JPH0368096B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Field This invention relates to an aluminum-based composite material used for vehicle engine parts, particularly pistons, that is, a dispersion-strengthened toughness material in which aluminum is used as a matrix and dispersion-strengthening particles are uniformly dispersed in the matrix. The present invention relates to an excellent aluminum matrix composite material, 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 have poor heat-resistant strength, toughness, and wear resistance. It is required that the material has excellent properties and 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. To meet these demands, the most commonly used lightweight piston materials are AC8A,
Al-Si-Cu-Mg-Ni-based Lo-ExAl such as AC8B
Alloys 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℃.
mm ² and has a strength of only about 7 Kgf/mm ² at 300° C., it has not been possible to achieve sufficiently satisfactory thinning and weight reduction of the piston. Of course, further improvements were desired in terms of other required properties such as wear resistance, toughness, and low coefficient of thermal expansion. This invention is based on the above technical background,
An aluminum matrix composite material with particularly excellent toughness that can achieve even higher satisfaction with the above-mentioned required properties than conventional Lo-ExAl alloys, a method for manufacturing the same, and a material manufactured using the composite material. The purpose of this design was to provide a piston that Means for Solving the Problems For the above-mentioned purpose, the present inventors have conducted various experiments and research, and have determined that, in particle dispersion reinforced aluminum matrix composite materials, the Al purity of aluminum powder used as a matrix and the ceramics used as reinforcing particles can be improved. By combining particle hardness, coefficient of thermal expansion, particle size, and dispersion content within a specific range, heat resistance strength superior to that of the conventional alloys can be achieved.
The present invention was completed based on the discovery that various properties such as toughness, wear resistance, and low coefficient of thermal expansion can be obtained. Therefore, this invention uses a pure aluminum material with an Al purity of 99.0% or more as a matrix, and has a hardness
Ceramic particles with a Hv of 1000 or more, a thermal expansion coefficient of 10×10 ^-6 /℃ or less, and an average particle size of 3 to 0.1 μm are used as dispersion-strengthened particles, and the dispersion-strengthened particles have a volume fraction of Vf5 to 20.
The basic gist is an aluminum matrix composite material with excellent toughness, which is characterized by being uniformly dispersed in a matrix at a ratio of 1.5%. To enumerate more preferable conditions, the purity of the aluminum material used as the matrix is 99.5% or more, the hardness under the reinforcing grains is Hv 1500 or more, the coefficient of thermal expansion is 8 x 10 ^-6 /°C or less, and the average particle size is 1 to 1. It is in the range of 0.3 μm. In addition, the dispersed volume fraction Vf of reinforcing particles is 10
It ranges from ~18%. The composite material according to the present invention is manufactured using a well-known powder metallurgy method, but in order to improve the uniform dispersibility of reinforcing particles, matrix Al powder and reinforcing particle powder are mixed and ball milling is performed. Therefore, a method can be suitably employed in which a composite powder having a strong bond between the matrix material and the reinforcing particles is created, and this composite powder is hot-molded to obtain a predetermined molded body. The above-mentioned forming includes the usual steps of powder metallurgy, such as degassing, creating a solidified billet by hot compaction, and forging this billet from an extruded material, as well as powder forging. The piston is manufactured by further subjecting the molded body obtained above to necessary secondary processing such as forging, cutting, and polishing. 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
The reason why it is limited to 99.0% or more, particularly preferably 99.5% or more is as follows. 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 ceramic reinforcing particles and fine aluminum oxides and carbides uniformly dispersed in the aluminum 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 can be maintained up to high temperatures, and a decrease in strength can be prevented even when the temperature rises. However, when 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 it is particularly difficult to add alloying elements. has no meaning. On the contrary, the harmful effects of forming crystallized substances and precipitates and reducing toughness increase. Therefore, it is advantageous to use high-purity aluminum as a composite material for pistons, which must have both heat resistance strength and toughness.
This requires the use of pure aluminum with a purity of 99.0% or higher. Most preferably purity 99.5
% or more, but even if you use a product with a purity exceeding 99.9%, you cannot expect a significant increase in effectiveness, and the disadvantage of increased material cost will be greater, so it is recommended to use less than 99.9%. It is necessary and sufficient to use one with a purity of . The hardness, thermal expansion coefficient, particle size, and amount of dispersion of the ceramics used as reinforcing particles are important factors in 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 10×10 ^-6 /°C, the composite material will have a large coefficient of thermal expansion, making it unsuitable as a piston material due to problems such as wear and seizure. Most preferably the coefficient of thermal expansion is 8
×10 ^-6 /℃ or less is good. In view of the above-mentioned requirements for hardness and coefficient of thermal expansion, AlO ₃ , SiC, etc. can be optimally used as the type of ceramic particles.
TiO ₂ , ZrO ₂ and the like are also suitable, but MgO is not suitable for use because it lacks hardness and has a high coefficient of thermal expansion. The average particle size of ceramic particles is 3μm.
If it is too large, the toughness of the composite material will decrease. On the other hand, if it is too small (less than 0.1 μm), 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, and most preferably in the range of 1 to 0.1 μm.
It is preferable to use a material in the range of 0.3 μm. The dispersed content of ceramic particles needs to be in the range of Vf5 to 20% in terms of volume fraction.
When the volume fraction is less than 5%, the wear resistance of the composite material deteriorates, and a sufficient increase in heat resistance strength cannot be expected.
Moreover, if it exceeds 20%, the toughness of the composite material decreases. The most preferred range is about 10 to 18%. Examples Example 1 In this example, the relationship between the Al purity of the aluminum material used as the matrix and the strength and toughness of the composite material was investigated. Therefore, the average particle diameter of 40 μm was obtained with various purity levels.
_Aluminum powder produced by the atomization method of Premixed for 4 minutes. Then, add 3/8(d) to this mixture in an Ar gas atmosphere.
By a ball mill using 30kg of steel balls,
A composite powder was produced by ball milling at 280 rpm for 5 hours. In this ball milling step, 30 c.c. of ethanol was added as an anti-seize agent. Next, the composite powder obtained above was filled into an Al powder container in an Ar gas atmosphere, and 3×10 ^-3 torr×5
After vacuum degassing treatment for several hours, powder compaction is performed using a hot press machine under the conditions of 500℃ x 7000Kgf/ ^cm2 , and the resulting billet is extruded at an extrusion ratio of 10:1 and an extrusion temperature of 450℃. Various aluminum matrix composite materials in the shape of round bars were obtained. Then, we measured the tensile strength of these various composite materials after holding them at room temperature and 300℃ for 1000 hours, measured the Shapey impact strength (room temperature, without notches), and determined the AC8A-T ₅ mold casting as the current material. compared with that of wood. The results are shown in Table 1. In addition, the heat treatment of both A6061 and 2014 matrix materials was _T4 .

[Table] From the results shown in Table 1, quantitatively, the current
Toughness higher than that of AC8A-T ₅ mold casting material (evaluated by Charpy impact value) can be obtained when an aluminum material with an Al purity of 99.0% or more is used as the matrix, especially with an Al purity of 99.5% or more. It is preferable that the purity is 99.99%, and even if a high purity one is used, the difference between 99.5% and 99.5% is small and there is no particular meaning. Example 2 This example describes the types of dispersed ceramic particles,
In particular, the relationship between the hardness and the wear resistance of the composite material was investigated. As matrix aluminum particles
Using A1050 (purity 99.5%, average particle size 40 μm), dispersed ceramic particles (average particle size
0.5 μm), and the amount of dispersion of the ceramic particles was kept constant at a volume fraction Vf: 15%.
Various composite materials were obtained by the same manufacturing method as in Example 1 above. Then, we measured the specific wear amount of these various composite materials,
It was compared with that of the current AC8A-T ₅ mold cast material.
The wear resistance test was performed using an Okoshi type dry wear tester under the following conditions: mating material: FC30, friction speed: 1.99 m/S, friction distance: 600 m, final load: 2.1 kg.
The results are shown in Table 2.

[Table] From the results in Table 2, in order to obtain wear resistance equal to or higher than the current AC8A-T ₅ material, it is necessary to use ceramic particles with a hardness of Hv1000 or higher, and Hv1500 or higher. Since there is almost no change, it is clear that it is preferable to use 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 compared with the current AC8A-T ₅ material. The results are shown in Table 3 below.

[Table] According to Table 3 above, in order to obtain a thermal expansion coefficient equal to or lower than that of the current AC8A-T ₅ material, the thermal expansion coefficient of ceramic particles must be 10×
It is necessary to use a material with a temperature of 10 ^-6 /℃ or less,
Therefore, ceramic particles such as ZrO ₂ , TiO ₂ , AlO ₃ , SiC, etc. can be used, but among them, ceramic particles with a thermal expansion coefficient of 8
It is preferable to use less than ×10 ^-6 /℃,
It can be seen that TiO ₂ , AlO ₃ and SiC are suitable. 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 μm), ceramic particles: Dispersion volume ratio of Al ₂ O ₃ ceramic particles
Vf is 15%, and the average particle diameter of ceramic particles is
Using various variations in the range of 0.1 to 5 μm,
Various composite materials were manufactured using the same manufacturing method as in Example 1 above. The Shape impact value (room temperature, no notch) and abrasion resistance of these various composite materials were measured and compared with those of the current material AC8A-T ₅ . The wear resistance test was conducted under the same conditions as in Example 2. The results are shown in Table 4.

[Table] As shown in Table 4 above, the current AC8A-
The particle size range of ceramic particles, which is not inferior in toughness and wear resistance to _T5 material, is 3 to 0.1 μm,
It can be seen that the thickness is preferably 1 to 0.3 μm. Example 5 This example describes the dispersion volume ratio of ceramic particles.
This study investigated the relationship between changes in Vf and the wear resistance, toughness, and heat resistance strength of composite materials. Volume fraction Vf of dispersed ceramic particles from 0 to 25%
Various composite materials were manufactured using the same materials and manufacturing methods as in Example 4, except that the values were changed within the range of . The abrasion resistance, tensile strength (after being held at 300°C for 1000 hours), and sharpie impact value (without notches at room temperature) of these various composite materials were measured and compared with current materials. The results are shown in Table 5.

[Table] According to Table 5 above, the dispersion volume ratio of ceramic particles must be 5.
It can be seen that the same volume fraction should be 20% or less in order to obtain toughness higher than that of the current material. In order to obtain particularly good results over current materials, the volume fraction is preferably in the range of about 10 to 18%. Example 6 A1050 with an average particle size of 40 μm as a matrix
A composite material obtained by the same manufacturing method as in Example 1 using atomized powder, AlO ₃ particles with an average particle size of 0.5 μm as the dispersed ceramic, and a dispersion volume ratio of 15% was used to produce a composite material with the shape shown in attached Figure 1. Piston A for an internal combustion engine was manufactured. Since the composite material used for this piston has the physical properties shown in the Vf15% column of Example 4, the piston has better performance compared to the piston manufactured using the current AC8A-T ₅ mold casting material. , 50 due to thinning
We were able to achieve a weight reduction of over %. Effects of the Invention According to the invention described in claims 1 to 3, a composite material having comprehensively superior properties in terms of heat resistance strength, toughness, coefficient of thermal expansion, and abrasion resistance compared to the conventional general-purpose AC8A material is produced. It is suitable for use in mechanical parts that are used under harsh conditions, and can achieve significant weight reduction. In addition, the piston according to claim 4 can achieve remarkable weight reduction compared to the conventional AC8A alloy made piston as in Example 5, and therefore improves the characteristics of internal combustion engines, particularly reduces noise and improves output. , which can contribute to reducing vibration.

[Brief explanation of drawings]

FIG. 1 is a front view of a piston for an internal combustion engine according to an embodiment of the present invention. A... Piston.

Claims (1)

[Scope of Claims] 1 A pure aluminum material with an Al purity of 99.0% or more is used as a matrix, and ceramic particles having a hardness of Hv1000 or more, a thermal expansion coefficient of 10×10 ^-6 /°C or less, and an average particle size of 3 to 0.1 μm are dispersed. An aluminum matrix composite material having excellent toughness, characterized in that the dispersion-strengthening particles are uniformly dispersed in a matrix at a volume fraction Vf of 5 to 20% as reinforcing particles. 2 The Al purity of the matrix is 99.5% or more,
According to claim 1, the dispersion-strengthened particles have a hardness of Hv1500 or more, a thermal expansion coefficient of 8×10 ^-6 /°C or less, an average particle diameter of 1 to 0.3 μm, and a dispersed volume fraction of the reinforcing particles of Vf10 to 18%. Aluminum matrix composite material with excellent toughness. 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. 3. A method for producing an aluminum matrix composite material with excellent toughness according to 1 or 2. 4. A piston made of the composite material according to claim 1 or 2.