JP2695289B2 - Method for producing Al alloy mixed powder and Al alloy sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to an Al alloy mixed powder as a raw material for an Al alloy sintered body used for machine parts and the like, and a method for producing an Al alloy sintered body using the same. Regarding

[Prior Art and Problems to be Solved] Recently, in the field of office equipment and computer-related equipment, it is necessary to reduce the weight of aluminum alloy parts because of the necessity of reducing power consumption, preventing noise due to vibration, and improving portability. Usage is increasing.

Conventionally, a die-casting method has been generally used as a method for producing a complex-shaped component of an Al alloy. However, while the die-casting method has the advantage that three-dimensionally complex parts can be manufactured, the dimensional accuracy is insufficient, and it is necessary to taper for die cutting, requiring high-cost machining after casting. In many cases In addition, due to casting defects such as blowholes, there was a problem that the reliability was poor in terms of characteristics.

As another method, there has been adopted a method in which a wrought material starting from a molten ingot is used as a raw material and is manufactured by machining using a lathe or the like. However, it requires a considerable number of man-hours for machining, and the machining yield is low, resulting in an increase in the price of parts.

In order to solve such a problem, a method of manufacturing by a powder metallurgy method that can make use of the features of the near net shape method has been tried (for example, ASTM Designatio).
n: B595-84).

The conventional green compacting and sintering method of molding a powder and sintering the powder has a great advantage, particularly in terms of cost, because a near net shape part can be manufactured by a simple process.

As a method of manufacturing such an Al alloy sintered body part, pure Al
A so-called blended elementa mixing method that uses liquid phase sintering using a mixed powder that is a powder of a single powder of an alloying element such as Cu, Si, or Mg that forms a low melting point eutectic with Al
l method) is well known. However, this method is unlikely to produce a liquid phase because the melting point of the elemental element powder is high,
There is a problem that unreacted element powder is likely to remain after sintering and it is difficult to obtain a sintered body having good mechanical properties.

On the other hand, the alloy powder method (Pr
In the case of the ealloy method), since the powder is hard, the molding compressibility is poor, and it is not possible to obtain a good molded product by ordinary mold molding. Furthermore, since the melting point of the powder is low, the sintering temperature cannot be raised sufficiently, and diffusion and sintering cannot be satisfactorily advanced.

Further, as a method of improving the above element powder mixing method, a method of using a mixed powder prepared by producing a mother alloy powder in which an alloying element is previously alloyed with Al and mixing this mother alloy powder with pure Al powder, so-called Master alloy method
Has also been proposed (for example, Japanese Patent Laid-Open No. 1-294833). In this method, pure Al powder that is easy to mold is used as the main raw material, and the alloying element has already been alloyed with Al, and in many cases, it is adjusted to a composition that easily forms a multi-component low-melting eutectic. Therefore, the liquid phase sintering is likely to proceed, and it becomes possible to obtain a sintered body having more excellent mechanical properties.

However, even when the above-mentioned mother alloy method is used to produce a component having a complicated shape, there is a problem in that the fluidity of the powder is poor and the powder is not uniformly filled in the mold, and the density becomes low depending on the site of the molded sintered body. In addition, the master alloy powder melts, diffuses and disappears, and remains as a relatively large bore, resulting in mechanical properties,
In particular, there are problems that ductility is poor and surface properties are poor.

[Means for Solving the Problems] Among the compacting and sintering methods, the master alloy method can take advantage of the characteristics of the near net shape method and can obtain an Al alloy sintered body having relatively good mechanical properties. It is possible. However, even in such a mother alloy method, the mechanical properties or surface properties are insufficient depending on the application, and therefore the present inventors sought to further improve the characteristics, and the pure Al powder and the mother alloy powder as the main raw material powder in the mother alloy method were used. It has been found that by strictly controlling the particle size, it is possible to improve the fluidity of the mixed powder, facilitate molding, and obtain an Al alloy sintered body having good mechanical properties and surface properties of the sintered body. Came to.

That is, the present invention is a mixture of pure Al powder and Al master alloy powder.
A raw material powder for producing an Al alloy sintered body, which is pure Al
An Al alloy mixed powder characterized in that the average particle size of the powder is 53 μm or more and 105 μm or less, the average particle size of the mother alloy powder is 63 μm or less, and the difference between the average particle sizes of the two is 20 μm or more. The point is to use.

 The details are described below.

First, the reason for limiting the particle size of the pure Al powder used as the main raw material powder will be described.

In the powder compacting and sintering method, the raw material powder is first supplied into the recess of the mold and press-molded, so that the fluidity of the powder is required to be good. Poor fluidity makes it difficult for the powder to fill the narrow part, and also causes the filling rate to vary depending on the part.
Furthermore, the filling amount for each part is also different, which causes variations in density depending on the parts of the molded product, weight of individual molded products, and therefore variations in dimensions, which reduce the product quality and eventually increase the defective rate. Cause. In order to eliminate such a problem, it is desirable that the particle size of the mixed powder as a raw material is large.

In particular, it was found that the fluidity is greatly influenced by the particle size of pure Al powder used as the main raw material powder in a large amount among the mixed powders, and the fluidity of the entire mixed powder can be improved by increasing the particle size. That is, from the above viewpoint, the average particle size of the pure Al powder is set to 53 μm or more. On the other hand, in the mother alloy method, since the alloy elements are supplied as mother alloy powder, it is necessary to make the alloy elements diffuse and uniform in the pure Al powder in addition to the bonding of the powders in the sintering process. However, as the particle size of pure Al powder increases, the time required to diffuse and homogenize the alloying elements by sintering increases, which means that the cost of sintering is the highest in terms of cost in the production of Al alloy sintered compacts. Further increase and become economical. For this reason, the average particle size of the pure Al powder is set to 105 μm or less. From the viewpoint of maintaining good fluidity as described above and shortening the time required for uniform diffusion, the average particle size of pure Al powder is 53 μm or more,
It was set to 105 μm or less.

Next, the reasons for limiting the average particle size of the mother alloy powder will be described.

Since the mother alloy powder is melted in the sintering process, leaks and spreads on the surface of the pure Al powder, and diffuses and disappears in the pure Al powder, most of the traces of the original mother alloy powder remain as pores, that is, outflow holes. These pores reduce the mechanical properties of the sintered body due to the notch effect. Further, these pores are also present on the surface of the sintered body, which deteriorates the surface properties and reduces the commercial value. In order to prevent deterioration of mechanical properties and manifestation properties due to such causes, the average particle size of the master alloy powder may be reduced. From such a viewpoint, the average particle size of the master alloy powder should be 63
The average grain size of the pure Al powder is 20 μm or more. In most cases, the amount of the master alloy powder in the mixed powder is about 3% to 12%, which is smaller than that of the pure Al powder. There are few adverse effects. By such a method, it becomes possible to obtain a sintered body in which the mixed powder has good fluidity, is easy to mold, and has good mechanical properties and surface properties.

Further, the reason why the maximum grain size of the mother alloy powder is defined in claim 2 is that the notch toughness and fatigue strength are affected by the maximum grain size outflow holes existing in the material.
Since the maximum diameter of such outflow holes is almost proportional to the maximum particle diameter of the mother alloy powder, the maximum particle diameter was limited to 105 μm. Further, the flowability of the mixed powder is greatly influenced by the ratio of the fine powder in the whole powder together with the average particle size, so that the ratio of the powder of 44 μ or less is limited to 3% or less.

Here, the average particle size of the powder is a particle size at which the cumulative particle size distribution is 50%. In the case of pure Al powder and Al alloy powder obtained by the atmospheric atomizing method, which is an economical mass production method, the shape of the powder is not spherical but irregular, and the particle size in that case is the diameter when converted to sphere. Is almost equal to, or the maximum particle size corresponds to the opening of the sieve in the sieving method.

 Next, the composition of the mother alloy powder will be described.

The mother alloy powder plays a role of adding Mg, Si, or Cu that contributes to aging precipitation strengthening, and at the same time, itself starts melting at a sintering temperature or lower, or pure Al- which is a main raw material powder.
It plays the role of promoting the sintering by generating a liquid phase by the eutectic reaction with the powder. In order to achieve such an object, it is desirable that the composition on the low concentration side of the composition range of the mother alloy powder be close to the eutectic composition of the Al-Si-Mg ternary alloy, specifically, Si: 12% or more. , Mg is preferably 4% or more. Further, since the mother alloy powder is a high alloy and hard, increasing the blending amount impairs the formability. Therefore, in order to add a predetermined amount of alloying elements with a smaller blending amount, it is advantageous to add more alloying elements to the mother alloy powder. On the other hand, if the Si content exceeds 30% and the Mg content exceeds 20%, the temperature at the end of melting of the alloy, that is, the temperature in the liquidus increases, making it difficult to melt during powder production and eutectic during sintering. Since the formation reaction is less likely to occur, it is necessary to set Si to 30% or less and Mg to 20% or less. In addition, Mg increases the activity of the molten metal with its increase and is easily oxidized, and it becomes extremely difficult to manufacture by the atmospheric atomizing method, which is an economical Al alloy powder manufacturing method,
From such a viewpoint, Mg should be 20% or less.

Furthermore, by adding an appropriate amount of Cu to this master alloy powder, it becomes possible to further lower the melting start temperature (solidus temperature) of the master alloy powder, which promotes sintering and eventually the mechanical properties of the sintered body. It is possible to further improve the property. Therefore, as a more preferable mother alloy composition, addition of 5% or more of Cu is desirable. Further, Cu is a strong age hardening element in the Al alloy, and is an extremely effective alloy element particularly when trying to obtain a high-strength Al alloy, and the mother alloy powder is also used for the purpose of increasing the Cu concentration in the sintered body. It is desirable to actively increase. However, when Cu is added in a large amount, the corrosion resistance of the sintered body deteriorates and the ductility also decreases. When Cu is added, if the Cu content in the master alloy powder exceeds 45%, the melting end temperature (liquidus temperature) of the master alloy rises, making it difficult to manufacture the powder. desirable.

As described above, the master alloy powder is preferably Al-Si-Mg system or Al-Si-Cu-Mg system, the composition of the master alloy powder, Si: 12 ~ 30%, Mg: 4 ~ 20% When adding the balance Al and further Cu, Cu: 5 to 45% is considered to be appropriate.

Other mother alloy powders such as Al-Mg alloys, Al-Si alloys, Al
-Cu-based binary alloys or Al-Cu-Mg, Al-Si-Cu ternary alloys and other Al alloy powders can be blended with one or more master alloy powders. .

Next, the blending amount of the master alloy powder blended with the pure Al powder will be described.

By adding Mg and Si to Al, and further adding Cu as required, the melting start temperature and pure
It becomes possible to adjust the temperature at which the liquid phase is generated by the reaction with the Al powder. Also, by adjusting the alloying amount of these elements, it becomes possible to widen the adjustment range of the compounding amount of the mother alloy in the raw material mixed powder.

Regarding the blending amount of this mother alloy, if the amount is too small, it is not possible to secure a sufficient amount of liquid phase in an Al alloy in which liquid phase sintering is indispensable, and it becomes impossible to obtain a sintered body with good characteristics. . On the other hand, if the amount is too large, the amount of liquid phase generated becomes too large, and it becomes impossible to obtain a sintered body having a good surface property due to a sweating phenomenon. From such a viewpoint, the blending amount of the master alloy is 2% or more, 15
% Or less is suitable.

Further, by mixing a lubricant with the alloy powder, it is possible to improve the lubricity between the powders, improve the lubricity between the powder and the wall surface of the mold, and enhance the formability. Lubricant content is 0.5%
If the amount is less than 2%, not only the effect will be saturated, but also the fluidity and moldability of the powder will be impaired, and the lubricant will be volatilized and scattered at the time of sintering, unnecessarily in the sintering furnace. Or, in vacuum sintering, 0.5 ~
2% is desirable. As the kind of the lubricant, it is preferable that all of the lubricant be volatilized and scattered below the sintering temperature and have no detrimental effect on the material properties. From such a viewpoint, amide-based lubricants are preferable to metal salt-based lubricants (eg, zinc stearate, lithium stearate, aluminum stearate, etc.), and for example, ethylene bisstearamide is the most suitable lubricant. Can be mentioned.

In addition, wear resistance, increased friction coefficient,
Ceramic particles can be mixed with these powders in order to impart functions such as a low coefficient of thermal expansion. At that time, if the addition amount is 2 Vol% or less, the effect is insufficient, and if the addition amount is 20 Vol% or more, the mechanical properties of the sintered body, particularly ductility are remarkably deteriorated, and therefore it is necessary to set it below that. In addition, blending solid lubricants such as graphite and hexagonal BN or metal powders such as Fe, Ni, Mn, Ti, Zr and Si is also effective for improving properties such as wear resistance.

 Next, a method for manufacturing a sintered body will be described.

If the molding pressure is less than 2 ton / cm ² , the compact will not be sufficiently densified and the powder particles will not contact each other sufficiently, so that good strength and ductility of the sintered body cannot be obtained. Therefore, it is necessary to mold at 2 ton / cm ² or more. Further, when attempting to increase the density of the molded body and molding at a higher molding pressure, problems such as shortening the life of the mold, occurrence of lamination, and galling of the mold occur. Therefore, a molding pressure exceeding 8 tons / cm ² is not appropriate in actual operation.

Further, by molding the raw material powder in a state of being heated to 70 ° C. to 250 ° C., it is possible to further densify the molded body.

Regarding the sintering atmosphere, it is necessary to sinter in a vacuum or in a non-oxidizing atmosphere such as a nitrogen gas or argon gas atmosphere in order to prevent the oxidation of the active Al alloy powder particles and allow the sintering to proceed sufficiently. When sintering in vacuum, the degree of vacuum is 0.1 torr
r or less, preferably 0.01 torr or less. In addition, sintering under a reduced pressure and flowing a small amount of an inert gas such as nitrogen gas after vacuum replacement of the inside of the sintering furnace also enhances the effect of removing gas components generated from the sintered body. When sintering in a nitrogen gas atmosphere or an inert atmosphere such as argon gas, the purity of the gas is important, and the moisture contained in the gas adversely affects the characteristics of the sintered parts. Must be controlled, preferably with a dew point of −40
It must be kept below ℃.

If the sintering temperature is lower than 500 ° C, the diffusion of elements will be insufficient and the sintering of the powders will be insufficient. On the other hand, if the temperature is higher than 620 ° C, a large amount of liquid phase is generated, and the shape of parts cannot be maintained as the temperature rises. Therefore, it is necessary to sinter at 500 ° C or higher and 620 ° C or lower.

Further, by recompressing the thus obtained sintered body, the structure can be densified and the mechanical properties can be further improved. In general, recompression is often aimed at dimensioning (sizing), and recompression conditions are selected along with it.
Usually, the recompression pressure is in the range of 3 to 11 ton / cm ² .

Further re-sintering can improve mechanical properties, especially ductility. By re-sintering the structure densified by re-compression, diffusion / sintering can be further advanced. The conditions at that time are basically the same as in the case of sintering.

Further, Cu, Mg and Si which are alloy components of these sintered bodies originally contribute to the improvement of mechanical properties by solution treatment and aging treatment. Therefore, as with ordinary Al alloys, it is effective to perform solution treatment and aging treatment to adjust and improve their mechanical properties.

[Operation] According to the present invention, flow is achieved by strictly controlling the particle diameters of pure Al powder and master alloy powder as the main raw material powder in the master alloy method, which is excellent as a near net shape manufacturing method for precision parts made of Al alloy. It becomes possible to mold while maintaining good properties, and it is possible to remarkably improve the mechanical properties and surface properties of the sintered body.

Examples of the Invention Hereinafter, examples of the present invention will be described.

Example 1 Pure Al powder produced by the atmospheric atomization method and Al-20% S
Si-10% Cu-10% Mg master alloy powder was sieved and blended again to prepare pure Al powder and master alloy powder having various average particle sizes shown in Table 1. They were mixed at a weight ratio of 95: 5 to obtain a compounding composition Al-1% Si-0.5% Cu-0.5% Mg. Further, 1% of an amide-based lubricant was added to obtain a raw material powder. It was molded into a tensile test piece shape specified in JIS Z2550 at a molding pressure of 4 tons / cm ² . The compact was sintered at 590 ° C. for 2 hours while keeping the atmospheric pressure at 1 to 3 torr by a method of constantly introducing a nitrogen gas from a nitrogen cylinder while operating a vacuum pump. Then, after recrystallizing the sintered body at 5 ton / cm ² , T
6 Heat treatment was performed and the tensile test was performed.

The fluidity of the raw material powder was evaluated by a method according to the test method specified in JIS Z2052. However, pure Al powder,
Considering that the Al alloy powder is lighter and bulkier than the iron-based powder, the test weight was reduced from 50 g specified in JIS to 25 g, and the time until the entire powder flow was determined. And in the table, those with a value of 40 seconds or less are ◎, those with a value of 50 seconds or less are ○,
Items that do not flow for 50 seconds or longer are indicated by ▲.

For surface properties, Rmax was obtained for the surface of the tensile test piece using a surface roughness meter, and the value in the table was calculated. Is indicated by ⊚ for 15 μm or less, ◯ for 20 μm or less, and ▲ for 25 μm or more.

Table 1 shows the flowability measurement results of the powder, the results of the tensile test, and the analysis results of the surface properties in correspondence with the average particle sizes of the pure Al powder and the mother alloy powder. As can be seen from this example, the alloy according to the present invention has an excellent powder fluidity, and also has excellent mechanical properties and surface properties of the sintered body.

Example 2 Pure Al powder and Al-6% Si produced by the atmospheric atomization method
-30% Cu-10% Mg master alloy powder was sieved and blended again to prepare pure Al powder and master alloy powder having various average particle sizes shown in Table 2. They were mixed in a weight ratio of 90:10 to obtain a compounding composition Al-0.6% Si-3% Cu-1% Mg. Further, 1% of an amide-based lubricant was added to obtain a raw material powder. Under the same conditions as in Example 1, they were subjected to a test as tensile test pieces.
The results are shown in Table 2 as in Example 1.

As can be seen from this example, the alloy according to the present invention is practical. Similar to Example 1, the fluidity of the powder was excellent, and the mechanical properties and surface properties of the sintered body were also excellent.

Example 3 Pure Al powder produced by the atmospheric atomization method and Al-20% S
Sift i-10% Cu-10% Mg master alloy powder and 95:
Mix in a weight ratio of 5 and mix composition Al-1% Si-0.5% Cu-0.5% M
g. In this test, the opening of the mother alloy powder was 1 before blending.
05 μm sieve (150 It was used after removing powder of 105 μm or more by sieving with a (mesh). Furthermore, before mixing the pure Al powder and mother alloy powder,
Each of the sieves was sieved with a sieve having an opening of 44 μm (325 mesh) to remove powder having a diameter of 44 μm or less. If such a step is not included, 2 to 5% of the powder of 105 μm or more in the master alloy powder before mixing is 4% in the mixed powder.
The ratio of powder having a size of 4 μm or less was 2 to 4%. Other methods were carried out according to Example 1. Table 3 shows the results. From the comparison between Table 3 and Table 1, by defining the maximum grain size of the master alloy powder and more strictly defining the content of the powder of 44 μm or less of the mixed powder, the fluidity of the powder is excellent and The mechanical properties and surface properties of the aggregate are also excellent.

[Effects of the Invention] According to the present invention, in the master alloy method, which is a method of manufacturing an Al alloy sintered body, which is excellent as a near net shape manufacturing technique, the particle diameters of pure Al powder and master alloy powder as main raw material powders are By strictly controlling, the fluidity of the raw material powder is kept good, which facilitates the molding of parts with complex shapes,
In addition, it becomes possible to obtain an Al alloy sintered body having good mechanical properties and surface properties of the sintered body, and it is possible to bring industrially extremely beneficial effects such as expansion of the application range.

Claims (5)

(57) [Claims] 1. A raw material powder for producing an Al alloy sintered body, which is a mixture of pure Al powder and Al mother alloy powder, wherein the pure Al powder has an average particle size of 53 μm or more and 105 μm or less. An Al alloy mixed powder, wherein the average particle size of the powder is 63 μm or less, and the difference between the average particle sizes of the two is 20 μm or more. 2. The mixed powder according to claim 1, wherein the mother alloy powder has a maximum diameter of 105 μm or less, and 4
An Al alloy mixed powder characterized in that the proportion of powder having a particle size of 3 μm or less is 3% or less. 3. A lubricant is added to the mixed powder according to claim 1.
An Al alloy mixed powder characterized by being mixed in an amount of 5 to 2%. 4. An Al alloy mixed powder, wherein ceramic particles are added to the mixed powder according to claim 1 or 2 in an amount of 2 to 20% by volume. 5. Claim 1, claim 2 or claim 3.
The mixed powder as described in the above item 1 is compacted under a pressure of ² to 8 ton / cm ² , and the compact is compacted in a non-oxidizing atmosphere at 500-620.
A method for producing an Al alloy sintered body, which comprises sintering in a temperature range of ° C.