CA2454169C

CA2454169C - A method for production of porous semiproducts from aluminum alloy powders

Info

Publication number: CA2454169C
Application number: CA2454169A
Authority: CA
Inventors: Alexander Ivanovich Litvintsev; Sergei Alexandrovich Litvintsev; Boris Alexandrovich Litvintsev
Original assignee: Litvintseva Maria
Current assignee: Litvintseva Maria
Priority date: 2001-07-17
Filing date: 2002-06-11
Publication date: 2016-08-09
Anticipated expiration: 2022-06-11
Also published as: RU2200647C1; US20040258553A1; WO2003008133A1; CA2454169A1

Abstract

A method for producing porous materials having high thermal, sound insulation, energy absorption, lightweight, incombustibility and ecological cleanness is described. The method comprises mixing wrought or cast aluminum alloy powders with a foaming agent and adding an aluminum oxide/aluminum hydroxide mixture or ground scrap particles of aluminum alloys. An attritor mixes the ground particles to obtain a mechanically alloyed powder alloy. The mixture is heated and poured in a container for vibro compaction and temperature maintenance, and transferred to a rectangular groove of a rolling mill for continuous hot compaction in a dead groove of horizontal rollers between 430°C-500°C according to H=h×.gamma.×.alpha., where H is an opening between the rolls along the arc of contact in mm, h is a thickness of the produced sheet in mm, .gamma. is a powder compaction ratio of the coefficient, and a is an experimental ratio coefficient equal to 1.5>=.alpha.>=4.5.

Description

A METHOD FOR PRODUCTION OF POROUS SEMIPRODUCTS
FROM ALUMINUM ALLOY POWDERS
FIELD OF THE INVENTION
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, automotive industry, aircraft industry and other branches of industry wherein combination of these properties can be desired.
DESCRIPTION OF THE BACKGROUND ART
Already known in the prior art, there is a method for production of porous semi-products from powder alloys based on aluminum and copper, that incorporates mixing of alloy powder with a foaming agent, filling of the mixture in a press container, simultaneous heating of the filled container and applying pressure at which the foaming agent 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).
Limitation of this method is a very small range of semi-products 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.
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, foaming agent, is the main and common operation.

The first variant includes placement of foaming agent-free metallic layer on the bottom floor of a press container, covering of the metallic layer with a powder mixture containing a foaming agent 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 he changed via subsequent hot rolling for formation of a new body wherein a high-porous foamed metallic layer appears between two metallic layers.
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 foaming agent. 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.
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 (US Patent 5,151,246 September, 1992, B 22 F 3/18, B 22 F 3/24).
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 1.0 wt 9/,; up to 10 wt % of total weight of powder mixture with a foaming agent 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 aluminum foam (Patent RU No. 2121904 of November 20, 1998, B 22 F 3/11).

2 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 cost of semi-products.
Said method and the above one are the most similar analogues (prototypes) in terms of the set of properties. 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). 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 foaming agent or a mixture of coarse particles having particle size of 0.5 ¨ 4.5 mm in size with a foaming agent mechanically alloyed in an attritor (industrial machine to produce powders by grinding and mechanical alloying) and also of ground particles of certain aluminum alloys in a rolling mills.
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¨ 3.0 square meters.
The most similar analogue of the invention is a method for production of porous semi-products from aluminum alloy powders. The method includes mixing of an aluminum alloy powder with a foaming agent showing a decomposition temperature above that of aluminum alloy powder melting, with addition of a copper powder ranging from 1.0 wt %
up to 10 wt % of total weight of powder mixture, 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 foaming process at a melting temperature of the aluminum alloy. In this case, alloys of Al-Cu-Mg, Al-Zn-Cu-Ma, Al-Zn-Mg, Al-Mg or Al-Si-Cu-Ma 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, November 20, 1998, B 22 F

3 The common signs of the known method and this invention are mixing of an aluminum alloy powder with foaming agent 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, inot compacting, extrusion, cutting-to-length, hot rollin.g to sheets, cutting of the sheets to the blanks, placing them in a form with heat-insulating material walls, with subsequent high temperature treatment for conduct of foaming process at melting temperature of the powder aluminum alloy and subsequent cooling.
BRIEF SUMMARY OF THE INVENTION
A. method comprises mixing in a blender 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 ranging from 0.5 wt % up to 1.5 wt ,4, of total weight of the powder mixture formed during atomization, with a powder mixture of aluminum oxide (A.1203) and aluminum hydroxide [Al(OH)3] ranging from 1.0 wt % up to 10 wt % of total weight of the powder mixture, and an active foaming agent (Ti.H.2) ranging from 0.5 wt % up to 1.2 wt % of total weight of the powder mixture showing a decomposition temperature above that powder aluminum alloy matrix melting, or mixing by mechanically alloying in an attritor of ground scrap particles of certain wrought aluminum alloys which meet requirements specified for hard wrought aluminum alloys: 3003, 6063, 6061, 5754, 5056, 2024 and soft wrought aluminum alloys which meet requirements specified for 1070, 1230 (scrap particles being 0.5 ¨ 4.5 rum in size) with a powder mixture of aluminum oxide Al2O3)( and aluminum hydroxide [Al(OH)3] and a foaming agent (Ti1I2). Addition of aluminum oxide together with aluminum hydroxide ranging from 1.0 wt % up to 10 wt 'A of total weight of the powder mixture, both in aluminum alloy powder and the ground scrap particles of certain aluminum alloys ensures a noticeable increase in viscosity of melt. The powder mixture from a blender or the mechanically alloyed powder mixture produced in an attritor is fed through a bin 1 as a uniform layer on a conveyer 2 of a heating furnace 4. Heating of said mixture is carried out in nitrogen atmosphere (dew point is -40 C) at a temperature ranging from 450 C to 600 C under an excessive pressure from 10 mm up to 100 mm 1120. The heated powder mixture is poured in a loading bin 5 of a vertical rectangular chute 6 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

4 rectangular chute is prevented as it gets through a heating furnace wherein the desired temperature is maintained in a range between 450 C and 600 C depending on powder alloy composition and other process parameters. Travel speeds of said mixture on the conveyer of the pre-heating 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 a 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 a closed rectangular space which forms final sizes of a compacted sheet semi-product 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 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 forming a closed space, 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 sheet from 150 up to 1500 mm in width and from 3 up to 15 mm in thickness.
Conditions of formation of a continuous hot-compacted or hot-extruded flat sheet semi-product between the special rolling mill rolls which form a closed space can be described by the following equati.on.:

5 =
H¨hxyx a, where:
H is an opening between the rolls along the arc of contact, mm;
h is a thickness of the compacted sheet, mm;
y is a compaction. coefficient a is an experimental coefficient, where 1.5 < < 4.5.
As is well known, the compaction coefficient? is calculated by dividing the compacted density of a powder by its density prior to compaction.. Thus, the compaction coefficient y is always a number greater than 1.
As a result of application of forces close to volume-stressed state in the yield elongation zone and at a temperature of 450 C ¨ 500 C, active interactions of the powder mixture particles develop. Powder particles drawn 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-to-particle interface. As a result of a temperature and by forces in the yield elongation zone, due to active diffusion, new strong metallic bonds are generated between powder particles both in contact areas with pure juvenile surfaces and in contact areas with metallized oxide film. These strong metallic bonds 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 into 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 a net with small mesh. A 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 thermostatic 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. melt edge appears above the form wall. The tbnn is taken out of a furnace, its surface is cooled down and the foaming process is arrested at the desired height.
The technical result obtained due to realization of the invention incorporates high output, creation of waste-free manufacturing process, low production costs of porous sheet semi-

6 products due to the use of own manufacturing scrap with subsequent grinding in the attritor for production of the mixture with desired chemical composition.
The invention relates to the field of powder metallurgy and can be used for production of porous material for building machinery, road construction, automotive industry, space and 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 where absolute environmental safety are desired.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows a front view of an apparatus useful in practicing the inventive method.
Figure 2 shows a side view of a portion of the apparatus (rolling mill 9) of Figure 1.
DETAILED DESCRtPTION OF THE INVENTION' A method of the present invention differs from the prior art by the fact that it comprises the mixing of certain wrought or cast aluminum alloy powder with a foaming agent and aluminum oxide (A1203) and aluminum hydroxide [A1(011)31 powders in a blender, or the mixing of a foaming agent and the aluminum oxide and aluminum hydroxide with coarse particles of a certain wrought aluminum alloy having particle size of 0.5 ¨ 4.5 mm in the attritor to produce mechanically alloyed powder alloy, heating of either of these powder mixtures in a heating furnace and after heating, filling of the heated mixture in a rectangular chute installed vertically to ensure simultaneous vibratory compaction and maintenance of a temperature of the powder mixture, followed by hot consolidation (compaction or extrusion) by feeding of the said powder mixture in the grooved horizontal rolls of a rolling mill at a temperature of 430 C ¨ 500 C
providing that the following conditions are satisfied:
H=hxy xa , where:
H is an opening between the rolls along the arc of contact, min;
h is a thickness of the compacted sheet, inm;
y is a powder compaction coefficient;
a is an experimental coefficient, where 1.5 < a < 4,5.
The present invention concerns a method for production of porous semi-products from aluminum alloy powders comprising the steps of:

7 I. Mixing in blender 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) and 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 (A.I.203) and aluminum hydroxide [A.1(OH)3] ranging from 0.5 wt % up to 10 wt % of the total weight of the powder mixture and an active foaming agent (TiH2) ranging from 0.5 wt % up to 1.2 wt % of the total weight of the powder mixture showing a decomposition temperature above that of powder aluminum alloy matrix melting or mixing of coarse particles of ground scrap of the wrought aluminum alloys 3003, 6063, 6061, 5754, 5056, 2024 (hard wrought aluminum alloys) and the soft wrought aluminum alloys 1070, 1230 (scrap particles being 0.5 ¨ 4.5 mm in size) with a mixture of aluminum oxide and aluminum hydroxide with a foaming agent in the attritor by the mechanical alloying technique;
II. Feeding of the powder mixture 3 (Fig. I) of step I as a uniform layer on a conveyer 2 in a heating furnace 4. Heating of the mixture in nitrogen atmosphere at a temperature range of 450 C ¨ 600 C under an excessive pressure from 10 mm up to 100 mm 1-1.20;
TIT. Feeding of the pre-heated mixture from step TT in a loading bin 5 of a vertical chute 6 wherein the pre-heated mixture is uniformly compacted by a vibrating system 7 and transferred from top downwards;
IV. Filling of the pre-heated mixture of step III in a heating furnace 8 wherein the desired temperature is maintained at a range of 450 C ¨ 600 C depending on powder alloy composition and other process parameters to prevent cooling-down of said mixture during transportation in the chute 6; travel speeds of said mixture on the conveyer of the pre-heating furnace and in the chute are the same;
V. Feeding of the pre-heated mixture of step IV from the funneled opening of the chute 6 to a rolling mill with horizontal rolls 9, with each roll having an internal turned groove I I
(Fig. 2), where the depth of the grooves is equal to a half of thickness of a hot-compacted sheet semi-product to be produced. A chosen rolling speed or speed of pulling of 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 6 and with that of powder transportation on the conveyer in case of powder preheating in the furnace 4 .
under nitrogen atmosphere of step II. Side ridges of the turned grooves of each roll touch

8 each other and thereby create a closed rectangular space which forms final sizes of a hot-compacted sheet semi-product 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 rectangular space under certain 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 sheet 10 from 50 mm up to 1500 mm in width and from 3 trim up to 10 mm in thickness h.
Conditions of formation of a continuous hot-compacted or hot-extruded flat sheet semi-product between special rolling mill rolls which form a closed groove in the rolling mill can be described by the following equation:
H=hxyxa,where H is an opening between the rolls along the arc of contact, mm;
h is a thickness of the compacted sheet, mm;
7 is a powder compaction coefficient;
a is an experimental coefficient, where 1.5 < a <
As a result of application of forces close to volume-stressed state in the yield elongation zone and at a temperature of 430 C ¨ 500 C, active interaction of powder mixture particles is developed. Powder particles are drawn together by forces, undergoing partial destruction of oxide films, which is accompanied by formation of juvenile surfaces, or direct convergence when the oxide film is in particle-particle interface. As a result of a certain temperature and by forces in the yield elongation zone, due to active diffusion, new strong metallic bonds are

9 generated between powder particles both in contact areas with pure juvenile surfaces and in contact areas with metallized oxide film. These strong metallic bonds did 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 then cut to blanks which are placed into 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. The bottom of the forms is made from a refractory steel sheet or a net with small mesh_ The form, on the one hand, is a means of transport in which the blanks arc fed to heat treatment and, on the other hand, they create a thermostatic space for the blanks heated during heat treatment. High-temperature heat treatment is carried out by heating of the blanks above a temperature of solid-liquid phase transformation, which results in foaming, Termination of the foaming process is determined visually, when a contrast aluminum edge appears above the form wall. The form is taken out of a furnace, the upper surface of semi-product is cooled down intensively and the-foaming process is arrested at the desired height.
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 the furnace with lower temperature, and for formation of the upper smooth surface of the porous semi-product, a smooth heat-insulating material plate which does not react with liquid aluminum is placed on the top of the form. Then the form is taken out of the furnace, the plate is taken away and the porous semi-product produced is cooled down intensively.
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 an embossed surface which forms a replicated impression on the solidifying aluminum surface of the porous semi-product.
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 the form in a technological space of the furnace with lower temperature, a heat-insulating material plate with a smooth or an embossed surface, which does not react with molten aluminum, is put on top of the form. Under pressure of the said plate, the stamped sheet will clad the lower surface of the porous semi-product.
Then, the form is taken.

out of the furnace, the plate is taken away and the porous semi-product produced is cooled down intensively.
In addition, in the particular case of the realization of the method, when ground scrap of the certain wrought aluminum alloys is mixed in the attritor, additions of a :foaming agent and the mixture of the aluminum oxides and aluminum hydroxide are made together with additions of powders of copper and other plastic metals with. particles sizes of 1.0 ¨ 100 In addition, in the particular case of the realization of the method, when ground scrap of the certain wrought aluminum alloys is mixed in the attritor, additions of a foaming agent and the mixture of the aluminum oxide and aluminum hydroxide are made together with additions of refractory particles of aluminum oxide, boron carbide and silicon carbide having particle size of 5 ¨ 100 gm.
In addition, in the particular case of the realization of the method, when ground scrap of the certain wrought aluminum alloys is mixed in the attritor, additions of a foaming agent and the mixture of aluminum oxide and aluminum hydroxide are made together with additions of refractory intermetallic particles, comprising NiA13,NiA.1, Cr2A1.6 with particle size 10 ¨ 100 um.
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 strips which pass through the vibrating chute into the grooved rolls of the rolling mill.
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 strips can be carried out due to feeding of the powder mixture between moving pre-heated steel or titanium strips which pass through the vibrating chute into the grooved rolls of the rolling mill with subsequent folding of ends of the strips 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 C ¨ 520 C, with degree of deformatio.n.
being 2 ¨ 5%..
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 strips can be carried out due to feeding of the powder mixture between moving pre-heated aluminum strips which pass through the vibrating chute in the grooved rolls of the rolling mill with subsequent folding of the ends of the strips for formation of a seam, in this case also, some proportions for filling of the powder : e mixture are specified and a temperature of the powder mixture in the yield elongation zone should be maintained between 430 C ¨ 450 C.
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 between of the form's wall and aluminum, as well as the appearance of a light belt of aluminum above the form wall.
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 An example of the realization of the method for producing flat porous semi-products is as follows. Al-Mg-Cu-Mn aluminum alloy powder with a melting temperature of the alloy ranging from 640 C ¨ 645 C, of 500 kg of mass and with a temperature of low-melting point non-equilibrium eutectic between 535 C. ¨ 540 C was mixed with an active foaming agent (Fiff2) of 1.5 5.4 kg of mass with a decomposition temperature of 690 C and with a mixture of A1203 and All(OH)3 of 12.5 kg of mass and was filled in a bin 1 (Fig. I). Then, using a special measuring machine, the powder mixture was spread on a belt conveyer 2 of the heating furnace 4 as a uniform layer with a bulk weight of 1.23 ¨ 1.32 giem3. The powder mixture 3 was heated in the furnace 4 under nitrogen atmosphere at a temperature of 500 C. The heated powder mixture was then fed into a load bin 5 of the vertical rectangular chute 6 joined up with the vibrating system 7, which serves for pre-compaction of said powder mixture to obtain a density of 1.6 ¨
1.8 glem3 and transportation of the powder from top downwards. The vertical chute traverses the furnace 8 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 into a receiving bin of the rolling mill with a design opening between the rolls 9 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 between 430 C ¨ 450 C and under a specific pressure from 300 =
up to 600 MPa, hot compaction takes place (relative density is 0.98 ¨ 0.99) and a 400 kg sheet was continuously produced in the rolling mill. The hot-compacted sheet was cut to length into blanks of 1000 x 120-200 x 6 mm in size on a shear behind the rolling mill and split into two parts.
The first part of the hot-compacted blanks was fed for free foaming. These blanks were placed into forms, sizes of which corresponded to those blanks, with heat-insulating material sidewalls and a refractory steel sheet bottom and were subjected to high-temperature treatment at a temperature of 760 C. When the temperature of the hot-compacted blank exceeded the temperature of the solid-liquid phase transformation for said aluminum alloy, the foaming process began. The termination of the foaming process was evaluated visually when a contrast aluminum layer appeared above the form's wall of 27 mm in height. Then the form was taken out of the furnace and the porous semi-product produced was cooled down intensively. Sizes of the porous semi-product 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/eml. Porous semi-product yield was 100%.
The second part of the hot-compacted blanks was foamed in the same forms as discussed above, at a temperature of 760 C. After appearance of a contrast aluminum layer above the form's wall of 27 mm in height, the form was transferred in the technological space of the furnace with lower temperature, wherein a plate with a smooth surface from heat-insulated material was placed on top of the form and after fixation of the smooth upper surface of the foam the plate was taken off, the form was taken out of the furnace and the foamed porous semi-product was cooled down intensively. In this case, both 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 was 0.60 ¨ 0.63 g/cm3. Porous semi-product yield was 100%.
The production process offered by the present invention is developed in such a way that process scrap was practically absent. Heating of the powder mixture under nitrogen atmosphere and feeding of said heated mixture in the rolling mill was a scrap-free operation. Only in case of hot compacting, would the edges be slightly torn and should be trimmed. These small amounts of scrap in the form of trimmed edges of the hot compacted sheets are ground and recycled in the powder mixture. The optimized production process of foaming the dense hot-compacted sheets 1:3 in the forms made from heat-insulating offers a high product yield. Therefore, said final product yield of 95¨ 97% corresponds to the real value.
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.), which is not applicable for foaming.
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 the active foaming agent particles of titanium hydride (TiH2), the overheating above 600 C is adverse to the most extent, as it accelerates decomposition of TiH2, results in loss of a noticeable fraction of hydrogen in the foaming agent 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 interaction between sorbate H20 molecules and aluminum cat-ions which diffuse through oxide films.
Hydrogen liberated during beating of Tail and surface hydrogen liberated into the conveyer furnace space increase hydrogen concentration and create certain hazard in case of heating of the powder mixture.
To establish safety, this production process requires necessary conditions to prevent potential hazards. Therefore, beating of the powder mixture is carried out in the conveyer furnace under nitrogen atmosphere with an excessive pressure from 10 mm up to 100 mm H20, which eliminates the possibility of oxygen intake in the powder mixture heating zone.
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 creates 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 relative high density up to 0.97 ¨ 0.99 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, transfers 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 the temperature of the powder in the yield elongation zone does not reduce below 450 C. The use of higher rolling speeds helps to maintain the temperature of the powder mixture and simultaneously results in heating of the roll surfaces. Heating of the roll surfaces up to a temperature of 100 ¨
150 C allows for the reduction of the temperature 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.
Correction of the 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 Tah foaming agent decomposition and maintains a compaction temperature within a range of 430¨ 450 C.
Example 2 The example of the realization of a method for producing of flat porous semi-products with the use of ground particles of certain aluminum alloys is as follows.
Aluminum alloy particles of 0.5 ¨ 4.5 mm in size, produced by ground of 2024 alloy scrap (a melting temperature range of the alloy is 640 ¨ 645 C, a temperature of formation of equilibrium low-melting point eutectic is 505¨ 510 C) of 300 kg of mass were mixed in a water-cooled attritor under nitrogen atmosphere with additions of 3.25 kg of active foaming agent Ti.H2 (a decomposition temperature is 690 C) and mixture of .A.1.203 and .A.1(OH)3 of 10.5 kg to produce 2024 mechanically alloyed aluminum alloy with uniform distribution of foaming agent and aluminum oxides particles. This 2024 alloy-based mechanically alloyed powder was filled in bin 1 (Fig. 1). Then, using a special measuring machine, the powder was spread on a belt conveyer 2 of the heating furnace 4 as a uniform layer with a bulk weight of 1.35 ¨ 1.41 gicm3. The powder was heated in the furnace 4 under nitrogen atmosphere at a temperature of 500 C. The heated powder 3 was fed in a loading bin 5 of the vertical rectangular chute 6, joined up with a vibrating system 7, which serves for pre-compaction of said 2024 mechanically alloyed aluminum alloy powder to obtain a density of 1.6 ¨ 1.8 glems and transports the powder from top downwards.
The vertical chute traverses the furnace 8 for heating of the powder and maintaining the desired temperature up to 500 C. From the funneled opening of the chute, the hot pre-compacted 2024 t alloy powder was fed in a receiving bin of the rolling mill 9 with a design opening between the rolls and a preset rolling speed. The opening in the yield elongation zone was 6 mm. All plant items wherein the powder was 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 was 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 .M,Pa, hot compaction took 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 x 120 x 6 mm in size and was split into two parts.
The first part of the hot-compacted blanks was fed for free foaming. These blanks were placed into forms, sizes of which corresponded to those blanks with heat-insulating material sidewalls and refractory steel bottom and were subjected to high-temperature treatment at a temperature of 760 C. When the temperature of a hot-compacted blank exceeded that of a temperature of solid-liquid phase transformation, the foaming process began. A
termination of the foaming process was evaluated visually when a contrast aluminum layer appeared above the form wall, Then the form was taken out of the furnace and the foamed blank was cooled down intensively. 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 glcm.3. Porous semi-product yield was 100%.
The second part of the hot-compacted blanks was foamed in the same heat-insulating material forms at a temperature of 760 C and after appearance of a contrast aluminum edge above the form wall, the form was transferred from the furnace in its technological space with lower temperature, wherein the plate with a smooth surface from heat-insulating material was put on top of the form and after fixation. of the smooth upper surface, the plate was-taken away, the form was taken out of the furnace and the foamed porous semi-product was cooled down intensively. 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/cml with yield 100%.
Example 3 The example of the realization of a method for producing of flat hot-extruded semi-products from ground particles of the certain aluminum alloys in the rolling mill is as follows.

Aluminum alloy particles of 1.0 ¨ 4.5 mm in size, produced by ground of 2024 Al-Cu-Mg-Mn alloy scrap (a melting temperature range of the alloy is 640 ¨ 645 C, a temperature of formation of equilibrium low-melting point eutectic is 505 ¨ 510 C) of 300 kg of mass were Filled in a bin 1 (Fig. 1). Then; using a special measuring machine, the 2024 aluminum alloy ground particles were spread on a belt conveyer 2 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 4 under nitrogen atmosphere at a temperature of 500 ¨ 550 C. The heated particles were fed in a load bin 5 of the vertical rectangular chute 6, joined up with a vibrating system 7. The particles filled the whole volume of the vertical chute 6 full and while passing a zone of the vertical chute that is joined up with a vibrating system 7 they were pre-compacted to obtain a green density of 1.6 ¨ 1.7 glern.2.
Simultaneously, the pre-compacted particles passing the vertical chute were heated through the heating furnace 8 to a desired temperature ranging from 500 C ¨ 550 C. Then, the hot the 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 13 (Fig. 1) of the rolling mill.
The arc of contact 13 of the rotating cold rolls 9 were 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 these ground 2024 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 2024 alloy particles were fed into 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 took place (relative density is 0.97 ¨ 0.99). The 2024 alloy particles up to 300 kg in mass were continuously delbrmed in the rolling mill to sheet product. As a result of continuous hot compaction conditions, a continuous sheet from the particles was produced and was cut to blacks of 1000 mm length at the shears behind the rolling mill.

Claims

1. A method for producing aluminum porous semi-products comprising the steps of:
mixing either wrought or cast aluminum alloy powder, selected from the group consisting of cast alloys (Al-Si-Cu-Mg, Al-Cu-Mg-Si, Al-Mg-Si and Al-Mg-Cu-Si) and wrought alloys (Al-Cu-Mg-Mn, Al-.Mg-Cu, Al-in-Cu-Mg and Al-Zn-Mg-Cu) with an active foaming agent, namely TiH2, and the mixture of aluminum oxide (Al2O3) and aluminum hydroxide [Al(OH)3] ranging 1 wt % up to 10 wt % of the total weight of the powder mixture in a blender, or ground scrap of wrought aluminum alloy particles, consisting of hard wrought aluminum alloys (3003, 6063, 6061, 5754, 5056 and 2024) and soft wrought aluminum alloys (1070 and 1230) having a particle size of 0.5 ¨ 4.5 min with aluminum oxide (Al2O3) and aluminum hydroxide [Al(OH)3)] ranging from 1 wt % up to wt % of the total weight of the powder mixture and an active foaming agent in attritor;
heating the mixture at a temperature ranging from 450°C to 600°C
in a heating furnace;
transferring the heated mixture into a loading bin of a vertical rectangular chute to provide simultaneous vibratory compaction and to maintain the temperature of said mixture in a range between 450°C to 600°C;
feeding the heated mixture into rectangular grooves of a rolling mill to conduct continuous hot compaction in a closed rectangular space formed by side ridges of the grooves of the rolls, at a temperature of 430°C ¨ 500°C to produce a hot compacted sheet providing that the following conditions are satisfied:
H = h× .gamma.× .alpha., where H is an opening between the rolls along the arc of contact, mm:
h is a thickness of the produced sheet, mm;

.gamma. is a powder compaction coefficient;
.alpha. is an experimental coefficient, where 1.5 <=.alpha.<= 4.5, cutting to length the hot-compacted sheet into blanks; and heat treating said hot-compacted blanks in a form comprising heat-insulating sidewalls and a refractory steel. sheet or small mesh net bottom in a furnace to cause foaming at a temperature above the solid-liquid phase transformation of the :mixture.

2. The method as defined in claim 1 further comprising the steps of:
placing a form into a space of a furnace set at a lower temperature than the temperature of the heat treatment after the foaming process terminated;
placing a smooth plate from heat-insulating material which does not react with molten aluminum on top of the form for formation of smooth upper surface of the heated blank;
taking the form out of the furnace; and removing the plate from the form and cooling down rapidly the porous semi-product.

3. The method as defined in claim 2, wherein the said heat-insulating plate is made with an em.bossed lower surface forming a replicated impression on a solidified aluminum surface.

4. The method as defined in claim 3, wherein prior to the heat treatment, a stamped sheet is placed on the bottom. of the form and the blank is placed on said sheet in order to clad the lower surface of the porous semi-product.

19 The method as defined in claim 1, wherein the powder mixture comprising the ground scrap of the wrought aluminum alloys further comprises copper powder and other plastic metals powder with a particle size of 10 ¨ 1.00 µm.

6. The method as defined in claim 1, wherein the powder mixture comprising the ground scrap of the wrought aluminum alloys further comprises refractory particles of aluminum oxide, boron carbide and silicon carbide having a particle size of 5 ¨100 µm.

7. The method as defined in claim 1, wherein the powder mixture comprising the ground scrap of wrought aluminum alloys further comprises refractory intermetallic particles comprising NiAl3, NiAl-, CrAl6 with a particle size of 10 ¨ 100 µm.

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

9. The method as defined in claim 1, wherein during the hot compaction of the powder mixture, cladding of the hot compacted sheet with steel or titanium strips is carried out by feeding of the powder mixture between moving, pre-heated steel or titanium strips which pass through by the vibrating chute into the grooved rolls of the rolling mill with subsequent folding of ends of the strips form of a seam.

10. The method as defined in claim 1, wherein during the hot compaction of the powder mixture, cladding of the hot compacted sheet with aluminum strips can be carried out by feeding of the powder mixture between moving pre-heated aluminum strips which pass through the vibrating chute into the grooved rolls of the rolling mill with subsequent folding of the ends of the strips for formation of a seam.

11. The method as defined in claim 1, wherein during the hot compaction of the powder mixture, pack cladding is carried out via feeding of packs with cladding sheets, 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%.

12. The method as defined in claim 1, wherein termination of the forming process of the heat treatment can be determined visually by evaluating the difference in the degree of blackness between form's walls and molten aluminum, and an appearance of a light belt of aluminum above form wall during foaming of a product.

13. The method as defined in claim 9, wherein a temperature of the powder mixture in a yield elongation zone being increased up to 500 ¨ 520°C, with a degree of deformation of 2 ¨
5%.

14. The method as defined in claim 10, wherein a temperature of the powder mixture in a yield elongation zone is maintained up to 430 ¨ 450°C.