JPS5858241A - Manufacture of isotropic mn-al-c magnet - Google Patents

Abstract

PURPOSE:To manufacture a lightweight isotropic Mn-Al-C magnet with superior magnetic characteristics without using expensive starting materials such as Co by sintering Mn-Al alloy powder with low oxygen concn. and superior compressibility in an evacuated CO atmosphere. CONSTITUTION:An Mn-Al alloy contg. 30wt% Al and 0.02-0.001wt% oxygen is pulverized by an atomizing method, and this alloy powder is mixed with about 0.3-1.5wt% powdered carbon material. The powdered mixture is cold-molded to a prescribed shape and sintered in an evacuated gaseous CO atmosphere u nder 1-100Torr partial pressure of gaseous CO. The sintered body is made dense and subjected to soln. heat treatment by hot hydrostatic press molding at 1,000- 1,100 deg.C. Thus, a lightweight isotropic Mn-Al-C magnet with higi magnetic energy per unit weight is obtd. at a low cost. The magnet is suitable for improving the performance of a magnet apparatus and for reducing the weight and thickness.

Description

[Detailed Description of the Invention] The Mn-A C-free magnet is a material that does not use CO, which is a rare resource, and is therefore highly economical. It is also lightweight and has a large magnetic energy per weight, making it suitable for high-performance magnet-applied equipment. It is suitable for improving performance, reducing weight, and reducing thickness, and has been actively developed for practical use.

This material has excellent machinability when compared to other magnet materials such as alnico alloys, but its hardness is HRc50-55.
Because of its high surface strength, it is also a difficult material to cut, and the efficiency of processing the raw material and drilling is extremely poor, which poses a problem in practical use.

Powder metallurgy may be used as one of the methods for manufacturing magnetic components that are difficult to cut.

However, it has been extremely difficult to produce Mn-Al, -C based materials using conventional powder metallurgy methods.

This is because, as mentioned above, Mn-A-C-based materials are hard and brittle, making it difficult to press and mold them, and because the main components are Mn and AJ, which have extremely high bonding strength with oxygen, they easily oxidize during heating. This is because sintering hardly progresses. For this reason, for example, a method was proposed in which the sintering atmosphere was made of high-purity hydrogen, but this method had no significant effect and could not be used as a magnet because a sintered body with sufficient density could not be obtained. or,
Method of sintering by adding low melting point elements (Japanese Unexamined Patent Publication No. 55-10
No. 0944) has been proposed, but its magnetic properties were not sufficient.

As described above, it has been difficult to manufacture high-performance sintered Mn-A No. 0 magnets using conventional powder metallurgy methods.

The present invention uses Mn-A, 12 alloy powder with low oxygen concentration and excellent compressibility to sinter in a reduced pressure atmosphere with a CO gas partial pressure of 1 to 100 Torr. ), or the sintering of magnets with higher performance than sintering in a closed air atmosphere, and furthermore, this sintered body was isotropically densified by hot isostatic pressing, and the sintered body was We have discovered a method of obtaining a magnetic material that has almost the same performance as molten material by eliminating most of the holes.

A method of obtaining a dense molded body without voids or voids by hot isostatic pressing (hereinafter abbreviated as HIP) a sintered body has already been widely put into practical use.

However, in Mn-1'JC materials, this HI
Conventionally, it was impossible to densify by applying P.

This is because sintered bodies produced by conventional powder metallurgy have a high porosity and more continuous pores than independent pores, so gas is used as the pressure medium. This is because the medium easily penetrates and the pores do not undergo any volume change due to plastic deformation.Of course, there is also a method of sealing such a sintered body in an airtight container and HIPing it. There is no point in using this material because the economical efficiency is significantly impaired.

However, according to the method of the present invention, a high-density embossing molded body can be obtained, and the porosity is low and has almost no continuous pores.
Furthermore, since a good sintered body containing less oxides can be obtained, it has become possible to easily perform HIP treatment.

In the present invention, low-oxygen Mn-1'J alloy powder of 0.02 to 0.001 wt% 0□ was obtained by an atomization method.

This Mn-M alloy powder is much softer and has better compressibility than Mn-A)-〇 produced by pulverization, so it is molded and sintered after adding and mixing an appropriate amount of carbon to achieve the desired composition. It is.

First, sintering in reduced pressure CO gas will be explained.

In Mn-AU-C alloys, Mn and AI oxides are formed on the powder surface, so these oxides cannot be reduced and removed during sintering in a conventional atmosphere, and the remaining oxides become magnetic. It was inevitable that the characteristics would be damaged.

However, it was found that by using a low oxygen Mn-A1 alloy powder, the adverse effects of residual oxides were significantly improved.

The oxide of Mn is mainly MnO, and the dissociation pressure of this oxide is ΔG'=91950-17, IT in the formula MnOw Mn + -02, so when the maximum heating temperature is 1200°C, IQ -I
n or more, and it was impossible to decompose it under normal vacuum.

On the other hand, the method of reducing MnO with carbon is MnO+
Since C = Mn + CO ΔG0 = 65250-38.35T, MnO cannot be reduced unless the heating temperature is 1428°C or higher, and at this temperature Mn -
The Al1-C alloy turned into a melt and could not be sintered. However, in the method of the present invention, by reducing the pressure of the CO gas in the above reaction, that is, pco-
It has been found that by setting iτ to ]7, a good sintered body can be obtained by lowering the 'P equilibrium reaction temperature to below the melting point. If the partial pressure of CO gas is lower than I Torr, the atmosphere will be similar to a high vacuum atmosphere, and although based on simple thermodynamic calculations it seems that the reduction reaction will occur even more easily, in reality it is of C is consumed,
This is undesirable as it deviates from the optimum composition range. That is, it has been found that supplying an appropriate amount of C from the atmosphere is a condition for obtaining a good sintered body. On the other hand, PCO is not necessarily M
Even if nO is higher than the theoretical partial pressure that can be reduced at that temperature,
We also discovered that sufficient sintering can be achieved using low-oxygen powder. The reason for this is that the oxygen partial pressure in the atmospheric gas is low (Mn-A
This seems to be because oxidation of the I-C alloy is suppressed.

As a result of the experiment, good sintering was possible when Pco was 1 to ]00 Torr.

A requirement of the present invention is to manufacture a high-performance M n -A No. 0 series magnet sintered body by densifying the thus obtained sintered body by HIP.

The temperature of HIP treatment is 1000~ with low high temperature deformation resistance]
It was discovered that by heating to 100'C, not only the effect of densification can be obtained in a relatively short time, but also solution treatment is performed at the same time, and solution treatment can be completed simply by controlling the cooling rate. .

Although HIP treatment is possible even in the above temperature range, for example,
At 00°C, it takes an extremely long time to achieve the densification effect, and at higher temperatures, the heat treatment becomes complicated due to solution treatment, which is not preferred. By HIPing in the above temperature range, it is possible to manufacture in a short time.

Note that if the oxygen content of the powder is 0.02 wt% or more, a good magnet cannot be obtained because there are many oxides remaining;
If the powder is less than 1 wt%, it will be difficult to handle during production and will be expensive, so a range of 0.001 to 0.02 wt% is desirable.

Next, an example will be explained.

Example 1゜70wt%Mn-29,5wt%A No〇,005wt
An atomized powder having a composition of %02 was obtained. 5 times this powder
After sintering at 1210"C for 30 minutes in a reduced pressure atmosphere with a CO gas partial pressure of 3 Q Torr, the pressure was reduced to 1080
HIP treatment was performed in Ar gas at 1600 atm for 2 hours at °C.

The obtained sintered body has a specific gravity of 4.96 g/cc, and a maximum energy product (BH) of magnetic force of 3.4 MG.
2) Ivy in Oe.

Example 2 A sintered body obtained in the same manner as Example 1 was heated at 119σC for 3
10 minutes after HIP treatment in Ar gas at 1600 atm.
Solution treatment was carried out continuously for 1 J by rapid cooling to 50° C. and further controlled cooling for 1 hour. The obtained sintered body had a specific gravity of 4.95 g/cc and a maximum energy product of 3.2 MGOe.

As explained above, by the method of the present invention, an isotropic Mn-A No. It has become possible to manufacture products with complex shapes with a high material yield without cutting. Representative Patent Attorney Tetsu Shodai 7 A>4 encouraged 7/Sear 15

Claims (1)

[Claims] Mn-30wt% A no 0.02 to 0.001 wt
9t: ; 0.3 to 1.5 to 07 atomized alloy powder
After adding and mixing wt% carbon and cold forming into a fixed shape, C
A method for producing an isotropic Mn-AJ-C magnet, characterized by sintering in a reduced pressure atmosphere with an O gas partial pressure of 1 to 100 Torr, further densifying it by hot isostatic pressing, and then subjecting it to solution heat treatment. . (2. In claim (1), 1000 to
A method for producing an isotropic Mn-A4-C magnet, characterized by performing hot isostatic pressing at 1100°C and solution treatment at the same time.