Method for manufacturing R-T-B sintered magnet

Abstract

To provide a manufacturing method of an R-T-B system sintered magnet, suppressing deformation of a rare earth sintered magnet after the sintering.SOLUTION: A manufacturing method of an R-T-B system sintered magnet in a present disclosure, contains: a step of preparing an alloy powder of an R-T-B system (R is a rare earth element, and contains at least one selected from a group of Nd, Pr, and Ce, T is at least one kind of a transition metal element, and essentially contains Fe); a step of manufacturing a rectangular parallelepiped molding body by molding the R-T-B system alloy powder; a step of beveling a side end part of at least one surface of the molding body; a step of mounting the molding body onto the support plate after the beveling a surface obtained by beveling the side end part contacts the support plate; and a step of sintering the molding body mounded onto the support plate.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method for manufacturing an R-T-B sintered magnet.

Background Art

[0002] In recent years, rare earth sintered magnets have shown high demand. Among them, R-T-B sintered magnets (where R is at least one of rare earth elements, including at least one of Nd and Pr; T is mainly Fe; and B is boron) are known as the most high-performance magnets and are used in various motors such as voice coil motors (VCM) of hard disk drives, motors for electric vehicles (EV, HV, PHV, etc.), and motors for industrial equipment, as well as in household electrical appliances. R-T-B sintered magnets contribute to energy conservation and reduction of environmental load through miniaturization and weight reduction of various motors and the like.

[0003] Such R-T-B sintered magnets are manufactured, for example, through a process of preparing an R-T-B alloy powder, a process of producing a compact by molding the R-T-B alloy powder, and a process of sintering the compact. When sintering the compact, for example, a sintering container in which the compact is placed on a support plate made of a high melting point metal material such as molybdenum is heated to a temperature of about 1000°C to 1100°C for sintering treatment. At this time, for example, in addition to the direct influence of the sintering container, deformation of the sintered body may be caused by the influence of oxygen, carbon, etc.

[0004] Patent Document 1 proposes placing a getter material in a sintering case to remove oxygen in the sintering atmosphere, thereby suppressing deformation of the sintered body in the rare earth sintered magnet after sintering.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Although it is possible to reduce the influence of oxygen and carbon by the method described in Patent Document 1, it may be insufficient to prevent deformation of the sintered body. An embodiment of the present disclosure provides a method for manufacturing an R-T-B sintered magnet that suppresses deformation of a sintered body in a rare earth sintered magnet after sintering.

Means for Solving the Problems

[0007] The method for manufacturing an R-T-B sintered magnet of the present disclosure, in an exemplary embodiment, includes a step of preparing an R-T-B alloy powder (where R is a rare earth element and necessarily includes at least one selected from the group consisting of Nd, Pr, and Ce, and T is at least one of transition metal elements and necessarily includes Fe), a step of producing a rectangular parallelepiped-shaped compact by molding the R-T-B alloy powder, a step of chamfering side edge portions of at least one surface of the compact, a step of placing the chamfered compact on the support plate such that the chamfered surface of the side edge portion contacts the support plate, and a step of sintering the compact placed on the support plate.

[0008] In an embodiment, when the shortest side of the rectangular parallelepiped-shaped compact is taken as the thickness, the chamfered surface of the side edge portion is a surface perpendicular to the thickness direction. End is a surface perpendicular to the thickness direction.

[0009] In an embodiment, the thickness is 7 mm or less.

Advantages of the Invention

[0010] According to an embodiment of the present disclosure, it is possible to provide a method for manufacturing an R-T-B sintered magnet that suppresses deformation of a sintered body in a rare earth sintered magnet after sintering.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2A

Figure 2B

Figure 3

[0012] The present inventors conducted a detailed study of the effects of oxidation during sintering of rectangular parallelepiped compacts. They found that the edges of the compact are more susceptible to oxidation than the center, resulting in thicker edges than the center. Therefore, the center of the compact is lifted using the edges (all edges around the surface of the compact that contacts the support plate) of the surface of the compact that contacts the support plate during sintering as fulcrums. This causes the center to sag under its own weight during sintering, resulting in deformation (warping) of the resulting sintered compact. Furthermore, they found that this tendency is particularly pronounced in thin (7 mm or less) flat rectangular parallelepiped compacts. Based on these findings, further investigations revealed that deformation can be suppressed even for thin (7 mm or less) flat rectangular parallelepiped compacts by chamfering at least one edge of the compact and placing the compact on the support plate so that the chamfered surface is in contact with the support plate. This is thought to be because by chamfering the edge of the surface of the molded body that comes into contact with the support plate, it is possible to eliminate the fulcrum at the center of the molded body for lifting it up.

[0013] (RTB sintered magnet) The RTB based sintered magnet of the present disclosure has, for example, the following composition. R: 27-35 mass%, B: 0.80 to 1.20 mass%, Ga: 0 to 1.0 mass%, Cu: 0 to 0.5 mass%, T: Contains 60 mass% or more.

[0014] (R: 27 to 35 mass%) R is a rare earth element and necessarily contains at least one selected from the group consisting of Nd, Pr, and Ce. If R is less than 27 mass%, a liquid phase may not be sufficiently formed during the sintering process, making it difficult to sufficiently densify the sintered body. On the other hand, if R exceeds 35 mass%, grain growth may occur during sintering, and H cJ may decrease. The content of R is preferably 29.5 to 33.0 mass%. If R is within such a range, a higher B r can be obtained.

[0015] (B: 0.80 to 1.20 mass%) If B is less than 0.80 mass%, B r may decrease. On the other hand, if B exceeds 1.20 mass%, H cJ may decrease. The content of B is preferably 0.88 to 0.90 mass%. If B is within such a range, a higher H cJ can be obtained.

[0016] (Ga: 0 to 1.0 mass%) The content of Ga is preferably 0 to 1.0 mass%, more preferably 0.2 to 0.7 mass%. If Ga is within such a range, a higher H cJ can be obtained.

[0017] (Cu: 0 to 0.50 mass%) The content of Cu is preferably 0 to 0.50 mass%, more preferably 0.05 to 0.30 mass%. If Cu is within such a range, a higher H cJ can be obtained.

[0018] (T: 60 mass% or more) T is at least one of transition metal elements and necessarily contains Fe. If the content of T in the sintered magnet is less than 60 mass%, the magnetic properties may be significantly degraded. The content of T is preferably 61.5 to 69.5 mass%. Also, when the total amount of T is 100 mass%, up to 10 mass% of it can be replaced with Co. For example, 90 mass% of the total amount of T can be Fe and 10 mass% can be Co. Alternatively, the total amount of T (100 mass%) can be Fe. Containing Co can improve the corrosion resistance, but if the replacement amount of Co exceeds 10 mass% of Fe, a high B r may not be obtained. The sintered magnet of the present invention may further contain any other element.

[0019] Hereinafter, a method for manufacturing an R-T-B-based sintered magnet will be described. (1) Step of preparing an R-T-B-based alloy powder Prepare metals or alloys of respective elements so as to have a target composition, and produce a flaky alloy using a strip casting method or the like. Hydrogen pulverize the obtained flaky alloy, and make the size of the coarsely pulverized powder, for example, 1.0 mm or less. Next, by finely pulverizing the coarsely pulverized powder with a jet mill or the like, for example, a finely pulverized powder (alloy powder) having a median diameter d 50 (value obtained by the laser diffraction method by the air flow dispersion method) of 2.5 μm ≤ d50 ≤ 4.5 μm is obtained. Note that a known lubricant may be used as an auxiliary agent for the coarsely pulverized powder before jet mill pulverization, the alloy powder during jet mill pulverization, and the alloy powder after jet mill pulverization. d50 can be measured by the air flow dispersion type laser diffraction method (conforming to the 2013 revised edition of JIS Z 8825). That is, in the present disclosure, d50 means the particle diameter (median diameter) at which the cumulative particle size distribution (volume basis) from the small particle size side becomes 50%. Note that d50 in the present disclosure is measured in the particle size distribution measuring device "HELOS&RODOS" manufactured by Sympatec Dispersion pressure: 4 bar Measurement range: R2 Calculation mode: HRLD and indicates the d50 measured under the conditions of.

[0020] (2) Step of manufacturing a rectangular parallelepiped-shaped compact Perform molding in a magnetic field using the obtained alloy powder to obtain a compact. The molding in a magnetic field may use any known method of molding in a magnetic field, including a dry molding method in which the dried alloy powder is inserted into the cavity of a mold and molded while applying a magnetic field, and a wet molding method in which a slurry in which the alloy powder is dispersed is injected into the cavity of the mold and molded while discharging the dispersion medium of the slurry. An example of the rectangular parallelepiped-shaped compact in the present disclosure is shown in FIG. 1. In the present disclosure, the edge portions of at least one surface of the compact, for example, in FIG. 1, all the edges 2 around the surface 1 of the compact 100 are referred to as edge portions. Also, the thickness in the present disclosure is the shortest side of the rectangular parallelepiped, and for example, in FIG. 1, the edge 3 is the thickness. The dimensions of the rectangular parallelepiped-shaped compact can be, for example, a length of 20 mm × a width of 10 mm × a thickness of 5 mm. In the present disclosure, since deformation can be suppressed even for a flat rectangular parallelepiped-shaped compact with a small thickness, the thickness of the compact is preferably 7 mm or less, more preferably 5 mm or less.

[0021] (3) Step of chamfering the edge portions of at least one surface of the compact Chamfer the edge portions of at least one surface of the obtained compact. FIG. 2A is an explanatory view showing an example of a rectangular parallelepiped-shaped compact before chamfering, and FIG. 2B is an explanatory view showing an example of a rectangular parallelepiped-shaped compact after chamfering. As shown in FIGS. 2A and 2B, by chamfering the edge portions of the surface 4 (all the edges 5 around the surface 4) of the compact 200 in FIG. 2A, the edge portions of the surface 4 of the compact 200 are in a chamfered state as shown in FIG. 2B. The chamfering is preferably performed by cutting at a depth of 0.5 mm to 2 mm (C0.5 to C2 mm) from the tip of the corner at the edge portion. The chamfering method is not particularly limited. It may be performed by a known method. For example, it may be cut off with a spatula or a knife.

[0022] (4) Step of placing the compact on a support plate In the step (3), the molded body with chamfered at least one surface is placed on the support plate. FIG. 3 is an explanatory view showing a state where the molded body after chamfering is placed on the support plate such that the chamfered side end surface contacts the support plate. As shown in FIG. 3, in the present disclosure, the molded body 200 is placed on the support plate 6 such that the surface 4 having the chamfered side end portion contacts the support plate 6. Thereby, since it is possible to suppress the central portion of the molded body from being lifted during sintering, it is possible to suppress deformation of the sintered body in the obtained sintered rare earth magnet. Preferably, as shown in FIG. 3, the chamfered side end surface is a surface perpendicular to the thickness direction. Since the surface perpendicular to the thickness direction, which is the shortest side, is more likely to be deformed, deformation of the sintered body obtained by chamfering this surface can be more reliably suppressed. Further, examples of the material of the support plate include molybdenum and stainless steel.

[0023] (5) Step of sintering The molded body placed on the support plate is sintered. Sintering may be performed by a known method. For example, the molded body placed on the support plate is placed in a sintering container and heated to 1000°C to 1100°C for sintering. In order to prevent oxidation due to the atmosphere during sintering, sintering is preferably performed in a vacuum atmosphere or an atmosphere gas. As the atmosphere gas, it is preferable to use an inert gas such as helium or argon.

[0024] (6) Step of performing heat treatment For the sintered magnet obtained according to the embodiment of the present disclosure, heat treatment may be further performed for the purpose of further improving the magnetic properties. For example, single-stage heat treatment may be performed at a temperature lower than the sintering temperature (400°C or higher and 600°C or lower). Alternatively, after performing the first heat treatment at a relatively high temperature (700°C or higher and lower than the sintering temperature), the second heat treatment may be performed at a relatively low temperature (400°C or higher and 600°C or lower) (two-stage heat treatment). Specific examples of the two-stage heat treatment may include a first heat treatment at a temperature of 750°C or higher and 850°C or lower for about 5 minutes to 500 minutes, and a second heat treatment at a temperature of 440°C or higher and 550°C or lower for about 5 minutes to 500 minutes. Between the first heat treatment and the second heat treatment, it may be cooled to room temperature or cooled to a temperature of 440°C or higher and 550°C or lower.

[0025] The resulting sintered magnet may be subjected to machining such as grinding to form the final product shape. In this case, heat treatment may be performed either before or after machining. Furthermore, the resulting sintered magnet may be subjected to a surface treatment. The surface treatment may be any known surface treatment, such as Al vapor deposition, Ni electroplating, or resin paint. [Example]

[0026] The present disclosure will be explained in more detail with reference to examples, but is not limited thereto.

[0027] Example 1 An RTB alloy powder was prepared having a composition of Nd: 24.5 mass%, Pr: 5.5 mass%, B: 0.93 mass%, Cu: 0.3 mass%, Ga: 0.5 mass%, Co: 0.45 mass%, Al: 0.12 mass%, Zr: 0.05 mass%, and the balance Fe. The particle size d50 of the powder was 3.2 μm. A compact was produced using this powder in a wet press. The dimensions of the obtained compact were a rectangular parallelepiped with dimensions of 82.3 mm length x 49.0 mm width x 5.3 mm thickness. The density of the obtained compact was 4.3 Mg / m 3 The edge of the resulting compact, measuring 82.3 mm long and 49.0 mm wide (the surface perpendicular to the thickness direction), was chamfered. The chamfering was performed by scraping off a 1.0 mm depth (C1.0 mm) from the tip of the corner of the edge with a spatula. The chamfered compact was then placed on a molybdenum support plate so that the chamfered surface was in contact with the support plate. The compact placed on the support plate was then sintered (a temperature was selected that would sufficiently induce densification by sintering) to produce sintered compact A (an RTB-based sintered magnet), an example of the present invention. As a comparative example, sintered compact B (an RTB-based sintered magnet) was produced in a similar manner except that the compact was not chamfered.

[0028] The amount of deformation of the obtained R-T-B sintered magnet was examined. The amount of deformation was measured with a three-dimensional measuring machine (NEXIV manufactured by Nikon). As a result of the measurement, the amount of deformation of the sintered body A of the present invention example in which chamfering was performed on the compact was 0.2 mm, whereas the amount of deformation of the sintered body B of the comparative example in which chamfering was not performed on the compact was 0.6 mm. Therefore, the deformation of the sintered body is significantly suppressed in the present invention example (sintered body A) as compared with the comparative example (sintered body B).

Explanation of Signs

[0029] 1, 4 surfaces 2, 3, 5 sides 6 support plates 100, 200 compacts

Claims

1. A step of preparing an R-T-B-based (where R is a rare earth element, necessarily including at least one selected from the group consisting of Nd, Pr, and Ce, T is at least one of transition metal elements, and necessarily includes Fe) alloy powder; A step of producing a flat rectangular parallelepiped-shaped compact having a thickness of 5 mm or more and 7 mm or less by molding the R-T-B-based alloy powder while applying a magnetic field; A step of chamfering all corners where at least one surface perpendicular to the thickness direction of the compact intersects with a surface parallel to the thickness direction, at a depth of 0.5 mm to 2 mm from the tip of the corner; A step of placing the compact on the support plate such that a surface perpendicular to the thickness direction with all corners chamfered contacts the support plate; A step of sintering the compact placed on the support plate; A method for manufacturing an R-T-B-based sintered magnet, comprising the above steps.

2. The method for manufacturing an R-T-B-based sintered magnet according to Claim 1, wherein the chamfering is a C chamfer.

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