JPH01240633A - Aluminum-based composite material, its manufacture and piston - Google Patents

Abstract

PURPOSE:To obtain the subject composite material having excellent characteristics in heat-resistant strength, toughness, thermal expansion coefficient and wear resistance by mixing pure Al powder as a matrix and ceramic grains as reinforcing grains into composite powder and subjecting it to hot molding into the prescribed shape. CONSTITUTION:Al powder as a matrix having >=99.9% purity and ceramic grains as reinforcing grains having >=1,000Hv hardness, <=10X10<-6>/ deg.C thermal expansion coefficient, 3-0.1mu average grain size and 5-20% volume rate are premixed by a mixer. The mixture is subjected to ball mill treatment by a ball mill to manufacture composite powder. The composite powder is packed into a compacting vessel made of Al in the atmosphere of an Ar gas, is subjected to vacuum degassing and is thereafter subjected to hot molding by a hot presser. By this method, the material having excellent heat-resistant strength, toughness, wear resistance and low thermal expansion coefficient in which ceramic grains as dispersion reinforcing grains are uniformly dispersed into the matrix of pure Al material can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to an aluminum-based 1M composite material used for vehicle engine parts, particularly pistons, in which aluminum is used as a matrix and dispersed reinforcing particles are uniformly dispersed in the matrix. The present invention relates to a dispersion-strengthened aluminum matrix composite material for pistons, a method for manufacturing the same, and a piston for internal combustion engines using the composite material.

Conventional Technologies and Issues Pistons for internal combustion engines are parts that are used under physically harsh conditions at high temperatures of 150 to 400 degrees Celsius, so the materials used for them are highly resistant to heat, toughness, and wear resistance. Excellent for 1. It is also required to have a low coefficient of thermal expansion.

On the other hand, since the piston reciprocates at high speed, the inertia force becomes large. Therefore, in order to reduce vibration, increase engine output, and improve responsiveness, it is desirable that the engine be as light as possible.

AC8A has been the most commonly used lightweight piston material to meet these demands.

Afl-Si-Cu-Mg-Nl-based Lo-Ex A0 alloys such as AC8B are known.

However, the above-mentioned Lo-Ex aluminum alloys are still insufficient in terms of high-temperature strength. For example, the tensile strength is 17Kgf at 200℃/-1300℃
Since the piston has a strength of only about 78 ff'/-, it has not been possible to achieve sufficiently satisfactory thinning and weight reduction of the piston. Of course, further improvements have been desired in terms of other required properties such as wear resistance, toughness, and low coefficient of thermal expansion.

Based on the above technical background, this invention has been developed based on the conventional L
To provide an aluminum-based composite material especially for pistons that can obtain even higher satisfaction with the above-mentioned required properties than the o-Ex A2 alloy, a method for manufacturing the same, and a piston manufactured using the composite material. It was done for the purpose of

Means for Solving the Problems For the above-mentioned purpose, the present inventors, as a result of various experiments and research, found that in a particle dispersion reinforced aluminum matrix composite material, the purity of the aluminum powder used as the matrix and the ceramic used as the reinforcing particles were determined. By combining particle hardness, coefficient of thermal expansion, particle size, and dispersion content within specific ranges, properties such as heat resistance strength, toughness, wear resistance, and low coefficient of thermal expansion that are superior to those of the conventional alloys can be obtained. He discovered that this could be done and completed this invention.

Therefore, this invention uses a pure aluminum material with a purity of 99.0% or more as a matrix, and has a hardness of Hv1000 or more, a thermal expansion coefficient of 10 x 10-6/℃ or less, and an average particle size of 3.
~0. ．． 1 μm ceramic particles are used as dispersion-strengthening particles, and the dispersion-strengthening particles are uniformly dispersed in a matrix at a volume fraction Vr of 5 to 20%.
The basic gist is aluminum matrix composite materials.

To enumerate more preferable conditions, the purity of the aluminum material used as the matrix is 99.5% or more, the hardness of the reinforcing particles is Hv1500 or more, and the expansion coefficient is 8 x 10.
-6/'C or less, and the average particle diameter is in the range of 1 to 0.3 μm. Further, the dispersed volume fraction V'' of the reinforcing particles is in the range of 10 to 18%.

The composite material according to the present invention is manufactured by a well-known powder metallurgy method. For the purpose of improving the uniform dispersibility of reinforcing particles, matrix AQ powder and reinforcing particle powder are mixed, and the above-mentioned material is formed by ball milling. Preferably, a method can be adopted in which a composite powder having a strong bond between the matrix material and reinforcing particles is created, and this composite powder is hot-molded to obtain a predetermined molded body. For the above-mentioned forming, preparation of a solidified billet by degassing treatment and hot compaction treatment is required.1. This includes forging from this extruded billet material, as well as normal powder metallurgy processes such as powder forging. The piston is
The molded body obtained in the above manner is further subjected to necessary secondary processing such as forging, cutting, and polishing to produce the molded body.

Next, reasons for limiting each of the constituent elements in this invention will be explained.

The purity of the aluminum material used as the matrix is 99.0%
The reason why it is particularly preferably limited to 99.5% or more is due to physical reasons. In other words, in order to increase the heat resistance strength of an aluminum material, it is common to alloy it, but on the other hand, the strengthening mechanism that determines the heat resistance strength of a particle-dispersed composite material is , the interaction between the ceramic reinforcing particles and fine aluminum oxides and carbides uniformly dispersed in the alumina matrix and the high density of dislocations.

That is, since the dispersion-strengthening particles are stable in the matrix even at high temperatures, the dislocation pinning effect is maintained up to high temperatures, and even when the temperature rises, the strength is prevented from decreasing due to the scales. However, as the piston is exposed to high temperatures of 150 to 400°C, alloying elements tend to precipitate and coarsen over time, and they no longer contribute to maintaining strength through the pinning effect of dislocations, so they are not added. There's no particular meaning.

On the contrary, the harmful effects of forming crystallized substances and precipitates and reducing toughness increase. Therefore, it is advantageous to use a high-purity aluminum material as a composite material for a piston, which must have both heat resistance strength and toughness. This requires the use of 99.0% or more pure aluminum. Most preferably purity 9
9.5% or more should be used, but 99.9%
Even if a material with a purity higher than that is used, no significant increase in effectiveness can be expected, and the disadvantage of increased material cost will be greater, so it is sufficient to use one with a purity lower than that.

The hardness, thermal expansion coefficient, particle size, and amount of dispersion of the ceramic used as reinforcing particles are important factors for controlling the wear resistance and thermal expansion coefficient of the composite material. If the hardness of the ceramic particles is less than Hv1000, the wear resistance of the composite material will be poor.

Particularly preferably, the hardness is Hv1500 or more. Furthermore, if the coefficient of thermal expansion exceeds 10 x 10-6/''C, the coefficient of thermal expansion of the composite material will also be large, making it unsuitable as a piston material due to problems such as wear and seizure. Most preferably the coefficient of thermal expansion is 8.
It is preferable that the temperature is below X10'/°C. In view of the above-mentioned requirements for hardness and coefficient of thermal expansion, AQ03, SIC, etc. can be optimally used as the type of ceramic particles, and TlO2
, ZrO2, etc. are also suitable, but Mg 2 O is not suitable for use because it lacks hardness and has a high coefficient of thermal expansion.

If the average particle size of the ceramic particles is too large, exceeding 3 μm, the toughness of the composite material will decrease. On the contrary, 0.1μ
If it is too small (less than m), the wear resistance will deteriorate. Therefore, in order to satisfy both toughness and wear resistance, particles with an average particle size in the range of 3 to 0.1 μm should be used, most preferably in the range of 1 to 0.3 μm. .

The dispersed content of ceramic particles is Vr in volume fraction
It is necessary to set it as the range of 5-20%. volume ratio is 5
If it is less than %, the abrasion resistance of the composite material will deteriorate and a sufficient increase in heat resistance strength cannot be expected. Moreover, when the amount exceeds 20%, the toughness of the composite material is reduced. The most preferred range is about 10 to 18%.

Examples Example 1 In this example, A of the aluminum material used as the matrix
This study investigated the relationship between purity and the strength and toughness of composite materials.

Aluminum powder with an average particle size of 40 μm of different purity was produced by atomization, and hep03 particles (average particle size of 0.5 μm) were used as ceramic particles for dispersion strengthening.
) were weighed to give a volume ratio of ceramic particles Vf of 15% and a total weight of ffi I Kg, and the mixture was heated at 2000 rpm with a mixer.
Premixed aX for 4 minutes.

Then, this mixture was added to A with a ball mill using 30 kg of 3/8” steel balls in a gas atmosphere.
A composite powder was produced by ball milling with Orp ■ for 5 hours. In this ball milling step, 30 cc of ethanol was added as an anti-seize agent.

Next, the composite powder obtained above was mixed with A in a gas atmosphere.
Filled into a JJ powder container and heated to 3X10-3torrX5
After performing vacuum degassing treatment for several hours, compaction was performed using a hot press machine under the conditions of 500°C x 700ONgf/d, and the resulting billet was extruded at an extrusion ratio of 10:1 and an extrusion temperature of 45°C.
Extrusion molding was carried out at 0° C. to obtain various aluminum-based laminated materials in the shape of round bars.

For these various composite materials, room temperature and 300℃
In addition to measuring the tensile strength after being held at ℃ for 1000 hours, the Charpy impact value (room temperature, no notch) was measured and compared with that of the current AC8A-T5 mold casting material. The results are shown in Table 1. In addition, A of the matrix
The tempering of all 6061.2014 materials was T4.

Table 1: Matrix An purity and composite strength and toughness From the results shown in Table 1, it is quantitatively clear that the current A
Toughness higher than that of C8A-T5 mold casting material (evaluated by Charpy impact value) can be obtained when an aluminum material with a purity of 99.0% or higher is used as the matrix, especially 99.5% or higher. It is preferable that it is % or more,
It can be seen that even if one with a high purity of 99,899% is used, the difference between it and 99,596 is small and has no particular significance.

Example 2 This example investigated the relationship between the type of dispersed ceramic particles, particularly their hardness, and the wear resistance of the composite material.

A1050 as matrix aluminum particles
(purity 99.5%, average particle size 40 μm) and dispersed ceramic particles (average particle size 0.5 μm) as reinforcing material.
Various composite materials were obtained by the same manufacturing method as in Example 1, using various types of ceramic particles and setting the amount of ceramic particles dispersed at a constant volume ratio of 15%.

Then, the specific wear amount of these various composite materials was measured, and the current material A
It was compared with that of C8A-75 mold casting material. The wear resistance test was carried out using an Okoshi dry abrasion tester using a mating material: Fe12.
, friction speed: 1.99 m/s, friction distance: 600 m, final load: 2°1 Kg. The results are shown in Table 2.

Table 2: Types of dispersed ceramics and wear resistance of composite materials From the results in Table 2, in order to obtain wear resistance equivalent to or higher than the current AC8A-T5 material, it is necessary to use ceramic particles with a hardness of Hv1000 or higher. Since there is almost no change at Hv1500 or higher, it is understood that it is preferable to use a Hv1500 or higher.

Example 3 In this example, the relationship between the type of ceramic particles, particularly the coefficient of thermal expansion thereof, and the coefficient of thermal expansion of the composite material was investigated.

The thermal expansion coefficients of various composite materials obtained using the same materials and manufacturing methods as in Example 2 were measured, and the current material AC8A was measured.
-Compared with 75 material. The results are shown in Table 3 below.

[Margin below]

Table 3: Types of dispersed ceramics and thermal expansion coefficients of composite materials According to Table 3 above, in order to obtain a thermal expansion coefficient that is equal to or lower than the current AC8A-75 material, the thermal expansion coefficient of the ceramic particles must be adjusted. is 10 x 10-6/℃
It is necessary to use the following, therefore Zr
Ceramic particles such as 02, Ti 02, Al2O3, and SIC can be used, among which ceramic particles with a thermal expansion coefficient of 8
It is preferable to use Ti of 10-6/℃ or less.
It can be seen that 02, A[03, and SiC show suitability.

Example 4 In this example, the particle diameter of dispersed ceramic particles and the toughness and wear resistance of the composite material were investigated.

Matrix: A1050 (particle size 40.czm), ceramic particles: AQ203 The dispersion volume ratio Vf of ceramic particles was 15%, and the average particle diameter of the ceramic particles was varied in the range of 0.1 to 5 μm. Various composite materials were manufactured using the same manufacturing method as in Example 1.

The Charpy impact value (room temperature, no notch) and abrasion resistance of these various composite materials were measured, and the current material AC8A
- compared with that by T5. Wear resistance test is Example 2
It was carried out under the same conditions as in the case ['Q]. The results are shown in Table 4.

[Margin below]

Table 4 2 Changes in Dispersed Ceramic Particle Size and Composite Materials As shown in Table 4 above, the particle size range of ceramic particles that is not inferior in toughness and wear resistance to the current AC8A-C5 material is 3 to 3. 0.1 μm, preferably 1 to 0
．． It can be seen that the diameter is 3 μm.

Example 5 In this example, the relationship between changes in the dispersed volume fraction Vf of ceramic particles and the wear resistance, toughness, and heat resistance strength of a composite material was investigated.

Various composite materials were manufactured using the same materials and manufacturing methods as in Example 4, except that the volume fraction vf of the dispersed ceramic particles was varied in the range of 0 to 25%.

The abrasion resistance, tensile strength (after being held at 300° C. for 1000 hours), and Charpy impact value (room temperature, no notch) of these various composite materials were measured and compared with the current materials. The results are shown in Table 5.

[Margin below]

Table 5 2. Abrasion resistance, heat resistance strength, and toughness of composite materials when dispersed ceramic vr changes According to Table 5 above, in order to provide abrasion resistance higher than the current level, the dispersion volume ratio of ceramic particles must be 5%. It can be seen that the above is necessary, and that the same volume fraction should be 20% or less in order to obtain toughness higher than the current one. In order to obtain particularly good results over current materials, the above volume fraction should be between 10 and 10.
A range of approximately 18% is suitable.

Example 6 A1050 atomized powder with an average particle size of 40 μm was used as a matrix, and an average particle size of 0 as a dispersed ceramic.
．． Using 5μm AQO3 particles, the dispersion volume ratio was 15
A piston (A) for an internal combustion engine having the shape shown in attached FIG. 1 was manufactured using a composite material obtained by the same manufacturing method as in Example 1.

Since the composite material used for this piston has the physical properties shown in the column of Vl'15% in Example 4, it was compared with a piston manufactured using the current AC8A-T5 mold casting material. By making the wall thinner, we were able to achieve a weight reduction of over 50%.

Effects of the Invention According to the invention described in claims (1) to (3), it has comprehensively superior properties in heat resistance strength, toughness, coefficient of thermal expansion, and wear resistance compared to conventional general-purpose AC8A material. This makes it possible to provide a composite material having the following characteristics, which is suitable for use in mechanical parts used under severe conditions, and which makes it possible to achieve significant weight reduction.

Further, the piston according to claim (4) is the piston according to the fifth embodiment.
Since it is significantly lighter in weight than conventional AC8A alloy products, it can contribute to improving the characteristics of internal combustion engines, particularly reducing noise, increasing output, and reducing vibration.

[Brief explanation of the drawing]

FIG. 1 is a front view of a piston for an internal combustion engine according to an embodiment of the present invention. (A)... Piston. that's all

Claims (4)

[Claims] (1) Pure aluminum material with Al purity of 99.0% or more is used as a matrix, hardness is Hv1000 or more, thermal expansion coefficient is 10×10^-^6/℃ or less, and average particle size is 3 to 0.1.
An aluminum matrix composite material, characterized in that the dispersion-strengthened particles are uniformly dispersed in a matrix at a volume fraction Vf of 5 to 20% using micrometer ceramic particles as dispersion-strengthened particles. (2) The Al purity of the matrix is 99.5% or more, and the dispersion-strengthening particles have a hardness of Hv1500 or more, a thermal expansion coefficient of 8 x 10^-^6/℃ or less, and an average particle diameter of 1 to 0.3μ.
The aluminum matrix composite material according to claim 1, wherein the reinforcing particles have a dispersed volume fraction of Vf of 10 to 18%. (3) A claim characterized in that pure aluminum powder as a matrix and ceramic particles as reinforcing particles are mixed to form a composite powder by a ball milling method, and then the composite powder is hot-formed into a predetermined shape. The method for producing an aluminum matrix composite material according to (1) or (2). (4) A piston made of the composite material according to claim (1) or (2).