Method for production of porous semi-products from aluminum alloy powders

Abstract

The invention relates to powder metallurgy and can be used for producing porous materials having high thermal and sound insulation and energy absorption combined with light mass, incombustibility and the ecological cleanness thereof. According to said invention, during mixing a powder of an aluminum alloy with porophores, the powders of aluminum oxide and aluminum hydroxide ranging from 1 to 10% and crushed particles of secondary aluminum alloys of the dimensions ranging from 0.5 to 4.5 mm are added to the powder mixture. The particles are mixed in an atrittor until a mechanically alloyed powder alloy is obtained. The powder mixture being heated, it is poured in a vertical container which vibrocompacts the mixture and maintains the temperature thereof. Afterwards, said mixture is transferred to the rectangular groove of a rolling mill in order to carry out a continuous hot compaction in a dead groove of horizontal rollers at a temperature ranging from 430 to 500° C. according to the following condition: H=h×&ggr;×a, where H is an opening between rollers along the arc of contact in mm, h is the thickness of the produced sheet, &ggr; is a compaction ratio of the powder, a is an experimental ratio equal to 1.5=a=4.5. Said invention reduces production cost by using aluminum alloy refuses, expanding the range of sheets and plates and increases the efficiency of the production thereof.

Description

FIELD OF THE INVENTION

[0001] The invention relates to the field of powder metallurgy and can be used for producing porous materials showing a number of unique properties such as good thermal and sound insulation and energy absorption in combination with light weight, incombustibility and absolute environmental safety. Material with this set of physical and mechanical properties can be used for production of components for building machinery, road construction, motor-vehicle industry, aircraft industry and other branches of industry wherein combination of these properties can be desired.

[0002] The method comprises mixing of powders of an aluminum alloy selected from the group consisting of Al—Si—Cu—Mg, 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), which contain surface aluminum oxide (0.5-1.5 wt %) formed during atomization, with powders of Al2O3 and aluminum hydroxide ranging from 1.0 up to 10 wt % and active porophore TiH2 from 0.5 up to 1.2 wt % showing a decomposition temperature above that of powder aluminum alloy matrix melting, or mixing of crushed scrap particles of certain wrought, aluminum alloys which meet requirements specified for AM, A31, A33, AM3, AM5, 16 and cast alloys (scrap particles being 0.5-4.5 mm in size) with a mixture of aluminum oxides and porophore by mechanical alloying. Addition of aluminum oxide together with aluminum hydroxide ranging from 1.0 up to 10% both in aluminum powder and in mixed crushed scrap ensures a noticeable increase in viscosity of melt. The powder mixture or mechanically alloyed mixture produced in an attrittor is fed as a uniform layer on a conveyer of a heating furnace. Heating of said mixtures is carried out in nitrogen atmosphere (dew point is −40° C.) in a temperature range from 450 up to 600° C. under an excessive pressure from 10 up to 100 mm H2O. Each heated powder mixture is poured in a loading bin of a vertical rectangular chute wherein the preheated mixture is uniformly compacted due to vibration and transferred from top downwards. Cooling-down of said mixture during transportation in the vertical rectangular chute is prevented as it gets through a heating furnace wherein the desired temperature is maintained in a range of 450-600° C. depending on powder alloy composition and other process parameters. Travel speeds of said mixture on the conveyer of the preheating furnace and in the vertical chute are the same. From the funneled opening of the chute the heated mixture is fed to a rolling mill with rolls arranged horizontally and each of them has an internal turned groove with a depth equal to a half of a thickness of a hot-compacted semi-product to be produced from said powder mixture. A chosen rolling speed or speed of pulling the hot powders in a hot compaction zone between the rolls should be in agreement with that of powder transportation by means of the vertical vibrating chute and with that of powder transportation on the conveyer in case of powder preheating in the furnace under nitrogen atmosphere. Side ridges of the turned grooves of each roll touch each other and thereby create close rectangular space which forms final sizes of a compacted sheet semiproduct produced from the powder mixture. The side ridges of the rolls confine transverse movement of powder particles when they fall within a field of forces applied vertically in a closed space. Creation of the stringent closed space in the force application area of the yield elongation zone results in a change of the scheme of the stress-strained state. Namely, the scheme of the stress-strained state, in case of rolling with the use of the smooth rolls, ensures deformations in three direction: the most intensive deformation in the rolling direction and slight deformation in the transverse direction, which causes widening of the sheets during rolling. In case of the use of the grooved rolls forming a closed groove, under certain conditions of powder feeding, proposed by the present invention, conditions for formation of the stress-strained state corresponding to extrusion with the unidirectional deformation vector, as in case of hot extrusion on a hydraulic press, are created, i.e. plastic deformation develops in the direction of the main deformation vector. Under certain conditions proposed by the present invention, hot compaction of the powder mixture can be carried out between the rolls of the rolling mill to obtain a relative compact density up to 0.97-0.99% and to produce a hot-compacted continuous strip or sheet from 150 up to 1500 mm in width and from 3 up to 15 mm in thickness.

[0003] Conditions of formation of a continuous hot-compacted or hot-extruded flat sheet semiproduct between the special rolling mill rolls which form a closed space of a powder rolling mill can be described by the following equation: H=h×&ggr;×&agr;, where:

[0004] H is an opening between the rolls along the arc of contact, mm;

[0005] h is a thickness of the compacted sheet, mm;

[0006] &ggr; is a compaction coefficient

[0007] &agr; is an experimental coefficient, where 1.5≧&agr;≧4.5.

[0008] As a result of application of forces close to volume-stressed state in the yield elongation zone and at a temperature of 450-500° C., active interactions of powder mixture particles or particles develop. Powder particles drawing together by forces undergo partial destruction of oxide films, which is accompanied by formation of juvenile surfaces, or direct convergence when the oxide film is particle-particle interface. As a result of a temperature and by forces in the yield elongation zone, due to active diffusion, new strong metallic bondings are generated between powder particles both in contact areas with pure juvenile surfaces and in contact areas with metallized oxide film. These strong metallic bondings can sustain noticeable tensile stresses in case of the change of stress-strained state and transition from hot compaction to hot extrusion in the rolling mill when a continuous sheet with a preset thickness is produced. The hot compacted sheet produced is cut to blanks. Such blanks are placed in forms lateral side of which are made from heat-insulating material. The degree of blackness of this material is noticeably differed from that of aluminum. Bottoms of the forms are made from a refractory steel sheet or a net with small mesh. The form, on the one hand, is a transport means in which the blank is fed for heat treatment, and, on the other hand, it creates a thermostating space for the blank heated during heat treatment. High-temperature heat treatment is carried out by heating of the blank above a temperature of solid-liquid phase transformation. Termination of the foaming process is determined visually, when contrast aluminum edge appears above the form wall. The form is taken out of a furnace, its surface is cooled down and the foaming is arrested at the desired height.

[0009] The technical result obtained due to realization of the invention incorporates high output, creation of waste-free production, low production costs of commercial porous sheet semiproducts due to the use of scrap or secondary aluminum alloys both in case of production of atomized powder and in case of production of grinded particles of certain aluminum alloys with subsequent milling in the attritor for production of the mixture with desired chemical composition.

[0010] The invention relates to the field of powder metallurgy and can be used for producing porous semiproducts for building machinery, road construction, motor-vehicle industry, aircraft industry and other branches of industry wherein combination of unique properties of this material, such as isotropy of properties, energy absorption, thermal and sound insulation, light weight, buoyancy and absolute environmental safety are desired.

BACKGROUND OF THE INVENTION

[0011] Already known in the prior art, there is a method for production of porous semiproducts from powder alloys based on aluminum and copper, that incorporates mixing of alloy powder with a porophore, filling of the mixture in a press container, simultaneous heating of the filled container and applying pressure at which the porophore does not decompose, simultaneous cooling and release of the pressure, disassembling of the container followed by pushing of the solid briquette out of it, which is immediately heat treated to produce a porous body or is subjected to preliminary hot deformation via extrusion and subsequent rolling for production of sheets which are cut to length and heat treated (German patent No. 4101630, B 22 F 3/18, B 22 F/24, 1991).

[0012] Limitation of this method is a very small range of semiproducts in terms of sizes and shape, which can be produced by this method as weight of the briquette is 2-5 kg. In addition, this method shows a very low output because of the prolonged heating of the large size press container filled with the powder mixture. Even in the case where the powder mixture would be heated in a container of 100 mm in diameter and 400 mm in height, the heating operation would be unprofitable.

[0013] Also known, there is a method for production of porous semi-products, which incorporates several variants for production of compact briquettes followed by rolling for sheet production. However in cases of all variants of this method, mixing of a metallic powder with at least one powder, porophore, is the main and common operation.

[0014] The first variant includes placement of porophore-free metallic layer on the bottom floor of a press container, covering of the metallic layer with a powder mixture containing a porophore and then covering of the powder mixture with the second metallic layer. After heating of the container wherein the filled powder mixture is between two installed plates hot compaction is carried out. This operation completes the method. The hot-compacted shape of a body produced can be changed via subsequent hot rolling for formation of a new body wherein a high-porous foamed metallic layer appears between two metallic layers.

[0015] The second variant includes installation of a large-size solid metal disc in an empty press container (extrusion tooling) and filling of the container space with a powder mixture containing a porophore. Then, the container with the powder mixture is subjected to heating followed by application of a pressure of about 60 MPa. Due to the applied pressure, the central part of the hard metallic disc which blocks the press die hole begins flowing through this hole and ensures extrusion process. During subsequent extrusion stages the compacted powder mixture plastically deforms and flows through the die hole also. In this case the hard metal covers the extruded powder mixture which able to foam under the hard metallic layer. Then, the hot-extruded clad strip is rolled in sheet. The hot-rolled sheet is cut to blanks and subjected to heat treatment. After foaming of this combined body the metallic layer covers a core consisting of high porous foam.

[0016] The combined hot-compacted and hot-extruded briquettes produced via both variants of the method should be further subjected to hot rolling for production of sheets or plates. Due to a heat treatment temperature the powder core is transformed in a porous metallic body (U.S. Pat. No. 5,151,246. September, 1992. B 22 F 3/18, B 22 F 3/24).

[0017] Also known in the prior art, there is a method for production of porous semi-products with the usage of reusable split cans. The method includes filling of a mixture of aluminum and copper powder (from 1 up to 10%) with a porophore in these cans, sintering of the mixture in an inert gas flow in the split can, pushing of the hot solid briquette in a press container for subsequent extrusion to produce a bar. The bar with a clad layer or without it is cut to length and is rolled to sheets of commercial sizes and then heat treatment is carried out for production foamed aluminum (Patent RU No. 2121904 of Nov. 20, 1998, B 22 F 3/11).

[0018] In spite of some advantages in comparison with the above method, said method has a number of limitations peculiar to it, namely inadequate output and product yield, that results in an increased production costs of semiproducts.

[0019] Said method and the above one are the most similar analogues (phototypes) in terms of the set of properties.

[0020] Limitations of this method as well as all the above methods are limited possibility of production of semi-products, especially sheets of commercial sizes, low product yield and output, high production costs. Low product yield is attributed to formation of large amount of scrap during extrusion (butt-ends, head and back ends) and during rolling (side crops and back end crops).

[0021] The purpose of the present invention is production of continuous hot-compacted or hot-extruded sheets of commercial sizes by means of direct hot compaction or hot extrusion of a mixture of powders of various chemical composition with a porophore or a mixture of coarse particles of 0.5-4.5 mm in size with a porophore mechanically alloyed in an attritore and also of grinded particles of certain aluminum alloys in a rolling mill.

[0022] The task of the invention is a noticeable improvement in output, product yield up to 95-97%, a reduction in production costs due to the use of aluminum alloy scrap, widening of a range of sheets and plates with an increase in sheet area up to 2.5-3% square metres.

[0023] The most similar analogue of the invention is a method for production of porous semiproducts and aluminum alloy powders. The method includes mixing of an aluminum alloy powder with a porophore showing a decomposition temperature above that of aluminum alloy powder melting, with addition of a copper powder from 1 up to 10%, filling of this mixture in a mould, heating of this mould filled with the powder mixture, pushing of the hot mixture in a press container, hot extrusion for production of a solid briquette, cooling, hot deformation, for example, rolling, cut of a rolled sheet to length, placement of the blanks produced in forms with heat-insulating material walls and subsequent high temperature treatment for conduct of forming process at a liquidus temperature of the powder alloy. In this case, alloys of Al—Cu—Mg, Al—Zn—Cu—Mg, Al—Zn—Mg, Al—Mg or Al—Si—Cu—Mg systems are used as powder aluminum alloys and nitrogen or argon are used as inert gases during heating of the powder mixture. For production of clad strip heating of the powder mixture is carried out in the mould wherein aluminum disc is placed on the bottom (RU 2121904, Nov. 20, 1998, B 22 F 3/11).

[0024] The common signs of the known method and this invention are mixing of an aluminum alloy powder with porophores showing a decomposition temperature above that of aluminum alloy powder melting, filling of the mixture in a mould, heating of the mould in an inert gas atmosphere, hot compaction, extrusion, cutting-to-length, hot rolling to sheets, cutting of the sheets to blanks, placement of them in a form with heat-insulating material walls, subsequent high temperature treatment for conduct of foaming process at a liquidus temperature of the powder alloy and cooling.

DESCRIPTION OF THE INVENTION

[0025] The method of the present invention differs from the prior art by the fact that during mixing of an aluminum alloy powder with porophores, oxide and hydroxide aluminum powder additions from 1.0 up to 10% are made in the mixture or porophores to be added and aluminum oxides are mixed with coarser aluminum alloy particles from 0.5 up to 4.5 mm in size in an attritor to produce mechanically alloyed powder alloy, after heating the various powder mixtures are filled in a mould installed vertically which ensures simultaneous vibratory compaction and maintenance of a temperature of the powder mixture, and hot consolidation (compaction or extrusion) is carried out by feeding of the powder mixture in the grooved horizontal rolls of a rolling mill at a temperature of 430-500° C. provided that the following conditions are observed:

H=h×&ggr;×&agr;, where:

[0026] H is an opening between the rolls along the arc of contact, mm;

[0027] h is a thickness of the compacted sheet, mm;

[0028] &ggr; is a powder compaction coefficient;

[0029] &agr; is an experimental coefficient, where 1.5≧&agr;≧4.5.

[0030] The present invention concerns a method for production of porous semi-products from aluminum alloy powders comprising the steps of:

[0031] I) Mixing of powders of an aluminum alloy selected from the group consisting of Al—Cu—Mg—Mn, Al—Si—Cu—Mg, 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) with addition of a mixture of aluminum oxide and aluminum hydroxide ranging from 0.5 up to 10 wt % and active porophore TiH2 ranging from 0.5 up to 1.2 wt % showing a decomposition temperature above that of powder aluminum alloy matrix melting or mixing of coarse particles of crushed scrap of certain wrought aluminum alloys AM, A31, A133, AM3, AM5, 16 and other cast alloys (scrap particles being 0.5-4.5 mm in size) with a mixture of aluminum oxide and a porophore in an attritore by the mechanical alloying technique.

[0032] II) Feeding of the powder mixture of step I as a uniform layer on a conveyer of a heating furnace. Heating of the mixture in nitrogen atmosphere at a temperature range of 450-600° C. under an excessive pressure from 10 up to 100 mm H2O;

[0033] III) Feeling of the pre-heated mixture of step II in a loading bin of a vertical chute wherein the pre-heated mixture is uniformly compacted due to vibration and transferred from top downwards;

[0034] IV) Filling of the pre-heated mixture of step III in a heating furnace wherein the desired temperature is maintained in a range of 450-600° C. depending on powder alloy composition and other process parameters to prevent cooling-down of said mixture during transportation on the chute; travel speeds of said mixture on the conveyer of the preheating furnace and in the chute are the same;

[0035] V) Feeding of the pre-heated mixture of step 1V from the funneled openting of the chute to a rolling mill with horizontal rolls, with each roll having an internal turned groove which depth is equal to a half of thickness of a hot-compacted sheet semiproduct to be produced. A chosen rolling speed or speed of pulling said pre-heated mixture in a hot compaction zone should be in agreement with that of pre-heated mixture transportation by means of the vertical vibrating chute and with that of powder transportation on the conveyer in case of powder preheating in the furnace under nitrogen atmosphere of step II. Side ridges of the turned grooves of each roll touch each other and thereby create close rectangular space which forms final sizes of a hot-compacted sheet semiproduct produced from said powder mixture. The side ridges of the rolls confine transverse powder particle movement by rolling forces. Creation of the stringent groove in the force application area of the yield elongation zone results in a change of the scheme of the stress-strained state. Namely, the scheme of the stress-strained state, in case of rolling with the use of the smooth rolls, ensures deformations in three directions: the most intensive deformation in the rolling direction and slight deformation in the transverse direction, which causes widening of the sheets during rolling. In case of the use of the grooved rolls, proposed by the present invention, which form a closed groove under certain conditions, conditions for formation of the stress-strained state corresponding to extrusion with the unidirectional deformation vector, as in case of extrusion, are created, i.e. plastic deformation develops in the direction of the main force vector. Under certain conditions proposed by the present invention hot compaction of said powder mixture can be carried out between the rolls of the rolling mill to obtain a relative compact density up to 0.97-0.99% and to produce a hot-compacted continuous strip or sheet from 50 up to 1500 mm in width and from 3 up to 10 mm in thickness.

[0036] Conditions of formation of a continuous hot-compacted or hot-extruded flat sheet semiproduct between special rolling mill rolls which form a closed groove in the rolling mill can be described by the following equation:

H=h×&ggr;×&agr;, where

[0037] H is an opening between the rolls along the arc of contact, mm;

[0038] h is a thickness of the compacted sheet, mm;

[0039] &ggr; is a powder compaction coefficient;

[0040] &agr; is an experimental coefficient, where 1.5≧&agr;≧4.5.

[0041] As a result of application of forces close to volume-stressed state in the yield elongation zone and at a temperature of 430-500° C., active interactions of powder mixture particles develop. Powder particles drawing together by forces undergo partial destruction of oxide films, which is accompanied by formation of juvenile surfaces, or direct convergence when the oxide film is particle-particle interface. As a result of a temperature and by forces in the yield elongation zone, due to active diffusion, new strong metallic bondings are generated between powder particles both in contact areas with pure juvenile surfaces and in contact areas with metallized oxide film. These strong metallic bondings can sustain noticeable tensile stresses in case of formation of a continuous dense hot-extruded sheet with a preset thickness. The hot-compacted or hot-extruded sheet produced is cut to blanks which are placed in forms lateral sides of which are made from heat-insulating material. The degree of blackness of this material is noticeably differed from that of aluminum. Bottoms of the forms are made from a refractory steel sheet or net with small mesh. The form, on the one hand, is a transport means in which the blank is fed to heat treatment and, on the other hand, it creates a thermostating space for the blank heated during heat treatment. High-temperature heat treatment is carried out by heating of the blank above a temperature of solid-liquid phase transformation. Termination of the foaming process is determined visually, when contrast aluminum edge appears above the form wall. The form is taken out of furnace, surface is cooled down and the foaming is arrested at the desired height.

[0042] In addition, in the particular case of realization of the method, after termination of the foaming process the form with heat-insulating material walls is placed in a technological space of a furnace with lower temperature and for formation of upper smooth surface, a smooth heat-insulating material plate which does not react with aluminum is put on the end of the form. Then the form is taken out of the furnace, the plate is taken away and the upper smooth surface of the semiproduct produced is cooled down intensively.

[0043] In addition, in the particular case of the realization of the method, the heat-insulating material plate which does not react with liquid aluminum is made with embossed surface which forms a replicated impression on the solidifying aluminum surface.

[0044] In addition, in the particular case of the realization of the method, prior to high-temperature treatment, a stamped sheet is placed on the bottom of the form, and the blank is placed on said sheet. After placement of said form in a technological space of the furnace with lower temperature the heat-insulating material plate which does not react with molten aluminum and made with embossed surface is put on the end of the form to produce replicated impression on the upper aluminum surface. Then the form is taken out of the furnace, the plate is taken away and the upper surface of the semiproduct produced is cooled down intensively.

[0045] In addition, in the particular case of the realization of the method, for aluminum powder use is made of grinded scrap of aluminum alloy semiproducts both extruded and rolled ones, made from soft aluminum alloys AO, A1 and wrought alloys AM, A31, A33, AM3, AM5, 16, as well as copper, plastic metals and alloys, with particle size being from 0.5 up to 4.5 mm.

[0046] In addition, in the particular case of the realization of the method, in case of mixing of an aluminum alloy with porophores in the attritor, use is made of grinded particles of aluminum alloys and copper and other plastic metals with size fractions of 0.5-2.5 mm, 1.0-3.0 mm, 1.5-4.5 mm.

[0047] In addition, in the particular case of the realization of the method, when grinded scrap of aluminum alloys AO, A1 and hard wrought alloys AM, A31, A33, AM3, AM5, 116 are mixed in the attritor, additions of a porophore are made together with additions of refractory particles of aluminum oxide, boron carbide and silicium carbide with a range of size being 5-100 &mgr;m.

[0048] In addition, in the particular case of the realization of the method, when grinded scrap of aluminum alloys is mixed in the attritor, additions of refractory intermetallics particles, for example, N, Al3, NiAl, Cr2Al6 with a range of size being 10-100 &mgr;m are made in the mixture.

[0049] In addition, in the particular case of the realization of the method, for a reduction in thickness of a sheet to be produced during hot compaction, the powder mixture is fed between moving steel sheets passed by the vibrating chute in the grooved rolls of the rolling mill.

[0050] In addition, in the particular case of the realization of the method, during hot compaction of the powder mixture, cladding of the compact with steel or titanium sheets can be carried out due to feeding of the powder mixture between the moving hot sheets passed by the vibrating chute in the grooved rolls of the rolling mill with subsequent folding of ends of the sheets for formation of a seam. In this case also, some proportions for filling of the powder mixture are specified and a temperature of the powder mixture in the yield elongation zone should be increased up to 500-520° C., with degree of deformation being 2-5%.

[0051] In addition, in the particular case of the realization of the method, during hot compaction of the powder mixture, cladding of the compact with aluminum sheets can be carried out due to feeding of the powder mixture between the moving hot sheets passed by the vibrating chute in the grooved rolls of the rolling mill with subsequent folding of the ends of the sheets for formation of a seam. In this case also, some proportions for filling of the powder mixture are specified and a temperature of the powder mixture in the yield elongation zone should be maintained up to 430-450° C.

[0052] In addition, in the particular case of the realization of the method, when the foaming process is carried out, it is possible to determine termination of the process visually and objectively due to a difference in the degree of blackness of the form wall and aluminum and appearance of light belt of aluminum above the form wall.

[0053] The possibility of replication of the invention characterized by the above-mentioned set of 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

[0054] The example of the realization of the method for production of flat porous semiproducts is as follows.

[0055] Al—Mg—Cu—Mn aluminum alloy powder (a liquidus temperature of the alloy is 640-645° C., a temperature of low-melting point non-equilibrium eutectic is 535-540° C.) of 500 kg in weight was mixed with TiH2 porophore (a decomposition temperature is 690° C.) of 5.4 kg in weight and with a mixture of Al2O3 and Al2O3 (H2O) of 12.5 kg in weight and filled in a bin. Then, using a special measuring machine, the powder mixture was spread on a belt conveyer of the heating furnace as a uniform layer with a bulk weight of 1.23-1.32 g/cm3. The powder mixture was heated in the furnace under nitrogen atmosphere at a temperature of 500° C. The heated powder mixture was fed in a receiving funnel of the vertical rectangular chute joined up with a vibrating system which serves for pre-compaction of said powder mixture to obtain a density of 1.6-1.8 g/cm3 and transportation of the powder from top downwards. The vertical chute traverses the furnace for heating of the powder mixture and maintenance of the desired temperature up to 500° C. Then, from the funneled opening of the chute the hot pre-compacted powder mixture is fed in a receiving bin of the rolling mill with a design opening between the rolls and a preset rolling speed. The critical specified parameter is a rolling speed or speed of pulling the hot powder in the hot compaction zone with an opening of 6 mm. All other plant items wherein the powder mixture is transported ensure synchronous continuous feeding of said mixture to the rolling mill and maintain regularity of volume, weight and temperature variables of the production process. When the hot powder mixture is fed in the closed space of the yield elongation zone at a temperature of 430-450° C. and under a specific pressure from 300 up to 600 MPa, hot compaction takes place (relative density is 0.98-0.99). A 400 kg sheet was continuously produced in the rolling mill. The hot-compacted sheet was cut to length on shears behind the rolling mill. Some first hot-compacted blanks were fed for free foaming. These blanks were placed in the forms, sizes of which corresponded to those of the blanks, with walls made of heat-insulating material and were subjected to high-temperature treatment. When a temperature of a hot-compacted blank exceeded that of solid-liquid phase transformation, the foaming of this powder blanks began and when aluminum layer appeared above the form wall of 27 mm in height, termination of the foaming was evaluated visually. The form was taken out of the furnace and the foamed blank was cooled down intensively. Sizes of the porous semiproducts produced corresponded to those of the form. Bottom surface of the porous sheets was smooth, while the top surface had indications of swells because of internal pores. Side surfaces of the foamed plate were smooth. Density of the porous plates produced was 0.58-0.61 g/cm3. Porous semiproduct yield was 100%.

[0056] The second part of the hot-compacted blanks of 1000×120-200×6 mm in size was foamed in the same heat-insulating material forms at a temperature of 760° C. and after appearance of aluminum edge above the form wall of 27 mm in height termination of the foaming process was evaluated visually. The form was transferred from the furnace in its technological space with lower temperature, wherein the plate with a smooth surface was put on the end of the form and after fixation of the smooth surface the plate was taken away, the form was taken out of the furnace and the foamed semiproduct was cooled down intensively. Size of the porous semi-products produced was 1000×120-200×27.5 mm. In this case, top and bottom surfaces of the porous plates were smooth. Side surfaces of the foamed plates were smooth as well. Density of the porous semiproducts was 0.60-0.63 g/cm3. Porous semiproduct yield was 100%.

[0057] The production process offered by the present invention is developed in such a way that process scrap is practically absent. One can see that the main operation, namely hot compaction between the rolls of the rolling mill should not form scrap by its nature. Heating of the powder mixture under nitrogen atmosphere and feeding of said heated mixture in the rolling powder mill are scrap-free operations also. Only in case of hot compaction, edges can be slightly teared but they should be trimmed. Some small amounts of the scrap in the form of trimmed edges of the hot compacted sheets are grinded and recycled in the powder mixture. The optimized production process of foaming of the dense hot-compacted sheets in the heat-insulating material forms offers high product yield. Therefore, said final product yield of 95-97% corresponds to the real value.

[0058] The effect of a temperature of the powder mixture heating prior to hot compaction between cold rolls of the rolling mill should be discussed specifically. If heating of the powder mixture is carried out at temperatures below 450° C., intensive cooling of the powder mixture in the yield elongation zone results in both a sharp increase in forces applied to the rolls and a retardation of diffusion processes. As a result, hot compaction of the mixture does not take place and a sheet structure is brittle and porous (relative density is 0.80-0.85) body which is not applicable for foaming.

[0059] If heating of the powder mixture is carried out at temperatures above 600° C., overheating results in formation of low-melting point eutectics and appearance of large amounts of liquid phase inside oxidized particles and, thereby, loss of flow ability of the powder mixture. For TiH2 porophore particles the overheating above 600° C. is adverse to the most extent as it accelerates decomposition of TiH2 porophore, results in loss of a noticeable fraction of hydrogen in the porophore and reduces its future activity during foaming of the hot-compacted sheet. The first source of hydrogen liberation is decomposition of TiH2 at a heating temperature. The second one is surface hydrogen formed due to reaction of interaction between sorbed H2O molecules and aluminum cations which diffuse through oxide films. Hydrogen liberated during heating of TiH2 and surface hydrogen liberated into the conveyer furnace space increase hydrogen concentration and create certain hazard in case of heating of the powder mixture.

[0060] Organization of safe production process calls for creation of necessary conditions for accident prevention. Therefore, heating of the powder mixture is carried out in the conveyer furnace under nitrogen atmosphere with an excessive pressure from 10 up to 100 mm H2O, that excludes the possibility of ingress of oxygen in the powder mixture heating zone.

[0061] Heating up to temperatures of 450-500° C. is not critical for atomized powders in terms of formation of low-melting point eutectics. As the atomized powders have a non-equilibrium structure, formation of low-melting point eutectics is shifted to a zone of higher temperatures by 20-30° C. Overheating up to 500-550° C. has certain risk of formation of low-melting point eutectics, however, due to close contact with the cold rolls of the rolling mill liquid eutectic solidifies and ensures, thereby, high properties of the hot-compacted sheets. Heating up to 500-550° C. is recommended only at an initial stage of the process. This overheating created artificially caries a large reserve of heat energy in the bulk of the powder under compaction and in spite of the fact that the rolls of the rolling mill are cold, a temperature of the powder in the yield elongation zone does not reduce below 450° C. The use of higher rolling rates favours maintenance of a powder mixture temperature and simultaneously results in heating of rolling roll surfaces. Heating of the roll surfaces up to a temperature of 100-150° C. allows one to reduce a temperature of heating of the powder mixture in the conveyer furnace with nitrogen atmosphere and in the furnace for maintenance of a temperature during transportation of the powder mixture in the vertical chute.

[0062] Correction of a temperature in the direction of its reduction down to 450-500° C. at initial stages of heating of the powder mixture results in a noticeable reduction in intensity of TiH2 porophore decomposition and maintains a compaction temperature within a range of 430-450° C.

EXAMPLE 2

[0063] The example of the realization of the method for production of flat porous-semiproducts with the use of grinded particles of certain secondary aluminum alloys is as follows.

[0064] Aluminum alloy particles of 0.5-4.5 mm in size, produced by grinding of 16 alloy scrap (a liquidus temperature of the alloy is 640-645° C., a temperature of formation of equilibrium low-melting point eutectic is 505-510° C.) of 300 kg in weight were mixed in the water-cooled attritor under nitrogen atmosphere with additions of TiH2 porphore of 3.25 kg in weight (a decomposition temperature is 690° C.) and mixtures of Al2O3 and Al2O3 (H2O) of 10.5 kg in weight to produce 16 mechanically alloyed alloy with uniform distribution of porophore and aluminum oxides particles added to the alloy. This 16 alloy-based mechanically alloyed powder was filled in a bin. Then, using a special measuring machine, the powder was spread on a belt conveyer of the heating furnace as a uniform layer with a bulk weight of 1.35-1.41 g/cm3. The powder was heated in the furnace under nitrogen atmosphere at a temperature of 500° C. The heated powder was fed in a receiving funnel of the vertical rectangular chute joined up with a vibrating system which serves for pre-compaction of said 16 mechanically alloyed alloy powder to obtain a density of 1.6-1.8 g/cm3 and transportation of the powder from top downwards. The vertical chute traverses the furnace for heating of the powder and maintenance of the desired temperature up to 500° C. Then from the funneled opening of the chute the hot pre-compacted 16 alloy powder is fed in a receiving bin of the rolling mill with a design opening between the rolls and a preset rolling speed. The opening in the yield elongation zone is 6 mm. All plant items wherein the powder is transported ensure synchronous continuous feeding of the mixture to the rolling mill and maintain regularity of volume, weight and temperature variables of the production process. When the hot powder is fed in the closed space of the yield elongation zone at a temperature of 430-470° C. and under a specific pressure from 300 up to 600 MPa, hot compaction takes place (relative density is 0.98-0.99). A 300 kg sheet was continuously produced in the rolling mill. The hot-compacted sheet was cut to blanks of 1000×120×6 mm in size. Some first hot-compacted blanks were fed for free foaming. These blanks were placed in the forms, sizes of which corresponded to those of the blanks (1000×120-200×27 mm), with walls made of heat-insulating material and were subjected to high-temperature treatment at a temperature of 760° C. When a temperature of a hot-compacted blank exceeded that of solid-liquid phase transformation, the foaming of this powder blank began and when aluminum layer appeared above the form wall of 27 mm in height, termination of the foaming was evaluated visually. The form was taken out of the furnace and the foamed blank was cooled down intensively. Size of the porous semiproducts was 1000×120-200×28.5 mm. Bottom surface of the porous plate was smooth, while the top surface had indications of swells because of internal pores. Side surfaces of the foamed plate were smooth. Density of the porous plates produced was 0.58-0.61 g/cm3. Porous semi-product yield was 100%.

[0065] The second part of the hot-compacted blanks of 1000×120-200×6 mm in size was foamed in the same heat-insulating material forms at a temperature of 760° C. and after appearance of aluminum edge above the form wall of 27 mm in height termination of the foaming process was evaluated visually. The form was transferred from the furnace in its technological space with lower temperature, wherein the plate with a smooth surface was put on the end of the form and after fixation of the smooth surface the plate was taken away, the form was taken out of the furnace and the foamed semiproduct was cooled down intensively. Size of the porous semiproducts produced was 1000×120-200×27.5 mm. In this case, top and bottom surfaces of the porous plates were smooth. Side surfaces of the foamed plates were smooth as well. Density of the porous semi-products produced was 0.60-0.63 g/cm3: Porous semiproduct yield was 100%.

EXAMPLE 3

[0066] The example of the realization of the method for production of flat hot-extruded semiproducts from grinded particles of various secondary aluminum alloys in the rolling powder mill is as follows.

[0067] Aluminum alloy particles of 1.0-4.5 mm in size, produced by grinding of 16 Al—Cu—Mg—Mn alloy scrap (a liquidus temperature of the alloy is 640-645° C., a temperature of formation of equilibrium low-melting point eutectic is 505-510° C.) of 300 kg in weight were filled in a bin. Then, using a special measuring machine, the 16 aluminum alloy grinded particles were spread on a belt conveyer of the heating furnace as a uniform layer with a bulk weight of 1.30-1.36 g/cm3. The particles were heated in the furnace under nitrogen atmosphere at a temperature of 500-550° C. The heated particles were fed in a receiving funnel of the vertical rectangular chute joined up with a vibrating system. The particles filled the whole volume of the vertical bin full and passing a zone of the vertical chute joined up with a vibrating system they were pre-compacted to obtain a green density of 1.6-1.7 g/cm2. Simultaneously the pre-compacted particles passing the vertical chute were heated up to 500-550° C. Then the hot 16 alloy particles were fed in a receiving bin of the rolling mill and then in the design opening between the rolls which governed the arc of contact of the rolling mill. The arc of contact of the rotating cold rolls pulled the hot particles in the yield elongation zone wherein a partial cooling and consolidation of the particles and compaction of them with a degree of deformation from 5 up to 10% took place. The opening in the yield elongation zone was 6 mm. Thickness of the sheet produced from grinded 16 alloy particles was 6 mm. All plant items wherein the particles were transported ensured synchronous continuous feeding of the particles to the rolling mill and maintained regularity of volume, weight and temperature variables of the production process. When the cooled but still rather hot 16 alloy particles are fed in the closed space of the yield elongation zone at a temperature of 430-450° C. and under a specific pressure from 300 up to 600 MPa, hot continuous compaction or extrusion takes place (relative density is 0.97-0.99). The 16 alloy particles up to 300 kg in weight were continuously deformed in the rolling mill to sheet product. The hot-compacted sheet was cut to blanks at the shears behind the rolling mill. As a result of continuous hot compaction conditions, a continuous sheet from 16 alloy particles was produced and was cut to 1000 mm lengths at the shears.

EXAMPLE 4

[0068] The example of the realization of the method for production of aluminum-clad hot-extruded sheets from grinded particles of various aluminum alloy scrap in the rolling mill is as follows.

[0069] Aluminum alloy particles of 1.0-4.5 mm in size, produced by grinding of 16 Al—Cu—Mg—Mn alloy scrap (a liquidus temperature of the alloy is 640-645° C., a temperature of formation of equilibrium low-melting point eutectic is 505-510° C.) of 300 kg in weight were filled in a bin. Then, using a special measuring machine, the 16 aluminum alloy grinded particles were spread on a belt conveyer of the heating furnace as a uniform layer with a bulk weight of 1.30-1.36 g/cm3. The particles were heated in the furnace under nitrogen atmosphere at a temperature of 500-530° C. The heated particles were filled on moving hot aluminum sheets (450° C.), thickness and width of the sheets being 1 and 120 mm respectively. Prior to it the coiled aluminum sheets traversed a heating device wherein said sheets were heated up to 450° C., then they entered a receiving funnel of the vertical rectangular chute and were pressed against its walls inside. Thus, contact of the moving sheets with walls of the vertical chute joined up with a vibrating system was carried out. Then the aluminum sheets were pulled through a receiving bin of the rolling powder mill and fed in the yield elongation zone of the rolls, wherein the width of the hot-extruded sheet was formed. Sheet ends leaving the rectangular groove of the rolls were folded edgewise to produce a seam. When the line of the cladding sheets was mounted, hot 116 alloy particles were filled in a receiving bin and then they were fed in a design opening between the aluminum sheets. Then, the 16 alloy particles together with the cladding sheets were fed in a receiving bin of the rolling mill and then in the design opening between the rolls which govern the arc of contact of the rolling mill. This opening was constant from the vertical receiving bin up to design opening between cold rolls which govern the arc of contact of the rolling mill. The arc of contact of the rotating cold rolls pulled the hot cladding sheets together with the particles in the yield elongation zone wherein a partial cooling and consolidation of the particles and compaction of them with a degree of deformation from 5 up to 10% took place. The particles filled the whole space between the sheets to the entire length of them from the vertical receiving bin up to the seam under the rolls and passing a zone of the vertical chute joined up with a vibrating system they were pre-compacted to obtain a green density of 1.6-1.7 g/cm2. Simultaneously the pre-compacted particles passing the vertical chute were heated up to 500-530° C. When the space between the cladding aluminum sheets was filled with the particles, the rolling mill and all sinchronized particle feeding system were started up. The opening in the yield elongation zone was 6 mm. Thickness of the cladding aluminum sheet was 1 mm. Thickness of the sheet produced from grinded 16 alloy particles was 4 mm. The design space between the cladding sheets ensured plastic deformation of 5%. The opening between the rolls whereto the receiving bin of the rolling mill enters should be increased by a thickness of the two aluminum sheets. All plant items wherein the particles were transported ensured synchronous continuous feeding of the particles to the rolling mill and maintained regularity of volume, weight and temperature variables of the production process. When the cooled, but still rather hot (450° C.) particles are fed in the closed space of the yield elongation zone under a specific pressure from 300 up to 600 MPa, hot continuous compaction takes place (relative density is 0.98-0.99). The 16 alloy particles up to 300 kg in weight were continuously deformed in the rolling mill to sheet product. The hot-extruded clad sheet was cut to blanks at the shears behind the rolling mill. As a result of conditions of continuous extrusion of the aluminum-clad 16 alloy particles, a continuous sheet up to 120 mm in width was produced and cut to 1000 mm length at the shears. In the end, 16 alloy sheets clad with 1 mm thick aluminum layer on both sides were produced. Thickness of the cladding aluminum or aluminum alloy can be chosen from 0.3 up to 1 mm and more.

[0070] A temperature of heating of the aluminum alloy particles prior to rolling to obtain standard properties of an alloy prepared from inexpensive grinded scrap should correspond to hard plastic state, i.e. be below that of low-melting point eutectic formation by 20-50° C. In accordance with the present invention, the recommended high temperatures of alloy particle heating, which exceed those of low-melting point eutectic formation are caused by the main condition, namely the cold rolls with which the rolling process always begins. Therefore, overheating of the particles fed in the rolling mill allows one, in the first place, to produce the hot-extruded sheets with desired properties, with the clad layer or without it. In the second place, when the overheated particles are fed between the rolls of the rolling powder mill, the surfaces of the rolls are heated due to heat transfer from the bulk of the particles under rolling. Even in the case of heating of the roll surfaces up to 150° C., temperature gradient between a roll temperature and a temperature of the heated particles reduces. To obtain a particle temperature of 450° C. in the yield alongation zone, a temperature of heating of the particles in the furnace can be reduced down to 500° C. This temperature does not cause formation of liquid phase in the form of low-melting point eutectic in the alloy particles and ensures conduct of the hot compaction process when new structural conditions arise in the particles.

[0071] Therefore, for creation of optimum conditions for conduct of the process, both for powders and particles, with economically and technically attractive indices, the rolling should be carried out with the use of plastic one-phase alloy scrap overheated up to 600° C. for heating of the rolls at the initial stage. When roll surfaces were heated up to 100-150° C., chemical composition of the fed material was changed on the furnace conveyer, for example, powder were filled, and a temperature was controlled in a range of 490-500° C. rather than 500-530° C. Intensity of TiH2 decomposition reduces already at these temperatures, while properties of the hot-compacted sheets are kept completely, as compaction is carried out at optimum temperatures of 430-460° C.

[0072] As a result, in case of the properly chosen process parameters, the dense continuous hot-compacted sheets made from powders and hot-extruded sheets made from grinded particles are formed with relative density and thickness being 0.97-0.99 and from 3.0 up to 10 mm respectively.

[0073] The described examples of the realization of the invention in accordance with all variants of the method ensure the possibility of the realization of the invention and attainment of the above-mentioned technical results in all cases which solicited scope of protection is spread to, but they do not exhaust all potentialities of the realization of the invention characterized by the set of signs shown in the claim.

Claims

1. A method for production of porous semiproducts from aluminum alloy powders, including mixing of an aluminum alloy powder with porophores showing a decomposition temperature above that of aluminum powder melting, filling of a mixture produced in a mould, heating of said mould filled with said powder mixture under inert gas atmosphere, hot compaction, cooling, rolling to sheet, cutting of the sheet to blanks, placement of said blanks in a form with heat-insulating material walls, high-temperature treatment to conduct the foaming process at a liquidus temperature of the powder alloy and repeated cooling. The method differed from the prior art by the fact that during mixing of an aluminum alloy powder with porophores, oxide and hydroxide powder additions from 1 up to 10% are made in the mixture, as well as grinded secondary aluminum alloy particles of 0.5-4.5 mm in size and mixing with said particles is carried out in an attritor for production of a mechanically alloyed powder alloy and after heating a powder mixture produced is filled in a vertical mould which ensures simultaneous vibratory compaction and maintenance of a temperature of said powder mixture which is fed in a rectangular groove of a rolling mill to conduct continuous hot compaction in a closed groove formed by horizontal rolls at a temperature of 430-500° C. provided that the following conditions are observed:

H=h×&ggr;×&agr;, where

H is an opening between the rolls along the arc of contact, mm:

h is a thickness of the produced sheet, mm;

&ggr; is a powder compaction coefficient;

&agr; is an experimental coefficient, where 1.5≧&agr;≧4.5.

2. A method as defined in claim 1, differed by the fact that after termination of the foaming process the form with heat-insulating material walls is placed in a technological space of a furnace with lower temperature and for formation of upper smooth surface, a smooth heat-insulating material plate which does not react with molten aluminum is put on the end of the form. Then the form is taken out of the furnace, the plate is taken away and the upper smooth surface of the semiproduct produced is cooled down intensively.

3. A method as defined in claim 1, differed by the fact that the heat-insulating material which does not react with molten aluminum is made with embossed surface which forms a replicated impression on the solidifying aluminum surface.

4. A method as defined in claim 1, differed by the fact that prior to heat treatment, a stamped sheet is placed on the bottom of the form and a blank is placed on said sheet. After placement of said from in a technological space of the furnace with lower temperature the heat-insulating material plate which does not react with molten aluminum and made with embossed surface is put on the end of the form to produce replicated impression on the upper aluminum surface. Then the form is taken out of the furnace, the plate is taken away and the upper surface of the semiproduct produced is cooled down intensively.

5. A method as defined in claim 1, differed by the fact that instead of aluminum powder use is made of grinded scrap of aluminum alloy semiproducts both extruded and rolled ones, made from soft aluminum alloys AO, A1 and wrought alloys AM, A31, A33, AM3, 16, as well as copper, plastic metals and alloys, with particle size being from 0.5 up to 4.5 mm.

6. A method as defined in claim 1, differed by the fact that in case of mixing of an aluminum alloy with porophores in the attritor, use is made of grinded particles of aluminum alloys and copper and other plastic metals with size fractions of 0.5-2.5 mm, 1.0-3.0 mm, 1.5-4.5 mm.

7. A method as defined in claim 1, differed by the fact that when grinded scrap of aluminum alloys AO, A1 and hard wrought alloys AM, A31, A33, AM3, AM5, 16 are mixed in the attritor, additions of a porophore are made together with additions of refractory particles of aluminum oxide, boron carbide and silicium carbide, with a range of size being 5-100 &mgr;m.

8. A method as defined in claim 1, differed by the fact that when grinded scrap of aluminum alloys is mixed in the attritor, additions of refractory intermetallics particles, for example, NiAl3, NiAl, Cr2Al6 and others with a range of size being 10-100 &mgr;m are made in the mixture.

9. A method as defined in claim 1, differed by the fact that for a reduction in thickness of a sheet to be produced during hot compaction, a powder mixture is fed between moving steel sheets passed by the vibrating chute in the grooved rolls of the rolling mill.

10. A method as defined in claim 9, differed by the fact that during hot compaction of a powder mixture, cladding of the compact with steel or titanium sheets can be carried out due to feeding of said powder mixture between the moving hot sheets passed by the vibrating chute in the grooved rolls of the rolling mill with subsequent folding of ends of the sheets for formation of a seam. In this case also, some proportions for filling of said powder mixture are specified and a temperature of said powder mixture in the yield elongation zone should be increased up to 500-520° C., with degree of deformation being 2-5%.

11. A method as defined in claim 9, differed by the fact that during hot compaction of a powder mixture, cladding of the compact with aluminum sheets can be carried out due to feeding of said powder mixture between the moving hot sheets passed by the vibrating chute in the grooved rolls of the rolling mill with subsequent folding of the ends of the sheets for formation of a seam. In this case also, some proportions for filling of said powder mixture are specified and a temperature of said mixture in the yield elongation zone should be maintained up to 430-450° C.

12. A method as defined in claim 1, differed by the fact that during hot compaction of a powder mixture, pack cladding is carried out via feeding of packs with cladding sheets, for example, from titanium or steel, heated under inert gas atmosphere, with prepared surfaces being in contact with each other and with a welded front end of a pack in the groove of the rolling mill, with deformation being from 3 up to 15%.

13. A method as defined in claim 1, differed by the fact that due to a difference in the degree of blackness of the form wall and aluminum and appearance of light belt of aluminum above the form wall during foaming of a product, termination of the forming process can be determined visually.