R-fe-b based sintered magnet

Abstract

To provide an R-Fe-B-based sintered magnet stably exhibiting high coercive force even when a heat treatment temperature is changed.SOLUTION: The R-Fe-B based sintered magnet contains, by mass%, 28% ≤ R ≤ 33%, 0% ≤ Co ≤ 2.5%, 0.9% ≤ B ≤ 1.2%, 0.3% ≤ Al ≤ 1.0%, 0.05% ≤ Cu ≤ 0.5%, and 0.05% ≤ Ga ≤ 0.5%, where R is a rare earth element, and the balance Fe with inevitable impurities, wherein the content of Al is larger than the total content of Cu and Ga, and an R-T-M phase exists in a crystal grain boundary. Here, the element T indicates a set of Fe and Co, and the element M indicates a set of Al, Cu, and Ga.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an R—Fe—B based sintered magnet, and more particularly to an R—Fe—B based sintered magnet to which Al and Ga have been added. [Background technology]

[0002] Rare earth magnets are used in a variety of devices, including automobiles, industrial equipment, and household electrical appliances. Depending on the application, these rare earth magnets are required to have high magnetic properties, such as high coercivity. R-Fe-B sintered magnets (R is a rare earth element) are used as one type of rare earth magnet with high magnetic properties. However, among the various magnetic properties, R-Fe-B sintered magnets generally tend to have low coercivity. Therefore, in Patent Document 1, by one of the present inventors, a predetermined amount of Al is added to an R-Fe-B sintered magnet to generate an RFeAl phase at the grain boundaries, thereby achieving an improvement in coercivity. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-077843 Summary of the Invention [Problem to be solved by the invention]

[0004] Excellent magnetic properties, such as coercivity, are important for magnets. However, especially in mass-produced magnets, it is important to be able to consistently achieve high magnetic properties even when manufacturing conditions fluctuate to some extent. For example, if a large number of magnets are placed in a heating furnace for heat treatment such as aging and the like, and the heat treatment is performed at the same time, uneven temperature distribution within the furnace may occur, resulting in variations in the heat treatment temperature between individual magnets. Variations in the heat treatment temperature lead to variations in magnetic properties, and it is desirable to minimize such variations between individual magnets. As disclosed in Patent Document 1, adding Al to R-Fe-B sintered magnets can improve coercivity, but it is unclear whether such high coercivity can be consistently achieved even when the heat treatment temperature changes.

[0005] Therefore, an object of the present invention is to provide an R—Fe—B based sintered magnet that stably exhibits high coercive force even when the heat treatment temperature changes. [Means for solving the problem]

[0006] In order to solve the above problems, the R—Fe—B based sintered magnet according to the present invention has the following configuration.

[0007] [1] The R-Fe-B based sintered magnet of the present invention contains, by mass%, 28%≦R≦33%, 0%≦Co≦2.5%, 0.9%≦B≦1.2%, 0.3%≦Al≦1.0%, 0.05%≦Cu≦0.5%, and 0.05%≦Ga≦0.5%, with the remainder being Fe and unavoidable impurities, with the Al content exceeding the combined content of Cu and Ga, and with RTM phases present at the grain boundaries. Here, the element T refers to an aggregate of Fe and Co, and the element M refers to an aggregate of Al, Cu, and Ga.

[0008] [2] In the above aspect [1], the R—Fe—B based sintered magnet may further contain, by mass %, 0.05%≦Zr≦0.35%.

[0009] [3] In the above aspect [1] or [2], the total content of Al, Cu, and Ga may be 0.5 mass % or more.

[0010] [4] In any of the above aspects [1] to [3], the R—Fe—B based sintered magnet may contain a heavy rare earth element as part of the rare earth element R.

[0011] [5] In the above aspect [4], the R—Fe—B based sintered magnet may contain 2.0 mass % or more of Dy as the heavy rare earth element.

[0012] [6] In any of the above aspects [1] to [5], the content of O as an unavoidable impurity may be less than 1500 ppm. [Effects of the Invention]

[0013] The R-Fe-B based sintered magnet according to the present invention having the configuration [1] above has high coercivity, mainly due to the effect of including a predetermined amount of Al and the effect of the appearance of RTM phases at grain boundaries. Furthermore, mainly due to the effect of including a predetermined amount of Ga, magnetic properties such as high coercivity can be stably obtained even if the temperature of heat treatment such as aging varies. Furthermore, since there is no need to add a large amount of heavy rare earth elements to improve coercivity, material costs can be kept low.

[0014] In the above aspect [2], the R—Fe—B based sintered magnet contains a predetermined amount of Zr, which gives it a high coercive force and a high squareness ratio.

[0015] In the above aspect [3], the total amount of Al, Cu, and Ga is sufficiently large, which is particularly effective in improving the coercive force and stabilizing the magnetic properties when the heat treatment temperature changes.

[0016] In the above-mentioned embodiment [4], the R-Fe-B based sintered magnet contains a heavy rare earth element, resulting in a particularly high coercive force. In Patent Document 1, the main invention does not include a heavy rare earth element in the R-Fe-B based sintered magnet, and it was unclear whether adding a heavy rare earth element would result in the formation of an RTM phase at the grain boundaries. However, as shown in the Examples below, it has been confirmed that adding a heavy rare earth element to the R-Fe-B based sintered magnet of the present invention results in the appearance of an RTM phase at the grain boundaries, thereby improving coercive force. As mentioned above, the inclusion of predetermined amounts of Al and Cu is sufficiently effective in improving coercive force, so it is not necessary to add a large amount of a heavy rare earth element to improve coercive force.

[0017] In the above aspect [5], the R—Fe—B based sintered magnet preferably contains 2.0 mass % or more of Dy as the heavy rare earth element, which is particularly effective in improving the coercive force.

[0018] In the above aspect [6], the oxygen content is kept low, which suppresses the formation of rare earth oxides and the incorporation of Al and Ga into the oxide phase, thereby preventing a decrease in coercive force. [Brief explanation of the drawings]

[0019] [Figure 1] The figures show the results of FE-EPMA observation of the sintered magnet of Example 1. (a) is a BED image, and (b) to (f) show the concentration distribution of each indicated element. Color photographs will be submitted separately. [Figure 2] The results of FE-EPMA observation of the sintered magnet of Example 3 are shown. (a) is a BED image, and (b) to (f) show the concentration distribution of each indicated element. Color photographs will be submitted separately. [Figure 3] The magnetic properties of the sintered magnet of Example 1 were evaluated at different aging temperatures. (a) shows the coercive force Hcj, (b) shows the residual magnetic flux density Br, and (c) shows the squareness ratio SQ. [Figure 4]The graph shows the variations in magnetic properties of a plurality of sintered magnets of Example 1 and Comparative Example 1 when they were subjected to aging treatment in a large heat treatment furnace. [Figure 5] For each sample of Examples 1 to 4 and Comparative Example 1, the coercive force Hcj when the aging temperature is changed is shown normalized by the respective maximum values. [Figure 6] The graph shows the results of evaluating the magnetic properties by changing the aging temperature for different Ga contents. (a) shows the coercive force Hcj, (b) shows the residual magnetic flux density Br, and (c) shows the squareness ratio SQ. [Figure 7] The graph shows the evaluation results of magnetic properties when aging treatment was performed at the optimum aging temperature for different Al contents: (a) coercive force Hcj, (b) residual magnetic flux density Br, and (c) squareness ratio SQ. DETAILED DESCRIPTION OF THE INVENTION

[0020] An R-Fe-B based sintered magnet (hereinafter sometimes simply referred to as a sintered magnet) according to one embodiment of the present invention will be described in detail below. In this specification, the content of each component is expressed in mass% based on the entire sintered magnet, and the composition formula showing the alloy composition of each phase is expressed in atomic%. Furthermore, various properties refer to values ​​measured at room temperature (23°C) in air.

[0021] [Component composition and phase structure of R-Fe-B sintered magnets] An R—Fe—B based sintered magnet according to one embodiment of the present invention contains the following elements, with the remainder being Fe and unavoidable impurities. 28%≦R≦33% 0%≦Co≦2.5% 0.9%≦B≦1.2% 0.3%≦Al≦1.0% 0.05%≦Cu≦0.5% 0.05%≦Ga≦0.5%

[0022] Here, R refers to a rare earth element. The rare earth element R may consist of only one type, or may contain multiple types. The sintered magnet according to this embodiment may not contain Co. Furthermore, in addition to containing the above elements, the sintered magnet according to this embodiment contains more Al than the combined content of Cu and Ga (Al≧Cu+Ga).

[0023] The sintered magnet according to this embodiment may further contain the following optional elements in addition to the elements described above. 0.05%≦Zr≦0.35%

[0024] Among the above-mentioned content ranges for each component element, the following ranges can be listed as particularly preferred ranges. The content ranges and upper and lower limits of each element can be independently adopted as suitable values. 30%≦R; R≦32% 0.5%≦Co; Co≦1.5% 0.94%≦B; B≦1.1% 0.4%≦Al; Al≦0.7% 0.1%≦Cu, and further 0.2%≦Cu; Cu≦0.3% · 0.1%≦Ga, further 0.2%≦Ga; Ga≦0.3% 0.10%≦Zr; Zr≦0.20%

[0025] As described above, the Al content is greater than the combined content of Cu and Ga (Al≧Cu+Ga). It is more preferable that the Al content be 1.5 times or more the combined content of Cu and Ga (Al≧1.5(Cu+Ga)), or even 2.0 times or more the combined content of Cu and Ga (Al≧2.0(Cu+Ga)). While there is no particular upper limit to the Al content based on the combined content of Cu and Ga, it is preferable to limit the Al content to no more than 6 times the combined content of Cu and Ga in order to prevent, for example, a significant decrease in remanence Br and Curie temperature due to excessive Al atoms being contained in the main phase. Furthermore, it is preferable that the combined amount of Al, Cu, and Ga (Al+Cu+Ga) be 0.5% by mass or more, or even 0.8% by mass or more. While there is no particular upper limit to the combined amount of Al, Cu, and Ga, it is preferable to limit it to no more than 1.5% by mass in order to prevent, for example, a significant decrease in remanence Br due to a decrease in the volume fraction of the main phase.

[0026] In the sintered magnet according to this embodiment, the type of rare earth element R is not particularly limited. It may be composed solely of light rare earth elements such as Nd and Pr, or may contain heavy rare earth elements such as Tb and Dy in addition to these light rare earth elements. As will be described later, the sintered magnet according to this embodiment has high magnetic properties, including high coercivity, mainly due to the addition of Al. Therefore, adding a heavy rare earth element to improve coercivity is not necessarily required, and even if added, it can be kept to a small amount. However, adding a heavy rare earth element to the sintered magnet can further improve coercivity. For example, adding 2.0% or more, or even 2.5% or more, or even 3.0% or more of Dy can effectively increase coercivity. On the other hand, from the perspective of reducing material costs, it is recommended that the content of heavy rare earth elements such as Dy be kept below 5.0%, or even below 4.0%.

[0027] Examples of unavoidable impurities contained in the sintered magnet according to this embodiment include the following. Cr≦0.1% Mn≦0.1% Ni≦0.1% O<1500 ppm, preferably O<1000 ppm, and even more preferably O<600 ppm C<2000ppm, preferably C<1000ppm, and even more preferably C<500ppm N<2000 ppm, preferably N<1000 ppm, and even more preferably N<300 ppm Reducing the contents of O, C, and N, and especially reducing the content of O, suppresses the formation of compounds between rare earth elements and these impurity elements at grain boundaries and the incorporation of Al and Ga into these compound phases, making it easier to maintain high magnetic properties of the sintered magnet, such as coercivity. To reduce the contents of these elements in a sintered magnet, for example, sintering and heat treatment can be carried out in a vacuum or in an inert gas atmosphere, as described below.

[0028] The sintered magnet according to this embodiment is mainly R2T 14 The alloy has a main phase composed of rare earth element R, element T, and element M, excluding unavoidable impurities. Here, element T is a transition metal element and refers to a combination of Fe and Co. Element M is an additive metal element and refers to a combination of Al, Cu, and Ga.

[0029] In particular, the RTM phase is R6T 13 It has an approximate composition expressed as R6T 13 The approximate composition of R6T 14-x M x (0.2≦x≦3.5). The majority of element M, Al, is present in the grain boundary phase as a tetragonal R6Fe 13 However, due to the substitution of part of Fe with Co, the substitution of part of Al with Cu and Ga, and the formation of lattice defects, the atomic ratio of R:(T+M) in the alloy composition of the RTM phase deviates from 6:14, resulting in the R6T 14-x M x(0.2≦x≦3.5). In addition to the RTM phase, the grain boundary phase may include an R-rich phase containing a higher concentration of rare earth element R than the main phase, and / or a B-rich phase containing a higher concentration of B than the main phase.

[0030] [Method of manufacturing R-Fe-B sintered magnets] The sintered magnet according to this embodiment can be manufactured by pulverizing a raw material alloy containing each component element in a predetermined ratio to produce magnetic powder, and then molding and sintering the magnetic powder. The resulting sintered body can then be subjected to an aging treatment as a heat treatment.

[0031] The magnet powder can be produced by, for example, strip casting an alloy ingot having a predetermined composition and then pulverizing it. Preferably, the alloy ingot is brought into contact with hydrogen gas to absorb hydrogen molecules, embrittling the alloy ingot, and then pulverizing it. Examples of pulverization methods include mechanical coarse pulverization followed by fine pulverization using a jet mill or the like. The particle size of the pulverized magnet powder can be, for example, an average particle size D50 of 5 μm or less.

[0032] Next, the magnet powder thus obtained is molded into a predetermined shape and sintered. Sintering is preferably performed after orienting the magnet powder in a magnetic field. In particular, from the perspective of reducing the impurity content in the sintered compact, it is preferable to use the PLP (press-less process), which sinters without press molding during and after orientation. For example, the magnet powder can be filled into a container corresponding to the shape of the magnet to be manufactured in a vacuum or in an inert gas atmosphere, and then sintered while the magnet powder is still filled in the container by applying an external magnetic field to orient the magnet powder. Examples of sintering temperatures include a range of 900°C to 1050°C. The raw material magnet powder contains residual hydrogen molecules that were absorbed during milling. During sintering, these hydrogen molecules are released into the gas phase by desorption due to heating and by reaction with carbon atoms present in the magnet powder as impurities. In particular, by heating in an inert gas such as Ar until the temperature reaches a predetermined temperature, such as 450 to 550°C, during the temperature rise to the sintering temperature, the hydrogen molecules absorbed in the alloy do not desorb as hydrogen molecules but rather react more easily with carbon atoms, which is highly effective in reducing carbon as an impurity. After the predetermined temperature is reached, the subsequent heating and sintering can be carried out in a vacuum atmosphere.

[0033] Once the sintered body is obtained in this manner, it is recommended to subject the sintered body to aging treatment as a heat treatment, which facilitates obtaining a sintered magnet structure having a main phase and a grain boundary phase, with the grain boundary phase further containing an R-Fe-Al phase.

[0034] As for the aging treatment, it is preferable to perform a first aging treatment at a relatively high temperature, followed by a second aging treatment at a lower temperature than the first aging treatment. The heating temperature for the first aging treatment can be 700°C or higher and 900°C or lower, and the heating temperature for the second aging treatment can be 440°C or higher and 580°C or lower. The temperature of the second aging treatment can easily affect the magnetic properties of the sintered magnet, including coercivity. However, as explained below, the sintered magnet according to this embodiment exhibits stable magnetic properties even if the temperature of the second aging treatment fluctuates to some extent due to the effect of its component composition. It is more preferable that the heating temperature for the second aging treatment be 480°C or higher and 520°C or lower. The aging treatment is also preferably performed in a vacuum or an inert gas atmosphere.

[0035] [Characteristics of R-Fe-B sintered magnets] The sintered magnet according to this embodiment has the above-mentioned component composition, and therefore has excellent magnetic properties, including high coercivity. The high coercivity is obtained by adding Al, Ga, and Cu, especially Al, to the sintered magnet, and by forming an RTM phase based on an R-Fe-Al phase as the grain boundary phase. The mechanism behind this is as follows. If Al, Ga, and Cu were not added to an R-Fe-B based sintered magnet, an Fe-rich phase (R2T) with high saturation magnetization would be formed at the grain boundary. 17 ) is formed, but when Al, Ga, and Cu are added, at least a portion of this Fe-rich phase is replaced by the RTM phase. Because the RTM phase has a smaller saturation magnetization than the Fe-rich phase, when a reverse magnetic field is applied to a magnetized sintered magnet and the magnetization of some of the main phase crystal grains is reversed, the magnetization of other adjacent main phase crystal grains is less likely to be reversed due to ferromagnetic interactions via the grain boundary phase.

[0036] The sintered magnet according to this embodiment contains sufficient amounts of Al, Ga, and Cu, especially Al, so that it is highly effective in improving coercivity without adding large amounts of heavy rare earth elements. However, as mentioned above, adding a heavy rare earth element such as Dy can provide an even greater improvement in coercivity. Heavy rare earth elements are distributed in large amounts in the grain boundary phase, but as will be shown in the examples below, adding a heavy rare earth element such as Dy to the sintered magnet according to this embodiment forms an RTM phase in the grain boundary phase, maintaining its contribution to improving coercivity, and does not result in a situation where the addition of Dy adversely affects the magnetic properties.

[0037] The magnetic properties of the sintered magnet according to this embodiment after undergoing a second aging treatment at an optimal aging temperature can be exemplified as follows: Here, the optimal aging temperature refers to the aging temperature that provides the highest coercive force Hcj when the temperature of the second aging treatment is changed. Coercive force (Hcj): 16 kOe or more. Furthermore, when Dy is included as a heavy rare earth element, the coercive force increases by approximately 2 kOe per 1.0% of Dy content. Residual magnetic flux density (Br): 12kG or more Squareness ratio (SQ): 94% or more Here, the squareness ratio (SQ) is calculated as Hk90 / Hcj, where Hk90 is the value of the magnetic field H when the value of the magnetic flux density B is 90% of the residual magnetic flux density Br on the demagnetization curve, and Hcj is the coercive force.

[0038] Furthermore, the sintered magnet according to this embodiment stably exhibits high magnetic properties, such as high coercivity, even when the temperature of heat treatment, such as aging, varies to some extent. In other words, it exhibits high robustness against changes in heat treatment temperature. This high robustness is mainly due to the addition of Ga. This is thought to be because the addition of Ga improves the wettability of the grain boundary phase, making it easier to uniformly disperse the grain boundary phase during the second aging treatment. The sintered magnet's high robustness against heat treatment temperature allows it to stably exhibit magnetic properties, such as high coercivity, even when heat treatment conditions vary. For example, when mass-producing sintered magnets, a large number of sintered magnets are placed in a heat treatment furnace and heat-treated. However, the heat treatment temperature to which each sintered magnet is subjected may differ depending on the position of each sintered magnet in the heat treatment furnace. Even if the heat treatment temperature varies among individual sintered magnets, the sintered magnet's high robustness against heat treatment temperature minimizes the variation in the magnetic properties of the sintered magnets obtained through heat treatment.

[0039] As an example of the robustness of the sintered magnet according to this embodiment to heat treatment conditions, attention can be paid to the behavior of the coercivity with respect to variations in the aging temperature. When the second aging treatment is performed at temperatures ranging from 440°C to 560°C, the aging temperature that gives the maximum coercivity Hcj is defined as the optimal aging temperature, and the maximum coercivity Hcj is defined as the optimal aging temperature. max In addition, among the aging temperatures within the range of ±40°C from the optimum aging temperature, the minimum coercive force is Hcj min At this time, the difference between the maximum coercive force and the minimum coercive force (ΔHcj = Hcj max -Hcj min ) is smaller, the sintered magnet can be evaluated as having higher robustness against the aging temperature. max and Hcj min The difference ΔHcj between the maximum coercive force and the magnetic field strength is preferably 2.0 kOe or less, more preferably 1.0 kOe or less, and even more preferably 0.6 kOe or less. max) is preferably 0.10 or less, more preferably 0.05 or less, and even more preferably 0.03 or less. max and Hcj min The smaller the difference between them, the more preferable, and there is no lower limit to their values.

[0040] The sintered magnet according to this embodiment contains 0.3% or more Al, which is highly effective in improving coercivity. Furthermore, the sintered magnet contains 0.05% or more Ga, which is highly effective in improving robustness against heat treatment temperatures. Limiting the Al content to 1.0% or less and the Ga content to 0.5% or less prevents the inclusion of large amounts of Al and Ga from adversely affecting magnetic properties. Although Ga is a more expensive element than Al, its price has recently fallen, so limiting its content to 0.5% or less does not significantly increase costs. Furthermore, when the sintered magnet contains the above-mentioned specified amount of Cu, the Al content is greater than the combined content of Cu and Ga, and the combined amount of Al, Cu, and Ga is 0.5% or more, particularly significant improvements in coercivity and robustness against heat treatment temperatures are achieved. This is thought to be due to the improved wettability of the grain boundary phase, which facilitates uniform dispersion of the grain boundary phase during the second aging treatment. The addition of Zr is optional, but adding it is effective in improving the squareness ratio (SQ) of the sintered magnet. [Example]

[0041] Examples of the present invention will be described below, but the present invention is not limited to these examples.

[0042] [1] Composition and magnetic properties First, the relationship between the composition and magnetic properties of sintered magnets having typical compositions was investigated.

[0043] [Sample preparation] Sintered magnets of Examples 1 to 4 and Comparative Example 1 were produced with the component compositions shown in Table 1 below. To produce the samples, alloy ingots produced by strip casting were first loaded with hydrogen molecules, followed by coarse mechanical pulverization and fine pulverization using a jet mill to obtain magnet powder with an average particle size of 3 to 4 μm. This magnetic powder was packed into a container, aligned in a magnetic field, and then sintered. The sintering temperature was 985 to 1035°C, and the sintering time was 4 to 6 hours. During sintering, an Ar atmosphere was used for the temperature rise from room temperature to an intermediate temperature, and the subsequent temperature rise and sintering were carried out in a vacuum. The intermediate temperature was set in the range of 450 to 550°C. The resulting sintered bodies were then subjected to aging treatment in a vacuum. The aging treatment consisted of a first aging treatment at 800°C for 30 minutes, followed by a second aging treatment at a predetermined second aging temperature for 30 minutes, followed by rapid cooling. The second aging treatment temperature (hereinafter sometimes simply referred to as the aging temperature) was set between 440°C and 560°C in increments of 20°C, and samples were independently prepared by subjecting them to second aging treatment at each temperature.

[0044] [Evaluation method] The magnetization curves of each sample obtained above were measured. Measurements were performed using a DC BH tracer. The values ​​of coercivity Hcj and remanence Br were recorded. The squareness ratio SQ was also evaluated from the shape of the demagnetization curve. Here, the value of the magnetic field H when the magnetic flux density value in the demagnetization curve is 90% of the remanence Br was defined as Hk90, the coercivity as Hcj, and the squareness ratio SQ was calculated as Hk90 / Hcj × 100%. The measurement samples were in the form of plates measuring 7 mm × 7 mm × 4.5 mm or 12 mm × 12 mm × 4.5 mm.

[0045] [Test Results] Table 1 shows the component compositions of the sintered magnets for each sample of Examples 1 to 4 and Comparative Example 1. The component compositions were obtained by analyzing each of the sintered magnets produced.

[0046] Table 2 shows the magnetic properties of each sample. In this example, as described above, the aging temperature in the second aging treatment was changed, but Table 2 shows the results when the aging temperature was set to 480°C as a representative example. The aging temperature of 480°C is the optimum aging temperature that gives the highest coercive force Hcj for each sample, or a temperature close to it (see FIG. 5).

[0047] [Table 1]

[0048] [Table 2]

[0049] As shown in Table 1, the sintered magnets of Examples 1 to 4 all have the component compositions of the sintered magnets according to the embodiments of the present invention described above. As shown in Table 2, Examples 1 to 4 each achieve a high coercivity Hcj. In particular, Example 2 achieves a high coercivity of nearly 18 kOe despite not containing the heavy rare earth element Dy. This is thought to be primarily due to the effect of the sufficient Al content. Meanwhile, Examples 1, 3, and 4 achieve an even higher coercivity Hcj of over 23 kOe by adding Dy. Regarding magnetic properties other than magnetic flux density, each of Examples 1 to 4 also achieves high properties, including a residual magnetic flux density Br of 12 kG or more and a squareness ratio SQ of 94% or more.

[0050] On the other hand, the sintered magnet of Comparative Example 1 contains less than 0.3% Al and no Ga. Although Comparative Example 1 contains more Dy than Examples 1, 3, and 4, it only achieves a coercive force Hcj comparable to that of Example 1 and significantly lower than that of Examples 3 and 4. This is thought to be mainly due to the insufficient Al content of the sintered magnet of Comparative Example 1. In other words, the sintered magnets according to embodiments of the present invention, such as Examples 1 to 4, achieve a high coercive force improvement mainly due to the effect of containing 0.3 mass% or more Al. The addition of Ga is thought to contribute mainly to improved robustness against heat treatment temperatures, as will be shown in Test [3] below.

[0051] [2] Composition of grain boundary phase Next, the composition of the grain boundary phase was confirmed for representative samples.

[0052] [Sample preparation] The sintered magnets of Example 1 and Example 3 produced in the above test [1] were used as samples.

[0053] [Evaluation method] The cross section of each sample was observed using a field emission electron microanalyzer (FE-EPMA). The composition of the phases that appeared was then analyzed. Specifically, the microstructure of the sample cross section was confirmed based on backscattered electron (BED) images, and the distribution of the grain boundary phase was evaluated. The concentration distribution of each element that makes up the sintered magnet was also evaluated, and the component composition was analyzed at several representative points.

[0054] [Test Results] Figure 1 shows (a) a BED image and the concentration distribution of each element (b) Fe, (c) Nd, (d) Al, (e) Cu, and (f) Ga for Example 1 and Example 3, respectively. Table 3 below shows the composition of each element at a representative point in the grain boundary phase. The positions of the representative points are indicated with numbers in the BED images in Figures 1 and 2. Table 3 shows the composition of each element in terms of atomic percent. The atomic ratios of the rare earth element R, element T (= Fe + Co), and element M (= Al + Cu + Ga) are also shown.

[0055] [Table 3]

[0056] In the BED images in Figures 1 and 2, the large, dark-colored regions correspond to the main phase crystal grains. The white areas, including the areas indicated by the white arrows, correspond to the R-rich phase within the grain boundary phase. This is indicated by the relatively low Fe concentration and high Nd concentration in the elemental distribution image in these areas. On the other hand, the areas indicated by the black arrows and other areas indicated in a lighter gray than the main phase crystal grains correspond to the RTM phase within the grain boundary phase. This is indicated by the high Al and Cu concentrations in these areas in the elemental distribution image. Furthermore, the Ga concentration in these RTM phases is higher than in other areas. This indicates that Ga is also incorporated into the RTM phase occupying the grain boundary phase and is distributed in high concentrations within the RTM phase.

[0057] The representative points showing the component composition in Table 3 are all located within the RTM phase. At these points, the ratio of R:T:M is close to 6:13:1, and the ratio of R:(T+M) is close to 6:14. This indicates that the RTM phase is R6T 13 The approximate composition can be written as M, i.e., R6T 14-x M x It was confirmed that the composition can be expressed as (0.2≦x≦3.5). It is believed that this RTM phase contributes to the improvement in coercivity Hcj confirmed in the above test [1]. Both Examples 1 and 3 contain Dy, and it was confirmed that the RTM phase appears at the grain boundaries even when the sintered magnet contains Dy, a heavy rare earth element.

[0058] [3] Effect of Ga addition Next, the effect of adding Ga to the sintered magnet according to the embodiment of the present invention was examined.

[0059] [Sample preparation] The sintered magnets of Examples 1 to 4 and Comparative Example 1 produced in the above test [1] were also used as samples here.

[0060] Furthermore, for Example 1 and Comparative Example 1, samples were mass-produced. That is, a large number of sintered magnets with the same component composition were produced and aging-treated in a large heating furnace. For each sample, a first aging treatment was performed at 800°C, followed by a second aging treatment aimed at 500°C. However, a temperature distribution of about 20°C was observed depending on the position in the furnace.

[0061] [Evaluation method] The magnetic properties of each sample were evaluated using the same method as in the above test [1]. Furthermore, for the mass-produced samples of Example 1 and Comparative Example 1, the coercive force Hcj and remanence Br were evaluated for each of the individual samples that were placed at different positions in the furnace and subjected to aging treatment, and the results were compared between the individual samples.

[0062] [Test Results] First, Fig. 3 shows the magnetic properties of Example 1 and Comparative Example 1 at various aging temperatures. (a) shows the coercive force Hcj, (b) shows the residual magnetic flux density Br, and (c) shows the squareness ratio SQ. Fig. 4 shows the distribution of the coercive force Hcj and residual magnetic flux density Br for each individual magnet, obtained in a mass-production test in which aging was performed in a large heat treatment furnace.

[0063] Looking at the behavior of the coercive force Hcj of Example 1 and Comparative Example 1 in Figure 3(a), the coercive force Hcj of Comparative Example 1 changes significantly over a range of nearly 4 kOe as the aging temperature changes. On the other hand, the change in coercive force Hcj of Example 1 is limited to about 2 kOe even when the aging temperature changes. In other words, the change in coercive force Hcj with respect to the change in aging temperature is smaller in Example 1. Regarding the squareness ratio SQ of Figure 3(c), although the difference is smaller than that of the coercive force Hcj, the change in the range of change with aging temperature is smaller in Example 1 than in Comparative Example 1. Regarding the remanence Br of Example 1 and Comparative Example 1, the data points almost overlap, and in both cases, there is almost no change with the aging temperature.

[0064] As described above, Example 1 shows less change in magnetic properties when the aging temperature of the second aging treatment is changed than Comparative Example 1. In particular, the change in coercivity Hcj is kept small. This shows that Example 1 provides more stable magnetic properties than Comparative Example 1, even when the heat treatment temperature is changed, that is, it exhibits higher robustness against the heat treatment temperature. While the sintered magnet of Comparative Example 1 does not contain Ga, the sintered magnet of Example 1 contains 0.1% Ga, and it is believed that the improved robustness against the heat treatment temperature is mainly due to the effect of the addition of Ga.

[0065] Figure 4 shows the distribution of magnetic properties for individual magnets in a mass-produced case where a large number of sintered magnets are aged in a large heat treatment furnace. The distribution ranges of the measured values ​​are different between Example 1 and Comparative Example 1. Specifically, the dispersion range of the data points along the horizontal axis, which indicates the coercivity Hcj, is narrower in Example 1 (●) than in Comparative Example 1 (×). In other words, the variation in coercivity Hcj for individual magnets is smaller in Example 1. As mentioned above, during the second aging treatment, a non-uniform distribution of the heating temperature of about 20°C occurs inside the large heat treatment furnace, and the variation in the data points reflects the difference in the heating temperature of the second aging treatment for each individual magnet. In other words, as shown in Figure 3, Example 1 is more robust to the aging temperature than Comparative Example 1, which is reflected in the result that the variation in magnetic properties due to the non-uniform distribution of the heat treatment temperature in the heat treatment furnace is suppressed.

[0066] Furthermore, Fig. 5 shows the behavior of the coercive force Hcj when the aging temperature is changed for Examples 1 to 4 and Comparative Example 1. Here, the maximum value (Hcj max The coercive force Hcj is normalized so that the coercive force Hcj is 1. Table 4 below also lists the representative values ​​of the coercive force Hcj for each sample. Here, the maximum coercive force (Hcj max ), the minimum value among the measurement points within ±40°C of the optimum aging temperature (Hcj min), and their difference (ΔHcj=Hcj max -Hcj min ), the difference normalized by the maximum value (ΔHcj / Hcj max ) is shown.

[0067] [Table 4]

[0068] In Examples 1 to 4, the maximum coercive force Hcj in Table 4 max As shown in Fig. 5, the magnitude of the coercive force Hcj differs depending on whether or not Dy is contained and the amount of Dy. However, as shown in Fig. 5, the change in coercive force Hcj with respect to the change in aging temperature is suppressed to a smaller value in all of Examples 1 to 4 than in Comparative Example 1. The values ​​summarized in Table 4 also clearly show this, and the maximum coercive force Hcj max and minimum coercive force Hcj min The difference value ΔHcj in Comparative Example 1 far exceeds 1.0 kOe, whereas it is suppressed to 0.6 kOe or less in Examples 1 to 4. max Although the coercivity Hcj exceeds 0.1 in Comparative Example 1, it is suppressed to 0.03 or less in Examples 1 to 4. As described above, the change in coercivity Hcj with respect to the change in aging temperature is suppressed to a small value in all of Examples 1 to 4 compared to Comparative Example 1. This is thought to be mainly due to the effect of the inclusion of Ga, as explained above in the comparison between Example 1 and Comparative Example 1.

[0069] [4] Effect of Ga content Furthermore, the effect of Ga content was examined.

[0070] [Sample preparation] Sintered magnets according to Samples 4A to 4C, having the component compositions shown in Table 5 below, were produced in the same manner as in Test [1]. Samples 4A to 4C differ from one another in the Ga content.

[0071] [Evaluation method] The magnetic properties of each sample were evaluated using the same method as in test [1] above.

[0072] [Test Results] Table 5 below shows the chemical compositions of the sintered magnets of Samples 4A to 4C. Analysis of O, C, and N has been omitted. Furthermore, Figure 6 shows the change in magnetic properties of each sample when the aging temperature is changed. The evaluation results are shown for (a) coercive force Hcj, (b) residual magnetic flux density Br, and (c) squareness ratio SQ.

[0073] [Table 5]

[0074] Figure 6 shows that as the Ga content increases, the change in Hcj, Br, and SQ magnetic properties with aging temperature tends to decrease. However, for all magnetic properties, the change in Hcj, Br, and SQ decreases significantly when the Ga content increases from 0.2% to 0.5%, whereas the decrease is not as significant when the Ga content increases from 0.5% to 0.8%. In other words, increasing the Ga content improves robustness against aging temperature, but this effect saturates at a content of around 0.5%. This suggests that it is sufficient to limit the amount of Ga added to sintered magnets to around 0.5% or less. In addition, in Figure 6(c), for all Ga addition amounts, the decrease in squareness ratio when the aging temperature is increased is greater than in Example 1 in Figure 3(c). However, this is mainly due to the low Al content in Samples 4A to 4C. By adding a sufficient amount of Al, such as 0.3% or more, along with 0.1 to 0.5% Ga to the sintered magnet, the decrease in squareness ratio can be kept sufficiently small.

[0075] [5] Effect of Al content Finally, the effect of Al content was examined.

[0076] [Sample preparation] Sintered magnets according to Samples 5A to 5C, having the composition shown in Table 6 below, were produced in the same manner as in Test [1]. Samples 5A to 5C differ from one another in the Al content.

[0077] [Evaluation method] The magnetic properties of each sample were evaluated using the same method as in test [1] above.

[0078] [Test Results] Table 6 below shows the chemical compositions of the sintered magnets of Samples 5A to 5C. Analysis of O, C, and N is omitted. Furthermore, Figure 7 shows the evaluation results for each sample in terms of (a) coercive force Hcj, (b) remanence Br, and (c) squareness ratio SQ. Here, the measured values ​​after second aging treatment at the optimal aging temperature are plotted against the Al content.

[0079] [Table 6]

[0080] According to Figure 7, as the Al content increases from 0.2% to 0.8%, the remanence Br decreases slightly, but the coercivity Hcj increases by approximately 15%. The squareness ratio SQ does not change significantly. This suggests that adding a large amount of Al to a sintered magnet is highly effective in improving the coercivity Hcj, and that an Al content of more than 0.2% is recommended. For example, an Al content of 0.3% or more would be sufficient. On the other hand, even if the Al content is increased to 0.8%, the decrease in remanence is kept to less than 5%, and there is no significant adverse effect on the magnetic properties, so it can be said that an Al content of up to approximately 1.0% is acceptable.

[0081] Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments and various modifications can be made.

Claims

1. The rare earth element is represented by R, and the mass % is 28%≦R≦33%, 0%≦Co≦2.5%, 0.9%≦B≦1.2%, 0.3%≦Al≦1.0%, 0.05%≦Cu≦0.5%, Contains 0.05%≦Ga≦0.5%; the balance being Fe and unavoidable impurities; The content of Al is greater than the total content of Cu and Ga, An R-Fe-B sintered magnet in which an R-T-M phase exists at the grain boundaries. Here, the element T refers to a group of Fe and Co, and the element M refers to a group of Al, Cu, and Ga.

2. Furthermore, in mass%, 2. The R—Fe—B based sintered magnet according to claim 1, containing 0.05%≦Zr≦0.35%.

3. 3. The R—Fe—B based sintered magnet according to claim 1, wherein the total content of Al, Cu, and Ga is 0.5 mass % or more.

4. 3. The R—Fe—B based sintered magnet according to claim 1, wherein a heavy rare earth element is contained as part of the rare earth element R.

5. 5. The R—Fe—B based sintered magnet according to claim 4, wherein the heavy rare earth element contains 2.0 mass % or more of Dy.

6. 3. The R—Fe—B based sintered magnet according to claim 1, wherein the content of O as an unavoidable impurity is less than 1500 ppm.

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