JPH04202601A - Manufacture of al alloy mixed powder and al alloy sintered body - Google Patents

Abstract

PURPOSE:To manufacture the above Al alloy sintered body excellent in mechanical characteristics and surface properties by mixing pure Al powder and Al alloy powder having specified particle size, mixing this mixed powder with a lubricant or, if required, with the powder of ceramics, subjecting this mixed powder to compacting and thereafter executing sintering. CONSTITUTION:The powder of pure Al having 53 to 105mum average particles size is mixed with the powder of an Al-Si-Mg series or Al-Si-Mg-Cu series alloy having <63mum average particle size, and the ratio of the powder having <=43mum particle size in this mixed powder is regulated to <=3%, in which, as a lubricant, zinc stearate or the like are mixed in the ratio of 0.5 to 2%. Or, according to necessary, the powder of graphite or the powder of ceramics such as hexagonal boron nitride or the like are furthermore mixed in the ratio of 2 to 20vol.%. This mixed powder is compacted under 2 to 8 ton/cm<2> and is thereafter sintered at 500 to 620 deg.C in the atmosphere of an Ar base inert gas.

Description

[Detailed Description of the Invention] U Industrial Field of Application j The present invention relates to Al alloy mixed powders that are raw materials for Al alloy sintered bodies used for machine parts, etc., and a method for producing Al alloy sintered bodies using the mixed powders. in between.

[Prior art and problems to be solved] Recently, in the fields of office equipment and computer listening equipment, lightweight aluminum has been used to reduce IR power consumption, prevent noise generation due to vibration, and improve portability. The use of alloy parts is increasing.

Conventionally, die-casting has been the most common method for manufacturing Al alloy parts with complex shapes. However, while the die-casting method has the advantage of being able to produce parts with complex three-dimensional shapes, the dimensional accuracy is insufficient, and it is necessary to create a taper for die cutting, which requires expensive machining after casting. There are many cases where it is necessary. In addition, there was a problem of lack of reliability in terms of characteristics due to casting defects such as blowholes.

Another method is to use a wrought material made from a molten ingot as a starting material, and manufacture it by machining with a lathe or the like. However, it requires a considerable number of machining steps and has a low processing yield, resulting in an increase in the price of the parts.

In order to solve these problems, attempts have been made to manufacture methods using powder metallurgy, which takes advantage of the features of the near net save method (for example, ASTM Des
ignation: 8595-84).

The conventional powder compacting and sintering method, in which powder is molded into a mold and then sintered, has a great advantage particularly in terms of cost, since near-net-shave parts can be manufactured through a simple process.

As a method for manufacturing such Al alloy sintered parts, pure A
Cu, Si, which forms a low melting point eutectic with Al in l powder.
The so-called blended elemental powder method utilizes liquid phase sintering using a mixed powder containing elemental powders of alloying elements such as Mg as a raw material.
) is well known. However, this method produces a liquid phase due to the high melting point of the single element powder, and unreacted element powder tends to remain even after sintering, making it difficult to obtain a sintered body with good mechanical properties. There were problems.

On the other hand, the alloy powder method (Pr
In the case of the alloy method, the powder is hard and has poor compressibility, and a good molded body cannot be obtained by ordinary molding. Furthermore, since the melting point of the powder is low, the sintering temperature cannot be raised sufficiently, and diffusion and sintering cannot proceed satisfactorily.

Roughly speaking, as an improved method of the above-mentioned elemental powder mixing method,
A method of manufacturing a master alloy powder in which alloying elements are pre-alloyed with Al and using a mixed powder in which this master alloy powder is blended with pure Al powder, the so-called master allo method.
y method) has also been proposed (for example, in Japanese Patent Application Laid-Open No.
-294833). This method uses pure Al powder, which is easy to mold, as the main raw material, and the alloying elements are already alloyed with Al, and in many cases, the composition is adjusted to facilitate the formation of a multi-element low melting point eutectic. Therefore, liquid phase sintering progresses easily, making it possible to obtain a sintered body with better mechanical properties.

However, when manufacturing complex-shaped cane parts using the above-mentioned master alloy method, there are also problems such as poor fluidity of the powder, which prevents it from being filled uniformly into the mold, and the density of the molded sintered body being lower in some parts. Were present. Furthermore, the mother alloy powder melts, diffuses and disappears, and remains as a relatively large bore, resulting in poor mechanical properties.
In particular, there were problems such as poor ductility and poor surface properties.

[Means for solving the problem] Among the powder compacting and sintering methods, the master alloy method takes advantage of the characteristics of the near net shave method, and it is also possible to obtain an Al alloy sintered body with relatively good mechanical properties. It is possible. However, even with such a master alloy method, the mechanical properties or surface properties are insufficient depending on the application, so the present inventors made efforts to improve the properties, and developed pure Al powder and master alloy powder as the main raw material powder in the master alloy method. It was discovered that by strictly controlling the particle size of the mixed powder, it is possible to improve the fluidity of the mixed powder and obtain an Al alloy sintered body that is easy to mold and has good mechanical properties and surface properties. This led to the invention.

That is, the present invention is a raw material powder for producing an Al alloy sintered body in which pure Al powder is mixed with Al master alloy powder,
An Al alloy characterized in that the average particle size of the pure Al powder is 53 μm or more and 105 μm or less, the average particle size of the mother alloy powder is 6371 m or less, and the difference in the average particle size between the two is 20 μm or more. The gist is to use mixed powder.

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 explained.

In the compacting and sintering method, raw material powder is first supplied to the recesses of a mold and press-molded, so the powder needs to have good fluidity. Poor fluidity makes it difficult to fill vertical narrow spaces with powder, and causes variations in the filling rate depending on the part.Furthermore, the amount of filling varies from part to part, which can lead to variations in density depending on the part of the molded product, and to individual molded products. The weight, and therefore the size, of the product deteriorates, resulting in a decrease in product quality and an increase in the defective rate. In order to eliminate such problems, it is desirable that the particle size of the mixed powder as a raw material be large.

In particular, the fluidity of the mixed powder is greatly influenced by the particle size of the pure Al powder used as the main raw material powder, which is larger in quantity, and it is possible to improve the fluidity of the entire mixed powder by increasing the particle size4. I found it. That is, from the above viewpoint, the average particle size of the pure Al powder was set to 53 μm or more. On the other hand, in the master alloy method, the alloying elements are supplied as master alloy powder, so in addition to bonding the powders together in the sintering process, it is necessary to diffuse and homogenize the alloying elements into the pure Al powder. However, pure A
As the grain size of the Al powder increases, the time required to diffuse and homogenize the alloy particles through sintering increases;
This greatly increases the sintering cost, which has the highest cost ratio in the production of alloy sintered bodies, making it uneconomical. For this reason, the average particle size of the pure Al powder was set to 1051 tm or less. As mentioned above, from the viewpoint of maintaining good fluidity and shortening the time required for uniform diffusion, the average particle size of the pure Al powder was set to 53 μm or more and 1057 μm or less.

Next, the reason for limiting the average particle size of the master alloy powder will be described.

The mother alloy powder melts during the sintering process, spreads over the surface of the pure Al powder, and further diffuses and disappears within the pure Al powder, so that most traces of the original mother alloy powder remain as bores, that is, outflow holes. These bores reduce the mechanical properties of the sintered body due to the notch effect.

Further, these bores are also present on the surface of the sintered body, causing deterioration of the surface quality and decreasing the commercial value. In order to prevent deterioration of mechanical properties and surface properties due to such causes, ζ
This can be achieved by reducing the average particle size of the mother alloy powder, and from this point of view, the average particle size of the mother alloy powder was set to 63 μm or less, and at least 20 μm smaller than the average particle size of the pure Al powder. The blended amount of master alloy powder in the mixed powder is about 3% to 12% in most cases, which is smaller than that of pure Al powder, so even if the particle size of the master alloy powder is reduced, it will not affect the fluidity. There are few negative effects. By such a method, it is possible to obtain a sintered body whose mixed powder has good fluidity, is easy to mold, and has good mechanical properties and surface properties.

Furthermore, the reason for specifying the maximum particle size of the master alloy powder in claim 2 is that the properties of notch toughness and fatigue strength in particular are affected by the maximum particle size of the outflow pores existing in the material. Since the maximum diameter of the pores is approximately proportional to the maximum particle diameter of the master alloy powder, the maximum particle diameter was limited to 106 μm. Furthermore, the fluidity of the mixed powder is greatly influenced by the average particle size as well as the proportion of fine powder in the total powder, and therefore the proportion of powder of 44 μm or less was limited to 3% or less.

Here, the average particle size of the powder is the particle size at which the cumulative particle size distribution is 50%. In addition, in the case of pure Al powder and Al alloy powder obtained by the economical mass production method, 7F atmospheric masing method,
The shape of the powder is not spherical but irregular, and in this case the particle size is approximately equal to the diameter when converted to a sphere, or the maximum particle size is equivalent to the sieve opening in the sieve method. .

Next, the composition ζ of the master alloy powder will be described.

The master alloy powder plays the role of adding Mg, Sl, or Cu, which contribute to aging precipitation strengthening, and at the same time, they themselves begin to melt below the sintering temperature, or they undergo a eutectic reaction with the pure Al powder, which is the main raw material powder. It has the role of generating a sticky liquid phase and promoting sintering.

In order to achieve such a purpose, # of the composition range of the master alloy powder is
, the 5A composition on the 'a degree side is preferably a composition close to the eutectic composition of the A I-51-Mg ternary alloy, and specifically, Si
: 12% or more, and Mg is preferably 4% or more. Moreover, since the mother alloy powder is highly alloyed and hard, increasing its blending amount impairs formability. Therefore, in order to add a predetermined amount of alloying elements in a smaller amount, it is better to include more alloying elements in the master alloy powder. on the other hand,
If sl exceeds 30% and Mg exceeds 20%, the temperature at which the melting of the alloy ends, that is, the temperature at the liquidus line, will rise, making it difficult to melt during powder production, and the eutectic formation reaction during sintering. Si is less than 30%, M
g needs to be 20% or less. In addition, as Mg increases, the activity of the molten metal increases and it becomes more susceptible to oxidation, making it extremely difficult to manufacture using the atmospheric atomizing method, which is an economical method for producing Al alloy powder. It should be less than 20%.

Furthermore, by adding an appropriate amount of Cu to this mother alloy powder, it is possible to further lower the melting start temperature (solidus temperature) of the mother alloy powder, promoting sintering, and ultimately improving the mechanical properties of the sintered body. It becomes possible to further improve the properties. Therefore, as a more preferable composition of the master alloy, it is desirable to add 5% or more of Cu. In addition, Cu is a strong age-hardening element in Al alloys, and is an extremely effective alloying element especially when trying to obtain high-strength Al alloys. It is desirable to actively increase this. However, when a large amount of Cu is added, the corrosion resistance of the sintered body deteriorates and the ductility also decreases. Furthermore, when adding Cu, if the Cu content in the master alloy powder exceeds 45%, the melting end temperature (liquidus temperature) of the master alloy will rise, making it difficult to manufacture the powder, so it is recommended that the Cu content be 45% or less. desirable.

As mentioned above, the master alloy powder is suitably Al-51-Mg-based or AlAl-9i-Cu-based, and the composition of the master alloy powder is Si: 12~30%, Mg: 4~
20%, balance Al, Cu when adding CLl to the grain
:5 to 45% is considered appropriate.

Other master alloy powders include Al-Mg alloy, Al-5
i-based alloy, Al-Cu binary alloy or Al-C
It is also possible to blend one type of Al alloy powder such as u-Mg and Al-51-Cu ternary alloy, or a master alloy powder of 2pi or more.

Next, the amount of the master alloy powder to be mixed with the pure Al powder will be described.

By adding Mg and Si to 81 and further adding CIJ as necessary, it is possible to adjust the melting start temperature of the master alloy and the temperature at which the rα phase is generated by reaction with pure Al powder. It becomes possible. Further, by adjusting the alloy amounts of these elements to tA, it becomes possible to widen the adjustment range of the blend amount of the master alloy in the raw material mixed powder.

Regarding the blended amount of this master alloy, is it too small? In Al alloys in which α-phase sintering is essential, a sufficient amount of liquid phase cannot be ensured, making it impossible to obtain a sintered body with good properties. On the other hand, if it is too large, the amount of liquid phase produced will be too large,
The sweating phenomenon makes it impossible to obtain a sintered body with good surface properties. From this point of view, the blending amount of the master alloy should be 2% or more, 1
5% or less is suitable.

Furthermore, by mixing a lubricant with the alloy powder, it is possible to improve the lubrication between the powders and the lubricity between the powder and the wall of the mold, thereby increasing the moldability. The amount of lubricant mixed is 0.5%
If it is less than 2%, the effect is insufficient, and if it is more than 2%, the effect not only becomes saturated, but also impairs the fluidity and moldability of the powder, and furthermore, the lubricant volatilizes and scatters during sintering, making it unnecessary to use the sintering furnace. Internal or vacuum sintering
．． 5-2% is desirable. The type of lubricant is preferably one that completely volatilizes and scatters below the sintering temperature and does not have a detrimental effect on the material properties. From this point of view, amide-based lubricants are more desirable than metal salt-based lubricants (e.g., zinc stearate, lithium stearate, aluminum stearate); for example, ethylene bisstearamide is the most suitable lubricant. It can be mentioned as follows.

Moreover, in order to further impart functions such as wear resistance, increased coefficient of friction, and low coefficient of thermal expansion to the sintered body parts, ceramic particles can be mixed with these powders. If the amount added at this time is 2Vo 1% or less, the effect is insufficient, and 2Vo
If it exceeds 1%, the mechanical properties, particularly the ductility, of the sintered body will be significantly reduced, so it is necessary to keep it below that range. Others, graphite,
Solid lubricants such as hexagonal crystal BN or Fe, Ni, Mn
It is also effective to blend metal powders such as Si, Tden, Z', and Si to improve properties such as wear resistance.

Next, a method for manufacturing the sintered body will be explained.

If the compacting pressure is less than 2 tosi/C+++2, the compact will not be densified enough and the contact between the powders will be insufficient, resulting in poor sintered compact strength and
Ductility cannot be obtained. Therefore, it is necessary to mold at 2 toss/Crr12 or more. Furthermore, when attempting to reduce the density of the molded product and molding with higher molding pressure, the life of the mold may be shortened,
Problems such as lamination and galling of the mold may occur.6 Therefore, in actual operation, a molding pressure exceeding 8 tons/c + n2 is inappropriate.

Furthermore, it is also possible to make the molded body more dense by molding the raw material powder while heating it to 70°C to 250°C.

Regarding the sintering atmosphere, in order to prevent oxidation of the active Al alloy powder particles and to allow sufficient sintering to proceed, it is necessary to sinter in a non-oxidizing atmosphere such as a vacuum or a nitrogen gas or argon gas atmosphere. When sintering in a vacuum, the degree of vacuum is 0.1
It is preferable to set it to below torr, preferably below 0.01 t, orr. Further, after the inside of the sintering furnace is evacuated, sintering is performed under reduced pressure while flowing a small amount of inert gas such as nitrogen gas, which increases the effect of removing gas components generated from the sintered body.

When sintering in an inert atmosphere such as a nitrogen gas atmosphere or argon gas, the purity of the gas is important. In particular, the moisture contained in the gas has a negative effect on the properties of the sintered parts, so the dew point must be kept sufficiently low. It is necessary to control the temperature and desirably keep the dew point below -40°C.

If the sintering temperature is lower than 500°C, the diffusion of elements will be insufficient and the powders will not be sintered together. -If the temperature is higher than 620°C, a large amount of liquid phase will be generated and the shape of the part cannot be maintained as the temperature rises, so it is necessary to sinter at a temperature of 500°C or higher and 620°C or lower.

Further, by recompressing the sintered body thus obtained, the structure can be made denser and the mechanical properties can be further improved. In general, the purpose of recompression is often to increase dimensions (sizing), and recompression conditions are selected in conjunction with this, and the recompression pressure is usually in the range of 3 to 11) sh/cff12.

Furthermore, mechanical properties, especially ductility, can be improved by resintering. By re-sintering the structure that has been densified by re-compression, diffusion and sintering can further proceed. The conditions at that time are basically the same as those for sintering.

Further, Cu, Mg, and Si, which are alloy components of these sintered bodies, originally contribute to improving mechanical properties through solution treatment and aging treatment. Therefore, like ordinary Al alloys, it is effective to perform solution treatment and aging treatment to adjust and improve its mechanical properties.

[Function] According to the present invention, flow is improved by strictly controlling the particle sizes of pure Al powder and master alloy powder as the main raw material powders in the master alloy method, which is excellent as a near net shave manufacturing method for Al alloy precision parts. It becomes possible to mold the sintered body while maintaining good properties, and it also becomes possible to significantly improve the mechanical properties and surface properties of the sintered body.

[Embodiments of the invention] Examples of the present invention will be described below.

Example 1 Pure Al powder produced by atmospheric atomization method ξ and Al
-20%5i-10%Cu-10%Mg master alloy powder were sieved and re-blended to prepare pure Al powder and master alloy powder having various average particle sizes shown in Table 1. 9 of them
Mixed at a weight ratio of 5:5, blending composition A+-1%5i-0
, 5% Cu-0.5% Mg. Further, 1% of an amide lubricant was added thereto to obtain a raw material powder. It was molded into the shape of a tensile test piece specified in J, 1SZ2550 at a molding pressure of 4 tons/cff12. The molded body was heated for 5 to
It was closed and sintered at 90°C for 2 hours. Next, the sintered body was
After being recompressed at cW12, it was subjected to T6 heat treatment and subjected to a tensile test.

Regarding fluidized dust of raw material powder, please refer to JTSZ 2.
The evaluation was made in accordance with the test method specified in 052.

However, considering that pure Al powder and Al alloy powder are lighter and bulkier than iron-based powder, the test weight was reduced from 50 g determined by )TS to 25 g, and the test weight was reduced until the powder finished flowing once. I asked for time. In the table, those with a value of 40 seconds or less are marked ◎, those with a value of 50 seconds or less are marked with ○, and those with a value of 50 seconds or more or with no flow are marked with a mark.

Regarding the surface properties, Rmax was determined for the surface of the tensile test piece using a surface roughness meter, and the values in Table 1 are shown as ◎ for 15 μm or less, and ◎ for 20 μm or less and 0.25 μm or more.

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

Example 2 Pure At powder and Al-6 produced by atmospheric atomization method
%5i-30%Cu-10%Mg master alloy powder were respectively sieved and blended to prepare pure At powder and master alloy powder having various average particle sizes shown in Table 2. 9 of them
Mixed at a weight ratio of 0:10, blending composition Al-0.6%5
It was set as 1-3%Cu-1%Mg. Further, 1% of an amide lubricant was added thereto to obtain a raw material powder. They were used as tensile test pieces under the same conditions as in Example 1 and subjected to testing. The results are shown in Table 2 in the same manner as in Example 1.

As can be seen from this example, the alloy according to the present invention has excellent powder fluidity similar to Table 2 Zettetsu 1, and also has excellent mechanical properties and surface properties of the sintered body.

Example 3 Pure At powder and At-2 produced by atmospheric atomization method
0%5i-10%Cu-10%Mg master alloy powder were sieved and mixed at a weight ratio of 95:5 to form a blending composition A.
l-1%5i-0,5%Cu-0,5%Mg. In this test, the master alloy powder was sieved with a sieve with an opening of 105 μm (150 Table 3 mesh) to remove powder with a size of 105 μm or more before use. Further, the pure At powder and the master alloy powder were each sieved using a sieve with a mesh size of 44 μm (325 mesh) to remove powders with a diameter of 44 μm or less before blending. In addition, if such a step is not included, the powder with a diameter of 105 μm or more in the mother alloy powder before mixing will be 2 to 5
%, the ratio of powder of 44 μm or less in the mixed powder is 2 to 4%
Met. Other methods were carried out in accordance with Example 1. The results are shown in Table 3. From a comparison between Table 3 and Table 1, it was found that by specifying the maximum grain size of the master alloy powder and more strictly specifying the content of powder of 44 μ or less in the mixed powder, the powder has excellent fluidized dust and is sintered. 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 for producing an Al alloy sintered body that is excellent as a near net sieve manufacturing technology, the particle sizes of pure Al powder as the main raw material powder and master alloy powder are By strictly controlling the flow dust of the raw material powder, it is possible to easily form parts with complex shapes, and to produce an Al alloy sintered body with good mechanical properties and surface properties. It is now possible to obtain extremely beneficial effects industrially, such as expanding the range of applications.

Patent applicant: Showa Denko Co., Ltd. Representative Patent Attorney Temple 1) Truth

Claims (1)

[Scope of Claims] 1) A raw material powder for producing an Al alloy sintered body made by mixing pure Al powder with Al master alloy powder, wherein the average particle size of the pure Al powder is 53 μm or more and 105 μm or less. An Al alloy mixed powder, characterized in that the average particle size of the mother alloy powder is 631 μm or less, and the difference between the average particle sizes is 20 μm or more. 2) In the mixed powder according to claim 1, the maximum diameter of the master alloy powder is 105 μm or less, and 43 μm in the mixed powder
An Al alloy mixed powder characterized in that the proportion of powder with a diameter of m or less is 3% or less. 3) Adding 0.5 to 2 lubricant to the mixed powder according to claim 1
% mixed Al alloy powder. 4) An Al alloy mixed powder, characterized in that 2 to 20 Vol% of ceramic particles are added to the mixed powder according to claim 1 or 2. 5) After compacting the mixed powder according to claim 1, claim 2 or 3 at a pressure of 2 to 8 tons/cm^2, the compact is placed in a non-oxidizing atmosphere. 500-62 inside
A method for producing an Al alloy sintered body, characterized by sintering in a temperature range of 0°C.