WO2007009547A1

WO2007009547A1 - Method for the alloying of aluminium to form components

Info

Publication number: WO2007009547A1
Application number: PCT/EP2006/005938
Authority: WO
Inventors: Zi Li; Enrico MÄHLIG
Original assignee: Gkn Sinter Metals Holding Gmbh
Priority date: 2005-07-15
Filing date: 2006-06-21
Publication date: 2007-01-25
Also published as: CN101273152A; CA2613177A1; KR20080027770A; JP2009501275A; US20080175750A1; CN101273152B; DE102005033073B3; MX2007016027A; EP1904662A1; BRPI0613051A2

Abstract

To achieve the object of providing a method by which the disadvantages entailed in the production of components from materials that contain aluminium are avoided, a method for alloying aluminium to form components is proposed, the alloying of aluminium taking place by adding an aluminium-containing material, the component being surrounded by at least one means receiving aluminium-containing material and the element that is formed in such a way being sintered. With preference, the component is wrapped in at least one metal nonwoven, an aluminium foil being arranged between the nonwoven and the component.

Description

Process for alloying aluminum to components

The present invention relates to a method for alloying aluminum to components as well as a manufactured by this method component.

Due to its special properties, aluminum is a preferred material, particularly in the aerospace and automotive industries. Made of aluminum or aluminum-containing materials components are compared with conventional, for example made of cast iron components easier. By reducing the weight of automobiles, for example, an increase in efficiency and a reduction in fuel consumption and an improvement in exhaust emissions can be achieved. For example, in engine and transmission construction currently the existing steel and castings are gradually replaced by those made of aluminum, or using aluminum. Since a combination of steel or castings with those made of aluminum causes problems due to the different physical behavior of the materials, it is desirable to replace as many classical steel or cast components as possible by those using aluminum. Because of this, problems due to differences in the materials used in terms of thermal expansion coefficients, thermal conductivity, elastic properties, etc. avoided. By the use of coordinated components, which are manufactured using aluminum, especially higher efficiencies are achieved.

Since many engine, clutch and transmission components are produced by powder metallurgy, there is great interest in providing methods by means of which aluminum components can be produced by powder metallurgy. A disadvantage of the powder metallurgical production of components using aluminum is in particular that aluminum and its alloys tend to occupy in air contact with an extremely stable metal oxide. As a result, in particular the specific surface is increased. The oxide skins located on the aluminum-containing material inhibit the diffusion of the particles of the powder material used, which is necessary for sintering. Furthermore, components made from aluminum-containing materials have reduced strength values, in particular a lower hardness, compared with those made of steel or cast iron. In addition, the oxide skins located on the aluminum-containing starting material hinder the usual compression Process the cold welding of the particles with each other.

A typical aluminum-containing steel is for example the one with the German material number 1.4767. When using such aluminum-containing steels, however, it is particularly disadvantageous that they adversely affect the sintering step due to the high oxygen affinity of the aluminum already described above. Also, water atomization of such aluminum-containing steels is not acceptable from an economic point of view. If such aluminum-containing steels are to be used as fibers and therefore precede the actual sintering by a wire drawing step, then the metal oxide skin also leads to severe wear of the drawing die used.

There is therefore a need for a process by means of which aluminum-containing components are produced without the disadvantages known from the prior art occurring in the production process. The object of the present invention is therefore to provide a method for alloying aluminum to such components, which does not have the aforementioned disadvantages.

This object is achieved by a method for alloying aluminum to components, wherein the alloying of aluminum by adding alumi- niumhaltigem material takes place, wherein the component with at least one aluminum-containing material receiving means surrounded and the thus formed element is sintered. For the purposes of the present invention, sintering is to be understood as meaning, in particular, the achievement of a sufficient temperature through which aluminum is converted into the gas phase and thereby at least partly precipitates on the surface of the relevant component and subsequently in the presence of sufficient temperatures the material of the component diffused into it. Thus, in particular components are obtained by the inventive method, which have increased levels of aluminum in a near-surface layer. A prerequisite for carrying out the method according to the invention is of course that the component to be provided with aluminum does not itself go into a liquid state in the temperatures necessary for the diffusion of the aluminum into the component. The component to be provided with aluminum may itself have aluminum contents (low-aluminum, in particular aluminum contents of less than 2% by weight, but this is preferably substantially free of aluminum.) The advantage over the admixture of powder / fibers, if they are available / would be that there is no change in material consistency with respect to pores caused by molten aluminum. The inventive method has the particular advantage that, for example, from conventional iron-chromium steels, optionally with levels of other metals, especially rare earths, starting initially components including green compacts can be produced with high strength values, which in a further step in terms of their properties the alloying of aluminum in particular influenced in the near-surface areas and targeted their aluminum content can be adjusted.

The aluminum-containing material such as an aluminum alloy, preferably pure aluminum, is liquefied in the sintering step upon reaching the melting temperature, which is, for example pure aluminum at a value of about 660 ⁰ C, the then liquid aluminum-containing material receiving from the aluminum-containing material Medium is recorded over a large area. As a result, dripping of the aluminum-containing melt is reduced and the concentration of aluminum in the immediate vicinity of the component to be provided with aluminum is thereby kept high. When falling below the vapor pressure, preferably above about 1000 ⁰ C, the aluminum-containing melt aluminum goes into the gas state and accumulates in the vapor. Since the aluminum-containing vapor develops in close proximity to the aluminum component, the gaseous aluminum may be at least partially deposited on the surface of the component concerned and will diffuse into the near-surface layers by reaching the sintering temperature of the component. The dissolved aluminum has a thermodynamically lower vapor pressure and remains stable in the component. Thus, the inventive method is characterized by a total of at least three temperature stages in the sintering step, wherein in the first temperature stage, the liquefaction of the aluminum-containing material, the second temperature stage characterizes the evaporation of aluminum, and in a third temperature level, the actual sintering with the diffusion of aluminum in the at least near-surface areas of the component takes place.

The aluminum-containing material receiving means preferably has a sufficiently large, in particular high pore volume, and is preferably constructed non-woven, with a non-woven of metal and / or ceramic is particularly preferably used. In principle, preferably the aluminum-containing material receiving means should have a large surface area, whereby evenly and over a large area, the molten after reaching the first temperature stage aluminum or aluminum-containing material received and thereby evenly to that of the aluminum-containing Material receiving means surrounding component is distributed around. As a result, if desired, a very uniform diffusion of the aluminum into the entire layer near the surface of the component can take place.

The sintering step of the process according to the invention is preferably carried out above the evaporation temperature of the aluminum-containing material, as already mentioned above. The temperature at which the aluminum is alloyed by diffusion into the near-surface layers of the component is preferably at least 1000 ^° C. The evaporation temperature of the aluminum or of the aluminum-containing material may be lower.

In a preferred embodiment of the method according to the invention, the component is selected from a group comprising sintered and / or unsintered parts, in particular compacts, nonwovens, powder heaps or fiber mats. The method according to the invention can thus be applied to components which have not yet undergone sintering, as well as to components which have already been sintered. For example, pressed green compacts before sintering according to the method of the invention with the aluminum-containing material receiving means are surrounded and sintered with the addition of aluminum-containing material, wherein simultaneously with the sintering and the addition of aluminum. However, the sintering of the component and the alloying of aluminum can also take place in separate steps.

The aluminum-containing material is preferably used in the form of a sheet metal foil, as a powder, as a wire, as a woven fabric and / or as a fiber. Particularly preferred is the use in the form of an aluminum foil, which is also additionally provided on at least one side with an embossing to increase the surface and easier transfer of the aluminum in the vapor phase. It is preferably provided that the aluminum-containing material consists of pure aluminum.

The aluminum-containing material can also consist of aluminum-containing alloys. These can be prepared, for example, from powder mixtures comprising 60 to 98.5% by weight, based on the total amount of the powder mixture, preferably 75 to 92% by weight, of an aluminum-based powder of metals and / or their alloys comprising aluminum, 0.2 to 30% by weight % Magnesium, 0, 2 to 40 wt% silicon, 0.2 to 15 wt% copper, 0.2 to 15 wt% zinc, 0.2 to 15 wt% titanium, 0, 2 to 10 wt% tin, 0, 2 to 5% by weight of manganese, 0.2 to 10% by weight of nickel and / or less than 1% by weight of arsenic, antimony, cobalt, beryllium, lead and / or boron, the weight percentages being Weil are based on the total amount of an aluminum-based powder. The powder mixture for producing an aluminum-containing alloy may additionally or alternatively be admixed with 0.8 to 40% by weight, preferably 7 to 15% by weight, based on the total amount of the powder mixture, of a metal powder selected from a group of metals and / or their alloys, consisting of iron, molybdenum, tungsten, chromium, vanadium, zirconium and / or yttrium.

In an alternative embodiment of the method according to the invention, first the aluminum-containing material is brought into contact with the component and then the component is surrounded by the means receiving at least one aluminum-containing material. In the context of the present invention, contacting means not only direct contact between the aluminum-containing material and the component, but also only partial or partial contact, as well as an arrangement of the aluminum-containing material close to or immediately adjacent to the component.

In a further alternative embodiment of the method according to the invention, the aluminum-containing material is first placed on the aluminum-containing material receiving means and then brought the material with the component in contact by surrounding the same with the agent. It can also be provided in a further alternative embodiment that aluminum-containing material is introduced into the area between the component and the means after the environment of the component with the aluminum-containing material. This alternative embodiment is particularly suitable when using aluminum-containing material as a powder and / or fiber or mixtures thereof.

In a further preferred embodiment of the method according to the invention, the component is wrapped with at least one metal fleece, wherein between the fleece and the component aluminum foil, in particular embossed, is arranged. This preferred embodiment has the great advantage that a relatively high proportion of aluminum can be simply and safely arranged in the immediate vicinity of the component, and that the thus formed coil can be handled easily in the subsequent sintering step or alloying step. In addition, by using foil, the concentration of aluminum in the vapor phase can be uniformly adjusted over the entire area surrounding the component. It can also be provided that either a single or multi-layer aluminum foil is used or a plurality of foil layers are used individually one above the other. In addition to aluminum, the aluminum foil should at most contain impurities of other metals. Can be used che, also known from the packaging industry embossed and unembossed aluminum foil.

If the method according to the invention is carried out starting from a green compact, then this green compact can also be subjected to a post-compaction (which can also be called intermediate compaction). Thus, for example, a pressed green compact can be re-introduced into a customary matrix mold and at least partially recompressed in it by corresponding pressing dies. Preferably, the recompression tools can be completely or partially conical, so that particularly high densities can be achieved at certain predetermined locations of the green compact. Before the alloying of aluminum or before sintering of the green compact, the green compact is preferably dewaxed. The dewaxing is preferably carried out under nitrogen, hydrogen, air and / or mixtures of said gases, in particular with targeted air supply. Furthermore, the dewaxing can be carried out with endogas and / or exogas, then preferably in a vacuum. The dewaxing can preferably be effected by superimposed microwaves and / or ultrasound or only by means of microwaves for temperature control. Finally, dewaxing can also be achieved by solvents such as alcohol or the like. or via critical carbon dioxide with or without the action of temperature, microwaves or ultrasound or a combination of the aforementioned methods.

The actual sintering step can subsequently be carried out on the step of alloying the aluminum. However, if the component is already present as a sintered component or solid component, a necessary heat treatment, in particular a homogenization annealing, may optionally be connected subsequently. In this case, the heat treatment can be carried out depending on the chemical composition of the component obtained. As an alternative or in addition to the heat treatment, the sintered component can also be quenched, preferably starting from the sintering or homogenizing annealing temperature, in water or else via a gas-fired cooling.

Before or after sintering or alloying of aluminum, additional surface compaction is possible, more generally: introduction of residual compressive stresses into surface areas, in particular by sand or shot blasting, rolling or the like. Likewise, a calibration can be carried out before or after the homogenization annealing. Here, the calibration is carried out at room temperature or elevated temperature. up to the forging temperature, even with pressures of up to 900 N / mm ² . Optionally, the calibration can be performed even above the solidus line, in which case the component can also be taken directly from the sintering heat or the temperature used in the alloying of the aluminum.

The present invention further relates to a component produced according to the method of the invention. The component produced according to the invention is characterized in particular by the fact that an increase in the aluminum content can be established in the regions near the surface. The resulting component may be at least partially provided in such areas with increased aluminum content.

The components obtained by means of the method according to the invention can be used in particular in the hot gas filtration, but especially in the exhaust gas filtration for internal combustion engines, and in particular as a carrier for catalysts or as a soot filter. Furthermore, the components produced by means of the method according to the invention can be used in membrane reactors in which gas reactions take place.

However, they can also serve as other substrates for non-metallic layers. In principle, the components produced by means of the method according to the invention have an increased resistance to oxidation compared with those without an increase in aluminum in the layer near the surface.

These and other examples are explained in more detail with reference to the following examples:

From a powder Inconel 600 (nickel-chromium alloy) with the German material number 2.4816 (aluminum-free), a green product was produced in the form of a tube. The powder mixture was isostatically pressed at room temperature to a green compact in the form of a tube. The density of the green compact was about 2.35 to about 2.38 g / cm ³ . Subsequently, the green compact thus produced was dewaxed at about 430 ^° C. for about 30 minutes.

Subsequently, the green compact thus produced was single-wrapped with commercial aluminum foil provided with at least one side embossment, taking care that the aluminum foil uniformly and tightly abutted the green tube. This component provided with the aluminum foil was then placed between two metal fleeces having a composition of 75% iron, 20% chromium and 5% aluminum, these metal fleeces having a porosity of 85%. The thus formed coil was introduced into a vacuum oven. When the temperature reaches the melting temperature of aluminum at about 660 ⁰ C, the aluminum foil begins to melt and the molten aluminum is large-area and uniformly absorbed by the two metal webs. As a result, a dripping of the aluminum melt and thus a reduction in the amount of aluminum present in the immediate vicinity of the component is prevented. When the evaporation temperature for aluminum is exceeded, it evaporates and deposits on a large area on the surface of the green compact produced from the aluminum-free steel. By the subsequent onset or simultaneous sintering of the green body at a temperature of about 1100 ⁰ C itself then takes place a diffusion of the aluminum in the near-surface regions of the Pumpenradgrünlings. The temperature in the oven can be increased stepwise, but it can also be immediately given a temperature above the evaporation temperature and, if desired, at the same time above the sintering temperature.

In another example, a fiber mat was sintered from the material with the German material number 1.4113 (aluminum-free) under normal conditions. Subsequently, the sintered fiber mat was uniformly provided with aluminum foil on both sides, and the aluminum foil-provided fiber mat was then sandwiched between two metal nonwovens having a lower porosity and larger surface area than the prepared fiber mat. Subsequently, the alloying of aluminum was carried out, as already described above concerning the Pumpenradgrünling. As a result, it was possible to obtain a fiber mat whose alloyed aluminum content was greater than 5% by weight, based on the total amount of the fiber mat. For example, if fiber mats made from a material with the German material number 1.4404 (aluminum-free) were used, the aluminum content of the finished fiber mat was more than 1% by weight, based on the total amount of the fiber mat, after aluminum had been alloyed under comparable conditions. For example, if a green compact was made from a powder of Inconel 600, the aluminum content after alloying according to the method described above using an aluminum foil of the finished sintered component was more than 1% by weight, based on the total amount of the component which is Inconel 601 equivalent.

Thus, the present invention provides a simple process whereby, in particular, aluminum-free materials are also subsequently produced Of sintered components of these with aluminum at least in the near-surface areas and thus can be provided with the advantageous properties thereof.

Claims

claims

1. A method for alloying aluminum to components, wherein the alloying of aluminum is carried out by adding aluminum-containing material, wherein the component is surrounded with at least one aluminum-containing material receiving means and the element thus formed is sintered.

2. The method according to claim 1, characterized in that as aluminum-containing material receiving means a fleece-like trained is used.

3. The method according to any one of the preceding claims, characterized in that as the aluminum-containing material receiving means a non-woven of metal and / or ceramic is used.

4. The method according to any one of the preceding claims, characterized in that the sintering step is carried out above the evaporation temperature of the aluminum-containing material.

5. The method according to any one of the preceding claims, characterized in that the Zulegierungstemperatur is at least 1000 ⁰ C.

6. The method according to any one of the preceding claims, characterized in that the component is selected from a group comprising sintered and / or unsintered parts, in particular compacts, nonwovens, fiber mats or Pulverhaufwerke.

7. The method according to any one of the preceding claims, characterized in that the component used is substantially free of aluminum or aluminum.

8. The method according to any one of the preceding claims, characterized in that the aluminum-containing material in the form of a sheet metal foil, as a powder, wire, fabric and / or fiber is used.

9. The method according to any one of the preceding claims, characterized in that the aluminum-containing material consists of pure aluminum.

10. The method according to any one of the preceding claims, characterized in that the aluminum-containing material is first brought into contact with the component and then the component with the at least one aluminum-containing material receiving means is surrounded.

11. The method according to any one of claims 1 to 9, characterized in that the aluminum-containing material is first placed on the aluminum-containing material receiving means and then the material is brought to the component in contact by surrounding the same with the aluminum-containing material receiving means.

12. The method according to any one of the preceding claims, characterized in that the aluminum-containing material in the region between the component and the aluminum-containing material receiving means is arranged.

13. The method according to any one of the preceding claims, characterized in that the component is wrapped with at least one metal fleece, wherein between the fleece and the component aluminum foil is arranged.

14. Component produced according to the method according to one of claims 1 to 13.