JPH10140273A - Composite material for brake disk for railway car - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new aluminum alloy matrix composite having high strength and excellent wear resistance, in order to reduce the weight of a brake disk for railway car by changing a material for the brake disk from a ferrous material such as cast iron to an aluminum alloy. SOLUTION: The high strength brake disk for railway car is composed of a composite material in which ceramic grains are dispersed in an aluminum alloy matrix. At this time, the average grain size of the ceramic grains is 1-20μm and the content of the ceramic grains in the composite material is 5-30wt.%, and further, an Al2 O3 dispersed phase substance of <1μm average grain size is contained by 0.01-1wt.% in the matrix. As the ceramic grains, grains of hard ceramics of >=500 Vickers hardness are preferred. As typical examples of the ceramics, SiC, Al2 O3 , AlN, and Si3 N4 are cited.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a material for a disk of a disk brake, which mechanically obtains a braking force by friction used in a railway vehicle.

[0002]

2. Description of the Related Art There are block brakes, drum brakes, disc brakes, and the like as mechanical braking systems for railway vehicles, automobiles, motorcycles, and the like. It has come to be.

[0003] A disc brake is a device that obtains a braking force by friction between a brake disc and a brake pad (friction material). In a disc brake of a railway vehicle, a sliding surface of a donut-shaped disc-shaped disc attached to a wheel is used. A braking force is obtained by pressing a brake pad. A disc-shaped component having this sliding surface is called a brake disc.

[0004] The material used for the brake disk has abrasion due to friction during braking and a sharp temperature rise.
It is required to have various characteristics such as abrasion resistance, heat resistance, and heat crack resistance.

Heretofore, an integrated iron-based material such as cast iron, forged steel or stainless steel has been used for the brake disk. However, attempts have been made to use an aluminum alloy also for the brake disc due to demands for speeding up the vehicle, reducing weight as an energy saving measure, and improving riding comfort by reducing unsprung weight.

[0006] Aluminum alloys are remarkably inferior in any of wear resistance, heat resistance and heat crack resistance as compared with cast iron and forged steel, but have high thermal conductivity, and the generated frictional heat is quickly dissipated. In addition, the temperature rise of the sliding surface can be suppressed much lower than that of the steel brake disk. Therefore, the heat resistance and the heat crack resistance do not decrease as much as estimated from the material strength. However, since the strength is low, the wear resistance is significantly inferior, and it is difficult to apply pure aluminum or the existing aluminum alloy itself to the brake disc.

As described above, as a brake disk utilizing aluminum because of its good thermal conductivity and light weight, the sliding surface of an aluminum alloy disk or drum is coated with an iron alloy having excellent wear resistance. The invention of the brake member described above is disclosed in JP-A-60-89558. However, in this case, there is a problem that peeling occurs at a boundary surface between the coated iron alloy layer and the base aluminum alloy due to a difference in elastic modulus or thermal expansion coefficient between the coated iron alloy layer and the base aluminum alloy due to repeated use.

On the other hand, JP-A-59-173234 discloses a method for improving the wear resistance of aluminum itself.
- a hypereutectic Si alloy to _{Al 2 O 3, SiC, Si} 3 N 4 ceramic of the brake rotor by dispersing invention such as is presented. However, this is intended for use in automobiles and motorcycles and cannot be used as it is for brake discs for railway vehicles.

Although the above-mentioned brake discs for lightening have been developed mainly for automobiles, the same applies to the improvement of riding comfort by increasing the speed, reducing the weight, or reducing the unsprung weight of railway cars. Is done. However,
Railway vehicles are more heavily loaded than automobiles.

The invention of an aluminum-based composite material for reducing the weight of a brake disk material for railway vehicles is also disclosed in Japanese Patent Laid-Open No. 2-25 / 1990.
Japanese Patent Application Laid-Open Nos. 538, 3-47945, 4-173936, 8-176712, etc. have been proposed. However, since the composite materials disclosed therein have insufficient strength, the composite materials must be increased in size in order to obtain the required strength, and as a result, a large weight saving effect cannot be obtained.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to reduce the weight of a railway vehicle by changing the brake disk material from an iron-based material such as cast iron to an aluminum alloy. It is an object of the present invention to provide a new aluminum alloy-based composite material having higher strength and higher abrasion resistance than the aluminum-based composite materials proposed so far.

[0012]

The gist of the present invention is the following aluminum alloy-based composite material.

A composite material in which ceramic particles are dispersed in a matrix of an aluminum alloy, wherein the average particle size of the ceramic particles is 1 to 20 μm, and the content of the ceramic particles in the composite material is 5 to 30% by weight; and further composite material for a railway vehicle brake disc of a high strength, characterized that the Al ₂ O ₃ dispersed phase substance having an average particle diameter of less than 1μm are contained 0.01 to 1 wt% in a matrix.

The ceramic particles are preferably hard ceramic particles having a Vickers hardness of 500 or more.
Typical ones _{SiC, Al 2 O 3, AlN} , and Si ₃ N ₄
It is desirable that one or more of these ceramic particles are added in a total amount of 5 to 30 wt% and dispersed in a matrix.

The above-mentioned Al ₂ O ₃ dispersoid is obtained by dispersing an oxide film on the surface of an aluminum alloy powder used as a raw material in a material in a process of densification by hot pressing or the like described later.

The aluminum alloy serving as the matrix is
Any type can be used as long as it can satisfy the basic mechanical properties required for a railway vehicle brake disc. For example, Mg: 2 to 5 wt%, Mn: 0.1 to 1 wt%
%, Cr: 0.05 to 0.35 wt%, balance: Al and alloys having compositions such as unavoidable impurities, or aluminum alloys containing appropriate amounts of Si and Fe can be used.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The composite material of the present invention comprises a matrix of aluminum alloy containing SiC, Al ₂ O ₃ , AlN, Si ₃ N ₄ ,
Other hard ceramic particles are dispersed.
The dispersion of these particles enhances the wear resistance, coefficient of friction and seizure resistance when rubbed with the brake pads.

If the above-mentioned ceramic particles have an average particle size of less than 1 μm, aggregation tends to occur, and it is difficult to produce a material in which such particles are uniformly dispersed.
On the other hand, if the average particle size exceeds 20 μm, a high coefficient of friction cannot be obtained, and a brake pad that is a friction partner is damaged. Furthermore, machining becomes difficult because the machinability of the material is significantly reduced.

If the content of the ceramic particles is less than 5% by weight, sufficient abrasion resistance and seizure resistance cannot be obtained.
If it exceeds 300, forgeability and machinability will be impaired.

The composite material according to the invention further comprises a fine Al ₂ O ₃ dispersoid of less than 1 μm. This increases the strength of the composite from ambient to elevated temperatures. Prevents loss of strength when repeatedly exposed to high temperatures using brakes. To obtain these effects, a content of at least 0.01 wt% is necessary.
However, if Al ₂ O ₃ dispersoids exceeding 1 wt% are present, the forgeability deteriorates.

The preferred alloy as the aluminum alloy serving as the matrix is Mg: 2 to 5 wt% and Mn: 0.1
It is an alloy containing 11 wt% and Cr: 0.05-0.35 wt%.

Mg, Mn and Cr in the alloy increase the strength of the matrix. If each is less than the lower limit, the strength is not sufficient, and excessive addition exceeding the upper limit degrades forgeability and corrosion resistance.

The composite material of the present invention can be produced, for example, as follows. That is, after the rapidly solidified aluminum alloy powder produced by the atomizing method is mixed with ceramic particles such as SiC particles, the mixture is densified by hot pressing or a combination of hot pressing and forging. The method using the rapidly solidified alloy powder has an advantage that a high-strength material having a fine structure can be obtained. Hereinafter, this manufacturing method will be described in detail.

First, a molten aluminum alloy having a predetermined composition is rapidly cooled and solidified by a gas atomizing method such as air or nitrogen to produce an aluminum alloy powder. The particle size of the powder is desirably as fine as possible to obtain high strength and high toughness and to uniformly disperse the hard particles.

Next, the above-mentioned aluminum alloy powder and predetermined ceramic particles are mixed by various kinds of agitating mixers or pulverizers such as ball mills. Thereafter, a degassing process is performed to remove moisture and gas adsorbed on the surface of the aluminum alloy powder. This is done by filling the mixed powder in a can and evacuating it at 400 to 500 ° C, or by pre-pressing the mixed powder in a cold atmosphere under an inert atmosphere or vacuum.
Performed by heating to ° C. At this time,
The oxide film formed on the surface of the aluminum alloy powder transforms from amorphous to crystalline and becomes brittle.

After degassing, the mixed powder is densified by hot pressing at 300 to 500 ° C. until the relative density becomes almost 100%. At this time, the embrittled oxide film (Al ₂ O ₃ ) is finely crushed and dispersed in the material. Furthermore, if forging is performed as necessary, it can be formed into a shape close to the product, and at the same time, the strength can be improved. Finally, cutting is performed to obtain the final product.

[0027]

EXAMPLES Table 1 shows the chemical composition of an aluminum alloy serving as a matrix. Table 2 shows an example of a composite material obtained by combining the matrix alloy of Table 1 and ceramic particles.

Nos. 1 to 16 and Nos. 19 and 20 in Table 2
This is a composite material manufactured by a powder method. That is, aluminum alloy powders having the respective matrix alloy compositions were produced by an air atomizing method, and classified into 150 μm. This and ceramic particles such as SiC particles shown in Table 2 were mixed for 15 minutes by a cross rotary mixer with forced stirring blades, and the mixed powder was filled in a container having an outer diameter of 90 mm and a height of 200 mm, and then left at 480 ° C for 1 hour. Vacuum degassed and sealed, loaded into a closed mold with an inner diameter of 94 mm,
Hot pressed with ton. Further, forging was performed at 400 ° C. by uniaxial free forging until the height became half, that is, at a forging ratio of 2.

The composite materials No. 17 and No. 21 shown in Table 2 were produced by the compo-casting method. That is, about 615 so that each matrix alloy is in a solid-liquid coexistence state.
While maintaining the temperature at 0 ° C, SiC particles were added and mixed with vigorous stirring, and cast into a thick disk mold having an inner diameter of 150 mm and a depth of 50 mm. The cast material was forged at 400 ° C. until the height became 40 mm, that is, at a forging ratio of 1.25.

The composite material of No. 18 was prepared by manufacturing a matrix alloy powder by a water atomizing method.
16 and Nos. 19 and 20 were prepared by the powder method under the same conditions.

The content of the Al ₂ O ₃ dispersoid in each of the above composite materials was determined by an infrared absorption method in an inert gas stream. Also, when the shape of the Al ₂ O ₃ dispersoid was observed and observed with a TEM (transmission electron microscope), No. 1 to 16 and No. 19
And the Al ₂ O ₃ dispersoids of the 20 materials were finely dispersed in a filament of 0.01 to 0.2 μm. The amount of the Al ₂ O ₃ dispersoid is 0.2 wt% for the material using the air atomized powder, and 0.005 wt for the material by the compo-casting method (Nos. 17 and 21).
%, 2.0% for material using water atomized powder (No.18)
Met. These results are also shown in Table 2.

[0032]

[Table 1]

[0033]

[Table 2]

The following tests were performed using the test materials prepared as described above. In Nos. 16, 18, and 19, cracks occurred during the forging process, but test pieces were cut out from places without cracks.

1. Strength test Strength was evaluated by tensile strength at normal temperature and 300 ° C.

2. Abrasion Resistance Test Abrasion resistance was represented by the depth of wear of a disk, using a disk as a test material in a pin-disk type wear test. The test conditions are as follows.

Surface pressure: 1 MPa, friction speed: 5 m / s, lubrication: none, mating pin material: copper-based brake pad material, friction time: 10 minutes The test results are shown in Table 3.

[0038]

[Table 3]

From Table 3, the following conclusions can be obtained.

The composite materials of Nos. 1 to 12 were prepared at room temperature and 3
High tensile strength at 00 ° C and small disc wear in wear test. On the other hand, in No. 13, the average particle size of the SiC particles was too fine, 0.5 μm, and the SiC particles were agglomerated and could not be uniformly dispersed. Therefore, both the strength and the elongation were low, and the disk was slightly worn. That is, this material is not suitable as a brake disc material.

In No. 14, since the average particle size of SiC was large, the wear amount of the disk was small in the wear test, but the brake pad material as the mating material was significantly damaged.
Further, the cutting workability is remarkably poor, and it is not suitable as a brake disc material.

No. 15 has a low abrasion resistance because of a small amount of SiC. Furthermore, seizure occurred about 7 minutes after the start of the test. On the other hand, No. 16 had a crack in the forging process due to excessive SiC content. Elongation in the tensile test is small, and none of them is suitable as a brake disc material.

No. 17 has a low tensile strength at room temperature and 300 ° C. because it contains substantially no Al ₂ O ₃ dispersoid.
On the other hand, in No. 18, the Al ₂ O ₃ dispersoid was excessive and cracks occurred in the forging process. The elongation in the tensile test is small, which is not suitable as a brake disc material.

No. 19 also has cracks due to forging. This is because the matrix aluminum alloy was inappropriate because it contained excessive Mg. No.20 is Mg
This is an example of using a matrix alloy having a low content of, but this has low tensile strength at room temperature and 300 ° C.

No. 21 has a strength that is substantially free of Al ₂ O ₃ dispersoids and that a precipitate such as an Al—Fe intermetallic compound does not become fine in the compocast method. And softening during heating is large.

[0046]

The composite material of the present invention is much lighter in weight and superior in thermal conductivity as compared with iron-based materials because it uses an aluminum alloy as a matrix. Moreover, as shown in the examples, it has high strength and excellent wear resistance. This composite material is very suitable for a brake disk of a railway vehicle.

────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code FI F16D 65/12 F16D 65/12 E (72) Inventor Seiichi Furuya 5-1-1109 Shimaya, Konohana-ku, Osaka-shi, Osaka Sumitomo Metal (72) Inventor Atsushi Sakaguchi 4-5-33 Kitahama, Chuo-ku, Osaka-shi, Osaka Sumitomo Metal Industries, Ltd. (72) Inventor Taizo Makino, Osaka-shi, Osaka 4-5-33 Kitahama-ku, Sumitomo Metal Industries Co., Ltd. (72) Inventor Kazuhisa Shibue 5-1-1-3 Shimbashi, Minato-ku, Tokyo Inside Sumitomo Light Metal Industries Co., Ltd. (72) Inventor Yoshimasa Okubo Minato-ku, Tokyo 5-11-3 Shimbashi Sumitomo Light Metal Industry Co., Ltd. (72) Inventor Hiroki Ezaki 5-11-3 Shimbashi, Minato-ku, Tokyo Sumitomo Light Metal Industry Co., Ltd. (72) Inventor Yasushi Daifukune Husband Within Sumitomo Light Metal Industry Co., Ltd., 5-1-1-3 Shimbashi, Minato-ku, Tokyo

Claims (3)

[Claims] 1. A composite material in which ceramic particles are dispersed in a matrix of an aluminum alloy, wherein the average particle size of the ceramic particles is 1 to 20 μm, and the content of the ceramic particles in the composite material is 5 to 30% by weight. it, and further a composite material for a railway vehicle brake disc of a high strength, characterized that the Al ₂ O ₃ dispersed phase substance having an average particle diameter of less than 1μm are contained 0.01 to 1 wt% in a matrix. 2. The method according to claim 1, wherein the ceramic particles are SiC, Al ₂ O ₃ , AlN.
2. The composite material for a railway vehicle brake disc according to claim 1, wherein the composite material is at least one particle selected from the group consisting of Si ₃ N ₄ and Si ₃ N ₄ . 3. An aluminum alloy serving as a matrix,
Mg: 2-5 wt%, Mn: 0.1-1 wt%, Cr: 0.05-0.35 wt
The composite material for a railway vehicle brake disk according to claim 1 or 2, wherein the alloy material comprises an alloy containing Al and inevitable impurities.