magnet of the present disclosure, R is at least one rare earth element and always includes Pr, T is Fe or Fe and Co, and the Fe content is 90% by mass or more based on the entire T. It is. Furthermore, the content of Pr in the RTB-based sintered magnet of the present disclosure is 75% by mass or more of the total R. If the content of Pr is less than 75% by mass of the entire R, high _Br may not be obtained at low temperatures. In order to obtain higher _Br at low temperatures, the content of Pr is preferably 80% by mass or more and 90% by mass or less of the total R.
The content of R is 28.5 to 33.0% by mass. If R is less than 28.5% by mass, densification during sintering may be difficult, and if it exceeds 33.0% by mass, the main phase ratio may decrease and high _Br may not be obtained. There is. The content of R is preferably 29.5 to 32.5% by mass. If R is within this range, higher B _r can be obtained.

(B: 0.80 to 1.50% by mass)
The content of B is 0.80 to 1.50% by mass. If B is less than 0.80% by mass, R ₂ T ₁₇ phase may be generated and high H _cJ may not be obtained, and if it exceeds 1.50% by mass, B _r may be decreased.

(Cu: 0.05-0.50% by mass)
The content of Cu is 0.05 to 0.50% by mass. If Cu is less than 0.05% by mass, it may not be possible to obtain high H _cJ , and if it exceeds 0.50% by mass, sinterability may deteriorate and high H _cJ may not be obtained. .
T is Fe or Fe and Co, and 90% by mass or more of T is Fe. Corrosion resistance can be improved by containing Co, but if the amount of Co substitution exceeds 10% by mass of Fe, high _Br may not be obtained. The content of T is 61.5% by mass or more and 70.0% by mass or less. If the T content is less than 61.5% by mass, _Br may be significantly reduced, and if it exceeds 70.0% by mass, H _cJ may be reduced.

[Method for manufacturing RTB sintered magnet]
Next, a method for manufacturing the RTB sintered magnet of the present disclosure will be described.
(1) Step of preparing RTB alloy powder Metals or alloys of each element are prepared so as to have the above composition, and a flake-shaped alloy is obtained using a strip casting method or the like.
The obtained flaky alloy is subjected to hydrogen pulverization, and the size of the coarsely pulverized powder is reduced to, for example, 1.0 mm or less. Next, by pulverizing the coarsely pulverized powder using a jet _mill or the like, for example, finely pulverized powder (R -T-B alloy powder) is obtained. Note that a known lubricant may be used as an auxiliary agent for the coarsely pulverized powder before jet mill pulverization, the RTB alloy powder during jet mill pulverization, and after jet mill pulverization.

(2) Step of preparing a compact The obtained RTB alloy powder is subjected to compacting in a magnetic field to obtain a compact. Molding in a magnetic field is a dry molding method in which dry RTB alloy powder is inserted into a mold cavity and molded while applying a magnetic field. Any known molding method in a magnetic field may be used, including a wet molding method in which a slurry in which system alloy powder is dispersed is injected and molded while discharging the dispersion medium of the slurry.

(3) Step of preparing a sintered body A sintered body (sintered magnet) is obtained by sintering the molded body obtained in the molding process in a sintering furnace. In the present invention, the molded body is heated at a temperature of 950° C. or higher and 1100° C. or lower. The heating time is 10 hours or more and 56 hours or less, and the heating time is such that the heating time is t (hours) and the Pr content (mass %) of the RTB-based sintered magnet is [Pr] , when the content (mass%) of R is [R], t≧0.859×e ^{(3.26×[Pr]/[R])} (e is Napier's number (2.7183...) ) is satisfied.
If the sintering temperature is lower than 950°C or higher than 1100°C, Br will decrease and high _Br may not be obtained even at low temperatures. Further, if the heating time t (hour) does not satisfy t≧0.859×e ^{(3.26×[Pr]/[R])} , H _k /H _cJ at room temperature decreases. Note that H _k /H _cJ of the RTB-based sintered magnet in the present disclosure is preferably 91% or more, more preferably 92% or more. In addition, as a method for measuring the sintering temperature, it is preferable to measure the temperature by bringing a thermocouple into contact with the compact in the sintering furnace. In addition, simply by measuring the temperature inside the sintering furnace and the temperature of another compact placed in the sintering furnace at the same time using a thermocouple, it is possible to The correspondence relationship with the temperature of the compact in the furnace may be investigated, and based on the correspondence, the temperature of the compact in the sintering furnace may be read from the temperature in the sintering furnace.
Further, the heating time t is defined as the time from when the molded body is heated in the sintering furnace and reaches a predetermined sintering temperature to when heating and holding at the predetermined sintering temperature is stopped.

(4) Heat treatment step The obtained sintered body (sintered magnet) may be subjected to heat treatment for the purpose of improving magnetic properties. The heat treatment temperature is, for example, 400°C or more and 900°C or less. Known conditions can be used for the holding time in the heat treatment step, and for example, it can be set to 60 minutes or more and 300 minutes or less. Note that the holding time is defined as the time from the time when the sintered body is heated in a heat treatment furnace and reaches a predetermined heat treatment temperature to the time when heating and holding at the predetermined heat treatment temperature is stopped. Further, in order to prevent oxidation caused by the atmosphere, it is preferable to perform the heat treatment in a vacuum atmosphere or an atmospheric gas. It is preferable to use an inert gas such as helium or argon as the atmospheric gas.

In the present invention, an additional heat treatment step may be performed one or more times after the sintering step and before the heat treatment step. As an additional heat treatment step, for example, the sintered body is heated to 400° C. or higher and lower than the sintering temperature, preferably 700° C. or higher and lower than 900° C. (for example, after heating at a lower temperature than the first time), and then cooled to room temperature. It's okay.

The obtained sintered magnet may be subjected to mechanical processing such as grinding for the purpose of shaping it into a final product shape. In that case, the heat treatment may be performed before or after machining. Furthermore, the obtained sintered magnet may be subjected to surface treatment. The surface treatment may be any known surface treatment, such as Al vapor deposition, electrolytic Ni plating, or resin coating.

The present disclosure will be explained in more detail with reference to Examples, but the present disclosure is not limited thereto.

Example 1
The RTB system sintered magnet is approximately alloy No. 1 in Table 1. Each element was weighed and cast by strip casting to obtain a flake-like alloy having the compositions shown in 1 to 4. The resulting flaky alloy was subjected to hydrogen embrittlement in a hydrogen pressurized atmosphere, and then subjected to dehydrogenation treatment by heating and cooling in vacuum to 550°C to obtain coarsely pulverized powder. Next, 0.04% by mass of zinc stearate was added as a lubricant to the obtained coarsely pulverized powder based on 100% by mass of the coarsely pulverized powder, and after mixing, the powder was milled using an air flow mill (jet mill device). The powder was dry-milled in a nitrogen atmosphere to obtain an RTB alloy powder having a _D50 of 4.0 μm. The results of component analysis of the obtained RTB alloy powder are shown in Alloy No. 1 in Table 1. Shown in 1 to 4. Each component in Table 1 was measured using inductively coupled plasma optical emission spectroscopy (ICP-OES).

A lubricant was added to the RTB alloy powder in an amount of 0.4% by mass based on 100% by mass of the finely pulverized powder, and the mixture was mixed and then compacted in a magnetic field to obtain a compact. The molding device used was a so-called right-angle magnetic field molding device (transverse magnetic field molding device) in which the magnetic field application direction and the pressing direction were perpendicular to each other.

The obtained molded body was heated at a temperature of 1000° C. or more and 1100° C. or less (set at a temperature that sufficiently densified each sample). Also, No. By preparing multiple samples with heating times ranging from 4 hours to 56 hours for each of Nos. 1 to 4, No. The heating times at which H _k /H _cJ for each of Examples 1 to 4 reached 89%, 91%, and 92% were determined. The results are shown in Table 2. Note that H _k /H _cJ was determined as follows. A sample measuring 7 mm in length, 7 mm in width, and 7 mm in thickness was prepared by machining an RTB-based sintered magnet, and measured with a B-H tracer. ) In the second quadrant of the curve, let H _k be the reading on the H axis at the position where J becomes 0.9 x J _r (J _r is residual magnetization, J _r = B _r ), and the demagnetization curve is The ratio H _k /H _cJ of this H _k to H _cJ was determined as H _k (kA/m)/H _cJ (kA/m)×100 (%). Furthermore, low-temperature _Br was machined into a sintered R-T-B magnet to produce a sample with dimensions of 2.8 mm in length, 2.8 mm in width, and 2.8 mm in thickness. Measured at -173°C. _Br was the same with no difference depending on the heating time. The results are shown in Table 2. In addition, in all of the invention examples in Table 2, the heating time was 10 hours or more and 56 hours or less, and t≧0.859×e ^{(3.26×[Pr]/[R]))} was satisfied. was. On the other hand, No. Comparative Examples 1 to 3 did not all satisfy t≧0.859×e ^{(3.26×[Pr]/[R]. In addition, No. 4 did not satisfy t≧0.859×e (3.26×[Pr]/[R].} time or less) were outside the scope of this disclosure.

As shown in Table 2, all of the examples of the present invention have high _Br at low temperatures and high H _k /H _cJ (91% or more) at room temperature. On the other hand, No. 1 in which the Pr content is less than 75% by mass of the entire R. In No. 4, high _Br was not obtained at low temperature. Furthermore, No. In No. 4, there is no difference in H _k /H _cJ at room temperature depending on the heating time. On the other hand, No. 1 in which the content of Pr is 75% by mass or more of the entire R. 1 and no. Comparing 2, No. No. 2 (Pr content is 80% by mass of the total R) has H _k /H _cJ at room temperature of 91% or more when the heating time is 12 hours. No. 1 (R is Pr) had H _k /H _cJ at room temperature of less than 91% even when the heating time was the same, 12 hours. No. 2 and no. The same thing can be said when comparing 3. This indicates that the heating time required to obtain high H _k /H _cJ at room temperature varies depending on the Pr content.

Claims (2)

R-T-B system sintered magnet (R is at least one rare earth element and always contains Pr, T is Fe or Fe and Co, and the content of Fe with respect to the entire T is 90% by mass or more) A manufacturing method,
A step of preparing RTB alloy powder;
a step of molding the RTB alloy powder to prepare a molded body;
sintering the molded body to produce a sintered body,
The content of Pr in the RTB-based sintered magnet is 75% by mass or more of the total R, and the step of preparing the sintered body includes heating the compact at a temperature of 950°C or higher and 1100°C or lower. , the heating time is 34 hours or more and 56 hours or less, and the heating time is t (hours), the Pr content (mass %) of the RTB sintered magnet is [Pr], and the R R-T-B system that satisfies t≧0.859×e ^{(3.26×[Pr]/[R])} (e is Napier's number) when content (mass%) is [R] Method of manufacturing sintered magnets. The method for producing an RTB-based sintered magnet according to claim 1, wherein the content of Pr in the RTB-based sintered magnet is 80% by mass or more of the total R.