JP2000087161A - Sintered composite material and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformly disperse graphite powder in Al or Al alloy without the aggregation even if the surface of the graphite powder is not coated with a metal and to manufacture a sintered composite material excellent in wear resistance and lubricity. SOLUTION: A powdery mixture of an Al-base metal powder and graphite powder whose shape is massive is prepd. The ratio of the particle diameter of the graphite powder to that of the metal powder is >=0.2. The powdery mixture is compacted and the resultant green compact is sintered to manufacture the objective sintered composite material contg. graphite particles dispersed in a continuous phase of Al or Al alloy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a sintered composite material and a method for producing the same, and more particularly, to an Al-based sintered composite material having excellent wear resistance and a method for producing the same.

[0002]

2. Description of the Related Art There is a considerable demand for aluminum-based alloys having wear resistance in the field of sliding members such as cylinder liners, bearings, oil pump side blades and compressors. Conventionally, a eutectic or hypereutectic Al-Si alloy, which is a wear-resistant aluminum-based alloy, exhibits excellent wear resistance because it has a structure in which primary and eutectic Si are dispersed in an Al matrix. It has been known.

Further, in order to further improve the wear resistance of an aluminum alloy, a sintered composite formed by adding hard particles such as ceramics and intermetallic compounds and / or lubricating particles such as a solid lubricant to a powder material. Materials are also known. As hard particles, SiC, Al ₂ O ₃ , Si ₃ N ₄ , T
iC, Ti ₃ Al, Al borate and the like are known. As the lubricating particles, molybdenum disulfide (MoS ₂ ), graphite and the like are known.

However, when hard particles such as ceramics and intermetallic compounds are added to the powder material, the wear resistance of the sintered composite material itself is improved, but the sintered composite material is used as one of the sliding members, for example. When used, it can cause a heavy attack on the opponent's metal, causing great friction. As a result, the life of the counterpart metal that constitutes the part is significantly reduced,
It is desirable that the coefficient of friction of the sintered composite be as low as possible.

Further, MoS _{2 is} used as lubricating particles in a powder material.
In the case where is added, a lubricating effect is not exhibited due to the reaction with Al, and oxidation with the air becomes a problem, so that a special sintering method must be used. Also, when graphite is used as the lubricating particles in the powder material, the graphite has a layered crystal structure, which is easily broken (cleaved) by an external force. Becomes That is, the graphite is destroyed during the mixing process with the Al powder, and the fine graphite powder generated thereby adheres to the surface of the Al powder and hinders the sinterability of the sintered composite material. In addition, the uniform dispersion of graphite becomes impossible due to the aggregation of fine graphite. In order to solve such problems, a method of coating a graphite powder with a metal in advance (Japanese Patent Application Laid-Open Nos. 57-89404 and 59-110702) is known. However, it is difficult to coat the graphite powder uniformly with the metal and to optimize the coating amount. Metal coatings also increase costs.

Accordingly, an object of the present invention is to provide a sintered composite material made of aluminum or an aluminum alloy which is improved in wear resistance and lubricity while improving the above-mentioned problems without performing metal coating, and a method for producing the same. It is in.

[0007]

The sintered composite material according to the present invention is characterized in that graphite particles are dispersed in a continuous phase of aluminum or an aluminum alloy.

Further, the method for producing a sintered composite material of the present invention comprises the steps of: pressing a mixed powder having an aluminum-based metal powder and a graphite powder having a particle diameter ratio (graphite powder diameter / metal powder diameter) of 0.2 or more. It is characterized in that powder compacts are formed and the compacts obtained by compacting are sintered.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The aluminum alloy used for the sintered composite material of the present invention may be an alloy containing manganese, silicon, magnesium, copper, zinc or the like in order to improve the properties of aluminum as a material. it can. Specifically, Al-Si based, Al-Cu based, Al-Mg
At least one alloy selected from the group consisting of Al-Si-Cu-based, Al-Si-Mg-based.

The sintered composite material of the present invention has a structure in which graphite particles are scattered in the continuous phase of such aluminum or aluminum alloy. When the aluminum or aluminum alloy forms the continuous phase, the strength and wear resistance can be improved while maintaining the lubricating property of the sintered composite material. The dispersed state of the graphite particles is preferably such that the graphite particles are uniformly dispersed.

In the sintered composite material of the present invention, the aspect ratio of graphite particles of 50% or more can be 5 or less. Preferably 70% or more, more preferably 80%
The graphite particles have an aspect ratio of 5 or less. The aspect ratio is preferably 3 or less. Specifically, the particle size of the graphite particles is 20 to 180 μm. The particle size of the graphite particles is preferably 50 to 120 μm.
m, and more preferably 70 to 100 μm.
Also, when viewed three-dimensionally, the sintered composite material of the present invention
The height / aspect ratio of graphite particles of 0% or more can be 5 or less. Preferably, the height / length ratio of the graphite particles of 70% or more, more preferably 80% or more, may be 5 or less.

[0012] Graphite, also called graphite, graphite, etc., is one of the allotropes of carbon. The graphite used in the composite material of the present invention includes both those produced naturally and those produced artificially.

The content of the graphite particles can be appropriately determined in consideration of improving the wear resistance and lubricity of the composite material, and can be, for example, 2 vol% or more. The content is preferably 5 to 10 vol%
It is.

As the powder of the sintered composite material of the present invention, a mixed powder of a matrix powder and a graphite powder is used. However, the graphite powder particle size is such that the particle size ratio (graphite powder diameter / metal powder diameter) to the matrix powder is 0.
Choose one that is 2 or more. The matrix powder may be the above-mentioned aluminum or aluminum alloy. The aluminum in the sintered composite material of the present invention includes not only high-purity aluminum but also aluminum containing a small amount of impurities such as Fe and Si. Furthermore, aluminum alloy metal powders include Al-Si, Al-Cu, Al
At least one selected from the group consisting of -Mg-based, Al-Si-Cu-based, and Al-Si-Mg-based can be given.

The particle size ratio between the metal powder containing aluminum and the graphite powder (diameter of graphite powder / diameter of metal powder) is 0.2 or more, preferably from 0.2 to 1.
8, more preferably from 0.5 to 1.2, and even more preferably from 0.7 to 1.0. When the particle size ratio is 0.
The reason why the number is 2 or more is to improve the abrasion resistance as compared with the existing composite material. The reason for setting the particle size ratio to 0.2 to 1.8 is to prevent the graphite powder from adhering to the metal powder containing aluminum and hindering the sinterability of the composite material. The lower limit is set to 0.2 because, for graphite powders below this, graphite powder adheres to the metal powder as in the prior art and hinders the sinterability of the sintered composite material. The reason for setting the upper limit to 1.8 is that if the graphite powder particle size is too large, the strength of the sintered composite material will decrease. However, when the use of the composite material is mainly intended for wear resistance, the upper limit of the particle size ratio is not particularly limited. Here, the particle size ratio means the ratio of the average particle size.

The shape of the graphite powder is not particularly limited as long as the particle size ratio to the metal powder is 0.2 or more.
For example, the shape may be a sphere, a flake, a lump, or the like. Preferably, a lump can be used. By using massive graphite powder,
Further, there is an advantage that the particle size destruction at the time of powder mixing is reduced, and the fine graphite is hardly attached to the surface of the Al powder.

Assuming that the average particle size of aluminum is about 100 μm obtained by a general powder manufacturing method, the average particle size is 2 μm.
0-180 μm graphite powder can be used. The range of the average particle size of the graphite powder to be used can be appropriately changed according to the particle size of the aluminum or aluminum alloy powder as the base material. For example, when a small aluminum powder obtained by a rapid solidification method or the like is used as a base material such as aluminum powder, graphite having a small average particle size can be used accordingly. If the aluminum powder of the base material is also small and fine, fine graphite becomes difficult to adhere, and as a result, the sinterability of the sintered composite material is hardly hindered.

The content of the graphite particles can be appropriately determined in consideration of improving the wear resistance and lubricity of the sintered composite material, and can be, for example, 2 vol% or more. The content is preferably from 5 to
10 vol%.

The graphite (particle size ratio: 0.2 or more) is mixed in the matrix powder to uniformly disperse it, and then compacted by cold pressing or the like.

Then, a mixed powder of matrix powder and graphite having a particle size ratio of 0.2 or more is compacted. In the compacting, generally, after a mixed powder is filled in a molding die, pressure is applied by a compressor (press). To obtain a product with higher density and higher strength, the molding pressure may be increased or re-pressing may be performed.

Thereafter, the compact obtained by compacting is subjected to a degassing treatment as required. This degassing process is mainly performed to remove the moisture of the green compact.

The green compact thus obtained can be sintered to produce a sintered composite material. Examples of sintering methods include hot pressing, powder extrusion, powder forging, powder rolling, and isostatic pressing.

The hot pressing method is a method in which the mixed powder is subjected to compression molding or filling in a sealed can or the like, degassing is performed as required, and compression is performed during heating to perform sintering. Powder extrusion is a method in which a mixed powder is extruded by an extruder and solidified by molding. The powder forging method is a method in which forging is performed by heat. The powder rolling method refers to a powder rolling method in which a mixed powder is directly rolled and formed into a thin plate. The isotropic pressing method is a method in which a mixed powder is filled in a container such as a sealed can or the like, and a pressure is applied to the container isotropically through a liquid medium or the like to form the container.
There is CIP performed cold with P.

Generally, by performing the above-described sintering,
A sintered composite can be obtained, but depending on the product,
After sintering, secondary processing such as heat treatment may be performed. For example, if you want to increase the strength of the product,
Aging treatment or the like may be performed.

[0025]

The present invention will be further described below with reference to examples. Example 1 A sintered composite material of the present invention was produced by a sintered metal production process of a hot press method. The production process is the same as the existing one, (1) prepare raw material powder, (2) mix powder, (3) produce green compact, (4) degas, (5) heat Hot pressing is performed to form (6) a sintered composite material.

As the sintered composite material according to the present invention,
For the matrix of (1), a hypereutectic Al-Si alloy was used. The average particle size is about 100 μm. The particle size ratio
10% by volume of graphite powder was added such that (diameter of graphite powder / diameter of metal powder) became 0.1, 0.5 and 1.0. These were mixed with the powder of the above (2) using a blender (mixer), and the green compact of the above (3) was formed by cold pressing. The resulting green compact was subjected to a vacuum heating degassing process as the degassing process (4). Then, the hot pressing of (5) is performed at 500 ° C. and 4 ton / cm ² for 5 minutes.
A sintered composite material (6) was obtained.

FIG. 1 shows that among the sintered composite materials obtained by the hot pressing method described above, the hypereutectic Al—Si alloy had a particle size ratio (diameter of graphite powder / diameter of metal powder) of 0.1 (FIG. 1).
(see FIG. 1 (a)), 0.5 (see FIG. 1 (b)) and 1.0 (see FIG. 1 (c)).
3) shows a micrograph of a structure of a sintered composite material obtained by adding the above graphite powder. Graphite is shown in black in FIG. 1, and the other parts are hypereutectic A of the base material.
1-Si alloy. For the sintered composite material having a particle size ratio of 0.1, as is apparent from the structure state of FIG. 1 (a), only aluminum does not form a continuous phase, and the interface is formed at the interface of the aluminum alloy particles as the base material. The graphite present also forms partly a continuous phase. On the other hand, the particle size ratio of 0.
In the sintered composite materials of 5 and 1.0, only the aluminum alloy forms a continuous phase in which graphite particles are uniformly dispersed. For a sintered composite material having a particle size ratio of 0.5, the average particle size of graphite particles is 50 μm, and for a sintered composite material having a particle size ratio of 1.0, the average particle size of graphite particles is 100 μm. there were.

With respect to these sintered composite materials, a test for evaluating wear characteristics was performed. As a test device, a ball-on-disk wear tester shown in FIG. 2 was used. This evaluation of wear characteristics is a method of rotating a sintered composite material while pressing a ball against a disc-shaped sintered composite material with a constant load using a ball-on-disk wear tester. The test conditions are as follows. Ball: Bearing steel (SUJ-2, diameter 6 mm) Load: 1.0 N Circumferential speed: 60 mm / sec Sliding distance: 200 × 10 ³ mm Test atmosphere: Unlubricated atmosphere

FIG. 3 shows the results of the test. The horizontal axis in FIG. 3 indicates the particle size of the graphite particles, and the vertical axis indicates the wear volume. The average particle size of the matrix powder was 100 μm.
m.

As is apparent from FIG. 3, when the particle size ratio between the matrix powder and the graphite powder is 0.2 to 1.8, the sintered composite material of the present invention has excellent wear characteristics because the wear volume is small. You can see that

Example 2 Next, as in Example 1, a sintered composite material prepared by a hot press method and a sintered composite material prepared by a powder extrusion method were prepared. The preparation process of the powder extrusion method is the same as the existing one, (1) prepare raw material powder, (2) mix powder, (3) produce green compact, (4) degas, (5)
Extrusion is performed to form (6) a sintered composite material.

FIG. 4 shows the hypereutectic Al-Si of the sintered composite material obtained by the hot pressing method and the powder extrusion method.
Particle size ratio (graphite powder diameter / metal powder diameter) 0.5 to alloy
2 shows a micrograph of a structure of a sintered composite material obtained by adding a graphite powder. However, the extruded product is a vertical cross-sectional photograph perpendicular to the extrusion direction. Graphite is black in FIG. 4, and the other part is hypereutectic A of the base metal.
1-Si alloy. In the hot pressed product, graphite is slightly attached to the surface of the matrix powder. On the other hand, in the extruded product, the graphite adhered by the extrusion is destroyed, which leads to improvement in sinterability.

Next, the mechanical properties (Rockwell hardness) of the sintered composite material obtained by the hot press method and the powder extrusion method when the particle size ratio was 0.5 were evaluated. The hardness is
It was measured using a Rockwell hardness tester. FIG. 5 shows the results. “F” in FIG. 5 shows a hot-pressed or extruded state, and “T6” in FIG. 5 shows a hot-pressed or extruded state, a solution treatment, and an aging treatment. As is apparent from FIG. 5, the sintered composite material obtained by the powder extrusion method is different from that obtained by the hot press method in that
The hardness of the sintered composite material could be improved.

Example 3 Friction and wear characteristics were evaluated between the sintered composite material according to the present invention and a sintered composite material according to the prior art. The same test apparatus as that described in Example 1 was used. The test conditions were the same as in Example 1.

As the sintered composite material according to the present invention, a sintered composite material produced with a particle size ratio of metal powder to graphite of 0.5 and an average particle size of graphite of 50 μm was prepared. As a comparison material for wear characteristics, existing A3
90 (cast material), an Al-16Si extruded material was prepared.
FIG. 6 shows the results of the test. FIG. 6A shows the wear volume for each material, and FIG. 6B shows the wear coefficient for each material. As is evident from the results, the sintered composite material of the present invention showed good results in both the amount of wear and the coefficient of wear as compared with the comparative material. That is, it is found that the lubricating property of the sintered composite material of the present invention is extremely excellent.

As a comparative material, a sintered composite material manufactured with a particle size ratio of metal powder to graphite powder of 0.1 was prepared. Further, a sintered composite material manufactured by preparing a metal powder and a powder in which the surface of graphite powder was previously coated with copper at a particle size ratio of 0.1 was prepared. The results of the test are shown in FIG. FIG. 7 (a)
Shows the wear volume for each material, and FIG. 7B shows the friction coefficient for each material. As is clear from FIG. 7, the sintered composite material of the present invention obtained the same performance as the Cu-coated material without Cu coating.

[0037]

According to the present invention, aluminum or an aluminum alloy, which is soft and has a high friction coefficient and is easily worn, is added with a graphite powder having a particle size ratio of 0.2 or more. Graphite particles can be scattered in a continuous phase of aluminum or an aluminum alloy without coating the graphite with a metal, and a sintered composite material having improved wear resistance can be obtained. Al-based metals have the advantage of being compatible with weight reduction, but are soft, have high friction coefficients, and are easily abraded, and thus have been conventionally subjected to surface treatment to impart abrasion resistance. The wear-resistant sintered composite material has high wear resistance without requiring a separate surface treatment.

Further, according to the present invention, even when the sintered composite material of the present invention is used as one of the sliding members, the aggressiveness to the counterpart metal can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a structure state in which a hypereutectic Al—Si alloy contains graphite.

FIG. 2 is a view showing a ball-on-disk wear tester.

FIG. 3 is a view showing the amount of wear of the sintered composite material of the present invention.

FIG. 4 is a view showing a structure state of a sintered composite material of the present invention by a hot press method and a powder extrusion method.

FIG. 5 is a diagram showing the hardness of the sintered composite material of the present invention by a hot press method and a powder extrusion method.

FIG. 6 is a view showing a wear amount and a wear coefficient of the sintered composite material of the present invention and a comparative material.

FIG. 7 is a view showing a wear amount and a wear coefficient of the sintered composite material of the present invention and a comparative material.

Claims (7)

[Claims] 1. A sintered composite material comprising graphite particles dispersed in a continuous phase of aluminum or an aluminum alloy. 2. The sintered composite material according to claim 1, wherein an aspect ratio of graphite particles of 50% or more is 5 or less. 3. The method according to claim 1, wherein the aluminum alloy is Al-Si based,
l-Cu, Al-Mg, Al-Si-Cu, Al
At least one selected from the group consisting of —Si—Mg based
The sintered composite material according to claim 1 or 2, which is a kind of alloy. 4. A powder mixture obtained by subjecting a mixed powder having a particle diameter ratio (a graphite powder diameter / a metal powder diameter) of at least 0.2 to a metal powder containing aluminum and a graphite powder to be powder compacted and compacted. A method for producing a sintered composite material, comprising sintering a compact. 5. A powder mixture obtained by subjecting a mixed powder having a particle size ratio of graphite powder to a metal powder containing aluminum (diameter of graphite powder / diameter of metal powder) of 1.8 or less to compaction and compaction. 5. The method according to claim 4, wherein the compact is sintered. 6. The method according to claim 4, wherein the shape of the graphite powder is a lump. 7. The method according to claim 4, wherein the sintering is performed by hot pressing, powder extrusion, powder forging, powder rolling, or isostatic pressing.