JP2017157738A - MANUFACTURING METHOD OF Mn-Al PERMANENT MAGNET AND Mn-Al PERMANENT MAGNET - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of Mn-Al permanent magnet not requiring addition of a C element, and to provide a Mn-Al permanent magnet manufactured by the manufacturing method mentioned above.SOLUTION: A material composed of Mn, Al and inevitable impurities is made by melting and casting. The material thus made is subjected to first heat treatment at a temperature at which the ε phase of a Mn-Al system is generated. The material, in which the ε phase is generated by first heat treatment, is then subjected to second heat treatment, while applying magnetic field. Thereafter, finish processing is performed, thus manufacturing a Mn-Al permanent magnet. Preferably, the temperature of second heat treatment is equal to or below the Curie-point of the material. Furthermore, in order to advance the phase transformation sufficiently in a limited heat treatment time, said temperature is preferably set to 300-350°C.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing a Mn—Al permanent magnet and a Mn—Al permanent magnet.

  In recent years, permanent magnets called neodymium magnets (Nd-Fe-B magnets) have been widely used for applications such as hybrid car motors. Although neodymium magnets have a high coercive force, they have a problem that the coercive force decreases with an increase in temperature associated with the use of a motor or the like. In order to satisfy this problem, a rare element, Dy element, is added to the Nd element in order to satisfy the requirement for high temperature and high coercive force.

  As an alternative to such neodymium magnets, there is a demand for materials having high magnetic properties, particularly at high temperatures, without adding rare elements. In this regard, Mn-based permanent magnet materials have a high elemental advantage, and therefore, various materials are being studied for practical use.

  An example of the Mn-based permanent magnet material is MnBi as disclosed in Patent Document 1.

  In addition, Mn—Al is known as an alloy magnet, and is excellent in workability. The feature as magnetic force is located between the ferrite magnet and the neodymium magnet.

  However, Mn—Al is difficult to stabilize because the τ phase that becomes a permanent magnet is a non-equilibrium phase. Therefore, the magnetic force actually obtained as a Mn—Al permanent magnet was very small.

  On the other hand, in order to stabilize the τ phase, as in Patent Document 2, about several weight% of C element is added to make a Mn—Al—C permanent magnet.

Japanese Patent Laying-Open No. 2015-63725 JP-A-10-270224

  Various studies have been made on Mn-based permanent magnet materials, but as described above, there is an increasing demand for materials satisfying high temperature and high coercive force. In addition, it is also demanded that it can be manufactured more easily with increasing demand.

  Accordingly, it is expected to provide a new manufacturing method and permanent magnet that replace the conventional Mn—Al—C manufacturing method for Mn—Al based permanent magnets.

  This invention is made | formed in view of the said subject, Comprising: It aims at providing the manufacturing method of the Mn-Al permanent magnet which does not require addition of C element. Moreover, an object of this invention is to provide the Mn-Al permanent magnet manufactured by the said manufacturing method.

In order to achieve the above object, a method for producing a Mn—Al permanent magnet according to the first aspect of the present invention includes:
Performing a first heat treatment at a temperature at which a Mn-Al-based ε phase is generated in a material comprising Mn, Al and inevitable impurities;
Performing a second heat treatment while applying a magnetic field to the material in which the ε phase is generated, and generating a τ phase.

The temperature of the second heat treatment is a temperature equal to or lower than the Curie temperature of the material.
It is good as well.

The temperature of the second heat treatment is 300 to 350 ° C.
It is good as well.

In order to achieve the above object, the Mn—Al permanent magnet according to the second aspect of the present invention is:
It is manufactured by the above-described method for manufacturing a permanent magnet.

  According to this invention, the manufacturing method of the Mn-Al permanent magnet which does not need addition of C element is obtained. Moreover, according to this invention, the Mn-Al permanent magnet manufactured by the said manufacturing method is obtained.

It is a flowchart which shows the manufacturing process of the Mn-Al permanent magnet which concerns on embodiment of this invention. It is a binary system equilibrium state diagram of Mn-Al. It is a figure which shows typically the phase transformation of the manufacture process of the Mn-Al permanent magnet which concerns on embodiment of this invention. It is a reference figure which shows typically the phase transformation of the manufacture process of the Mn-Al permanent magnet when not applying a magnetic field at the time of heat processing. (A) And (b) is a reference figure which shows typically the phase transformation of the manufacturing process of the permanent magnet of a MnBi sintered compact. It is a graph which shows the magnetization curve at the time of making the temperature and magnetic field at the time of heat processing differ from each other. (A)-(c) is a graph which shows the magnetization curve when the temperature at the time of heat processing differs mutually.

  Hereinafter, the manufacturing method of the permanent magnet which concerns on embodiment of this invention is demonstrated according to the flowchart of FIG.

  First, raw materials for permanent magnets are synthesized (step S10). The raw material of the permanent magnet in this embodiment is two types, Mn and Al. It is allowed to contain a trace amount of inevitable impurities that can be mixed in the manufacturing process.

  The permanent magnet according to the present embodiment is a binary material of Mn—Al, in which a τ phase having a CuAu structure that becomes a permanent magnet is formed. Therefore, the ratio of Mn in the raw material is in a range that can be a Mn-Al-based τ phase.

  The binary equilibrium diagram of Mn-Al is shown in Fig. 2 (Source: Inorganic Material Database (AtomWork, http://crystdb.nims.go.jp/) and Binary Alloy Phase Diagrams, II ed. (1990)) . In addition, for the description of this specification, an additional note was added to the cited binary system equilibrium diagram.

In FIG. 2, an approximately rectangular region of 840 ° C. or lower within a range of 48.5 to 59.5 at% of Mn is a region (τ phase generation region) that can be a τ phase that becomes a magnet. However, since the τ phase is a non-equilibrium phase, it cannot be generated by ordinary heat treatment. In the τ phase generation region, Mn ₁₁ Al ₁₅ (γ phase) and Mn (β phase) become an equilibrium phase.

Accordingly, the raw materials are blended within the τ phase generation region. However, as will be described later, an ε phase (Mn _0.55 Al _0.45 ) having an hcp (hexagonal close-packed) structure is generated by a heat treatment in the manufacturing process, so that it is approximately 55 at%.

  Subsequently, the raw material is melted in a furnace (step S20). The temperature at the time of dissolution is a temperature at which the liquid phase (L) is obtained in the binary system equilibrium diagram of FIG. 2, and is 1400 ° C., for example. The melting time is determined based on conditions such as the amount of raw material and furnace equipment so that the raw material is sufficiently dissolved.

  Subsequently, the melted raw material is cast in a predetermined mold to produce an ingot (step S30). Although the manufacturing method of an ingot may be a method used for a well-known Mn-Al-C permanent magnet, what is necessary is just what is suitable in order to use for the below-mentioned heat processing.

  Subsequently, a solution heat treatment (first heat treatment) is performed on the ingot to obtain a material in which an ε phase is generated (step S40). The temperature of the heat treatment is a temperature at which the ε phase can be generated, and is 1000 to 1100 ° C., for example. The heat treatment time is determined based on conditions such as the amount of ingot and furnace equipment so that the ε phase is sufficiently generated. When the predetermined heat treatment is completed, the material in which the ε phase is generated is rapidly cooled by quenching or the like.

  Subsequently, heat treatment (second heat treatment) is performed while applying a magnetic field to the material in which the ε phase is generated (step S50).

  The temperature of the heat treatment may be a temperature at which a τ phase transformed from the ε phase is generated, and is 350 ° C., for example. However, if the temperature of the heat treatment is too high, the τ phase is generated once, but with the heat treatment over time, the β phase and γ phase of the equilibrium phase are generated from the ε phase and the τ phase which is a non-equilibrium phase. End up. In addition, the ratio of the β phase and the γ phase generated from the ε phase increases. Therefore, these phase transformations may make it difficult to produce a permanent magnet having a sufficient magnetic force, that is, a sufficient fraction of the τ phase. Further, if the temperature of the heat treatment is too low, it takes too much time to generate the τ phase, which is not preferable. In order for the phase transformation to proceed sufficiently in a finite heat treatment time, the temperature is desirably 300 ° C. or higher.

  Therefore, the preferable heat treatment temperature for the production of the permanent magnet is equal to or lower than the Curie temperature (380 ° C.) in order to effectively stabilize the magnet phase by the magnetic field, and the time necessary for sufficient generation of the τ phase in the heat treatment. For example, it can be set to 350 ° C. The heat treatment time is determined in consideration of the temperature of the heat treatment, and is, for example, 48 hours.

  The strength of the magnetic field to be applied may be a value that is preferable for the generation of the τ phase, and may be 15 T, for example.

  When the predetermined heat treatment is completed, the material in which the τ phase is generated is cooled by furnace cooling or liquid cooling. In this case, it is preferable that the phase transformation from the τ phase to the β phase and the γ phase is suppressed.

  Thereafter, the material in which the τ phase is generated is finished (step S60), thereby completing a desired permanent magnet product.

  Next, the reason why a magnetic field is applied during the second heat treatment in this embodiment will be described.

  In a Mn—Al-based material, when the generated ε phase is heat-treated without applying a magnetic field at a temperature corresponding to the second heat treatment, as shown in FIG. To do. Moreover, it transforms from the ε phase to the β phase and the γ phase, which are equilibrium phases. In this case, even if the ratio of the generated τ phase is larger than the ratio of the β phase and the γ phase, the τ phase is further reduced by the phase transformation to the β phase and the γ phase with the passage of time. Therefore, it has been difficult to use the Mn—Al permanent magnet as a practical permanent magnet having a high magnetic force by a normal heat treatment.

  On the other hand, the reason why the magnetic field is applied during the second heat treatment as in the present embodiment is that the non-equilibrium τ phase having ferromagnetism can be selectively generated and stabilized. It is. FIG. 4 schematically shows the behavior in the second heat treatment.

  In the second heat treatment in which a magnetic field is applied, the ratio of the τ phase generated from the ε phase is significantly higher than that in the β phase and the γ phase. Further, since the phase transformation from the τ phase to the β phase and the γ phase is suppressed as compared with the case of FIG. 3, it is possible to secure a large amount of τ phase remaining in the material as compared with the conventional manufacturing method. it can.

  However, since the change from the τ phase to the β phase and the γ phase occurs even at a low rate as shown in FIG. 4, it is considered that the τ phase gradually decreases when heat treatment is performed for an excessively long time. It is done.

  Here, the difference from the prior art MnBi permanent magnet (Patent Document 1) will be described.

  As shown to Fig.5 (a), MnBi as a compound is produced | generated by sintering the mixture of Mn powder and Bi powder at 280 degreeC, for example. Further, as shown in FIG. 5B, when the sintering temperature is lowered to, for example, 250 ° C., MnBi is not usually generated. In Patent Document 1, a chemical reaction to MnBi is promoted as shown in FIG. 5 (a) by sintering the mixture while further applying a magnetic field under the temperature condition of FIG. 5 (b). Also, magnetic anisotropy is obtained in MnBi according to the direction of the magnetic field during sintering.

  On the other hand, since Mn—Al of this embodiment is an alloy, the meaning is greatly different from the application of a magnetic field to the reaction of the compound. When heat treatment is performed without applying a magnetic field from the ε phase of the hcp structure, a non-ferromagnetic β phase and γ phase are generated, so that it does not become a magnet. In the present embodiment, by applying a magnetic field, the ferromagnetic τ phase of the nonequilibrium phase is selectively generated and stabilized as described above.

  Moreover, the difference with the manufacturing method of the widely used Mn-Al-C permanent magnet is demonstrated.

  In the case of a Mn—Al—C permanent magnet, an extrusion process at about 700 ° C. is performed after the first heat treatment (corresponding to step S40 in FIG. 1) for generating an ε phase. When the uniaxial magnetic anisotropy is given to the permanent magnet, further upsetting is performed at about 700 ° C. in the direction of the extrusion axis. Thereafter, finishing (corresponding to step S60 in FIG. 1) is performed to manufacture a permanent magnet.

  As described above, the Mn—Al—C permanent magnet needs to be mechanically processed at a temperature of about 700 ° C. higher than that in the case of the present embodiment. On the other hand, in the present embodiment, the addition of carbon can be omitted, and processing can be performed in a relatively low temperature furnace below the Curie temperature instead of hot mechanical processing. Can be greatly simplified.

  As described above, according to this embodiment, a high-magnetism permanent magnet can be manufactured with two types of Mn and Al without using a C element as a raw material. Further, in order to generate the τ phase, it is possible to cope with a heat treatment apparatus having a relatively low temperature equal to or lower than the Curie temperature and requiring no equipment such as extrusion without performing extrusion at a high temperature.

  Hereinafter, representative examples of the present invention will be shown to clarify the present invention more specifically, but the present invention is not limited by the description of such examples. It goes without saying. In addition to the specific examples described above, the present invention includes various changes, modifications, improvements, and the like based on the knowledge of those skilled in the art without departing from the spirit of the present invention, in addition to the specific description described above. It should be understood that it can be added.

Example 1
The raw materials of Mn element and Al element were prepared so that Mn was 55 at% of the whole. These raw materials were blended and melted at high frequency, and then rapidly cooled with a rod-shaped mold having a diameter of 10 mm. The rod-shaped sample thus obtained was cut into a disk shape having a thickness of 2 mm to obtain a disk-shaped sample. The disk-shaped sample was subjected to a solution treatment at 1100 ° C. for 1 day and then rapidly cooled in ice water (first heat treatment).

  Thereafter, a heat treatment for generating a magnet phase (τ phase) was performed on the disk-shaped sample at a heat treatment temperature of 300 ° C. and 350 ° C. in a magnetic field of 15T, 10T, and 0T, respectively (second heat treatment). The heat treatment time was 12h, 24h, 48h, and 96h.

  After the second heat treatment, each sample was subjected to magnetization measurement at 27 ° C. against an external magnetic field of maximum 1.5 T. The result is shown in FIG.

  In FIG. 6, the horizontal axis represents heat treatment time (Annealing time (hour)), and the vertical axis represents magnetization (Magnetization (emu / g)) at 1.5T. From FIG. 6, the effect of selective generation of the τ phase clearly appeared and the magnetic force was improved in the samples heat-treated in any magnetic field in 10T and 15T. In addition, the magnetic field (15T) is applied by the heat treatment for a long time exceeding 48 hours even in the heat treatment at 300 ° C., which is considered to have a low effect of selective generation of the τ phase by the magnetic field because the heat treatment temperature is low and the generation takes time. In this case, it can be seen that the performance (magnetic force) as a permanent magnet is clearly improved as compared with the case where no magnetic field is applied (0T).

(Example 2)
A disk-like sample in which an ε phase was generated by the first heat treatment was prepared in the same manner as in Example 1. These disk-shaped samples were subjected to a second heat treatment for 4 h, which is the initial phase transformation from the ε phase to the τ phase. The temperature of heat processing is 300 degreeC, 350 degreeC, and 400 degreeC. For each temperature, the magnetic field strength applied during the heat treatment was 2 cases of 0T and 15T.

  After the second heat treatment, a magnetization curve was obtained for each sample. The external magnetic field was set to 1.2 T at maximum and measured at room temperature. The results are shown in FIGS.

  7A to 7C, the horizontal axis represents an external magnetic field (Magnetic field (T)), and the vertical axis represents magnetization (Magnetization (emu / g)). 7 (a) shows the measurement results at 300 ° C., FIG. 7 (b) shows the measurement results at 350 ° C., and FIG. 7 (c) shows the measurement results at 400 ° C. In each figure, the magnetic fields applied during the heat treatment are represented by 0T and 15T. It is described as two cases.

  In the case of 300 ° C. in FIG. 7A, it can be seen that both 0T and 15T are linear, and a clear magnetic field effect does not appear at the initial phase transformation (4h). That is, in any case, it can be said that almost no τ phase is generated.

  In the case of 350 ° C. in FIG. 7B, the magnetization curve of 0T is almost linear, whereas a clear ferromagnetic magnetization curve appears at 15T. That is, it can be said that the τ phase was selectively generated by applying a magnetic field of 15T. Further, since 350 ° C. is a temperature in the vicinity of the Curie temperature (380 ° C.) of Mn—Al, it is considered that the difference from 0T appears more remarkably.

  In the case of 400 ° C. in FIG. 7C, a large magnetization was observed, but both 0T and 15T have substantially overlapping magnetization curves. This indicates that the generation of the τ phase is more dominant than the generation of the magnetic field due to the application of the magnetic field. However, since the temperature factor is dominant, at a temperature higher than the Curie temperature, even if a magnetic field is applied, the rate of phase transformation from the τ phase to the β phase and the γ phase increases. After that, the remaining τ phase decreases, and the magnetic force is considered to decrease.

  From the comparison of FIGS. 7A to 7C, it can be seen that the magnetization is clearly improved by the heat treatment in the magnetic field. Moreover, it can be said that the heat treatment temperature is preferably 350 ° C., which is slightly lower than the Curie temperature and is expected to stabilize the τ phase by magnetic energy among the three types of the present embodiment.

Claims (4)

Performing a first heat treatment at a temperature at which a Mn-Al-based ε phase is generated in a material comprising Mn, Al and inevitable impurities;
Performing a second heat treatment while applying a magnetic field to the material in which the ε phase is generated, and generating a τ phase.
The manufacturing method of the Mn-Al permanent magnet characterized by the above-mentioned. The temperature of the second heat treatment is a temperature equal to or lower than the Curie temperature of the material.
The manufacturing method of the Mn-Al permanent magnet of Claim 1 characterized by the above-mentioned. The temperature of the second heat treatment is 300 to 350 ° C.
The manufacturing method of the Mn-Al permanent magnet of Claim 2 characterized by the above-mentioned.   The Mn-Al permanent magnet manufactured by the manufacturing method of the permanent magnet of any one of Claims 1-3.