JPS5858706A - Manufacture of mn-al-c family permanent magnet - Google Patents

Abstract

PURPOSE:To have maximum energy product which is nearly twice an isotropic ferrite by a method wherein sintering is done under the atmosphere of CO gas partial pressure of 1-100Torr by using a low oxygen content Mn-Al alloy powder having good compressibility. CONSTITUTION:After adding and mixing a suitable amount of carbon for forming objective composition to low O2 content Mn-Al alloy powder O2 of 0.02- 0.001% by wt O2, the powder is formed and sintered. When CO partial pressure is maintained at 1-100Torr at the time of sintering, good sintering is experimentally becomes possible. Residual oxygen is abundant at the oxygen content of 0.02% by wt or over, therefore, a good sintering permanent magnet cannot be obtained. As to a powder of 0.001% O2 or less by wt, treatment on manufacture requires much time and high costs follow. As a result, a powerful permanent magnet having maximum energy product which is twice an isotropic ferrite can be obtained by a powder metallurgy method.

Description

[Detailed Description of the Invention] The Mn-A no-C magnet is a material that does not use Co, which is a rare resource, and is therefore highly economical and lightweight.
It has a large magnetic energy per unit weight and is suitable for improving the performance of magnet-applied equipment and making it lighter and thinner, 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 HRo50-55.
Because of its high surface area, it is also a difficult material to cut, and the efficiency of turning 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 M n -A no-C materials using conventional powder metallurgy methods.

This is because, as mentioned above, Mn-Ai-C materials are hard and brittle, making it difficult to mold them, and since the main component is Mn JPfiJ, which has extremely high bonding strength with oxygen, ζ
This is because sintering hardly progresses because it is easily oxidized.

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.

In addition, a method of adding a low melting point element and sintering (Japanese Patent Application Laid-open No. 1986-
No. 100944) has been proposed, but the magnetic properties are insufficient.
It wasn't.

In this way, conventional powder metallurgy method + high performance sintered Mn-A
Manufacturing J2-C magnets was difficult.

The present invention uses Mn-A1 alloy powder with good compressibility and low oxygen concentration to sinter in a reduced pressure atmosphere with a CO gas partial pressure of 1 to 100 Torr. It was discovered that magnets can be sintered with higher performance than sintering in an atmosphere.

Although the Mn-A-no-C alloy powder was hard and brittle and could be easily powdered, it had poor compressibility and was difficult to mold. In the present invention, a low oxygen M n of 0.02 to 0.001 wt%02
-A1 alloy powder was obtained by an atomization method. This M n
-A1 alloy powder is much softer and has better compressibility than Mn-A no-C powder produced by pulverization, so it can be molded and sintered after adding and mixing an appropriate amount of carbon to achieve the desired composition.

In Mn-A No. 0 series alloys, Mn and M 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 are Impairment of magnetic properties was inevitable.

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

The oxide of Mn is mainly MnO, and the dissociation pressure of this oxide is ΔG0 = 919 ri 0-17.47 in the formula MnOwMn +-02, so when the maximum heating temperature is 1200 °C, the dissociation pressure of this oxide is 10
-10 or more, and decomposition was impossible under normal vacuum.

On the other hand, the method of reducing MnO with carbon is MnO+
C = Mn: + CO ΔG0 = 65,250 = 1.35T, so MnO cannot be reduced unless the heating temperature is 1428°C or higher, and at this temperature the Mn-A Noc alloy turns into a melt. This made it impossible to sinter. However, in the method of the present invention, by controlling the CO gas in the above reaction to, for example, 1 to 40 Torr, that is, Pco
By setting = 0.0018 to 0.05, free energy change ΔG1ΔG = 65250-38.85T
+RT no npc.

It is possible to lower the temperature to 993-1200°C. On the other hand, in this thermodynamic calculation, it seems that significantly lowering the CO gas partial pressure makes the reduction reaction more likely to occur, but in reality, the reduction reaction
is consumed and the composition deviates from the optimum composition range, which is undesirable.

In addition, sintering may proceed well even if the 00 partial pressure (Pco) is higher than the theoretical partial pressure because the oxygen partial pressure in the atmospheric gas is low (oxidation of the Mn-A-C alloy is suppressed). This seems to be for the purpose of

As a result of experiments, good sintering was possible when the PCO was 1 to 100 Torr.

When the sintering temperature is equal to or higher than the peritectic temperature, rapid sintering with a liquid phase is possible, and a sintered body with few residual pores can be obtained.

However, since the difference between the peritectic temperature and the melting temperature is small, it is necessary to use a sintering furnace with good temperature accuracy.

On the other hand, when performing solid-phase sintering below the peritectic temperature, the sintering time is long, but the sintering behavior is stable even with slight variations in the sintering temperature, so the temperature accuracy is poor. It has the characteristic that even when using a sintering furnace, a sintered body that does not lose its shape or melt can be obtained.

Furthermore, another feature of the present invention is that solution heat treatment is continuously performed in the ε phase region in the same furnace during cooling after sintering, which eliminates the long time required in conventional manufacturing methods such as casting. Solution heat treatment time and effort can be eliminated.

Since the sintering temperature is set in the ε phase region, homogeneous solution treatment proceeds almost simultaneously, and the solution treatment can be easily performed by controlling the cooling rate after sintering.

The present invention provides a new method for manufacturing Mn-A)-C magnets by powder metallurgy, and this method
It is effective when applied to an alloy having a weight percent of A of 29.5 weight percent and a weight of C095, but it is also effective even if the composition ratio is varied within a range that can be changed by a normal manufacturing method.

Additionally, Ni, Ti, B, or Ge'$ may be added to this alloy system in order to further improve its magnetic properties and workability; The manufacturing method according to the invention was useful.

Note that if the oxygen content of the powder is 0.02 wt% or more, a good sintered magnet cannot be obtained because there are many oxides remaining.
Powders with a weight of 1 wt% or less are rather time-consuming and expensive to handle during production, so 0.001 to 0.02 wt.
% range is preferred.

Next, an example will be explained.

Example 1 70wt, %Mn-29.5wt, %AJ-0
,005wt, an atomized powder having a composition of %0 was obtained. After adding and mixing 1 wt% of carbon to this powder, it was molded into a 10 x 10 x 55 JLIIL at a pressure of 5 t/l. This molded body was sintered at 1210°C for 115 minutes in a reduced pressure atmosphere with a CO gas partial pressure of 30 Torr.
After holding at 50°C for 30 minutes, forced cooling was performed at 10'C/min or more. The specific gravity of the sintered body obtained by further tempering at 550°C was 467 g/cc, and the maximum energy product (BH) max was 2.4 MG·Oe.

Example 2゜A molded body obtained in the same manner as in Example 1 was heated to a CO gas partial pressure of 1
Controlled cooling was performed after sintering at 1160° C. for 14 hours in a reduced pressure atmosphere of 0 Torr. The obtained sintered body has a specific gravity of +51
The maximum energy product ('B'H) max in g/cc was 1.9 I·Oe.

As is clear from the above results, by the method of the present invention,
A powerful magnet with a maximum energy product nearly twice that of isotropic ferrite was obtained by powder metallurgy.
This makes it possible to manufacture complex-shaped magnetic parts such as uneven cylinders and hollow pipes at low cost with a high material yield, which has high industrial value.

Claims (1)

[Claims] (1) Mn-3Qwt% Affl-0.02 to 0.0
0.8 to 1.01 wt% O2 atomized alloy powder.
Add 5wt% carbon, mix and cold-form into a predetermined shape.
A method for producing a Mn-A no-C magnet, which comprises sintering the magnet in a reduced pressure atmosphere with a CO gas partial pressure of 1 to IQ O Torr, and subsequently subjecting it to solution heat treatment during cooling. (2. A method for manufacturing a Mn-A No. 0-based magnet as set forth in claim (1), characterized in that the sintering temperature is higher than the peritectic reaction temperature. (8) Claim (1) In item 1), the method for producing a Mn-A no-C magnet, characterized in that the sintering temperature is lower than the peritectic reaction temperature.