WO2003069002A1

WO2003069002A1 - Expandable metal body, method for the production thereof and its use

Info

Publication number: WO2003069002A1
Application number: PCT/EP2003/001485
Authority: WO
Inventors: Joachim Baumeister; Georg Veltl; Norbert Zimmer
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2002-02-18
Filing date: 2003-02-14
Publication date: 2003-08-21
Also published as: AU2003210273A1

Abstract

The invention relates to a method for producing expandable metal bodies. To this end, a mixture consisting of at least one powdery or liquid metal and of a powdery or liquid metal-containing expanding agent intermediate material is firstly treated with a liquid or gaseous non-metal-containing expanding agent intermediate material. The non-metal-containing expanding agent intermediate material is added to the metal-containing expanding agent intermediate material whereby forming at least one expanding agent. This expanding agent-containing mixture is subsequently or simultaneously compacted to form a semi-finished product in which the particles of the at least one metal are tightly bound to one another and constitute a gas-tight seal for gas particles released from the expanding agent. The metal bodies produced in this manner can be expanded at a temperature that is higher than the decomposition temperature of the expanding agent in order to form porous metal bodies.

Description

Foamable metal body, process for its production and its

use

DESCRIPTION

Technical field

The invention relates to a method for producing foamable metal bodies according to the preamble of the main claim, foamable metal bodies producible with this method and their use.

State of the art

There are various methods for producing foamable metal bodies. In these processes, one or more blowing agent powders are admixed to a metal powder, which decompose when heated and thereby split off a gas which, during the final foaming, leads to pore formation and pore growth and thus to the expansion of the foamable material. In order to achieve foamability, the blowing agent-containing powder mixture is compacted before foaming.

Foamability occurs when the metal particles of the matrix metal form a gas-tight seal for the gas particles released by the blowing agent. For this the blowing agent powder particles must be completely surrounded by the metallic matrix. The metallic matrix must continue to be gas-tight, which means that it may contain no or only a few pores. A high density of the matrix metal containing blowing agent is required to achieve such a gas-tight seal. Adequate compression of the matrix is achieved by means of high pressures and / or high temperatures. If the compaction (compression) takes place at low temperatures, very high compaction pressures must be applied.

The disadvantage of these methods is that a high level of system engineering is required. When using high compaction temperatures, lower compaction pressures can be used. However, the amount is

Compacting temperature is severely limited by the decomposition temperature of the blowing agent or blowing agent mixture used, because this will prematurely outgas at too high temperatures.

Methods are known from DE 40 18 360 A1 and DE 41 01 630 A1, in which powder mixtures containing blowing agent also exceed the decomposition temperature of the

Blowing agent can be compacted. The compacting pressure is chosen so high that the decomposition of the blowing agent is prevented.

However, these methods have the disadvantage that they are limited to smaller dimensions or cross sections of the material to be compacted. Larger components are available in the above-mentioned processes by means of compacting using hot isostatic pressing (HIP), but this process is very expensive.

Presentation of the invention

The object of the present invention is to overcome the disadvantages of the prior art and to provide a method for producing foamable metal bodies which allows foamable metal bodies to be produced inexpensively. This object is achieved by the method described in claim 1, the foamable metal body described in claim 14 and the use according to claims 1 5-17. The subclaims indicate advantageous further developments.

According to the invention, a mixture of a powdery or liquid metal and a powdery or liquid metal-containing blowing agent starting material is treated with a liquid or gaseous non-metal-containing blowing agent starting material. The non-metal-containing blowing agent raw material reacts in an addition reaction with the metal-containing blowing agent raw material, so that the blowing agent is formed. This mixture is compacted at the same time or later into a semifinished product in such a way that the particles of the metal are in a solid connection with one another and form a gas-tight seal for gas particles released from the blowing agent, a foamable metal body being formed.

Metal hydrides, metal salt hydrates and metal hydroxides are to be regarded as blowing agents in the sense of this invention. According to the invention, these blowing agents are obtainable in particular by oxidative additions of the non-metal-containing blowing agent starting material to the metal-containing blowing agent starting material or Lewis acid-base reactions (the non-metal-containing blowing agent starting material being the Lewis base), which are generally reversible, that is to say the equilibrium reactions are. The metal-containing blowing agent precursors (these are in particular metals in elemental form, alloys and metal salts, such as metal oxides) react with low molecular weight, in particular diatomic or tri-atomic, non-metal-containing blowing agent precursors (such as hydrogen or water) to give the blowing agents according to the invention.

The powdery or liquid metals to be foamed can be pure metals (e.g. aluminum or iron), metal alloys and / or other metal compounds that have a metallic character.

The process according to the invention has the advantage that no expensive blowing agent has to be used, since the blowing agent is formed from cheap starting materials during or shortly before the compacting. Reaction conditions are preferably selected in which the metal-containing blowing agent raw material does not react with the metal to be foamed, so that a reactivity of the non-metal-containing blowing agent raw material with the metal-containing blowing agent raw material is ensured. If, for example, the metal-containing propellant titanium is added to an aluminum melt, it forms

Titanium aluminides, which do not have sufficient storage capacity for hydrogen, the reactivity with the surrounding medium hydrogen is lost. If, on the other hand, aluminum powder is used, the formation of titanium aluminides does not take place since the aluminum powder particles are surrounded by an oxide layer. In general, intermetallic phases do not form if the metal powder particles are passivated by an oxide layer.

The metal-containing primary blowing agent is particularly preferably present in a melt; it is then so reactive that by gassing it with the non-metal propellant raw material, e.g. reacts with hydrogen to the blowing agent. Fumigation can be carried out by holding / storing the solidified, partially liquid or liquid melt in a hydrogen-containing or moist atmosphere, or by directly introducing gas, chips, damp wood, or the like into the melt.

The non-metal-containing blowing agent starting material is preferably a hydrogenating agent and thus the blowing agent formed with the metal-containing blowing agent starting material is a metal hydride. This hydrogenating agent is particularly preferably hydrogen gas or a mixture containing hydrogen gas, such as, for example, welding argon or forming gas. The hydrogen gas diffuses through the possibly pre-compressed mixture of the metal and the metal-containing blowing agent raw material and reacts there with the metal-containing blowing agent raw material to form metal hydrides. The use of hydrogen or hydrogen-containing mixtures or, more generally, the use of inexpensive, non-metal-containing blowing agent starting materials has the advantage that, in contrast to the previously known processes, the use of expensive blowing agents can be dispensed with. The process according to the invention is furthermore preferably carried out at temperatures of 300 ° -700 ° C., particularly preferably at 400 ° -600 ° C.

This has the advantage that the compacting to the foamable metal body is facilitated. The ease of compacting is a result of the high process temperatures. According to the invention, compaction temperatures are now permissible which are higher than in the previously known methods, since the blowing agent is only formed and therefore cannot decompose completely, especially in reactions under equilibrium conditions. At these higher process temperatures, sintering processes, improving ductility and rollability and / or reducing the forming resistance or other temperature-assisted processes make the process easier

Compacting achieved. At high process temperatures and long process times, sintering processes continue to occur, so that compacting into a foamable material occurs already during the formation of the blowing agent. This foamable material can then be foamed directly from the sintering heat. This has the advantage that intermediate cooling and reheating to the foaming temperature is not necessary and energy is saved. The atmosphere during foaming can consist of the non-metal-containing blowing agent raw material or a mixture with this non-metal-containing blowing agent raw material. Compacting is effected at high temperatures at which sintering occurs; decomposition of the blowing agent or a back reaction to metal-containing and non-metal-containing blowing agent precursors, however, does not take place or only partially. The temperature is therefore preferably chosen such that the decomposition of the blowing agent just formed does not take place completely, so that a sufficient residual amount of blowing agent is retained in the material.

Another advantage of the method according to the invention is that any pressing aids are removed by decomposition and / or evaporation at the high process temperatures. In general, the method according to the invention compared to the previously known The advantage of this method is that no high system engineering effort is required and there is no high tool wear. The method also has the advantage that foamable metal bodies of any size can be produced inexpensively for the first time, since the size used is no longer limited by the compacting method used.

In a variant of the method according to the invention, the mixture of the metal-containing blowing agent raw material and the metal powder is precompressed before the reaction with the non-metal-containing blowing agent raw material. In particular, cold isostatic pressing (CIP), hot isostatic pressing (HIP), axial pressing and powder rolling can be used as the pre-compression process. Except for pre-compaction using HIP, the pre-compacted material is not rollable, i.e. it has low ductility.

This variant has the advantage that the duration of the compaction to the foamable metal body can be shortened.

The pre-compressed mixture of the metal-containing primary blowing agent and the metal powder preferably has an open porosity.

This has the advantage that the non-metal-containing blowing agent primary material quickly penetrates the entire cross-section of the precompressed material and reacts there everywhere. If the porosity is open, any pressing aids can be removed more easily by decomposition or evaporation. The formation of the blowing agent from the metal-containing and the non-metal-containing

Propellant preform can also be made with closed porosity or non-porous pre-compressed material. Longer reaction times and higher reaction temperatures are then required. Press aids are not used.

In a further variant, sintering aids (for example magnesium powder) are added to the mixture of the metal and the metal-containing blowing agent starting material. The addition of Sintering aids have the advantage that mixtures with metal powders (such as aluminum powder), the powder particles of which are passivated by an oxide layer, can be sintered at lower temperatures. In the method according to the invention, the mixture of metal, blowing agent and blowing agent starting materials is thus compacted by sintering processes already during the reaction of the blowing agent starting materials to the blowing agent.

Furthermore, pressing aids (such as waxes and the like) can be added to the mixture of the metal and the metal-containing blowing agent starting material. In addition, rolling aids can be added to the mixture of the metal and the metal-containing blowing agent starting material, which promote the compaction and the rolling of the mixture of metal, blowing agent and blowing agent starting materials.

The compacting to the foamable semi-finished product is preferably carried out by means of a sintering process, a casting process or a forming process.

The sintering process can take place simultaneously with or subsequent to the reaction of the non-metal-containing and the metal-containing blowing agent starting material to the blowing agent. Sintering can reduce the porosity of the mixture of metal, blowing agent precursors and blowing agent to such an extent that foamability is achieved solely by sintering. Further compacting is then not necessary; compacting has already taken place by sintering and the material is already foamable.

A better ductility is achieved by the sintering and thus the compactability is facilitated by a further subsequent compacting process. The better ductility is achieved on the one hand by the volume shrinkage and the reduction of the porosity, on the other hand by sintering the powder particles, which creates a metallic bond. The mixture of metal and blowing agents can also in the invention Conditions are partially or completely melted, whereby it in turn densifies and can be further processed by casting, for example on casting machines.

Further compacting by means of a casting process can be achieved in particular by die casting, thixo casting or rheogasting. The use of a casting process is particularly advantageous when the sintering or the reaction of non-metal-containing and metal-containing primary blowing materials takes place at very high temperatures. The mixture of metal and blowing agent formed can also be additionally heated for further processing by means of a casting process. The resistance to deformation of the material is greatly reduced at high temperatures and further compacting is promoted. If the temperature is so high that liquid phases occur during the reaction or sintering, the material can be cast. The use of a casting process has the advantage that, in addition to further compacting, a further shaping is achieved, so that complexly shaped foamable components are available. The compacting according to the invention by means of a casting process advantageously takes place immediately from the heat of reaction of the reaction to the blowing agent or the sintering process. This has the advantage that additional energy savings occur.

Furthermore, the compacting can be carried out by a forming process. Rolling, pressing or forging is particularly suitable. Here too, the compacting advantageously takes place at the reaction temperature of the reaction / sintering process.

The foamable metal body that can be produced with the method according to the invention can be used for the production of sandwich materials. Here, the metal body is coated using a plating process. Any materials can be used as ceiling layer materials. The plating process is also arbitrary, for example it can be done by roll plating, drawing process, thermal spraying, explosive plating,

Coextrusion, extrusion plating, HIP plating and dipping are done. Plating with steel and / or aluminum materials is preferably carried out as the plating method then roll cladding is preferred. The cover layer materials can already be inserted into the corresponding molds in the pre-compression process (especially in cold isostatic processes), provided that no undesired reactions of the cover layer materials (for example with the non-metal-containing blowing agent starting materials) are to be expected during the reaction.

Another use of the foamable metal body produced by the process according to the invention is the foaming to porous metal bodies by heating to a temperature above the decomposition temperature of the blowing agent. This foaming of the foamable metal body preferably takes place immediately after the compacting, so that there is no interim cooling and energy is saved. To foam the material, the temperature is increased to such an extent that the decomposition of the blowing agent leads to foaming of the material. The temperature increase can take place in the reaction chamber, where the reaction of the two blowing materials containing the blowing agent or the sintering process took place, but the material can also be rearranged in another furnace, in which the foaming takes place. The furnace atmosphere during foaming can in particular consist of air, noble gases, hydrogen, cracked gas, ammonia gas, nitrogen, or any mixtures of these gases.

Examples

Without restricting generality, the method according to the invention is explained in more detail below using several examples:

Example 1 :

Commercially available aluminum powder with a particle size <160 μm is mixed with 7% by weight silicon powder, 1% by weight titanium powder (metal-containing blowing agent starting material) and 0.6% by weight magnesium powder (sintering aid) and by cold isostatic pressing (CIP) to form a cuboid rolling bar with a apparent (integral) density of 2.1 g / cm ³ compacted. The cold isostatically pre-compressed ingot is reacted at 500 ° C with pure hydrogen gas (non-metal-containing blowing agent precursor). In this reaction, the hydrogen diffuses to the metal-containing blowing agent starting materials (here the titanium powder particles) in the interior of the ingot, and reacts there, with hydrides, in particular titanium hydride, being formed. In addition to the formation of the blowing agent, sintering processes also take place under these conditions, so that the pre-compressed ingot can now be rolled. After the sintering process is complete, the ingot is cooled and removed from the reaction furnace. The billet is preheated to a temperature of 480 ° C for rolling. Rolling is carried out with 80% deformation, which compresses the ingot. After rolling, there is foamable material.

Example 2:

Commercial aluminum powder with a particle size <160 μm is mixed with 1% by weight of titanium powder (metal-containing blowing agent precursor) and 0.6% by weight of magnesium powder (sintering aid) and by cold isostatic pressing (CIP) to form a parallelepipedic ingot with an apparent (integral) density of 2.2 g / cm ³ compressed. The cold isostatically pre-compacted ingot is reacted with a hydrogen-containing atmosphere (welding argon or forming gas) at 550 ° C. In this reaction, the hydrogen diffuses to the blowing agent precursors (titanium powder particles) in the interior of the ingot and reacts there, whereby hydrides, in particular titanium hydride, are formed.

After the reaction is complete, the ingot is removed from the furnace and rolled without intermediate cooling. Rolling takes place with 80% deformation, which compresses the ingot. After rolling, there is foamable material.

Example 3: Commercial aluminum powder with a particle size <160 μm is mixed with 7% by weight of silicon powder, 1% by weight of titanium powder (metal-containing propellant starting material) and 0.6% by weight of magnesium powder (sintering aid) and by cold isostatic pressing (CIP) to form a cylindrical bolt with a apparent (integral) density of 2.2 g / cm ³ compressed. The cold isostatically pre-compressed stud is reacted at 670 ° C with a hydrogen-containing atmosphere (welding argon or forming gas). The reaction forms the titanium hydride and the powder particles of the bolt melt. The liquid bolt is placed in the casting barrel of a die casting machine and cast. The die casting process compresses the bolt material and simultaneously forms it into a component. The component can be foamed.

Claims

Foamable metal body, process for its production and its use

1 . Process for the production of foamable metal bodies, in which a mixture containing at least one metal and at least one gas-releasing blowing agent is compacted into a semi-finished product such that the particles of the at least one metal are in a solid connection with one another and a gas-tight seal for gas particles released to the blowing agent, characterized in that a mixture of the powdery or liquid at least one metal and a powdery or liquid metal-containing blowing agent raw material is treated with a liquid or gaseous non-metal-containing blowing agent raw material and thereby adds the non-metal-containing blowing agent raw material to the metal-containing blowing agent raw material, so that the at least one blowing agent is formed.

2. The method according to claim 1, characterized in that the non-metal-containing blowing agent raw material is a hydrogenating agent and the blowing agent formed is a metal hydride.

3. The method according to claim 2, characterized in that the hydrogenating agent is hydrogen gas or a hydrogen-containing gas mixture.

4. The method according to one or more of claims 1 to 3, characterized in that the reaction of the non-metal-containing blowing agent raw material with the metal-containing blowing agent raw material is carried out at 300-700 ° C, preferably at 400-600 ° C.

5. The method according to one or more of claims 1 to 4, characterized in that the mixture of the metal-containing blowing agent raw material and the at least one metal is pre-compressed before the reaction with the non-metal-containing blowing agent raw material.

6. The method according to claim 5, characterized in that the pre-compression is carried out by means of cold isostatic pressing, hot isostatic pressing, axial pressing or powder rolling.

7. The method according to claims 5 or 6, characterized in that the pre-compressed mixture of metal-containing propellant raw material and the at least one metal has an open porosity.

8. The method according to one or more of claims 1 to 7, characterized in that the compacting to the semi-finished product takes place by means of a sintering process, a casting process and / or a forming process.

9. The method according to claim 8, characterized in that the casting process is carried out by means of die casting, thixo casting or rheogasting.

10. The method of claims 8 or 9, characterized in that the forming process is carried out by means of rolling, pressing or forging.

1 1. The method according to one or more of claims 8 to 10, characterized in that a sintering aid is added to the mixture of the at least one metal and the metal-containing blowing agent precursor.

12. The method according to one or more of claims 1 to 1 1, characterized in that the metal-containing blowing agent precursor contains titanium, zirconium, tantalum and / or magnesium and / or an alloy with one of these elements and / or a metal salt of one of these elements.

13. The method according to one or more of claims 1 to 12, characterized in that the at least one metal is aluminum and / or iron.

14. Foamable metal body, obtainable by the method according to one or more of claims 1 to 13.

1 5. Use of the metal body produced in the process according to one or more of claims 1 to 13 for the production of sandwich materials by coating the metal body by means of a plating process.

16. Use of the metal body produced in the process according to one or more of claims 1 to 13 for producing a porous metal body by heating to a temperature above the decomposition temperature of the blowing agent.

17. Use according to claim 16, characterized in that the method for producing the porous metal body is carried out immediately after the compacting and that there is no interim cooling of the foamable metal body.