WO2008109898A1

WO2008109898A1 - Vehicle component

Info

Publication number: WO2008109898A1
Application number: PCT/AT2008/000057
Authority: WO
Inventors: Christoph Wachmann
Original assignee: Capital Technology Beteiligungs Gmbh
Priority date: 2007-03-09
Filing date: 2008-02-22
Publication date: 2008-09-18
Also published as: AT504924A9; AT504924A1

Abstract

The invention relates to a method for the production of a vehicle component, particularly a vehicle component subject to dynamic load having high heat resistance, comprising the following steps: a) providing gas atomized particles composed of aluminum or an aluminum alloy, the average size of said particles being less than 10 µm, b) compacting the particles, optionally in combination with reinforcement particles, to form a structurally stable block, then c) forming the block at a temperature of at least 250°C, and d) producing the vehicle component from the formed block or parts thereof.

Description

vehicle component

The invention relates to a method for producing a particular dynamically loaded vehicle component such as a piston or another part of an internal combustion engine.

Furthermore, the invention relates to a vehicle component.

In use to moving components of internal combustion engines, such as pistons, are preferably made of lightweight materials as possible. Here, inter alia, one resorts to aluminum or its alloys, which are known to have a relatively low density.

In order to impart a high strength to the alloys used, as is necessary for many applications, they are precipitation hardened, so that components can be obtained which have a high tensile strength at room temperature. However, it is often disregarded that the components can be exposed to operating temperatures of several hundred degrees Celsius, especially in extreme situations. In this case, a precipitation-hardened component in high-temperature use can lose its high tensile strength at room temperature very rapidly. Thus, with the frequently used aluminum alloy 2618 at 300 ^° C. and a holding time of 20 hours, a decrease in strength of almost 50% is evident. Such a drop in strength and the associated dangers can only be compensated for by a previously more massive design of components, which in turn precludes the desired principle of a lightweight construction of moving components.

On this basis, the invention has the object to provide a method of the type mentioned, with which a lightweight vehicle component can be provided, which has a consistently high heat resistance.

Another object of the invention is to provide a lightweight vehicle component which has a consistently high thermal stability. The procedural object of the invention is achieved in a method of the type mentioned in that it comprises the following steps: a) providing gas atomized particles of aluminum or an aluminum alloy, wherein an average size of the particles is less than 10 microns, b) compressing the Particles, optionally in combination with reinforcing particles, to a dimensionally stable block, then c) reshaping the block at a temperature of at least 250 ^° C., d) creating the vehicle component from the formed block or parts thereof.

The inventive concept is to provide a compact dimensionally stable or self-supporting block of small aluminum or aluminum alloy particles, which block in the sequence, for example, by drop forging is formed with a degree of deformation of at least fourfold. The intended precompression in step b) is required in order to obtain a substantially dense body after the subsequent forming. During the forming itself, the oxide skins, which are due to the high affinity of aluminum to oxygen on the surfaces of the particles are broken from temperatures of about 250 ⁰ C, so that during the forming, in which also a further compression of the material takes place, oxides are finely dispersed in the matrix material or incorporated into this, wherein at the same time the fine particles, which have an average size of less than 10 microns before reshaping, can undergo a decrease in size. The oxides finely distributed in the matrix metal prevent or hinder dislocation movements in the grains, which causes a high tensile strength of the material thus produced. The material or the material is thus structurally solidified and retains a high tensile strength over long periods of time at high temperatures of, for example, 300 ^° C. The material is excellently suited for the production of vehicle components with a stable high heat resistance.

The particles of aluminum or an aluminum alloy with a size of less than 10 microns can be atomized under oxygen, but also under nitrogen. In the latter case as well, the desired oxide layer in the context of the invention forms with a ratio of metal core to oxide skin that is suitable for structural solidification. It is favorable if an average size of the particles of aluminum or an aluminum alloy is less than 5 μm, preferably 0.1 μm to 1.5 μm. The smaller the gas atomized particles are, the higher becomes a relative proportion of the oxide skin formed on atomization or thereafter on the total volume of a particle. As a result, a proportion of finely dispersed oxide in the processed material also increases, which in turn benefits effective structural consolidation and thus high heat resistance. An optimum alumina content of the particles is 5% to 12% with respect to a total volume thereof.

In order to achieve high tensile strengths it can be provided that in step b), for example, reinforcing particles of an amorphous metal and / or an amorphous alloy are added. Due to a lack of a crystalline structure and thus of slip planes dislocations are even more hampered by such particles, with the advantage that also a strength, in particular heat resistance, is increased. When reinforcing particles of aluminum or an aluminum alloy are used, good incorporation of the reinforcing particles into the matrix-forming particles can be achieved.

If reinforcing particles are used, they preferably have an average size of less than 500 μm, preferably less than 200 μm.

With regard to optimum strength and toughness on the one hand and good processability of the particle mixture on the other hand, it may be appropriate that a volume fraction of the reinforcing particles is 5% to 45%, preferably 15% to 35%.

The inventively provided compression of the gas atomized aluminum or aluminum alloy particles can be done by a known per se cold isostatic pressing.

With regard to a reshaping of the block thus produced at a temperature of at least 250 ^° C., there are several possibilities: On the one hand, the deformation can be carried out by extrusion or extrusion. In this case, on the one hand, the pressing causes a break-up and distribution of the oxide skins located on the aluminum or aluminum alloy particles. On the other hand, the precompressed block is simultaneously consolidated so that a porosity of the reshaped material can typically be less than one percent by volume.

Alternatively, on the other hand, it is also possible and preferred in terms of mechanical properties if, for the time being, in step b) hot isostatic pressing is additionally carried out and then the forming of the block is carried out by forging at a temperature of at least 250 ^° C. In hot isostatic pressing, a further compression of the already cold isostatically precompressed block takes place. During the subsequent forging, the already described breaking up of the oxide skins and a finely dispersed distribution of oxide fragments in the material are achieved on further densification thereof. In comparison with an extrusion process, it is advantageous that the oxide skins break up homogeneously over the entire cross section of the block, whereas in the case of extrusion block diameters of, for example, 95 by 40 millimeters, in some cases only cracking of oxide skins in the region of the block edge is observed these areas can be set for further processing. One explanation is probably that during die forging the processed or processed material, in contrast to extruding has no alternative and the forming energy can be optimally distributed over the entire cross-section of the material introduced into this.

In connection with hot isostatic pressing, it has surprisingly also been found that at least partially amorphous reinforcing particles of aluminum or an aluminum alloy, such as strips of an at least partially amorphous aluminum alloy, for example, spun from a melt and increasingly cooled tapes of so-called "rapidly solidified" Al ₉₄ V ₄ Fe ₂ with amorphous, crystalline and quasicrystalline fractions, this process step with respect to a structure substantially unchanged survive and therefore can be used as reinforcing particles. As a particularly favorable temperature window for forming the optionally hot isostatically pressed block has a temperature between 350 ⁰ C and 500 ⁰ C _1, preferably 350 ⁰ C to 400 ⁰ C, proved. At temperatures of less than 350 ⁰ C, it may happen that the individual particles oxidüberzogenen slide or roll, without causing a disruption of the oxide skins together. On the other hand is a temperature over 400 ⁰ C, in particular more than 500 ⁰ C, a processing can be difficult because a softening of the matrix material no longer permits a decomposition of the oxide films.

The further object of the invention is achieved by a vehicle component, such as a piston of an internal combustion engine, by compacting particles of aluminum or an aluminum alloy with an average size of less than 10 microns, optionally together with reinforcing particles, into a block and then forming the block a temperature of at least 250 ⁰ C with a conversion rate of, for example 4: 1 or more, is available.

The advantages achieved with a vehicle component according to the invention are in particular the fact that it has a high heat resistance, even with longer periods of use at elevated temperatures of for example 300 ⁰ C. Due to a high tensile strength at high temperatures over long periods and good bending fatigue and Zugdruckwechselfestigkeit now components can be created, which are less massive than components according to the prior art and yet meet desired safety criteria. In other words, over-dimensioning of components in order to compensate for a loss of strength at elevated service temperatures is no longer necessary or not necessary to the extent required hitherto.

It is favorable, as already described, if an average size of the particles of aluminum or of an aluminum alloy is less than 5 μm and preferably in a range of 0.1 μm to 1.5 μm.

Furthermore, it can be provided that the vehicle component comprises reinforcing particles of an amorphous metal and / or an amorphous alloy. Because of the compatibility of the aluminum or aluminum alloy particles with the reinforcing material, the amorphous alloy is desirably an aluminum alloy. The reinforcing particles themselves preferably have an average size of less than 500 μm, preferably less than 200 μm. In this case, a volume fraction of the reinforcing particles is preferably 5% to 45%, in particular 15% to 35%.

Further advantages, features and effects of the invention will become apparent from the context of the description and the following embodiments.

Show it:

1 shows a TEM image (TEM ... transmission electron microscope) of a microstructure of a piston blank in the edge area;

2 shows a TEM image in the center of the piston blank from FIG. 1.

Commercially available aluminum particles with an average size of approx. 1 μm (d ₅₀ , arithmetic mean) evaporated under nitrogen were cold isostatically pressed into self-supporting bolts. The thus produced bolts with a relative density of about 0.8 were then subjected to a vacuum heat treatment and then hot isostatically pressed at about 475 ⁰ C and thereby compressed to a relative density of greater than 0.95. Subsequently, so prepared material was forged at about 350 ⁰ C with a degree of deformation of greater than four times on blank dimensions of an engine piston, wherein the material underwent a final compression and the aluminum particles against each other verschert and welded together.

The thus prepared exhibited by milling into a final shape to be brought piston blanks over the cross section viewed on an average hardness of greater than 80 HB at 25 ° C, which is converted corresponding to a tensile strength of about 275 MPa at 25 ⁰ C. The blanks were then held for 20 hours at a temperature of 300 ⁰ C, before the thus treated blanks at 300 ⁰ C tensile tests were performed. These tensile tests showed that a tensile strength R _m for all blanks was more than 200 MPa. Values of more than 184 MPa were obtained for the yield strengths R _p0i2 . In comparison, a piston made of an alloy 2618 despite higher tensile strength at 25 ⁰ C. (440 MPa) after soaking at 300 ⁰ C only 110 MPa, which value after a holding time of 20 hours at this temperature again reduced by about 45%.

Microstructural investigations by transmission electron microscopy (TEM) showed that the blanks both in the edge region (FIG. 1) and in the center (FIG. 2) have a non-porous structure of aluminum particles (light) and oxides distributed in these or at the particle boundaries. Micrometer range (appearing black in Figs. 1 and 2).

A vehicle component produced according to the invention has the following useful potential:

- weight reduction of components with the same safety;

- higher operating temperatures with temperature-loaded components;

- Tighter service life at elevated temperatures without significant decrease in material properties;

- in terms of engines or pistons higher efficiencies;

- Good damping properties to reduce a noise emission.

Claims

claims

1. A method for producing a particular dynamically loaded vehicle component, such as a piston or another part of an internal combustion engine, comprising the following steps: a) providing gas atomized particles of aluminum or an aluminum alloy, wherein an average size of the particles is less than 10 microns, b ) Compacting the particles, optionally in combination with reinforcing particles, into a dimensionally stable block, then c) reshaping the block at a temperature of at least 250 ^° C., d) creating the vehicle component from the formed block or parts thereof.

2. The method of claim 1, wherein an average size of the particles of aluminum or an aluminum alloy is less than 5 microns.

3. The method of claim 1 or 2, wherein an average size of the particles of aluminum or an aluminum alloy is 0.1 microns to 1, 5 microns.

4. The method according to any one of claims 1 to 3, wherein the particles of aluminum or an aluminum alloy have an alumina content of 5 percent by volume to 12 percent by volume.

5. The method according to any one of claims 1 to 4, wherein in step b) reinforcing particles of an amorphous metal and / or an amorphous alloy are added.

6. The method of claim 5, wherein reinforcing particles of aluminum and / or an aluminum alloy are used.

7. The method of claim 5 or 6, wherein the reinforcing particles have an average size of less than 500 microns, preferably less than 200 microns.

8. The method according to any one of claims 5 to 7, wherein a volume fraction of the reinforcing particles is 5% to 45%, preferably 15% to 35%.

9. The method according to any one of claims 1 to 8, wherein the compression in step b) is carried out by cold isostatic pressing.

10. The method according to any one of claims 1 to 9, wherein step b) comprises a hot isostatic pressing.

11. The method of claim 10, wherein the vehicle component is created in step d) by forging and optionally subsequent machining.

12. The method according to any one of claims 1 to 11, wherein the treatment of the block in step c) takes place at a temperature between 350 ⁰ C and 500 ⁰ C.

13. Vehicle component, in particular piston of an internal combustion engine, obtainable by compacting particles of aluminum or an aluminum alloy having an average size of less than 10 microns, optionally together with reinforcing particles, into a block and then forming the block at a temperature of at least 250 ⁰ C. at a forming rate of, for example, 4: 1 or more.

14. The vehicle component of claim 13, wherein an average size of the particles of aluminum or an aluminum alloy is less than 5 microns.

15. The vehicle component according to claim 13 or 14, wherein an average size of the particles of aluminum or an aluminum alloy is 0.1 μm to 1.5 μm.

16. Vehicle component according to one of claims 13 to 15, wherein reinforcing particles of an amorphous metal and / or an amorphous alloy are provided.

17. The vehicle component of claim 16, wherein the amorphous alloy is an aluminum alloy.

18. Vehicle component according to claim 16 or 17, wherein the reinforcing particles have an average size of less than 500 microns, preferably less than 200 microns.

19. Vehicle component according to one of claims 16 to 18, wherein a volume fraction of the reinforcing particles is 10% to 45%, preferably 15% to 35%.

20. Vehicle component according to one of claims 13 to 19, wherein the vehicle component is forged and optionally created by subsequent machining.

21. Vehicle component according to one of claims 13 to 20, wherein the vehicle component after 20 hours at 300 ⁰ C has a tensile strength R _m of more than 200 MPa.

22. Use of hot isostatically pressed starting material containing gas atomized particles of aluminum and / or an aluminum alloy having an average particle size of less than 10 microns and optionally reinforcing particles for forging piston blanks.