Method for production of metal foam or metal-composite bodies

Abstract

A method for the production of foamable or foamed metal pellets, parts and panels. The method comprises the steps of: i) providing a mixture of a metal alloy powder with a foaming agent powder, ii) pre-compacting the mixture of step i); iii) heating the pre-compacted mixture of step ii) to a temperature below a decomposition temperature of the foaming and at which permanent bonding of the particles occurs v) hot compacting the body for producing a compacted body made of a metal matrix embedding the foaming agent; and vi) reducing the compacted body into metal fragments and thereby obtaining dense foamable metal chips. A method for the production of a foam metal using a closed volume metal shell is also disclosed. The method comprises the steps of: a) providing metal pieces and reducing said metal pieces into smaller metal particles; b) mixing the metal particles with an additive having a decomposition temperature that is greater than a solidus temperature of said metal particles; c) pouring the mixture of step b) into a closed volume metal shell having a given thickness and providing the metal shell with at least one passage for gases to escape; d) reducing the thickness of the metal shell by applying pressure; e) heating the metal shell to a temperature above said solidus temperature of the metal particles and below said decomposition temperature of the additive, and immediately applying pressure on the metal shell sufficient to compress the metal particles and to create micro shear conditions between the metal particles so as to obtain a dense metal product.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the invention will become apparent upon reading the detailed description and upon referring to the drawings in which FIGS. 1 to 7 are schematic representations of the sequence of steps of a method according to a preferred embodiment of the invention. The detailed description of each figure is as follows:

FIG. 1 schematically represents the step of mixing of metal powders with a foaming agent powder;

FIG. 2 represents the step of pouring the mixture into a reusable shell and of pre-compacting the mixture by vibration;

FIG. 3 represents the step of sintering;

FIG. 4 represents the step of pushing a sintered briquette from a reusable can into press mould;

FIG. 5 represents the step of compaction of the sintered briquette;

FIG. 6 represents the step of reducing the body into foamable chips;

FIG. 7 a represents the step of hot rolling the mixture of powders in a closed volume metal shell, FIG. 7b is an enlarged view of the powder mixture at the nip formed by the two rolls, the micro-shear condition within the mixture of powders is illustrated with the arrows;

FIG. 8 is a phase diagram of the powder alloy: Al—Si;

FIG. 9 is a phase diagram of the powder alloy: Al—Mg—Cu—Mn;

FIG. 10 represents the steps of continuous or batch rolling of chips or the powder mixture in a metal shell formed by two metal strips;

FIG. 11 represents the steps of continuous rolling of chips or the powder mixture in a metal shell formed by two continuous metal strips; and

FIG. 12 represents the steps of continuous rolling of chips or the powder mixture in a closed volume metal shell.

While the invention will be described in conjunction with example embodiments, it will be understood that it is not intended to limit the scope of the invention to such embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included as defined by the appended claims.

DESCRIPTION OF PREFERRED EMBODIMENTS

The purpose of the present invention is the production of complex and simple shape products out of continuous hot-rolled sheets of commercial sizes made from the chips produced from hot-compacted briquettes. The technical result obtained due to realization of the invention incorporates a dramatic increase in product yield (creation of a waste-free technology), a reduction in manufacturing cost of porous products, broadening of the range of products in terms of their geometrical sizes, mechanical, thermal and acoustic absorption properties and density.

Referring to FIGS. 1 to 6, the method of production of porous products from aluminum alloys incorporates mixing of metal particles (1) including powder, scrap pieces, pellets, bits and/or chips of an aluminum alloy containing two or more alloying elements, for example, selected from the group consisting of: Al—Cu—Mg—Si, Al—Mg—Si, Al—Mg—Cu—Si (cast alloys), Al—Cu—Mg—Mn, Al—Mg—Cu, Al—Zn—Cu—Mg, Al—Zn—Mg—Cu (wrought alloys), as well as pure metals (with or without additives) with a powder of a foaming agent (2), the foaming agent (2) having a decomposition temperature exceeding that of solidus of the aluminum alloy powder matrix. The mixture (5) obtained is filled in a split reusable mould (6) that is heated with the powder mixture (5), as shown in FIG. 3. Heating of the powder mixture (5) is carried out at a temperature that ensures liquid-phase sintering after cooling to 10-20° C. below solidus temperature of the lowest melting point eutectic. As a result, the powder mixture now in the form of liquid phase sintered briquettes (12) loses its flowability. After disassembling of the mould (6), the hot mould is placed on the container (14) of a vertical press. The ram (13) of this press (14) pushes the sintered powder mixture (12) into the press container (14), then dummy-block is placed and hot compaction of the sintered powder mixture is carried out at a low specific pressure, as shown in FIG. 5. The hot-compacted briquettes (15) produced show a density of 86-92 rel. %. These briquettes (15) compacted at a low pressure are porous (8-14 rel. %) and brittle, thus easily breakable. Referring to FIG. 6, using highly efficient machines, the cooled briquettes (15) are reduced to fragment-shaped chips (18) with chips particles of 0.5-5.0 mm in size, chemical composition of which conforms to that of initial aluminum alloy powder with uniform distribution of the foaming agent.

Also preferably, the chips (18) are classified by grain sizes from 1.5 up to 40 mm, preferably up to 5 mm, each size fraction is mixed with fine refractory material powders passive to aluminum, then the mixture is filled in moulds and heated in a furnace up to a foaming temperature which exceeds the liquidus point by 50-70° C.; after completion of the foaming process, the mixture is screened to separate the refractory material powders from porous chips.

According to another preferred embodiment of the invention, the chips produced are classified by grain sizes from 1.5 up to 40 mm, preferably up to 5 mm, each size fraction is heated up to a temperature below the solidus point of the alloy by 10-100° C. and then dispersed as a monolayer on a flat heated surface and then the fragment-shaped chips are pelletized by circular movements of a heated massive disk-shaped plate; then each fraction of the pellets produced is mixed with fine refractory material powders passive to aluminum and then the mixture is filled in moulds and heated up to a foaming temperature which exceeds the liquidus point by 50-70° C.; after completion of the foaming process the mixture is screened to separate spherical porous granules from the fine refractory material powder.

According to a further preferred embodiment, the chips produced are classified by grain sizes from 1.5 up to 40 mm, preferably up to 5 mm each size fraction is dispersed as a monolayer on a special base, heated from below up to a temperature of phase transition to liquid state; when it is examined visually that the foamed pellets reach the desired size, they are removed out of the furnace.

The foamed pellets (also called porous pellets) may then preferably be mixed with a resin and injected into the internal space of any structural element comprising one or more hollow pieces. The resin is cured to increase stiffness and energy absorption of the structural element.

According to another aspect of the invention, the chips which are not screened to size fraction are used to form a composite block which contains a flat metallic sheet with special coating on the surface of which a layer of chips is dispersed and, above this layer, at a certain height, the second metallic sheet with special coating, stamped beforehand for the desired component, is located and after this, the composite block formed is heated in a furnace up to a foaming temperature which normally exceeds the liquidus point by at least 50-70° C. and when it is examined visually that the foamed pellets reach the upper metallic layer, the block with foamed powders is removed out of the furnace and cooled. (To provide for heating of the block in inert atmosphere).

Preferably in this case, to ensure bracing between the sheets, they are fastened together by connecting crosspieces which simultaneously play a role of fastening connecting elements.

Also preferably, the chips, which are not screened to size fraction, can be used to fill to the desired volume fraction the internal space of any structural element comprising one or more hollow pieces. The whole assembly is heated above a temperature of transition from solid to liquid state of an alloy to form porous filler (core).

According to a further aspect of the invention, the rolling of the heated foamable particles is conducted together and between two or more heated metal sheets to produce a composite body. The produced composite body is heated above a temperature of transition from solid to liquid state of an alloy to form a multi-layer structure with porous core and metallic bonds between core and facings

FIG. 7 a shows the step of hot rolling a closed volume metal shell (48) enclosing a mixture of small particles of metal (21), preferably metal alloy powders coming from recycled aluminium scrap, and a foaming agent powder. The metal shell (48) with the mixture is first heated in a heater (50), rolled between two rolls (22) where micro-shear conditions of the particles occur; and a semi-finished foamable dense product (41) is obtained at the exit of the rolling process. As can be appreciated, in front of the nip (21) formed by the two rolls (22), the mixture of particles is substantially loose or flowable. After being processed between the rolls (22), the mixture consists of a compacted foamable mixture (16) of powder alloy with foaming agent. This compacted structure (16) is obtained by subjecting the particles (19) to micro-shear conditions, such micro-shear conditions being created thanks to the use of the closed volume metal shell (48). As can be appreciated, in the nip formed by the two rolls (22) a zone of plasticity (17) is created followed by a zone of elasticity (18). As shown in FIG. 7b, the particles (19) in the zone of plasticity (17) are subjected to compression forces represented with arrow (52) and shear forces represented by arrows (54).

According to a further aspect of the invention shown in FIG. 10, the hot chips, and/or a hot mixture of aluminum powder and a foaming agent, are poured into a thermostatic feeder (32), where increase in density and movement of chips and/or mixture is induced by vibration, and rolled between two metal strips supplied by coils (36) heated at the furnace (33) to a temperature of about 100° C. higher than the temperature of the chips. The produced composite body (41) is heated above a temperature of transition from solid to liquid state of an alloy to form a sandwich structure with porous core and metallic bonds between core and facings.

According to a further aspect of the invention shown in FIG. 11, the hot chips, and/or a hot mixture of aluminum powder and a foaming agent, are poured into a thermostatic feeder (32), where increase in density and movement of chips and/or mixture is induced by vibration, and rolled between two continuous metal strips (40) heated at the furnace (33) to a temperature of about 100° C. higher than the temperature of the chips. The hot-rolled sheets (23) produced are cut to blanks, which are fed to a heat treatment.

According to a further aspect of the invention shown in FIG. 12, the hot chips, and/or a hot mixture of aluminum powder and a foaming agent, are poured into a thermostatic feeder (32), where increase in density and movement of chips is induced by vibration, then poured on a metal strip from the coil (36) moving on a roller table (43). The chips and/or mixture of powder are then covered by an upper metal strip from coil (37), moved to a machine (44) for forming a shell and for joining the edge of the lower and upper metal strips. A closed cross section metal shell (48) filled with chips and/or the mixture of powder is thus formed in that machine (44). The shell is then straightened and density of chips and/or mixture of powder increased in a straightening machine (45) and heated in a furnace (46). The heated shell is then hot rolled in a rolling mill (47). The produced composite body (41) is heated above a temperature of transition from solid to liquid state of the alloy obtained with the original mixture of powder to form a sandwich structure with porous core and metallic bonds between core and facings.

Alternatively, the metal shell (48) from the shell-forming machine (44) shown in FIG. 12 may be cut to blanks so to form a closed volume metal shell (48). Such closed volume metal shell (48) is then processed, as described above, to be straightened, heated, hot rolled and heated to a high temperature to form a sandwich structure with a porous core.

The possibility of realization of the invention characterized by the abovementioned set of the signs and the possibility of the realization of the purpose of the invention can be corroborated by the description of the following examples.

EXAMPLE 1

The example of the realization of the method for production of dense foamable chips is as follows.

Al—Mg—Cu—Mn aluminum alloy powder (a liquidus temperature of the alloy is 640-645° C., a temperature of low-melting point eutectic is 505° C.) of 300 kg in weight was mixed with TiH₂ foaming agent of 3.25 kg in weight (a decomposition temperature is 690° C. and filled in a split mould of 340 mm diameter, 800 mm in height with internal space of 290 mm in diameter. FIG. 8 shows a vertical cross section of the phase diagram of Al—Mg—Cu—Mn alloys. Hatched zone in this figure represents alloys used in the process. As can be appreciated, the average solidus temperature is 503° C. and the liquidus temperature is approximately 650° C. The powder mixture was compacted by vibration to obtain a density of 1.75-1.8 g/cm3. Weight of the mixture in each mould was from 97 up to 100 kg. The powder mixture was heated at a temperature of 510-515° C. to ensure liquid-phase sintering after cooling down to a temperature of 480-485° C., the powder mixture lost its flowability. After disassembling of the mould, the hot mould was placed on the container of a 10 MN or 15 MN capacity vertical press. The diameter and height of the container were 300 and 800 mm respectively. The ram of the press pushed the sintered powder mixture into the press container, then a dummy-block was placed and hot compaction of the sintered powder mixture was carried out at a low specific pressure of 140-200 MPa. The hot-compacted briquettes produced showed a density of 86-92 rel. %. After cooling the briquettes were reduced on special machines to fragment-shaped chips.

Heating of the primary powders above a temperature of appearance of low-melting point eutectic by 10-20° C. and subsequent cooling below this temperature by 20-30° C. ensure development of liquid-phase powder sintering. The powder mixture in this state loses its flowability and can be easily pushed from the mould into the press container. The first source of appearance of extremely low hydrogen amounts is decomposition of TiH₂ at a heating temperature. The second source is surface hydrogen appeared due to reaction of absorbed (H₂O molecules) with aluminum cations which diffuse through an oxide film. Surface hydrogen and hydrogen formed due to decomposition of TiH₂ leave the porous briquettes partially, while the largest hydrogen amount is capable of dissolving in appeared low-melting point eutectic.

Then, hot compaction operation at a low pressure of 140 or 200 MPa is carried out. Pressure applied to a sintered briquette is able to form only a porous briquette. The porous state is necessary only to facilitate production of the chips on special machines. The main operation i.e. hot compaction is a waste-free process.

If the heating of the primary powder mixture is performed at a temperature wherein the particles do not bond for example a temperature of 10-20° C. below that of low-melting point eutectic formation, the particle will not bond and the powder mixture obtained will retain its flowability. Transportation of the disassembled mould to the press container will be impossible, a briquette structure will be loose.

EXAMPLE 2

The example of realization of the method for production of porous semi-finished pellets from the foamable chips is as follows:

Al—Zn—Cu—Mg aluminum alloys powder (a liquidus temperature of the alloy is 630-640° C., a temperature of low-melting point eutectic formation is 480° C. of 210 kg in weight was mixed with CaCO₃ foaming agent of 12 kg in weight (a decomposition temperature is 720° C.) and filled in a split mould of 340 mm in diameter, 800 mm in height with internal space of 290 mm in diameter. FIG. 9 shows surfaces of crystallization (surfaces of liquidus) of the powder alloy Al—Zn—Cu—Mg containing Zn-4, 5%, Cu 3.5-4.5%, Mg-negligible, Al-balance. The alloys used are in the AL corner of the diagram (small hatched zone) and have a liquidus temperature of 650° C. Solidus of these alloys is in the interval of temperatures of 510-520° C. The powder mixture was compacted by vibration to obtain a density of 1.75-1.8 g/cm³. Weight of the mixture in each mould was from 97 up to 100 kg. The powder mixture was heated at a temperature of 490-500° C. to ensure liquid-phase sintering after cooling down to 450-460° C. and the mixture lost its flowability. After disassembling of the mould, the hot mould was placed on the container of a 10 MN or 15 MN capacity vertical press. The diameter and height of the container were 300 and 800 mm respectively. The ram of the press pushed the sintered powder mixture into the press container, then a dummy-block was placed and hot compaction of the sintered powder mixture was carried out at a low specific pressure of 140-200 MPa. The hot-compacted briquettes produced showed a density of 86-92 rel. %. After cooling, the briquettes were reduced on special machines to fragment-shaped chips.

To realise the method, the chips produced were graded into grain sizes of 2.0, 3.0, 4.0 and 5.0 mm, each size fraction was mixed with fine refractory material powders passive to aluminium, the mixture was filled in moulds, heated in a furnace at a foaming temperature which exceeds the transition temperature from solid to liquid state by 50-70° C.; after completion of the foaming process, the mixture was screened to separate the refractory material powders from porous pellets. The porous pellets from 3.0 up to 10.0 mm in size and 0.3 up to 0.9 g/cm3 in density are a good filling agent for any shape of cases for energy absorbing components used in the automotive industry.

An easier technique for realization of the chips of the same alloy, graded into grain sizes of 2.0, 3.0, 4.0 and 5.0 mm is discussed below. Each fraction was dispersed as a monolayer on a special base, heated in a furnace from below on overheated melt of salt up to a foaming temperature; when it was examined visually that the foamed pellets reached the desired size, they were removed out of the furnace and cooled. The pellets had a hemispheric shape with radius from 5.0 up to 20.0 mm and a density from 0.4 up to 1.0 g/cm3.

Porous pellets of this size and shape can find application for production of volumetric noise suppression and fire barrier components and also large-size shock absorption elements. Product yield is 100%.

EXAMPLE 3

An example of the realization of the method for production of flat porous semi-finished products is as follows.

Al—Mg—Cu—Mn aluminum alloy powder (a liquidus temperature of the alloy is 640-645° C., a temperature of low-melting point eutectic is 505° C.) of 30 kg in weight was mixed with TiH₂ foaming agent of 0.32 kg in weight and filled in 10 closed volume metal shells with length 500 mm, width 120 mm and thickness 10 mm. The powder mixture was compacted by vibration and a pass through the straightening machine to obtain a density of 1.8-2.0 g/cm3. Weight of the mixture in each shell was from 2.9 up to 3.2 kg. Then the powder mixture in a shell was heated at a high rate in a furnace to a temperature 515-550° C. and fed on a rolling mill on which 29 kg of 120×1000×5 mm blanks with metal facing and foamable core were rolled. The blanks were used for free foaming of sandwich panels. High-temperature heat treatment was carried out by heating of the sheet blanks from below on overheated melts of salts. At the required point, the foaming process was stopped by quick removal of the foamed sandwich panel from the furnace when thickness was 24.5 mm. The size of the panel with porous core was 122×1005×24.5 mm. The lower and upper surface of the panels was smooth. The density of the porous semi-finished products produced was 0.96-1.07 g/cm3. Panels yield was 95%.

Although preferred embodiments of the present invention have been described in detail herein and illustrated in the accompanying drawings, it is to be understood that the invention is not limited to these precise embodiments and that various changes and modifications may be effected therein without departing from the scope or spirit of the present invention.

Claims

1-32. (canceled)

33. A method for the production of a metal product comprising the steps of: introducing a mixture comprising metal particles and an additive having a decomposition temperature that is greater than a solidus temperature of said metal particles into a closed volume metal shell having a given thickness and providing the metal shell with at least one passage for gases to escape;increasing the density of the metal shell with metal particles and additive by applying pressure; andheating the metal shell to a temperature above a temperature equal to said solidus temperature minus 50-60 degrees Celsius and below said decomposition temperature of the additive, and immediately applying pressure on the metal shell sufficient to compress the metal particles and to create micro shear conditions between the metal particles so as to obtain a dense metal product.

34. The method of claim 33, further comprising pre-compacting the mixture before increasing the density of the metal shell with metal particles and additive.

35. The method of claim 34, wherein pre-compacting of the mixture is performed by vibration.

36. The method of claim 33, wherein the pressure is applied to said metal shell by hot rolling the metal shell.

37. The method of claim 36, wherein the hot rolling is performed with a compression force sufficient for obtaining a 95-100% dense metal product.

38. The method of claim 33, wherein the closed volume metal shell comprises two continuous longitudinal main surfaces with side edges, and is deformable in a cross direction.

39. The method of claim 38, wherein the continuous surfaces are at least partially closed at their side edges, said partial closing being made by a process selected from the group consisting of welding, bending, clamping and bonding.

40. The method of claim 38, wherein the hot rolling is performed by at least one roll moving along one of said surfaces of the shell.

41. The method of claim 33, wherein the closed volume metal shell is obtained by providing a flat pan with a lid; and wherein the mixture is introduced into the pan and closing the lid of the pan leaving said at least one passage.

42. The method of claim 33, wherein increasing the density of the metal shell comprises cold rolling the metal shell.

43. The method of claim 33, wherein the metal particles comprises recycled aluminium scraps.

44. The method of claim 33, wherein the metal particles are metal chips, a powder of finely dispersed metal particles, agglomerated powders, particles, or mixtures thereof.

45. The method of claim 33, wherein the additive comprises a foaming agent that decomposes into gas at a temperature greater than said decomposition temperature.

46. The method of claim 45, wherein the dense metal product obtained consists essentially in a dense foamable metal product comprising said metal particles and said foaming agent.

47. The method of claim 45, wherein the dense metal product obtained is a sandwich structure metal product comprising a dense foamable metal core comprising metal particles and said foaming agent; and two metal facings.

48. The method of claim 47, wherein said metal facings are made of said metal shell.

49. The method of claim 47, wherein said product comprises metallic bonds between said core and said facings.

50. The method of claim 45, wherein the foaming agent is chosen from TiH2, CaCO3, and a mixture thereof.

51. The method of claim 45, further comprising the step of heating the dense metal product to a temperature greater than the decomposition temperature of the foaming agent, for obtaining a foam metal product.

52. The method of claim 51, wherein the foam metal product obtained consists essentially in a porous metal product comprising said metal particles.

53. The method of claim 51, wherein the foam metal product obtained is a sandwich structure metal product comprising a porous metal core comprising metal particles; and two metal facings.

54. The method of claim 53, wherein said metal facings are made of said metal shell.

55. The method of claim 54, wherein said product comprises metallic bonds between said core and said facings.

56. A dense foamable metal product obtained by a method as defined in claim 45.

57. A dense foamable metal product obtained by a method as defined in claim 47.

58. A dense foamable metal product obtained by a method as defined in claim 48.

59. A foam metal product obtained by a method as defined in claim 52.

60. A foam metal product obtained by a method as defined in claim 53.

61. A sandwich structure metal product comprising a dense foamable core comprising metal particles and a foaming agent; and two metal facings, said product being characterized in that it comprises metallic bonds between said core and said facings.

62. A sandwich structure metal product comprising a porous metal core; and two metal facings, said product being characterized in that it comprises metallic bonds between said core and said facings.