EP3661678A1

EP3661678A1 - Method for producing a semi-finished product for a composite material

Info

Publication number: EP3661678A1
Application number: EP18773125.2A
Authority: EP
Inventors: Wolfgang Seeliger
Original assignee: Pohltec Metalfoam GmbH
Current assignee: Pohltec Metalfoam GmbH
Priority date: 2017-09-15
Filing date: 2018-09-14
Publication date: 2020-06-10
Also published as: CN111491752A; WO2019053192A1; KR20200079242A; CA3077586A1; US20200298307A1; DE102017121511A1; KR102355057B1; US11612934B2; CN111491752B

Abstract

The invention relates to a method for producing a semi-finished product comprising a foamable core comprising a foamable mixture that contains at least one first metal having an aluminium content of at least approximately 80 wt. %, in relation to the quantity of the at least one first metal, and at least one foaming agent, according to which a layer of at least one second metal in the form of a non-foamable solid material and with an aluminium content of at least approximately 80 wt. %, in relation to the quantity of the at least one second metal, is respectively applied to at least one first and second surface of the core. The invention also relates to a corresponding semi-finished product and to the use of such a semi-finished product for foaming a metal.

Description

Process for producing a semifinished product for a composite material

The present invention relates to a process for producing a semifinished product comprising a foamable core comprising a foamable mixture comprising at least a first metal containing at least about 80% by weight of aluminum, based on the amount of the at least one first Metal, and at least one propellant, wherein on at least a first and second surface of the core, in each case a layer of at least one second metal in the form of non-foamable solid material and having an aluminum content of at least about 80 wt .-%, based on the amount of the at least one second metal. Furthermore, the invention relates to a corresponding semifinished product and the use of such a semifinished product for foaming metal.

Metal foam sandwiches have been known for years. Specifically, these are of interest when the composite is a single-agent system, i. when using a certain metal and its alloys, such as in particular of aluminum and its alloys, and the connection between the core and cover layer is produced by means of a metallurgical bond. Corresponding methods for producing such composite materials and components made therefrom are known from various publications.

DE 44 26 627 C2 describes a method in which one or more metal powders are mixed with one or more propellant powders, and the powder mixture thus obtained by axial hot pressing, hot isostatic pressing or rolling compacted and in a subsequent operation with previously surface-treated metal sheets by roll-plating is assembled into a composite material. After the forming of the resulting semi-finished product by, for example, pressing, deep drawing or bending, this is heated in a final step to a temperature which is in the solidus-liquidus region of the metal powder, but below the melting temperature of the outer layers. Since the propellant powder is selected such that in this temperature range at the same time Gas separation takes place, thereby forming pores within the viscous core layer, along with a corresponding increase in volume. The subsequent cooling of the composite stabilizes the foamed core layer.

In a modification of the process known from DE 44 26 627 C2, in which the powder compact is already closed-pored, EP 1 000 690 A2 describes the production of such a composite material on the basis of a powder compact which was first produced open-pored and which did not become active until later Walzplattieren with the outer layers is closed pores. The remaining process steps are identical. By the original open porosity is to prevent that lead during storage of the powder compact possible gas splits of the propellant to geometry changes of the compact and thus to problems in the subsequent production of the composite with the outer layers. Furthermore, it is intended to facilitate the opening of the oxide layers forming during the storage of the compact in the production of the composite by the open porosity.

From DE 41 24 591 C1 a process for producing foamed composite materials is known, wherein the powder mixture is filled into a metal hollow profile and then rolled together with this. The deformation of the resulting semi-finished product and the subsequent foaming carried out in the same manner as described in DE 44 26 627 C2.

EP 0 997 21 5 A2 discloses a process for the production of a metallic composite material comprising solid metallic cover layers and a closed-pore, metallic core, which combines the production of the core layer and the connection with the cover layers in one step by mixing the powder mixture is introduced into the nip between the two outer layers and thus compressed between them. Furthermore, it is proposed to supply the powder in a protective gas atmosphere, so as to prevent the formation of oxide layers, which could adversely affect the required connection between the outer layers and powder mixture. In a further, known from DE 197 53 658 AI process for producing such a composite material, the process steps of composite production between the core and cover layers on the one hand and the foaming on the other hand united by the fact that the core introduced in the form of a powder compact between the cover layers located in a mold is and connects only by the foaming process with these. Due to the compressive force applied by the core during foaming, the cover layers are at the same time subjected to a deformation corresponding to the shape enclosing them.

US 5,972,521 A discloses a method for producing a composite blank in which air and moisture are removed by evacuation from the powder. Subsequently, the evacuated air is replaced by a gas which is inert to the core material under elevated pressure, before the powder is compacted and connected to the cover layers.

From EP 1 423 222 a process for producing a composite of cover layers and metal powder is known in which the entire production process takes place under vacuum. Especially the compaction of the powder bed and the subsequent rolling should be done under vacuum.

All of these known from the prior art method except that of EP 1 423 222 has in common that is enclosed by the production of the foamed core layer of air or inert gas in the compaction between the metal powder particles and compacted depending on the Kompaktierungsgrad. The resulting gas pressures, which increase even further during the temperature increase during the foaming process, lead to the formation of pores during heating even before reaching the temperature corresponding to the solidus-liquidus region of the metal powder material. In contrast to those aimed at by this method, by the outgassing of the propellant in the Solidus liquidus area of the metal powder taking place, closed, spherical pores, these are open, crack-shaped interconnected and irregularly shaped pores. While, for example, US Pat. No. 5,564,064 A1 discloses a process which specifically aims for such open porosity by expansion of enclosed gases below the melting temperature of the powder material, such pore formation is not desirable in the processes described above, since only the aspired closed, spherical pores allow optimal load transfer over the intact as possible, surrounding the pores cell walls, and thus contribute significantly to the strength of the core foams and thus the composite material.

DE 102 15 086 A1 discloses a method for producing foamable metal bodies by compacting a semifinished product. The gas-releasing propellant is here formed from powdered or liquid metal-containing propellant pre-material such as titanium, which is treated with a liquid or gaseous non-metal propellant Vor- material such as a hydrogenating agent, in particular H ₂ gas, but the propellant prematerial already in mixture with the metal to be foamed, such as aluminum, is present in a compacted semi-finished product. Although a pre-compaction of the mixture by means of cold isostatic pressing, hot isostatic pressing, axial pressing or powder rolling is provided, however, the actual blowing agent is only then formed by hydrogenating the mixture of metal-containing blowing agent pre-material and the at least one metal.

BR 10 201 2 023361 A2 discloses uniaxial compacting and pressing in the manufacture of a semifinished product for a closed-cell metal foam, wherein the semifinished product is a metal which is selected from the group consisting of Al, Zn, Mg, Ti, Fe, Cu and Ni, and a blowing agent selected from the group consisting of TiH ₂ , CaCO ₃ , K ₂ CO ₃ , MgH ₂ , ZrH ₂ , CaH ₂ , SrH ₂ and HfH ₂ and others. From WO 2007/014559 Al a method for powder metallurgical production of metal foam is known in which a powdered metallic material is pressed without blowing agent to a dimensionally stable semi-finished product and then foamed in a pressure-tight chamber by reducing the ambient pressure.

DE 199 33 870 C1 discloses a method for producing a metal composite body using a foamable compact, wherein the compact or semifinished product is produced by compacting a mixture of at least one metal powder and at least one gas-releasing propellant powder, wherein a sandwich Structure can be achieved by the fact that the compact is provided with cover layers by cold or hot rolling or diffusion bonding.

US Pat. No. 6,391,250 uses a foamable semifinished product obtained by powder metallurgical production processes. The starting material for the production of aluminum foam moldings is, for example, a powder mixture of aluminum or an aluminum alloy, homogeneously mixed with a blowing agent, preferably titanium hydride, and optionally further powdery additives. The mixture is compacted, such as by pressing, extruding, rolling or the like, to produce piece goods, ie bars, plates, profiles or similar semi-finished products, wherein preferably a density of the semi-finished product of over about 95% of the theoretical density of the metal matrix is achieved ,

US 2004/0081571 A1 relates to a method of producing metal shavings comprising the steps of: (i) providing a mixture of a metal alloy powder with a foaming agent powder; (ii) precompacting the mixture of step (i); (iii) heating the precompressed mixture of step (ii) to a temperature below the decomposition temperature of the propellant and allowing the particles to bind permanently; (iv) hot compacting the mixture obtained in step (iii) to produce a densified metal matrix body embedding the blowing agent; and (v) Smaller of the compacted body in metal fragments and thereby obtaining foamable metal shavings.

EP 0 945 197 A1 discloses a process for the production of deformable composite sheets or strips in sandwich structure, at least partially comprising blocks made of a blowing agent-containing aluminum alloy. These blocks are pressed, ie they no longer contain any powder, whereby foreign gases are also compressed; they are extruded into formats with rectangular ingot cross-section, which are clamped together on their narrow sides to form large-sized composite sheets and hooked and then provided by plating with a uniform coating layer. The composite sheets or strips produced from the clad rolled billets are reshaped and then foamed under pressure and temperature. Disadvantages known from the prior art are semi-finished products which can not be foamed homogeneously, ie without defects; rather often bulges and bulges occur during foaming, which make it difficult or impossible to use the foamed products as composites in precisely manufactured components such as in motor vehicle or aircraft. This is often due to the fact that the semi-finished products themselves already have manufacturing defects and inhomogeneities such as trapped foreign gases or moisture or inhomogeneous distribution of the metal and propellant powder and / or the semifinished products contain unsuitable blowing agents which develop the propellant gas too early during the foaming process and thereby Defects, so too large cavities of different and largely uncontrollable size form, which are also often open-pored and thus lead to instabilities in the structure of the metal foam formed. Finally, the known manufacturing methods for semi-finished products are either not suitable for sandwich structures, ie semi-finished products with a foamable core and massive metallic cover layers located thereon, or comprise too many steps, so they are too expensive.

It is therefore an object of the present invention to provide an improved process which is suitable for a likewise improved foamable starting material, including semifinished product called, consisting of solid metallic cover layers and an interposed, foamable core material to produce. The semi-finished product should be suitable for the production of a composite material and ultimately components made therefrom consisting of solid metallic cover layers and a closed-pore metal foam core arranged therebetween.

It is intended to produce a virtually flawless foamable metal core with as few process steps as possible, which is suitable for the later production of a virtually flawless foamed metal core. The process should therefore manage with as few process steps as possible. The composite of cover layer and core resulting from this process can then be foamed to form a sandwich or composite material.

Surprisingly, it has been found that a metal container or container or container with at least two metal walls is particularly well suited for producing a corresponding semifinished product having a sandwich-like structure, ie with a foamable core (foamable) and solid, on at least two sides of the core. ie from non-foamable solid material produced metallic cover layers, is suitable. In this case, at least two side surfaces of the container, that is to say approximately the bottom and lid of the container, are replaced by the solid, i. formed from non-foamable solid material produced metallic cover layers.

Furthermore, it has surprisingly been found that, with regard to further processability for semifinished products, in particular those metals or metal alloys which have an aluminum content of at least about 80% by weight (percent by weight) are suitable for both the core and the cover layers or% by weight) of aluminum, based on the metal or metal alloy. Finally, it has surprisingly been found that the mixing of the components required for foaming a metal, that is to say in particular of the metal to be foamed and of the blowing agent, leads to the foaming agent. This mixture forms an important influencing factor for the quality, ie in particular homogeneity and stability of the metal foam subsequently formed therefrom. The better the mixing of the components of the foamable mixture, the better the quality of the metal foam obtained therefrom.

The object underlying the invention is therefore achieved in that a homogeneous mixture of metal powder and propellant powder used and filled in such a container or container. For this purpose, a mixture of metal powder and propellant powder (gas-releasing powder) is filled into a container whose bottom and lid form the later cover layers or cover layers of the composite.

The present invention therefore provides:

(A) a process for producing a semifinished product comprising a foamable core comprising a foamable mixture comprising at least a first metal containing at least about 80% by weight of aluminum, based on the amount of the at least one first metal, and at least one propellant, wherein on at least a first and second surface of the core, in each case a layer of at least one second metal in the form of non-foamable solid material and having an aluminum content of at least about 80 wt .-%, based on the amount of at least one second metal, comprising the steps

(I) providing a container comprising the aforesaid layer of the at least one second metal as defined above on the at least one first and second surface of the container,

(II) providing a powder comprising powder particles of the at least one first metal,

(III) providing a powder comprising powder particles of the at least one blowing agent, and

(IV) filling the container with the powders provided in steps (II) and (III) to form the foamable core, wherein mixing of the powders provided in steps (II) and (III) to the foamable mixture takes place;

a semi-finished product obtainable by a process as defined under (A);

a semifinished product comprising a foamable core comprising a foamable mixture, the foamable mixture comprising a powder comprising powder particles of at least a first metal as defined herein and a powder comprising powder particles of at least one blowing agent as defined herein, wherein at least a first and at least one second metal layer as defined herein is applied to the second surface of the core; and the use of a semifinished product as defined under (B) or (C) for foaming metal, in particular for producing a composite material comprising metal foam and metal in the form of non-foamable solid material; and

a container for carrying out the method according to the invention with a first and a second surface, which form a bottom and a lid, and side walls, wherein at least one side wall has a buckling inward in the direction of a foamable mixture.

The invention thus relates to a process for producing a semifinished product, which is suitable for the production of a metallic composite material primarily of aluminum and its alloys, consisting of solid metallic cover layers and a metallic core foamed in between, which together form a sandwich or metal foam sandwich , This composite is produced from the cover layers and an interposed mixture of at least one metal powder. This composite (semifinished product) can optionally be converted to produce a component and then thermally treated such that the gas separation of a blowing agent powder or a metal powder for foaming of the core and formation of a metallic composite material having a sandwich-like structure, ie in the form of a metal foam sandwich, leads. The step of reshaping can also be omitted. Furthermore, components can be produced from such a metallic composite material. Is the term "about" or "substantially" used in reference to values or ranges of values in the context of the invention, or are certain values resulting from the use of these terms in the context (for example, can the phrase "a widening of the container be essentially prevented" or similar as a volume change, ie in general an increase in volume or volume reduction, understood in the amount of 0%), this is to be understood as that which the expert will regard in the given context as expertly common. In particular, deviations of the specified values from +/- 1%, preferably from +/- 5%, more preferably from +/- 2%, particularly preferably from +/- 1%, of the terms "approximately" and "essentially" includes.

For the purposes of the present invention, a semifinished product comprises a foamable starting material which, after foaming, gives rise to a composite material which has a metal foam and solid metallic cover layers. The metal foam is provided here as a core or core material, ie metal foam core, between the solid metallic cover layers. The semifinished product is thus suitable for the production of a composite material and ultimately components made therefrom consisting of solid metallic cover layers and a metal foam core arranged therebetween, which is preferably closed-body. The semifinished product is for example plate-shaped, but it can also be formed from preferably such a plate shape. Composite material in the context of the present invention is a metallic material in which two structurally different materials, namely foamed metal (metal foam) and metal in the form of solid, non-foamable solid materials combined with each other and form and / or stoffschlüs- sig are connected. The (final) material metallurgical connection between metal foam and solid metal takes place at their adjoining connecting surfaces by melting the same when foaming the foamable mixture with heat. However, the majority of the metallurgical connection between the foamable mixture and the solid material is already present in the semi-finished product: For example, can be generated by forming the foamable mixture or the core and the cover layers oxide-free surfaces that cause the powder particles of the foamable mixture and the solid solid material of the cover layer (s) connect, ie there is a kind of welding instead. Such a connection can also take place by precompression or compaction upstream of the forming without forming, such as by axial pressing of a plate-shaped semifinished product.

To achieve a good mechanical strength, in particular good strength and / or torsional rigidity of the composite comprising a metal foam, the metal foam is closed-pored. The so-called closed, spherical pores allow optimal load transfer over the intact as possible, the cell walls surrounding the pores, and thus contribute significantly to the strength of the metal foam and thus also of the composite material comprising the metal foam.

A metal foam is closed-pore, if the individual gas volumes therein, in particular two adjacent gas volumes, by a separating solid phase (wall) are separated or at most by small production-related openings (cracks, holes) whose respective cross-section in relation to the cross section of each two gas volumes separating solid phase (wall) is small, are interconnected.

According to the invention, the semifinished product is preferably suitable for producing a composite material comprising a substantially closed-cell metal foam. The essentially closed-cell metal foam is distinguished by the fact that the individual gas volumes are interconnected at most by small production-related openings (cracks, holes) whose cross-section is small in relation to the cross-section of the solids phase separating the volumes.

An advantage of the unfoamed semi-finished product according to the invention is its storability over a longer period of time, which makes it possible to produce the end product, here a metal foam or composite material comprising such a metal foam, quickly and easily if required. For this purpose, the semifinished product itself has a foamable core, which nerseits forms a precursor or a starting material for the available after foaming metal foam core. The foamable core contains or comprises for this purpose a foamable mixture which comprises at least one first metal which comprises at least one blowing agent and optionally at least one adjuvant or consists exclusively of these components. The foamable mixture preferably consists exclusively of the at least one first metal and the at least one blowing agent.

The foamable core is produced by powder metallurgy, ie it contains or comprises a foamable mixture which is present at least at the beginning of the production process in the form of powder comprising powder particles. The finished semifinished product may also contain the foamable mixture in powder form, but preferably the foamable mixture is present in the finished semifinished product in a compacted, in particular precompressed form. The (pre-) compaction of the powder leads to its solidification and can extend all the way to a metallurgical connection of the powder particles with one another, ie the individual grains or particles of the powder (powder particles) become intact by means of diffusion and formation of (first) intermetallic phases the mixture partially or completely connected together, instead of forming a loose powder. This (first) metallurgical bonding has the advantage of a more stable and compact foamable core, which forms almost no defects in the foam during foaming. The first metallurgical bonding also produces a stable rolling bar, ie the ductility of the semi-finished product, in particular by rolling, bending, deep drawing and / or hydroforming, is improved. Furthermore, due to the first metallurgical bonding, the powder particles are partially connected to the cover layers. The powder consists of powder particles having a particle size of about 2 μηι to about 250 μηι, preferably from about 10 μηι to about 150 μηι may have. These particle sizes have the advantage that this forms a particularly homogeneous mixture, ie a particularly homogeneous foamable mixture, so that later defects otherwise occurring during foaming are avoided. The foamable (foamable) mixture comprises at least a first metal having an aluminum content of at least 80% by weight and at least one blowing agent. The foamable mixture preferably comprises precisely one first metal with an aluminum content of at least 80% by weight and exactly one blowing agent. The foamable mixture may further comprise adjuvants. Preferably, however, the foamable mixture advantageously comprises no excipient, since with one or more excipients usually the structure of the foamable mixture and the foamable core is disturbed such that the later obtained therefrom foamed (foamed) core defects such as inhomogeneities in the foam structure, too having large pores or bubbles and / or open pores instead of closed pores. Particularly preferably, the foamable mixture contains only exactly a first metal with an aluminum content of at least 80 wt .-%, exactly one blowing agent, optionally one or more derivatives of the blowing agent and no further substances or auxiliaries. One or more derivatives of the blowing agent come in particular in question when the blowing agent is selected from the group of metal hydrides; In this case, the blowing agent as derivative (s) additionally comprise at least one oxide and / or oxihydride of the metal or metals of the metal hydride (s) used in each case. Such oxides and / or oxihydrides are formed in a pretreatment of the blowing agent and can its durability as well as its response to the foaming, ie the timing of the release of the propellant gas improve, so that the blowing agent used or the propellant not too early, but not release too late; too early or too late release of the propellant gas can produce oversized cavities and thus defects in the metal foam. By the term "first metal" and "second metal" herein is meant both a pure metal, so aluminum, as well as a metal alloy, ie an alloy of aluminum, wherein the first metal and the second metal are not identical, ie, both metals at least in an alloying constituent, the mass fraction or the weight fraction of at least one alloying constituent and / or in the nature (Powder versus massive solid material), so that the solidus temperature of the at least one second metal is higher than the liquidus temperature of the at least one first metal. In particular, however, the solidus temperature of the at least one second metal is higher than the liquidus temperature of the foamable mixture.

Due to the nature of the at least one second metal as solid, non-foamable solid material compared to the at least one first metal as in particular pre-compressed powder, this usually has a different melting behavior than that, i. The same metal or metal alloy as solid material begins to melt later in time at the same temperature due to a higher enthalpy of fusion than in the form of powder. However, solid material can also only start to melt at a somewhat higher temperature than if it is present as a particularly (pre-) compacted powder, especially if the latter is also mixed with a blowing agent, because this lowers the melting point of the mixture of metal powder and blowing agent. So the foamable mixture altogether.

It is advantageous for the composite material that the solidus temperature of the at least one second metal is higher than the liquidus temperature of the at least one first metal, in particular higher than the liquidus temperature of the foamable mixture. It is also advantageous if the at least one second metal begins to melt in time so much later (ie, sufficiently late) than the at least one first metal, so that the at least one second metal made in solid, non-foamable form at least one layer (Top layer, top layer), preferably exactly two layers or metallic cover layers, does not melt during the foaming of the foamable mixture or does not begin to melt. It has been found that otherwise, during the melting of the at least one layer during the foaming process, the latter is unintentionally deformed, in particular under the pressure of the gas released from the blowing agent. If the at least one second metal begins to melt on foaming of the at least one first metal, then it mixes with the at least one first metal beyond the boundary layers and decomposes. disturbs the foam or does not allow its formation or even foamed itself, so that the foaming process is completely uncontrollable.

The difference required between the solidus temperature of the at least one second metal and the liquidus temperature of the at least one first metal depends on the one hand on the (chemical) nature of the metals or metal alloys selected for the at least one first metal and the at least one second metal, on the other hand conditioned by their melting behavior. Advantageously, the at least one second metal has a solidus temperature which is at least about 5 ° C. higher than the liquor temperature of the foamable mixture. This higher solidus temperature and / or the temporally sufficiently early onset of melting of the at least one second metal can be realized according to the invention

with the shape or nature of the at least one second metal (as a solid solid material compared to a powder form of the at least one first metal), that is, a shape or texture that has a higher solidus temperature and / or higher

Entails melting enthalpy (since metal in powder form melts earlier and has a lower solidus temperature than solid metal in the form of solid material); and / or in that the at least one second metal has less alloying constituents than the at least one first metal and / or has at least one identical lower mass fraction of alloy in the alloy compared to the at least one first metal (ie the mass fraction of the alloy) in the at least one first and at least one second metal identical alloy component is in the at least one second metal lower or smaller than in at least one first metal).

Since the same metal aluminum with an aluminum content of at least about 80% by weight is used for both the core and the at least one layer (covering layer, cover layer) as main component, the different melting, solidus and / or liquidus temperatures are adjusted by different alloying additives in powder and solid material accordingly.

Preferably, the solidus temperature of the at least one second metal is at least about 5 ° C higher than the liquidus temperature of the at least one first metal. Depending on the metal or metal alloy, the solidus temperature of the at least one second metal is more preferably at least about 6 ° C, more preferably at least about 7 ° C, even more preferably at least about 8 ° C, even more preferably at least about 9 ° C, more preferably at least about 10 ° C, even more preferably at least about 1 1 ° C, even more preferably at least about 1 2 ° C, even more preferably at least about 1 3 ° C, more preferably about at least about 14 ° C, even more preferably at least about 15 ° C, even more preferably at least about 1 6 ° C, even more preferably at least about 1 7 ° C, even more preferably at least about 18 ° C, still further preferably at least about 1.9 ° C and even more preferably at least about 20 ° C higher than the liquidus temperature of the at least one first metal. In any case, with the difference between the solidus temperature of the at least one second metal and the liquidus temperature of the at least one first metal, it must be ensured that during the foaming process, which can be carried out later with the semifinished product, the cover layers applied to the core consist of the at least one second Do not soften or melt so much metal melt or melt, so that by the propellant gas formation and / or expansion unwanted bulges, bumps, cracks, holes and similar defects in the outer layers arise and / or the outer layers with the (foamed) core partially or completely merge or mix. Typically, the solidus temperature of the at least one second metal should be at least about 5 ° C higher, preferably about 10 ° C higher and most preferably about 1 5 ° C higher than the liquidus temperature of the at least one first metal; In special cases, the solidus temperature of the at least one second metal is at least about 20 ° C higher than the liquidus temperature of the at least one first metal. In particular, it has surprisingly been found that a solidus temperature of the at least one second metal, which is about 1 5 ° C higher than the liquidus temperature of the at least one first metal usually a good compromise between the strength of the metal foam structure and the cover layers on the one hand and the quality of the composite structure, so clear phase boundary between metal foam and cover layers and no fusion of metal foam and cover layers on the other hand, provides. Most preferably, the solidus temperature of the at least one second metal is higher than the liquidus temperature of the foamable mixture by the temperature stated above. A typical melting range of the at least one first metal is, for example, from 565 ° C to about 590 ° C and the at least one second metal from about 605 ° C to about 660 ° C.

In a preferred embodiment, the at least one first and second metal are not identical. For this purpose, the at least one second metal has less alloy components than the at least one first metal; the at least one second metal, alternatively or additionally to the at least one first metal, comprises at least one identical lower mass fraction alloying component in the alloy; As a result, the higher solidus temperature of the at least one second metal specified here relative to the liquidus temperature of the at least one first metal can be achieved. The higher solidus temperature of the at least one second metal set forth herein relative to the liquidus temperature of the at least one first metal has the advantage of providing a composite of at least one foamed first metal and at least one second metal in bulk form, i. can be produced in the form of a non-foamable solid material, because thereby the at least one second metal does not start to melt during foaming of the at least one first metal or the foamable mixture.

This goal can also be achieved by the nature of the at least one second metal as (solid, non-foamable) solid material against the at least one first metal as a particular (pre-) compacted powder. The same metal or the same Metal alloy begins as a solid material to melt at a slightly higher temperature zen than when it is present as a particular (pre-) compacted powder, especially if the latter there is also mixed with a blowing agent because this lowers the melting point of the mixture of metal powder and blowing agent , so the foamable mixture in total. If the at least one second metal would start to melt during foaming of the at least one first metal, it would mix with the at least one first metal and destroy the foam or not even enable it or even foaming it, so that the foaming process becomes completely uncontrollable would become.

According to the invention, the semi-finished product preferably contains exactly one second metal, i. Preferably, in each case a layer of exactly one second metal in the form of non-foamable solid material and with an aluminum content of at least 80 wt .-% is applied to at least a first and second surface of the core. Solid material is understood to mean solid metal which is not foamed and is not in powder form. The metal can also be a metal alloy. The solid material according to this invention is not foamable (foamable), in contrast to the inventive foamable mixture. The at least one first metal is in particular selected from the group consisting of

Aluminum,

higher-strength aluminum alloys selected from the group consisting of aluminum-magnesium-silicon alloys (6000 series) and aluminum-zinc alloys (7000 series), of which aluminum-zinc alloys (series 7000)

AIZn _{4; 5} Mg (Alloy 7020) is preferred, and

higher-strength aluminum alloys having a melting point of about 500 ° C to about 580 ° C, preferably higher-strength aluminum alloys having a melting point of about 500 ° C to about 580 ° C, comprising aluminum, magnesium and silicon. more preferably AISi6Cu7.5, AIMg6Si6 and AIMg4 (± 1) Si8 (± 1), even more preferably Al Mg6Si6 and AIMg4 (± 1) Si8 (± 1), more preferably AIMg4 (± 1) Si8 (± 1) ,

The at least one first metal is preferably selected from the group consisting of - higher-strength aluminum alloys selected from the group consisting of aluminum-magnesium-silicon alloys (series 6000) and aluminum-zinc alloys (series 7000), wherein among the aluminum-zinc alloys (series 7000)

AIZn _{4; 5} Mg (Alloy 7020) is preferred, and

higher-strength aluminum alloys having a melting point of about 500 ° C to about 580 ° C, preferably higher-strength aluminum alloys having a melting point of about 500 ° C to about 580 ° C comprising aluminum, magnesium and silicon, more preferably AISi6Cu7.5, AIMg6Si6 and AIMg4 (± 1) Si8 (± 1), even more preferably AIMg6Si6 and AIMg4 (± 1) Si8 (± 1), more preferably AIMg4 (± 1) Si8 (± 1). The at least one first metal may be aluminum or pure aluminum (at least

99% by weight of aluminum), with aluminum being preferred in which the content of aluminum is from about 80% to about 90% by weight, more preferably about 83% by weight, based on the at least one first Metal, amounts. In addition, the at least one first metal may be a higher-strength aluminum alloy. The higher strength aluminum alloy may be selected from the group consisting of aluminum-magnesium-silicon alloys (6000 series) and aluminum-zinc alloys (7000 series), of which AlZn4.5Mg (7020 alloy) is preferred among the aluminum-zinc alloys (series 7000). The at least one first metal can therefore be in particular AIZn4.5Mg (alloy 7020). The at least one first metal may be a higher strength aluminum alloy having a melting point of from about 500 ° C to about 580 ° C; preferred higher strength aluminum alloys are AISi6Cu7.5, AIMg6Si6 and AIMg4 (± 1) Si8 (± 1). The at least one first metal may also be a higher strength aluminum alloy having a melting point of about 500 ° C to about 580 ° C comprising aluminum, magnesium and silicon or composed solely of these chemical elements. Preferred higher strength aluminum alloy Those having a melting point of about 500 ° C to about 580 ° C, which include aluminum, magnesium and silicon, are AIMg6Si6 and AIMg4 (± 1) Si8 (± 1), of which

AIMg4 (± 1) Si8 (± 1) is particularly preferred. The indication (± 1) in the alloying formulas used herein means that the respective chemical element concerned may also have a mass percentage more or less than stated. In general, however, a correlation between two elements provided with such information in a formula, i. E. For example, if there is one more weight percent of the first element in the formula provided with (± 1), then one percent less by mass of the second element in the formula, which is also (± 1). The formula AIMg4 (± 1) Si8 (± 1) thus includes, among others, the formulas AIMg5Si7 and AIMg3Si9.

The at least one second metal is in particular selected from the group consisting of

Aluminum and

higher strength aluminum alloys selected from the group consisting of aluminum-magnesium alloys (5000 series), aluminum-magnesium-silicon alloys (6000 series) and aluminum-zinc alloys (7000 series).

The at least one second metal may be aluminum or pure aluminum (at least 99 weight percent aluminum), with aluminum being preferred in which the aluminum content is from about 85 weight percent to about 99 weight percent, more preferably about 98 Wt .-%, based on the at least one second metal is. In addition, the at least one second metal may be a higher strength aluminum alloy. The higher strength aluminum alloy may be selected from the group consisting of aluminum-magnesium alloys (5000 series), aluminum-magnesium silicon alloys (6000 series) and aluminum-zinc alloys (7000 series). The at least one second metal may in particular be an aluminum-magnesium alloy (series 5000). The at least one second metal can in particular an aluminum-magnesium-silicon alloy (series 6000), preferably Al 6082 (Al Si 1 MgMn). Finally, the at least one second metal may in particular be an aluminum-zinc alloy (series 7000). The terms "series" and "alloy" followed by a four digit number are terms commonly known to those skilled in the art for certain classes or series of aluminum alloys or a particular aluminum alloy, as noted herein.

The inventive at least one propellant releases from a certain temperature, the Ausgastemperatur of the blowing agent, by means of degassing or gas separation, a propellant, which serves to foam the at least one first metal. When using a metal hydride as blowing agent hydrogen is released as a propellant gas.

With regard to the choice of the blowing agent, it has surprisingly been found that the outgassing temperature of the at least one blowing agent should advantageously be equal to or lower than the solidus temperature of the at least one first metal in order later to achieve a closed-cell foam free of defects and an optimum result during foaming of the core , The outgassing temperature of the propellant should preferably be no more than about 90 ° C, more preferably no more than about 50 ° C below the solidus temperature of the at least one first metal. In any case, the outgassing temperature of the at least one propellant is less than the solidus temperature of the at least one second metal, since the second metal must not enter its solidus area during foaming, and therefore must not start to melt, as already explained herein. Surprisingly, it has been found that metal hydrides, in particular the metal hydrides mentioned herein, are particularly suitable as foaming agents for foaming metal containing at least about 80% by weight (% by weight) of aluminum, in particular of the metal alloys of the at least one first metal mentioned herein, are suitable because there are no defects in the foamed metal. Therefore, a corresponding semi-finished product has with one or more metal hydrides as blowing agent as particularly suitable for foaming the at least one first metal and for producing a corresponding, containing a metal foam composite material exposed. The blowing agent according to the invention thus preferably comprises at least one metal hydride, preferably at least one metal hydride, which is selected from the group consisting of TiH 2, ZrH 2, HfH 2, MgH 2, CaH 2, SrH 2, UBH 4 and UAIH 4. The at least one metal hydride is further preferably selected from the group consisting of TiH2, ZrH2, HfH2, LiBH4 and UAIH4, more preferably selected from the group consisting of TiH2, LiBH4 and

UAIH4, more preferably it is TiH2. For certain applications, in particular a combination of two propellants, wherein each of the two groups

(a) TiH ₂ , ZrH ₂ and HfH ₂ ; and

(b) MgH ₂ , CaH ₂ , SrH ₂ , LiBH ₄ and LiAlH ₄

each one blowing agent is selected; preferred of these is the combination of TiH ₂ with a propellant selected from the group consisting of MgH ₂ , CaH ₂ , SrH ₂ , LiBH ₄ and LiAlH ₄ ; particularly preferred is the combination of TiH ₂ with LiBH ₄ or LiAlH ₄ . According to the invention, exactly one blowing agent is preferably used, more preferably exactly one metal hydride as blowing agent, more preferably TiH ₂ , ZrH ₂ , HfH ₂ , LiBH ₄ or LiAlH ₄ , even more preferably TiH ₂ , LiBH ₄ or L1Al H ₄ , particularly preferably TiH ₂ . According to the invention, the blowing agent may additionally comprise at least one oxide and / or oxihydride of the metal or metals of one or more of the propellants used in each case, which arise in the pretreatment of the blowing agent and its durability as well as its response during foaming, ie the timing of release of the propellant gas improve. The improvement of the foaming response with respect to the timing of the release of the propellant gas is mainly a shift in the release of the propellant gas or the outgassing in the late direction to a too-fast outgassing and thus the formation of defects such as bubbles and holes instead ( closed) pores to avoid; This is achieved on the one hand by the oxides and / or oxihydrides mentioned, on the other hand achieved in that the at least one blowing agent, especially in the case of Use of one or more metal hydrides, in the matrix of the semifinished product, in particular in the matrix of the foamable core, after the first and optionally second metallic bonding is under high pressure. As a method of pretreating the blowing agent, the heat treatment in an oven at a temperature of 500 ° C over a period of about 5 hours is suitable. The oxide is particularly an oxide of the formula Ti _v O _w, where v is from about 1 to about 2, and w of about 1 to about. 2 The oxihydride is especially an oxihydride of the formula TiH _x O _y , where x is from about 1.82 to about 1.99 and y is from about 0.1 to about 0.3. The oxide and / or oxihydride of the blowing agent may form a layer on the grains of the powder of the blowing agent; the thickness of this layer may be from about 10 nm to about 100 nm.

The amount of the blowing agent or the total amount of all blowing agents using at least two different blowing agents can be from about 0.1% by weight (wt .-%) to about 1, 9 wt .-%, preferably from about 0.3 wt. % to about 1, 9 wt .-%, each based on the total amount of the foamable mixture comprising at least the at least one first metal and at least one blowing agent, amount. The amount of the oxide and / or oxihydride may be from about 0.01% to about 30% by weight, based on the total amount of the at least one blowing agent. The outgassing temperature of the at least one propellant is in a range of about 100 ° C to about 540 ° C, preferably in a range of about 400 ° C to about 540 ° C, more preferably in a range of about 460 ° C to about 540 ° C. For the metal hydrides according to the invention, in particular as propellants, the outgassing temperature is in each case as follows (specification of the outgassing temperature in parentheses): TiH ₂ (about 480 ° C.), ZrH ₂ (about 640 ° C. to about 750 ° C.), HfH ₂ (approx 500 ° C to about 750 ° C), MgH ₂ (approx

415 ° C), CaH ₂ (about 475 ° C), SrH ₂ (about 510 ° C), LiBH ₄ (about 100 ° C) and LiAlH ₄ (about 250 ° C). The "core" is a middle layer or core layer, which as such is located between two other layers, here the cover layers. The core layer and the two outer layers together form a sandwich structure or a sandwich. The foamable core of the semifinished product comprises the at least one first metal which comprises at least one propellant and optionally at least one auxiliary. The (later) foamed core of the composite material comprises the at least one first metal predominantly in the form of metal foam and at least one decomposition product of the at least one propellant which arises after the outgassing or release of the propellant gas during the foaming process, and optionally at least one auxiliary or its decomposition - product as a result of the foaming process.

"Area of the core" is understood to mean an area on the outer surface of the foamable or foamed core, ie on the surface formed by the foamable mixture or, later, the foamed core. This includes, in particular, the surfaces on which the cover layers are located and lateral surfaces or walls which are likewise covered with a layer, preferably a metal layer, particularly preferably a layer of the at least one second metal.

The two other layers or cover layers comprise at least one second metal, preferably exactly one second metal. Particularly preferably, the cover layers consist only or precisely of a second metal and no further metals. The second metals or the second metal of the cover layers are in the form of solid, non-foamable solid material which is not foamed later during foaming of the foamable core or the foamable core layer and therefore does not assume a porous structure in contrast to the core.

In order to simplify the production process for the semifinished product and thus ultimately also the composite material that can be produced from the semifinished product, the first and second surfaces delimiting the core and having the cover layers are replaced by a container, that is to say the container. set container formed, which for this purpose has two surfaces, which are preferably plane-parallel, and between the surfaces has a space for receiving the foamable mixture to form the core layer. In addition, the container further, outer or side surfaces in the form of side walls, which limit the gap on the other sides, so as to prevent trickling of the foamable mixture. These lateral surfaces can be advantageously formed, for ease of manufacture, of a layer of the same material as the cover layers. The container has at least one opening in the unfilled state, preferably in at least one of the two side walls. Preferably, at least two openings, preferably in the side walls, are provided. These can be connected to pipes that can be closed to open or close the container. Particularly preferably, the side walls in the direction of the interior of the container according to the invention, ie the foamable mixture, approximately in the center and parallel (that is, in the case of an arcuate buckling approximately in the region of a minimum) to a longitudinal edge of the cover layers, a buckling, which may also be arcuate. This buckling allows for a pre-compression, in particular by rolling, to achieve a second metallurgical connection, as described below, that the container does not open. The buckling, that is to say the inner angle between the two partial surfaces of the side wall, if not arc-shaped, preferably has an angle in a range between approximately 110 ° and approximately 117 °, preferably in a range from approximately 160 ° to approximately one 76 °. In an inwardly directed arcuate configuration of the side walls, this arc has a radius in a range of about 200mm to about 600mm. The side walls are preferably multi-layered, preferably at least three-layered. This further facilitates a precompression in particular according to step (VII) as described below. The present invention also relates to a container having two cover layers and at least two opposite side walls, which, as described above with a single buckling are formed. Preferably, all side walls on a buckling, as described above, on.

The lateral surfaces contain at least one opening, preferably two openings for filling the at least one first metal, the at least one first propellant, optionally the at least one adjuvant and / or the foamable mixture. This at least one opening is closed after filling of the container in step (IV) for the further manufacturing process of the semifinished product, so that the filled foamable mixture can not escape. Closing the opening of the container may be by a method selected from the group consisting of inserting a plug, attaching a closable flange, welding, attaching a metal tube, and then fully compressing the tube at one, two or more locations of the tube, in particular complete compression in the form of one, two or more notches or press seams, wherein in the case of two or more notches or press seams these are spaced apart, pressing or rolling of the entire filled container and similar methods and combinations thereof.

At least the first and second surfaces of the container are each formed by a layer or wall as cover layer or cover layer (for the foamable core and later foamed core) of the at least one second metal. To simplify the production, however, the remaining, lateral surfaces of the container can advantageously also be formed by walls of the same at least one second metal. Thus, preferably all outer surfaces of the container are made of walls made of the at least one second metal. Particularly preferably, the entire container consists of the at least one second metal, wherein welds may consist of a second metal or a metal similar to the second metal. The surfaces and / or side walls of the container can be arranged at any angle to each other, as long as the first and second surfaces are plane-parallel or substantially plane-parallel to each other. The container can to the shape of a box, a cylinder, in particular one flat cylinder having a height which is smaller than the diameter of the cylinder, a prism or a polygonal body.

In the case of a box, the first and second surfaces of the container are formed by the respective rectangular or square boundary surface at the top and bottom of the box. In the case of a cylinder, the first and second surfaces of the container are formed by the respective circular or elliptical boundary surface at the two ends of the cylinder. In the case of a prism, the first and second surfaces of the container are formed by the respective triangular boundary surface at the two ends of the cylinder. In the case of a polygonal body, the first and second surfaces of the container are formed by the respective polygonal boundary surface at the two ends of the polygonal body. Accordingly, the cover layer applied to the respective first and second surfaces respectively has the shape (ground plan) of the respective first and second surfaces, that is to say a rectangular, square, circular, elliptical, triangular or polygonal shape, but a substantially square one is preferred or rectangular shape. The container therefore preferably has a box shape, particularly preferably the shape of a flat box, in which the height, ie the distance between the surfaces of the first and second surface is less than the width and depth, ie the distances between the surfaces of the lateral Areas of the box, wherein the flat box in particular may have the shape of a plate.

Preferably, the at least one first surface of the container is arranged opposite to the at least one second surface of the container. The at least one first surface of the container preferably extends substantially plane-parallel to the at least one second surface of the container. Preferably, the foamable core is formed as a layer between the at least one first and second surface of the container.

The walls of the container, which form the first and second surfaces of the container and thus the cover layers, normally have a thickness or thickness of about 20 mm to some extent. wa 200 mm, preferably from about 50 mm to about 100 mm. The walls of the container forming the remaining lateral surfaces or side walls of the container normally have a thickness of from about 5 mm to about 50 mm, preferably from about 10 mm to about 30 mm.

The at least one first metal is provided in the form of a powder. The powder naturally comprises powder particles, ie metal particles which are ground so finely that the most homogeneous possible structure of the core is achieved without defects, so that even later during foaming no defects occur, so as to obtain the desired closed-cell metal foam. The powder particles of at least one first metal therefore advantageously have a grain size or grain size, ie particle diameter of about 2 μηι to about 250 μηι, preferably from about 2 μηι to about 200 μηι, more preferably from about 10 μηι to about 150 μηι on. The at least one propellant is also provided in the form of a powder. The powder naturally comprises powder particles, ie particles of the propellant, which are ground so finely that the most homogeneous possible structure of the core is achieved without defects and as complete as possible mixing with the powder of at least one first metal, so that later as possible during foaming can be completely foamed and foams also no defects arise, so as to obtain the desired closed-cell metal foam. The powder particles of the at least one propellant therefore advantageously have a grain size or grain size or from about 5 μηι to about 20 μηι. In order to achieve the said as homogeneous as possible structure of the core without defects, it is advantageous furthermore to mix the powder of the at least one first metal with the powder of the at least one blowing agent to form the foamable mixture. The mixing or mixing of the at least one first metal and at least one propellant preferably takes place before the container is filled, ie before the step (IV), or during the filling of the container, ie during step (IV), in each case with the at least one first metal and the at least one propellant. In the former case, the foamable mixture is prepared by mixing a powder of each of the at least one first metal and the at least one propellant before filling the container, in the latter case, the foamable mixture forms during the filling process by the powder of at least one first Metal and the at least one propellant together and in the correct mixing ratio in the container to be given. Mixing during filling of the container, ie during step (IV) has the advantage that a separate process step for mixing is saved and thus the process altogether manages with even fewer steps and thus is more economical to carry out.

The method according to the invention may additionally comprise a step

(V) drying

(V.1) the powder of the at least one first metal before step (IV) and / or the powder of the at least one blowing agent before step (IV), or

(V.2) of the foamable mixture before step (IV), or

(V.3) the foamable mixture and the container after step (IV)

include. In step (V.1), the drying of the powder of the at least one first metal can alternatively or additionally take place before step (II). In step (V.1), the drying of the powder of the at least one propellant may alternatively or additionally occur prior to step (III). The drying is carried out by methods known to those skilled in the art, such as heating, in particular to a temperature of about 100 ° C to about 450 ° C, preferably at a temperature in a range of about 200 ° C to about 370 ° C, more preferably to about 300 ° C, with suction of the moisture, by desiccant or combinations thereof. Heating or aspirating the moisture is preferred. Heating under suction of the moisture is particularly preferred. The drying has the advantage that when steaming no vapor bubbles from water vapor and corresponding defects can form.

Furthermore, the method according to the invention may additionally comprise a step (VI) first metallurgically combining the powder particles of the foamable mixture with each other and / or with the respective one layer of the second metal on the first and second surfaces of the core to form the foamable core after step (IV) or (V)

include.

The term "first metallurgical bonding" is understood according to the invention as follows: bonding of the powder mixture and the cover layers by means of diffusion and formation of first intermetallic phases within the mixture. The first metallurgical bonding has the advantage of a more stable and compact foamable core, which forms almost no defects in the foam during foaming. The first metallurgical bonding produces a stable ingot. Furthermore, the powder particles are partially connected to the cover layers. In particular, the first metallurgical bonding in step (VI) may be accomplished by precompressing the foamable mixture together with the container (container) using pressure in a range of about 0.05 MPa to about 1.5 MPa, preferably in a range of about zero , 1 MPa to about 1.1 MPa, and more preferably in a range of 0.15 MPa to about 0.45 MPa, and at a temperature of the foamable mixture and the container of about 400 ° C to about 490 ° C or from about 65% to about 90%, preferably from about 70% to about 85%, especially about 80%, of the solidus temperature of the foamable mixture or of the at least one first metal. The duration (holding period) may be from about 4 hours to about 48 hours, preferably from about 6 hours to about 32 hours, preferably to about 24 hours. In particular, the semifinished product can be heated to about 80% of the melting temperature of the foamable mixture and kept at this temperature for about 6 hours to about 32 hours, preferably up to about 24 hours. Preferably, the application of pressure is vertical to the first and second surface of the container, that is, vertical to the cover layers, wherein the first and second surface or the cover layers are arranged substantially plane-parallel to each other. The application of Pressure can be effected by means of two plane-parallel tools, for example a table with a horizontal plate movable thereon, in a pressing process. With regard to the temperature during precompression, a temperature of the foamable mixture and of the container of from about 65% to about 90%, preferably from about 70% to about 85%, in particular about 80%, of the solidus temperature of the foamable mixture is preferred.

The pre-compression of the container (container) can be done by means of two plane-parallel tools in a pressing process. Here, the precompression of the powder is carried out at a pressure in a range of about 0.05 MPa to about 1, 5 MPa, preferably in a range of about 0.1 MPa to about 1, 1 MPa, and more preferably in a range of 0, 1 5 MPa to about 0.45 MPa, and at a temperature in a range of about 400 ° C to about 490 ° C, preferably to about 470 ° C, more preferably to about 460 ° C, or about 65% to about 90% Preferably, about 70% to about 85%, in particular about 80%, of the solidus temperature of the foamable mixture or of the at least one first metal. Pre-compression of the powder preferably takes place at about 65% to about 90%, preferably about 70% to about 85%, in particular about 80%, of the solidus temperature of the foamable mixture or of the at least one first metal. The pressing process may in particular take place when the container is in an air atmosphere at ambient air pressure. This saves the effort for a protective gas atmosphere or the application of vacuum and / or work under vacuum. By pre-compression, which is preferably carried out by axial pressing, a stable ingot is produced. Furthermore, the powder particles are partially connected to the cover layers of the container. Alternatively, and preferred for the purposes of the present invention, the first metallurgical bonding in step (VI) may in particular be effected by heating the foamable mixture and the container to about 70% to about 90%, preferably about 75% to about 85%, preferably about 80%, the solidus temperature of the foamable mixture, wherein a widening of the container is largely prevented. The temperature is preferably in a range of about 450 ° C to about 495 ° C, even more preferably in a range of about 455 ° C to about 465 ° C. The duration (holding period) is about 4 hours to about 48 hours, preferably about 6 hours to about 32 hours, more preferably about 24 hours, even more preferably about 24 hours to about 32 hours. In particular, the container may be heated to about 80% of the melting temperature of the foamable mixture and maintained at that temperature for about 6 hours to about 24 hours. This can be done especially at ambient air pressure. This saves the effort for a protective gas atmosphere or the application of vacuum and / or work under vacuum. The expansion of the container in this alternative embodiment can be achieved by devices known to the person skilled in the art, for example by screw clamps, clamps, weights and / or a corresponding dimensionally stable and rigid support frame, which in each case or in combination force the container to remain in its original form, be effectively prevented. The holding frame may also be a kind of shape, similar to a casting mold. Furthermore, the expansion of the container by axial pressing, in particular by one or more presses, preferably perpendicular to the cover layers, which are fed before step (VI) of two or more sides of the container or along one or more axes of the container, without thereby compressing the container, be prevented. The applied pressure is preferably in a range of about 0.15 MPa to about 0.6 MPa, more preferably in a range of about 0.2 MPa to about 0.4 MPa. The (premature) outgassing of the blowing agent in step (VI) is prevented by the precompression of the foamable mixture, either by the application of externally generated pressure or by the pressure created by preventing the expansion of the container in its interior.

The method according to the invention may additionally comprise a step

(VII) second metallurgical bonding of the foamable obtained in step (VI)

Kernes with the layers of the at least one second metal on the first and second surfaces of the container

include. The term "second metallurgical bonding" is understood according to the invention to produce oxide-free surfaces by forming the core and the Cover layers, which causes the powder particles and the cover layers to connect, ie there is a kind of welding instead. The second metallurgical bonding allows a simple method of bonding, since, for example, no individual welds must be attached, and since it also provides a more stable connection than can be achieved by adhesive, which would not survive unscathed the temperatures occurring during subsequent foaming.

The second metallurgical bonding can be effected according to the invention by processes involving diffusion and rolling, but also axial or hydrostatic pressing, wherein rolling is preferred, under the effect of pressure on the container. In a rolling process, the pressure in the nip is preferably in a range of about 5000 to about 7000 tons, more preferably in a range of about 5600 to about 6500 tons. The temperature of the container is below the outgassing temperature of the at least one propellant, below the solidus temperature of the foamable core and below the solidus temperature of the at least one second metal. Preferably, the temperature in the second metallurgical bonding is from about 400 ° C to about 520 ° C, preferably from about 440 ° C to about 510 ° C, even more preferably in a range from about 470 ° C to about 500 ° C Temperature must always be below the Ausgastemperatur of at least one propellant so that there are no bubbles in the rolled material. In particular, the second metallurgical bonding can take place in which the container is hot rolled at a temperature below the decomposition temperature of the blowing agent. Subsequently, a cold rolling process can follow, preferably to achieve sheet thicknesses below 9 mm. By means of the rolling process or other techniques, such as axial compression or hydrostatic pressing, each in the specified temperature ranges, a second metallurgical bond of powder and liner is achieved and further the powder of the foamable mixture is compacted to about 90% to about 100% of its nominal density , The "nominal density" of the foamable mixture is the density which the would have foamable mixture, they would not be in powder form, but in a compact form as solid solid material. Subsequently, the resulting three-layer sheets are made up and optionally fed to the foaming process. The container can be opened so far that resulting gases during heating for the first and / or second metallurgical bonding in step (VI) and / or (VII) can escape. The container remains closed between the first and second metallurgical joints. Furthermore, the container can be opened so far that resulting gases during the first and / or second metallurgical bonding in step (VI) and / or (VII) can escape. In particular, the container can be opened so far that resulting gases during heating for the rolling process and during the rolling process in step (VII) can escape. The advantage here is that no gases are trapped during the rolling process and, especially with small sheet thicknesses, lead to gas-filled bulges before the foaming process. By the method according to the invention, a non-foamed semifinished product is available, which can be stored virtually indefinitely, without causing later disadvantages in the foaming process, ie in the production of a foamed composite material from the semifinished product. In particular, this prevents aging and premature outgassing of the propellant. In the semifinished product according to the invention, the foamable core can be formed as a layer between the two layers of the at least one second metal. As stated hereinbefore, in the semifinished product, the powder particles of the foamable mixture may be in powder form, but are preferably densified by the first and second powder metallurgy bonding. Particularly preferably, the powder particles are solidified. Most preferably, the (solidified) powder particles are partially or almost completely, in particular completely metallurgically bonded to one another: The individual grains or particles of the powder (powder particles) are partially or completely interconnected by means of diffusion and formation of (first) intermetallic phases within the mixture instead of forming a loose powder. This has the advantage of a more stable and compact foamable core, the foam almost no flaws in the foam forms. In addition, the first and second metallurgical compounds improve the ductility of the semi-finished product, in particular by rolling, bending, deep-drawing, hydroforming and hot pressing, as well as the strength of the connection between the foamed core and the cover layer, so that material fatigue can be avoided.

In the case of the semifinished product according to the invention, the foamable core is preferably metallurgically bonded to the layers of the at least one second metal, which allows a simple method of bonding, since, for example, no individual welds need to be applied, and since it also results in a more stable connection than by gluing , in particular with regard to the increased temperatures necessary for later foaming of the foamable core. The metallurgical bonding of the foamable core to a layer of the second metal on a surface of the container can be carried out by a process selected from the group consisting of rolling and diffusion, but also axial or isostatic pressing, at higher temperatures. The connection between the foamable core and the at least one second metal achieved by the (second) metallurgical bonding is so strong that it can withstand the elevated temperatures of the foaming process for which the semifinished product is produced. The semifinished product according to the invention can be used for foaming metal, ie for producing a metal foam. In particular, the semifinished product is suitable for use in the production of a composite material comprising metal foam and metal in the form of non-foamable solid material.

In a particular embodiment of the invention, the filled container is heated in one step to a temperature of about 300 ° C and the moisture is removed. Subsequently, the container is either at about 400 ° C to about 460 ° C, preferably at an external pressurization, in particular by axial pressing, with a pressure in a range of about 0.2MPa to about 1, 5MPa, preferably with a pressure in a range from about 0.2 MPa to about 1.1 MPa, precompressed or in a device which prevents expansion of the container to 80% of the solidus temperature of the core material (the foamable mixture) heated. Both methods also serve to increase the stability of the container for the subsequent rolling process. Furthermore, trickling out of the metal powder or the powder mixture is prevented by the container structure. This process step ensures that the powder bed is compacted, the aluminum powder is bonded to the cover layers by diffusion, and the composite thus has a higher shear strength for the subsequent rolling. Subsequently, the container is opened so far that resulting gases can escape during the heating for the rolling process and during the rolling process. The opening can be made by removing plugs or the like from at least two lateral openings of the container. The resulting composite can be reshaped and / or foamed directly by heating.

The invention will be explained in more detail with reference to the drawings and figures shown below and described, from which further advantageous embodiments of the invention will emerge, without, however, thereby the invention or individual features of the invention are necessarily limited thereto. Rather, features described there can be combined with each other and with the features described above to form further embodiments of the invention. Fig. 1 is an illustration of the container and shows the box-shaped bottom (3) and side walls (1) existing container base and the lid (3). The bottom and cover (3) form the layers or covering layers or covering layers which are made of the at least one second metal (covering layer material) and later cover the foamable core. The filling holes or openings (2) serve to fill the foamable mixture and, if appropriate, to escape gases during the first and / or second metallurgical bonding during steps (VI) and (VII).

2 is a representation of the container in an exploded view and also shows the side walls (1) having a Einknickung of about 1 75 °, filling holes or Öff- (2) and bottom and cover (3) as (later) cover layers or cover layers.

The invention will be explained in more detail with reference to the embodiments described below, without necessarily limiting the invention or individual features of the invention thereto.

example 1

For the production of the foamable semi-finished product for the production of aluminum foam sandwich structures, the following process steps were used. First, the powder mixture (foamable mixture) was prepared. For this purpose, 0.4 to 1.0% by weight TiH ₂ in powder form (% by weight, based on the aluminum alloy) was mixed with a powder of the aluminum alloy AISi8Mg4 as the first metal. Subsequently, this powder mixture was filled into an aluminum container of the alloy Al 6082 (Al Si 1 MgMn) as a second metal, in which two opposite walls formed the later cover layers of the three-layered semifinished material, which foamed into a sandwich structure (composite material). Here, the aluminum alloy of the container was chosen so that it had a solidus temperature which was higher than the liquidus temperature of the powder mixture (foamable mixture). After the container was completely filled with the powder mixture, the powder mixture was dried. The powder was heated to 300 ° C and the resulting moisture removed. Subsequently, the container was heated to about 80% of the solidus temperature of the powder mixture or of the at least one first metal and held for 6 to 24 hours at a temperature of 455 ° C to obtain a first metallurgical bonding, wherein a widening of the container was suppressed , In the following rolling process, the container was hot rolled at a pressure of about 6,000 t in the nip at a temperature of about 475 ° C to obtain a second metallurgical bond. Subsequently, if necessary, followed by a cold rolling process to achieve sheet thicknesses below 9 mm. By means of the rolling process, the second metallurgical compound of powder and cover layer was achieved and further the powder compacted to 98% to 100% of the density of the solid material. Subsequently, the resulting three-layer sheets were assembled and the Foaming process supplied. The above process was also carried out with the following aluminum alloys for the metal in the powder mixture and the container and the following propellants in the indicated amounts:

1 The amount of propellant in% by weight (wt .-%) is based on the total amount of the foamable mixture / powder mixture. The same procedure was carried out with TiH ₂ and the following propellants: ZrH ₂ , HfH ₂ , MgH ₂ , CaH ₂ , SrH ₂ , LiBH ₄ and LiAlH ₄ and the combinations of TiH ₂ with LiBH ₄ and TiH ₂ with LiAlH ₄ . Example 2

For the production of the foamable semi-finished product for the production of aluminum foam sandwich structures, the following process steps were used. First, the powder mixture (foamable mixture) was prepared. For this purpose, 0.4 to 1.0% by weight TiH ₂ in powder form (% by weight based on the aluminum alloy) was mixed with a powder of the aluminum alloy AISi8Mg4. Subsequently, this powder mixture was filled into an aluminum container (aluminum container) of the alloy AL 6082 (Al Si 1 Mg-Mn), in which two opposite walls formed the later cover layers of the three-layer semifinished product which foamed into a sandwich structure. Here, the alloy of the aluminum container was chosen so that it had a solidus temperature which was higher than the liquidus temperature of the powder mixture (foamable mixture). After the container is completely filled with the powder mixture was, the powder mixture was dried. The powder was heated to 300 ° C and the resulting moisture removed. Subsequently, the container was precompressed at a pressure of 0.2 MPa by means of two plane-parallel tools in a pressing process for about 28h for the first time. Here, the pre-compression of the powder was carried out at 400 ° C to 460 ° C. Pre-compaction produced a stable ingot. Furthermore, the powder particles were partially connected to the cover layers in the context of a first metallurgical compound. In the following second precompression rolling process, the vessel was hot rolled at a temperature of about 475 ° C and a nip pressure of about 6,000 t. This was followed, where appropriate, by a cold rolling process to achieve sheet thicknesses below 9 mm. By means of the rolling process, a second metallurgical bond of powder and top layer was achieved, and further the powder was compacted to about 98% to 100% of its nominal density. Subsequently, the resulting three-layer sheets were assembled and fed to the foaming process. The above process was also carried out with the following aluminum alloys for the metal in the powder mixture and the container and the following propellants in the indicated amounts:

¹ The amount of the blowing agent in% by weight (% by weight) is based on the total amount of the powder mixture. The same procedure was used instead of TiH ₂ with success the blowing agents: ZrH ₂ , HfH ₂ , MgH ₂ , CaH ₂ , SrH ₂ , LiBH ₄ and LiAlH ₄ and the combinations of TiH ₂ with LiBH ₄ and TiH ₂ with LiAlH ₄ .

Claims

claims

A method of making a semifinished product comprising a foamable core comprising a foamable mixture comprising at least a first metal containing at least about 80% by weight of aluminum, based on the amount of the at least one first metal, and at least one blowing agent wherein at least a first and second surface of the core are each provided with a layer of at least one second metal in the form of non-foamable bulk material and containing at least about 80% by weight of aluminum, based on the amount of the at least one second metal is, comprising the steps

(IV) filling the container with the powders provided in steps (II) and (III) to form the foamable core,

wherein mixing of the powders provided in steps (II) and (III) to the foamable mixture takes place.

The method of claim 1, wherein the at least one second metal

(a) has a solidus temperature which is at least about 5 ° C higher than the liquidus temperature of the foamable mixture; and or

(b) has less alloying constituents than the at least one first metal or at least one identical lower mass fraction alloy component in the alloy relative to the at least one first metal. A method according to claim 1 or 2, wherein

(a) the at least one first metal is selected from the group consisting of aluminum, higher strength aluminum alloys selected from the group consisting of aluminum-magnesium-silicon alloys (6000 series) and aluminum-zinc alloys (7000 series), and higher-strength aluminum alloys having a melting point of about 480 ° C to about 580 ° C; and or

(b) the at least one second metal is selected from the group consisting of aluminum and higher strength aluminum alloys selected from the group consisting of aluminum-magnesium alloys (5000 series), aluminum-magnesium-silicon alloys (6000 series) and aluminum-zinc alloys (7000 series) ,

A method according to any one of claims 1 to 3, wherein the mixing of the powders provided in step (II) and (III) to the foamable mixture occurs before or during step (IV).

The method of any one of claims 1 to 4, wherein the exhaust gas temperature of the at least one propellant is equal to the solidus temperature of the at least one first metal or below the solidus temperature of the at least one first metal, but not more than about 90 ° C below the solidus temperature of the at least one first metal is less than the solidus temperature of the at least one second metal.

A method according to any one of claims 1 to 5, wherein the at least one propellant comprises at least one metal hydride.

A method according to claim 5 or 6, wherein the at least one blowing agent additionally comprises at least one oxide and / or at least one oxihydride of the metal of the respective metal hydride. The method of claim 7, wherein at least one blowing agent is TiH ₂ and at least one

(a) oxide is an oxide of formula Ti _v O _w , where v is from about 1 to about 2 and w is from about 1 to about 2, and / or

(b) Oxihydride is an oxihydride of the formula TiH _x O _y and x is from about 1.82 to about 1.99 and y is from about 0.1 to about 0.3.

The method of any one of claims 1 to 8, wherein the amount of the at least one propellant is from about 0.1% to about 1.9% by weight, based on the amount of the at least one first metal.

A process according to any one of claims 7 to 9 wherein the amount of at least one oxide and / or oxihydride is from about 0.01% to about 30% by weight, based on the total amount of the at least one blowing agent.

A method according to any one of claims 1 to 10, wherein

(a) the at least one first surface of the container to the at least one second surface of the container

(a.1) is arranged opposite, and / or

(a.2) is substantially plane-parallel; and or

(B) the foamable core is formed as a layer between the at least one first and second surface of the container.

A method according to any one of claims 1 to 11, additionally comprising

step

(V) drying

(V.1) of the powder of the at least one first metal before step (IV)

and / or the powder of the at least one propellant before step (IV), or (V.2) of the foamable mixture before step (IV), or

(V.3) the foamable mixture and the container after step (IV).

A method according to any one of claims 1 to 12, additionally comprising the step

(VI) first metallurgically combining the powder particles of the foamable mixture with each other and / or with the respective one layer of the second metal on the first and second surfaces of the core to form the foamable core of step (IV) or (V).

The method of claim 1 3, wherein in step (VI) precompacting the foamable mixture together with the container by applying pressure at a temperature of the foamable mixture and the container from about 65% to about 90% of the solidus temperature of the foamable mixture.

The method of claim 1 3, wherein in step (VI) heating of the foamable mixture and the container is carried out to about 70% to about 90% of the solidus temperature of the foamable mixture, wherein a widening of the container is substantially prevented.

A method according to any one of claims 1 3 to 1 5, additionally comprising the step

(VII) second metallurgically bonding the foamable core obtained in step (VI) to the layers of the at least one second metal on the first and second surfaces of the container.

The method of claim 16, wherein said second metallurgical bonding is effected by processes including diffusion and rolling under pressure of the container at a temperature of the container below the exhaust gas temperature of the at least one propellant, below the solidus temperature of the foamable Kernes and below the solidus temperature of at least one second metal.

A process according to any of claims 1-3 to 1-7, wherein the temperature of the container at the beginning of the respective process step is from about 400 ° C to about 540 ° C.

1 9. A semi-finished product obtainable by a process as defined in any one of claims 1 to 18.

20. Use of a semifinished product according to claim 1 9 for producing a composite material comprising metal foam and metal in the form of non-foamable solid material.

21. Containers for carrying out the method according to one or more of claims 1 to 1 9 with a first and a second surface (3), which form a bottom and a lid, and side walls (1), wherein at least one side wall (1) a buckling to inside toward a foamable mixture.