JP2003510467A - Nd-Fe-B alloy containing less boron and method for producing permanent magnet made of the alloy - Google Patents

Abstract

(57) [Summary] At least one rare earth _element having the same remanent magnetization Br, having a higher coercive force H _cJ than conventional alloys, capable of lowering the temperature coefficient of remanent magnetization, and being corrosion-resistant, low in boron content, An alloy based on at least one transition metal and boron and a permanent magnet made of this alloy are provided. Nd-Fe-B permanent magnets with low boron content have high coercive force. This alloy has 26.9% by weight ≤ [SE] _eff ≤ 33% by weight, 2.185-0.0442 [SE] _eff ≤ [B] _eff ≤ 1.363 -1.0136 [SE] _eff , [Dy + Tb + Ho] ≤ 50% [SE] _eff , 0.5 wt% ≦ [Co] ≦ 5 wt%, 0.05 wt% ≦ [Cu] ≦ 0.3 wt%, 0.05 wt% ≦ [Ga] ≦ 0.35 wt%, 0.02 wt% ≦ [Al] ≦ 0.3 wt% Meet the conditions.

Description

Detailed Description of the Invention

The present invention relates to an alloy based on at least one rare earth, at least one transition metal and boron and a method for producing permanent magnets from this alloy.

[0002] This kind of alloy and a method of manufacturing the permanent magnet made of this alloy are described in European Patent Application Publication No. 012.
It is known from specification 4655. In this known method, an alloy based on neodymium, iron and boron is first melted. The molten alloy is poured into a mold and cast into a casting block, which is subsequently ground into powder. Raw material pieces are pressed from this powder in a magnetic field and finally sintered.

In various applications of Nd-Fe-B permanent magnets, especially in motors and drives,
The coercivity H _cJ at 150 ° C. is important for the quality of permanent magnets. When the magnetic field in the opposite direction is small, the coercive force H _cJ at 150 ° C. should be at least 4.5 kOe, preferably 5 kOe or more. 13 kOe at 150 ° C when the reverse magnetic field is strong
Even the above values are required. In addition to the high coercive force H _cJ , such magnets have to exhibit the highest possible remanence Br. For example remanence Br of Nd-Fe-B permanent magnet having a coercive force H _cJ of about 4.5kOe at 0.99 ° C. is at least 1.2 at room temperature
9T, preferably 1.35T or higher.

Further, for motors, the reversible temperature coefficient TK (Br) of residual magnetization is 20 to 150.
It must be better than -0.11% / K at a temperature of ° C. Furthermore, permanent magnets of this kind must be as resistant to corrosion as possible in order to avoid costly and expensive coatings. Therefore, for example, the mass loss of an uncoated magnet is 1 in the so-called HAST test.
Must be below 1 mg / cm ² after 0 days. During the HAST test, the permanent magnet is exposed to a pressure of 2.7 bar at a temperature of 130 ° C. and 95% relative humidity in the atmosphere.

[0005]   These requirements are not met by conventional Nd-Fe-B permanent magnets.

Starting from this prior art, the object of the present invention is to have a coercive force H _cJ higher than conventional alloys with the same remanent magnetization Br, a low remanent magnetization temperature coefficient and at least corrosion resistance. It is to provide an alloy for permanent magnets based on one rare earth, at least one transition material and boron.

[0007]   This task is solved by an alloy having the features of claim 1 of the present invention.

[0008]   Conventional Nd-Fe-B alloys mainly consist of three phases, namely Nd.₂Fe₁₄Composition of B
Hard magnetic ψ phase with Nd_1.1Fe_FourB_FourNon-magnetic η phase with a composition of
It consists of a non-magnetic wedge phase made entirely of chisel. This Nd-rich wedge phase is composed of ψ-phase particles.
Magnetically separated from each other, resulting in high coercive force H_cJBring However, if the boron concentration is
If it is too low, the coercive force H will be applied to the non-magnetic η phase._cJOf Nd with soft magnetic properties ₂ Fe₁₇There is a risk of phase formation. Unlike the conventional Nd-Fe-B alloy
In the alloy produced according to the present invention, the boron content in the nonmagnetic η phase is critical.
Below, this coercive force H_cJNd unfavorable to₂Fe₁₇Not the phase of
First, a series of non-magnetic gallium-containing phases is created. This Ga-containing phase is ferromagnetic Nd ₂ Fe₁₇Phase of the alloy, it contributes to the reduction of the magnetic coupling of the particles in the ψ phase,
Magnetic force H_cJAlso improves the temperature dependence.

A further object of the invention is to provide a method for producing permanent magnets from this alloy.

[0010]   This problem is solved by a manufacturing method having the features of claim 6.

With a suitable temperature control, a particularly high value of coercive force H _cJ can be achieved. in this case,
Particularly, by quenching, the coercive force H _cJ having an extremely suitable value can be obtained. Quenching is synonymous with effective utilization of the furnace. On the other hand, with slow cooling, a large permanent magnet member can be manufactured without forming cooling cracks in the permanent magnet portion and significantly reducing the coercive force H _cJ .

[0012]   The present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a phase diagram showing the composition of an Nd—Fe—B alloy depending on the effective contents of boron and rare earth. A tissue suitable for use as a permanent magnet is especially the phase triangle 1
Occurs within. Within this phase triangle 1, the alloy consists of ψ-phase hard magnetic particles having a composition of Nd ₂ Fe ₁₄ B, non-magnetic η phase particles having a composition of Nd _1.2 Fe ₄ B, and non-magnetic particles consisting of almost only Nd. It is composed of a wedge phase. The Nd-rich wedge phase magnetically separates the ψ-phase particles from each other, which is necessary for increasing the coercive force H _cJ .

[0014]   To determine whether a certain composition of this alloy is inside or outside the phase triangle 1.
Is a part of neodymium (Nd) of Nd oxide, Nd nickel carbide and Nd nitride.
Being bound to form, first modify the content of rare earth and boron to impurities
There is a need. Effective content of rare earth [SE]_effAnd boron effective content [B]_effIs next
It turns out by the formula. [SE]_eff= ([SE]-[ΔSE]) f [B]_eff= [B] f (In the formula, [SE] and [B] represent weight amounts of rare earth and boron, respectively. [ΔSE] represents Nd. ₂ O3, Nd₃Represents the amount of rare earth bound to CO and NdN compounds, f is the standard
Represents the conversion factor). [ΔSE] = 5.993 [O] +16.05 [C] +10.30 [N] f = 100 / (100- [ΔSE]-[O]-[C]-[N]) (Wherein [O], [C] and [N] represent the weight of O, C and N)
All descriptions are in weight percent.

The effective content of rare earths and boron affects the structure of the tissue. Phase eta point 1
In, the structure exists almost exclusively in the form of η phase. At the point ψ of the phase triangle 1, the alloy takes the form of the ψ phase, while at the point SE it consists of a wedge phase which is rich in Nd. In principle, the amount of the η phase may be arbitrarily small. However, if the boron content is too low, there is a risk that a soft magnetic Nd ₂ Fe ₁₇ phase will be formed in the nonmagnetic η phase, and therefore the coercive force H _cJ will be significantly reduced. Therefore, the composition of the Nd-Fe-B permanent magnet is chosen in a conventional manner so that it is always within the phase triangle 1, especially above the conode 2. Table 1 shows the values at each point in the phase diagram of FIG.

[Table 1]

However, the coercive force H _cJ at 150 ° C. is important for various applications of Nd-Fe-B permanent magnets, especially for all kinds of motors and drives. N used
The coercive force H _cJ of the d-Fe-B permanent magnet should be at least 4.5 kOe, preferably at least 5 kOe, when the demagnetizing field load is small. When a strong reverse magnetic field is applied, a higher value of 13 kOe or more at 150 ° C. is required. In addition to the high coercive force H _cJ at temperatures of 150 ° C., this type of Nd-Fe-B permanent magnet must also have a remanent magnetization Br as high as possible.

Especially for use in a motor, the reversible temperature coefficient TK (Br) of the residual magnetization is 2
It must be better than -0.11% / K in the temperature range 0-150 ° C.

Further, the Nd-Fe-B permanent magnet does not require an expensive and expensive coating,
It should be as corrosion resistant as possible.

It has been discovered that the addition of gallium to the alloy creates below the conode 2 a further phase region 3 in which a gallium-containing phase is present in addition to the hard magnetic ψ-phase and the non-magnetic Nd-rich phase. It was The conode 4 separates the phase region 3 from the phase region 5 in which another Nd ₂ Fe ₁₇ phase predominates. Surprisingly, alloys in phase region 3 can meet the demands placed on Nd-Fe-B permanent magnets used in motors. This improvement can be explained by the metallurgical model described below. That is, in the conventional Nd-Fe-B permanent magnet, when the content of boron is _less than the critical content illustrated by the limit line 2, the soft magnetic N detrimental to the coercive force H _cJ is obtained.
The d ₂ Fe ₁₇ phase occurs. When gallium, cobalt and copper are added to the Nd-Fe-B alloy, the non-magnetic η phase is replaced by the Nd ₂ Fe ₁₇ phase instead of the non-magnetic η phase, and a series of non-magnetic gallium-containing materials is first added. Phases occur. This gallium-containing phase is N
Unlike the d ₂ Fe ₁₇ phase, it contributes to the reduction of magnetic coupling of particles from the ψ phase. As a result, the coercive force H _cJ and its temperature coefficient are also improved. When the boron content is further reduced, the Nd ₂ Fe ₁₇ phase is eventually produced in the phase region 5, and the coercive force H _cJ disappears at the same time.

[0020]   In addition to gallium, cobalt and copper also have a favorable effect on the alloy.

[0021]   When cobalt is alloyed, the temperature of, for example, the residual magnetization of the Nd-Fe-B permanent magnet
The coefficient TK (Br) is improved. In particular, the temperature coefficient TK (Br) of the residual magnetization is 3
By alloying with wt.% Cobalt, about -0.12% / K to about -0.105% /
Improved to K. However, when only cobalt is alloyed, this is soft magnetic SECo. ₂ The Laves phase is formed, and therefore the coercive force H_cJIs considerably reduced. This
The detrimental Laves phase formation of can be prevented by alloying copper at the same time. 0.0
It has been found preferable to add 5 to 0.2% by weight of copper. In addition, contains copper
The Nd-Fe-B permanent magnet having is slowly cooled after the heat treatment performed during the manufacturing process.
If rejected, its coercive force H_cJDoes not decrease significantly.

The stability of the Nd-Fe-B permanent magnet against corrosion by water vapor can be improved by about 3 orders of magnitude as compared with the conventional Nd-Fe-B permanent magnet by additionally alloying Co, Cu and Ga. In that case, the wedge phase rich in Nd, which is particularly reactive, is treated with chemically inert Co or Cu.
And significantly replaces the Ga-containing phase.

By these measures, it was found that the Nd-Fe-B permanent magnet showed a mass loss of 1 mg / cm ² or less on the surface thereof after 10 days of so-called HAST test. In the so-called HAST test, Nd-Fe-B permanent magnets are exposed to a pressure of 2.7 bar at a temperature of 130 ° C. and 95% atmospheric relative humidity.

Further, when a part of Nd is replaced with Dy, Tb or Ho, the contents of rare earths are Fe and B.
The coercive force H _cJ can be increased without significantly changing the ratio with _respect to the content of. D
The magnetic moments of y, Tb and Ho, unlike Nd, are oriented antiparallel to the magnetic moment of Fe, thus necessarily lowering the achievable remanent magnetization Br. This means that an increase in the coercive force H _cJ is associated with a decrease in the remanent magnetization Br.

[0025]   This relationship is shown in FIG. 2 and Table 2 which belongs to it.

[Table 2]

The compositions of alloys A1 to A4 in Table 2 relate to conventional alloys. Also alloy B1
~ B3 indicate the composition of the alloy according to the present invention. From FIG. 2, it can be seen that as the Dy content increases, the coercive force increases but the remanent magnetization decreases.

Further, it can be seen from FIG. 2 that the alloy in which Co, Cu and Ga are additionally alloyed has a higher coercive force H _cJ than the conventional alloy with the same residual magnetization Br. The latter applies not only at room temperature, but especially at 150 ° C.

Nd-Fe-B alloys containing Dy in the range of 3 wt% were classified and investigated. The results of this inspection are shown in Tables 3 and 4. Within the scope of this investigation, it has been found that the magnetic properties of Nd-Fe-B permanent magnets are highly dependent on the temperature manipulation during the heat treatment carried out within the manufacturing process.

[Table 3]

[Table 4]

The Nd-Fe-B alloy is usually obtained by first melting an alloy having a desired composition and casting it into a molten block. The block is then ground into a powder and mixed with another powder to modify the final composition if necessary. The finished powder is oriented in a magnetic field and the magnetic field is oriented parallel or perpendicular or pressed into raw material pieces by isostatic molding. Subsequently, this raw material piece is subjected to a sintering step 6 as shown in FIGS. In the example of the temperature operation shown in FIG. 3, the heat treatment 7 is performed after the sintering step 6. Cooling from the annealing temperature may be performed slowly as shown in FIG. 3 or quickly as shown in FIG.

FIG. 5 shows the dependence of the coercive force H _cJ on the effective boron content and the cooling rate ΔT / Δt. From FIG. 5, it can be read that when the boron content is high, a high coercive force H _cJ can be obtained only within a narrow temperature range of 440 to 500 ° C. On the other hand, when the effective boron content is low, a high coercive force H _cJ can be obtained in a relatively large temperature range. Therefore, the coercive force H _cJ increases to almost 3 kOe as the boron content decreases. The coercive force H _cJ can be increased again by about 1 kOe by quenching to 750 ° C. or less within the range of the sintering process and quenching from the annealing temperature.

The high coercive force H _cJ that occurs despite the slow cooling with a low effective boron content of 0.92% by weight is extremely noteworthy. This is particularly advantageous when it is necessary to manufacture a Nd-Fe-B permanent magnet with a large cross section. This is because, in order to avoid cooling cracks, a low cooling rate of ΔT / Δt <10 K / min is only observed during sintering and heat treatment for this type of component. However, this low cooling rate causes only a slight deterioration of the magnetic properties. According to FIG. 5, as long as the Nd-Fe-B alloy has a low boron content, the Nd-Fe-B permanent magnet after heat treatment is slowed down by about 1 to 2 K / min without seriously adversely affecting its magnetic properties. Can be cooled at various cooling rates. Nd-Fe-B alloys with a low boron content are understood here as those alloys whose effective boron content is below the conode 2.

Tables 3 and 4 show the composition and magnetic properties of isostatically molded Nd-Fe-B permanent magnets having various effective rare earth and boron contents. Bold type refers to low boron alloys according to the present invention. All the Nd-Fe-B permanent magnets were manufactured by a usual powder metallurgy method and sintered at a temperature of about 1060 ° C to a density of 7.6 g / cm ³ or more. The Nd-Fe-B permanent magnets listed in Table 3 are slowly cooled from the sintering temperature to room temperature at about 1-2 K / min. Thereafter, these were annealed at a temperature of 440 to 560 ° C. for 1 to 2 hours, and again slowly cooled to room temperature at about 1 to 2 K / min. The magnets shown in Table 4 were first slowly cooled from the sintering temperature at about 2 K / min to about 750 ° C. and after a holding time of about 1 hour about 30-5.
It was rapidly cooled to room temperature at 0 K / min. This Nd-Fe-B permanent magnet is continuously used for 470
After annealing at ˜530 ° C., it was quickly cooled again to room temperature at about 30-50 K / min.

FIG. 6 shows the values of remanent magnetization Br depending on the effective contents of boron and rare earth in the alloys of Table 3. The two level lines clearly show the tendency for the remanent magnetization Br to increase with decreasing effective rare earth content and increasing effective boron content. With the Nd-Fe-B permanent magnet isostatically molded with an effective rare earth content of 30% by weight or less and an effective boron content of 0.93% by weight or more, a residual magnetization Br of 1.35 T or more is achieved. With respect to the boron content, the remanent magnetization Br passes the maximum value and reaches a little below the limit line 2 of the phase triangle 1.

FIG. 7 shows the dependence of the coercive force H _cJ at 150 ° C. of the slowly cooled Nd—Fe—B permanent magnet from Table 3. It can be seen from FIG. 7 that the coercive force H _cJ at 150 ° C. increases as the effective boron content decreases. The same applies to the coercive force H _cJ at 20 ° C.

Finally, FIG. 8 shows that slowly cooled Nd-depending on the effective contents of rare earth and boron.
The dependence of the temperature coefficient of the coercive force _HcJ of the Fe-B permanent magnet is shown. Again, it can be seen that the temperature coefficient increases to a preferred value as the effective boron content decreases. With increasing coercivity H _cJ, which is the coercivity H _cJ of the magnet which is slowly cooled at 4.5kOe less at 0.99 ° C., to be increased to a value greater than 5.5 kOe. This particularly high value of coercive force H _{cJ occurs} especially with a rare earth content [SE] _eff of 28.9% by weight or more,
At that time, the relationship with the effective boron content is 1.814-0.0303 [SE] _eff ≤ [B] _eff ≤ 1.396-0.01491 [SE] _eff .

The same figure shows an Nd—Fe—B permanent magnet quenched from about 750 ° C. and annealing temperature. According to FIG. 9 and FIG. 10, it is confirmed that Nd-Fe-B which was cooled slowly was used.
The temperature dependence and absolute value of the permanent magnet are slightly better than those of the permanent magnet. Therefore, the required characteristics, that is, remanent magnetization Br of 1.35T or more at room temperature and 150 ° C
The range of achieving a coercive force H _cJ of 5 kOe or more is expanded.

A particularly high value of the coercive force at 150 ° C. occurs at an effective content of rare earths of 28.5% by weight or more, especially 28.7% by weight, and the relationship with the effective boron content is 1.814− 0.0303 [SE] _eff ≤ [B] _eff ≤ 1.478-0.01801 [SE] _eff .

Finally, it should be added that Pr can be used in addition to Nd without impairing the magnetic characteristics of the permanent magnet.

[Brief description of drawings]

[Figure 1]   The partial view of the phase diagram of the Nd-Fe-B permanent magnet of the present invention.

FIG. 2 is a diagram showing a relationship between remanent magnetization Br and coercive force H _cJ of various Nd—Fe—B permanent magnets.

[Figure 3]   The diagram of temperature operation performed at the time of sintering and annealing.

[Figure 4]   Diagram of another possible temperature operation performed during sintering and annealing.

FIG. 5 is a diagram showing the coercive force H _cJ dependency of the type of temperature operation performed during sintering and annealing.

[Figure 6]   FIG. 5 is a diagram showing the remanent magnetization dependence of the effective contents of boron and rare earth.

FIG. 7 is a diagram showing the coercive force H _cJ dependence at 150 ° C. of the effective contents of slowly cooled boron and rare earths.

FIG. 8: Temperature coefficient TK of remanent magnetization of boron and rare earth effective contents when slowly cooled
A diagram showing (H _cJ ) dependence.

FIG. 9 is a diagram showing the dependency of the effective coercive force H _cJ at 150 ° C. on the effective contents of boron and rare earth in the case of rapid cooling.

FIG. 10: Temperature coefficient TK of coercive force of boron and rare earth effective contents when rapidly cooled
The diagram which shows the dependence degree of ( _HcJ ).

[Explanation of symbols]

1 phase triangle 2, 4 conode (limit line) 3, 5 phase region ψ Nd ₂ Fe ₁₄ B hard magnetic phase η Nd _1.1 Fe ₄ B nonmagnetic phase SE Nd rich wedge phase A1 to A4 Composition of alloy according to prior art B1 to B3 Composition of alloy according to the present invention

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C22C 33/02 C22C 33/02 K H01F 1/053 H01F 1/04 HF term (reference) 4K018 AA27 CA04 DA21 DA29 FA09 KA45 5E040 AA04 AA19 CA01 HB03 HB06 HB11 NN01 NN18

Claims (15)

[Claims] 1. An effective rare earth content [SE] _eff , effective boron in an alloy comprising iron and at least one rare earth element including yttrium, which contains elements of B, Co, Cu, Ga and Al and impurities resulting from manufacturing conditions. Content [B] _eff , Dy, T
b and Ho [Dy + Tb + Ho] joint content, cobalt content [Co], copper content [Cu] and gallium content [Ga], and aluminum content [Al] in a weight ratio of 26.9% by weight ≦ [SE] _eff ≤ 33 wt% 2.185-0.0442 [SE] _eff ≤ [B] _eff ≤ 1.363-0.0136 [SE] _eff [Dy + Tb + Ho] ≤ 17 wt% 0.5 wt% ≤ [Co] ≤ 5 wt% 0.05 wt% Nd-Fe-B alloy with low boron content, characterized in that ≤ [Cu] ≤ 0.3 wt% 0.05 wt% ≤ [Ga] ≤ 0.35 wt% 0.02 wt% ≤ [Al] ≤ 0.3 wt%. 2. The effective boron content [B] _eff has a weight relationship of 1.814-0.0303 [SE] _eff ≤ [B] _eff ≤ 1.363-0.0136 [SE] _{eff with} the rare earth element. The listed alloy. 3. The rare earth content [SE] _eff is 28.9% by weight or more, and the effective boron content [B] _eff and 1.814-0.0303 [SE] _eff ≤ [B] _eff ≤ 1.396-0.01491 [SE]. The alloy according to claim 1 or 2, which has a weight relationship of _eff . 4. The rare earth content [SE] _eff is 28.5% by weight or more, the effective boron content [B] _eff is 1.814-0.0303 [SE] _eff ≤ [B] _eff ≤ 1.478-0.01801 [SE. ] The weight relationship of _eff , The alloy of Claim 1 or 2 characterized by the above-mentioned. 5. The alloy according to claim 4, wherein the rare earth content [SE] _eff is 28.7% by weight or more. 6. The alloy according to claim 1, wherein the cobalt content is 2.5 to 3.5% by weight. 7. The alloy according to claim 1, wherein the Cu content is 0.1 to 0.2% by weight. 8. The alloy according to claim 1, wherein the Ga content is 0.20 to 0.30% by weight. 9. The alloy according to claim 1, wherein the rare earth element is selected from the group of elements Nd, Pr, Dy and Tb. 10. A method for producing a permanent magnet from an alloy as claimed in claim 1, wherein the powder produced by grinding at least one melt block is oriented in a magnetic field and pressed into raw material pieces. -Sintering the raw material pieces at a temperature of 1020 ° C to 1140 ° C; -cooling the raw material pieces to a temperature of 300 ° C or less, at which the average cooling rate ΔT ₁ / Δt ₁ <5K / Cooling in minutes, and-including the steps of annealing and cooling this piece of raw material, the annealing temperature TA according to the average cooling rate ΔT ₂ / Δt ₂ is
That is, when ΔT ₂ / Δt ₂ <5 K / min, [B] _eff <2.993-0.069 [SE] _eff 450 ° C. ≦ TA ≦ 550 ° C. [B] _eff > 2.993-0.069 [SE ] _Eff is 460 ° C. ≦ TA ≦ 510 ° C., 5 K / min ≦ ΔT ₂ / Δt ₂ ≦ 100 K / min, and 450 ° C. ≦ TA ≦ 550 ° C. 11. 700 for 0.5 to 2 hours after sintering this piece of raw material
11. The method according to claim 10, characterized in that the holding temperature is maintained at ˜800 ° C. 12. The average cooling rate ΔT3 / Δt from the holding temperature of the crude product after sintering.
The method according to claim 11, characterized in that cooling is performed at 3> 5 K / min. 13. A cooling rate ΔT ₂ / Δt ₂ and ΔT ₃ / Δt _{3 of 30} to 50 K /
13. The method of claim 12, wherein the minutes are minutes. 14. The method according to claim 10, wherein the crude product after sintering is cooled from the holding temperature at an average cooling rate ΔT ₃ / Δt ₃ <5 K / min. 15. The method according to claim 12, wherein the cooling rate ΔT ₁ / Δt ₁ to ΔT ₃ / Δt ₃ is 1 to 2 K / min.