JPH0247815A - Manufacture of r-fe-b permanent magnet - Google Patents

Abstract

PURPOSE:To improve it while maintaining corrosion resistance and magnetic characteristics and to enable a large quantity of composite covers to be processed by cooling a sintered body after heating and holding it within the specific temperature range, and further heating and holding it in molten bath of metal or metallic alloy, which shows the fused condition in the specific temperature range, so as to form a cover of second metal or metallic alloy. CONSTITUTION:The surface layer of the sintered body of an R-Fe-B permanent magnet, consisting of 2-28% B, 8-30% R (but R is at least one kind among rare earth elements including Y), and Fe (a part can be replaced with Co) for the rest by atom percentage, has construction that R, Fe, B are complicatedly intertwinded, but the wettability with the molten bath, etc., are improved remarkably by cooling it down to room temperature - 600 deg.C after heating and holding it at 750-1000 deg.C prior to molten bath treatment, and next it is soaked in molten bath of metal or metallic alloy which shows fused condition at 550-700 deg.C. The material to be processed is not taken out rapidly after being soaked in the molten bath, and this is held in a heating furnace. By this soaking treatment, a firm cover is attached.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention prevents oxidation in the heat treatment process by using a molten metal or metal alloy as a heat treatment bath, and provides a metal or metal alloy coating with good adhesion. 6. Related to the manufacturing method of R-Fe-B based sintered magnets that improve both corrosion resistance and magnetic properties [Prior art] In recent years, SmCo based magnets have been replaced by sintered magnets that are expensive and have concerns about raw material supply. There are great expectations for permanent magnets made of rare earth/iron/ferrous yarns (hereinafter abbreviated as R-Fe-B series) that are separated from Sm and Co, and are attracting attention as new materials.

However, R-Fe-B magnets contain a large amount of highly oxidizing R and Fe, so they have poor corrosion resistance.
, Zn, Zr) (Utility Model Publication No. 61-177407), or Al,
Si, Ti, V, Cr, Ni, Cu, Zn, Zr, Nb
, Mo, and Sn (Japanese Utility Model Publication No. 177408/1983).

Therefore, the PVD method (physical vapor deposition method) is illustrated as an example of the coating method.

Various methods have been considered for coating the metals or metal alloys mentioned above, but vapor deposition methods, ion blating methods, etc. have had problems from the viewpoint of industrial applicability.

This is because not only does it require expensive equipment because it uses high vacuum, but it is also difficult to process large items.

Therefore, a manufacturing method was invented in which the sintered body was immersed in a molten alloy to perform surface treatment and aging treatment (Japanese Patent Application Laid-open No. 63
-55907), the invention uses a molten alloy of 470 to 700
℃ and then subjected to one-stage aging heat treatment.

[Problems to be Solved by the Invention] The above-mentioned invention has the problem that because the temperature range is limited to 470 to 700°C, only a specific alloy can be used, and the range of selection is limited. Ta.

In fact, in the example of the above publication, in order to lower the melting point to below 700°C, Al-Cu, A1 5i, A
Limited to I Sn alloys. According to this invention, when
Even with A1, which has a melting point of 659°C, it cannot be heated too much and the viscosity cannot be removed, so the fluidity of the molten metal is poor, causing problems such as poor adhesion to the magnet and poor adhesion to the recesses of the magnet. .

Further, in the above-mentioned invention, metal coating is attempted to be performed in one treatment without pretreatment, and there is a problem in reliability of adhesion strength to the magnet body.

This is due to insufficient surface treatment.

[Means for Solving the Problems] In order to solve the above problems, the present invention provides B of 2 to 28% in atomic percentage and R of 8 to 30% (wherein R is at least one of the rare earth elements including Y). ) and the remainder Fe (part of which can be replaced with Go) is essentially R-Fe-B
In the method for manufacturing permanent magnets, the sintered body is heated and held at 750 to 1000°C, and then heated to room temperature to
R characterized by cooling to 600°C and further heating and holding in a molten metal or metal alloy that becomes molten at 550 to 700°C to form a second metal or metal alloy coating.
- A method for manufacturing a Fe-B based sintered magnet is provided.

The present inventors have studied in detail the wettability 1 alloying reaction between the molten alloy and the surface of the R-Fe-B magnet in the invention.

As a result, the problem with the conventional invention is that the surface is coated in a single heat treatment without any pretreatment, so the surface is coated without any modification such as surface leakage. It was there. Therefore, what is important is that it has been found that it is essential to perform a predetermined heat treatment before the immersion treatment in the molten metal.

That is, the surface layer of the sintered body has a structure in which R, Fe, and B are intricately intertwined, and has a different aspect from that of the magnet body. Therefore, the inventor of the present invention discovered that 750~
After heating and holding at 1000°C, cool to room temperature to 60°C (
It has been discovered that wettability with molten metal, etc. can be significantly improved by performing a primary heat treatment. The cause of this is currently under research, but it is due to diffusion during heat treatment.

Alternatively, it is thought that stress relaxation in a process-affected layer on the surface, seepage of a low melting point R-rich phase component, etc. are involved.

In the present invention, it is better to clean the surface of the sintered body after the first heat treatment. Known mechanical and chemical methods can be used for this purpose; examples of the former include removal with a wire brush, shot blasting, grid blasting, etc., and examples of the latter include pickling with nitric acid, dilute sulfuric acid, etc. can be used.

The reason for choosing the primary heat treatment at 750-1000℃ is 7.
This is because if the temperature is lower than 50°C or higher than 1000°C, sufficient coercive force cannot be obtained.

Thereafter, it is cooled to a temperature of room temperature to 600°C.

Cooling can be selected as appropriate depending on the application, the shape and size of the magnet, etc. For slow cooling, you can choose furnace cooling in which the magnet is left in a heat treatment furnace, and if you want to further increase the cooling rate, you can choose forced cooling using a fan. Alternatively, immersion in water, Si oil, molten metal, etc. may be performed.

Next, it is immersed in a molten metal or metal alloy that becomes molten at 550 to 700"C.Metals that can be used for this purpose include Al (melting point 659°C) and Zn (melting point 420"C).
℃), pb (melting point 327℃) 2Mg (melting point 651℃),
Not only simple metals such as Sn (melting point 232℃) but also Zn-A
1 alloy, Al-Cu alloy, etc. can be appropriately selected from the equilibrium diagram. Unlike electroplating, there are fewer restrictions on the metals or alloys that can be applied.

This heat treatment is performed at 550-700°C. This is because when the temperature is less than 550°C or more than 700°C, the coercive force is low.

Also, when taking out the workpiece from the molten metal after immersing it in the molten metal, it is better to keep it in the heating furnace as cracks are likely to occur if you take it out suddenly, or it is better to keep the molten metal in a temperature distribution and pull it out slowly. Good.

A second coating can also be applied at this point.

The metal or metal alloy of the first coating may be different depending on the application. Mutual diffusion can be easily performed in the case of metals, which may be formed between the two.

As described above, in the present invention, the wettability with the molten metal is significantly improved by the preceding heat treatment, and then a strong coating is attached by the immersion treatment in the molten metal or metal alloy. Compared to the case where the magnet is directly immersed in the molten alloy, the adhesion with the magnet body is significantly improved. Also, since it is easy to manufacture composite films,
It becomes possible to provide not only corrosion resistance but also multiple functions. For example, if the first layer is made of AI to provide corrosion resistance and the second layer is made of a solder alloy, R-Fe-
It is also possible to obtain B-based magnets. Alternatively, it is also possible to obtain a porous permanent magnet composite by anodizing the second layer with Al.

The reasons for limiting the components of the R-Fe-B magnet in the present invention are the same as those conventionally known (see, for example, Japanese Patent Laid-Open No. 132104/1983). In addition, the additive elements are A1,
Ti, V, Cr, Mn, Zr.

Hf, Nb, Ta, Mo, Ge, Sb, Sn, Bi2,
Addition of known additive elements such as Ni and W does not have any adverse effect on the effects of the present invention.

In the present invention, one or more types of R including Y can be used, but Nd is particularly preferred due to its magnetic properties.

Mainly Pr, Ce or Mitsubishi can be used for cost reduction purposes.

Although the sintered magnet has been described above, the manufacturing method according to the present invention is also applicable to other types of R-Fe-B magnets. In other words, it is a magnet made by hot-pressing flakes obtained by a molten metal quenching method.

Alternatively, the present invention can also be applied to warm-processed magnets that have been plastically deformed in warm conditions to impart magnetic anisotropy, or to cast magnets or warm-processed magnets.

Further, if the metal or metal alloy coating according to the present invention is subjected to a chemical conversion coating treatment such as chromate treatment, or further coated with a resin, the corrosion resistance will be significantly improved. Or AI, Mg
In the case of coating, anodizing treatment is also possible, and furthermore, pore sealing treatment 1 coloring treatment is also possible.

The present invention will be explained below with reference to Examples.

[Example 1 (Example 1) A material having a composition of 14% Nd, 8% B, 1.2% Nb, and the balance Fe was produced by arc melting in atomic percent. The obtained nine ingots were coarsely pulverized using a stamp mill and a disc mill, adjusted to 32 meshes or less, and then finely pulverized using a jet mill. The grinding media is nitrogen gas, and the grinding particle size is 3.5 tt
m (F, S, S, S), where F, S, S,
S stands for Fisher 5ub-Sieve 5izar, which is a particle size measurement method using air permeation method.
The particle size is measured using a measuring device manufactured by er company.

Next, the finely pulverized powder was subjected to transverse magnetic field molding in a magnetic field of 15 kOe (the direction of pressure and the direction of the magnetic field are perpendicular), and the molding pressure was 2 tons/c.
m! It is. The obtained molded body was heated for 11 hours in an argon atmosphere.
After sintering at 00℃ for 1 hour and holding at 785℃ for 1 hour, 5
The sintered body was cooled at a cooling rate of .degree. C./sec.Then, the sintered body was pickled with 2% dilute sulfuric acid, and then held in the A1 molten metal at 700.degree. C. for 1 hour. After taking it out, it was cooled down to room temperature by forced cooling using a fan. When the cross section of the sample was observed under a microscope, an A1 layer with a thickness of 80 μI was uniformly adhered to the surface of the magnet.

(Comparative example): After cooling the sintered body to room temperature without heat treatment, it was pickled and immersed in A1 molten metal at 700°C.

Heat treated. When the cross section of the sample was observed under a microscope, it was found that the adhesion between the magnet body and the A1 layer was non-uniform, and there were many pores. The thickness was 78 μm, which was almost the same as in this example, but the magnet was not uniformly attached to the recesses and corners.

The permanent magnet thus obtained was placed in a constant temperature and humidity chamber at a predetermined temperature, and the appearance, taping peeling test, and oxidation weight gain were measured before and after the test.In the case of the present invention, there was no change in appearance. In contrast, in the case of the comparative example, there was a lot of "blister"-like corrosion in which rust rose from under the coating. The taping peel test is a test method in which a specific cellophane tape with a width of 18 mm is attached and then visually observed to see how the film peels off.In the case of the present invention, there was no peeling at all. In the case of the comparative example, there were 5 peeled areas. The metal coating peeled off while remaining stuck to the tape, and oxidation of the underlying magnet body was also observed. Oxidation gain is 8
Weight change when held at 0°C and 90%RH for 600 hours (
This is a test to measure weight increase due to water content and oxidation. An electronic balance was used for the measurement, and after the humidity test, the temperature was 30℃40%R.
The sample was held at H for 2 hours, and then left in the atmosphere for 1 hour, and then its weight was measured.

The oxidation weight gain after holding for 600 hours was 0.94 in the comparative example.
g/cm2, compared to 0.07mg/cm”
It had a remarkable anti-corrosion effect.

(Example 2) By changing the type of molten metal in Example 1, Zn, Al,
The corrosion resistance of Mg, Sn, Pb, and Al-Cu alloys was evaluated. As a comparative example, Example 1 (
Each metal coating was applied by the method shown in Comparative Example). Here, the corrosion resistance can be easily evaluated in a short period of time using PCT (Pres
sure Cooker Te5t) test.

The evaluation standard was the durability time until corrosion occurred visually after the PCT test. As shown in Table 1 along with the results and magnetic properties, according to the present invention, compared to the conventional one-stage treatment,
It can be seen that results that fully satisfy both magnetic properties and corrosion resistance can be obtained.

Note that in Table 1, the $ mark next to sample No. indicates a comparative example. N0
A l / Cu of 07 is A170wt%, Cu30w
t% of alloy is shown.

Table 1 (Example 3) A magnet sintered body having the same composition as in Example 1 was subjected to the same treatment up to the step of immersing it in the molten alloy, and then Cu 3 was added at 1% by weight.
%, Si8%, Mg 0.2%, Feo, 7%, Mn
0.3%, Zn 0.6%.

The remainder was immersed in 740° C. molten alloy A1. The shape of the test piece was a plate of 80 mm square and 9 mm thick. The immersion time was 45 seconds. When pulling up from the molten metal, hot air at 600° C. was blown to blow away the adhering molten alloy and make the amount of adhesion uniform, and the temperature of the hot air was gradually lowered. Further, as a comparative example, the same treatment as shown in Example 1 was carried out.

The appearance of the obtained test piece showed no cracks, and after polishing the cross section, it was observed under an optical microscope that the magnet body and coating layer formed an alloy layer with a thickness of about 70 μm. Furthermore, SEM
/EDX (scanning electron microscope) analysis revealed that the surface layer had a structure in which Nd, Fe, and Al were intricately distributed. In the case of the comparative example, the Nd content in the surface layer was one order of magnitude higher than in the case of the present invention, and this seems to be associated with the deterioration of corrosion resistance.

[Effects of the Invention] According to the present invention, not only can the corrosion resistance of R-Fe-B permanent magnets be significantly improved while maintaining good magnetic properties, but also a simple and industrial method can be used for composite coating. It is easy to add other functions to corrosion resistance, such as magnets that can be soldered or composite magnets with a capacitive layer on the surface.

Claims (2)

[Claims] (1) R_2T_1_4B intermetallic compound whose main components are rare earth elements (R), boron (B), and iron (Fe) (where R is at least one rare earth element including Y, and T is Co
R-Fe-
In the method for manufacturing B-based permanent magnets, the sintered body is heated to 750 to 1
After heating and holding at 000°C, cooling to room temperature to 600°C,
A method for manufacturing an R-Fe-B sintered magnet, which further comprises heating and holding the metal or metal alloy in a molten metal that becomes molten at 550 to 700°C to form a metal or metal alloy coating. (2) 2-28% B and 8-30% R in atomic percentage
(However, R is at least one kind of rare earth element including Y),
The remainder is Fe (part of it can be replaced with a metal element containing Co).
The method for manufacturing an R-Fe-B permanent magnet according to claim 1, which consists essentially of