RU2180361C2 - Method for making products of foamed aluminum - Google Patents

Abstract

FIELD: metallurgy, possibly manufacture of products for building industry, automobile- and lift manufacture, aircraft construction and ship building, other industry branches needing articles of light weight with properties of buoyancy, incombustibility, ecological safety, absorption of shock energy and oscillations of acoustic and electromagnetic waves. SUBSTANCE: method comprises steps of preparing aluminum base melt; introducing blowing agent to melt; foaming it; pouring it to sliding cell at continuous casting process; cooling. Blowing agent is introduced to melt being cast to cell; drawing ingot at rate providing crystallization of aluminum-base melt containing blowing agent until starting its active decomposition. Ingot is subjected to hot deformation for making compact billet with configuration of ready product. Foaming is realized at subsequent high temperature heat treatment of compact billet placed in mold. Melt is prepared of aluminum base alloys with wide range of crystallization and of aluminum alloys reinforced by particles of refractory compounds with fraction size no more than 20 micrometers and with its content in melt 5-15% vol. EFFECT: enlarged assortment of products with enhanced operational properties. 5 cl, 2 ex, 1 tbl

Description

 The invention relates to the field of metallurgy and can be used for the manufacture of products for use in various industries (construction industry, automobile and elevator construction, aviation, shipbuilding, etc.), where a combination of such material properties as lightness, buoyancy, non-combustibility is required, environmental cleanliness, ability to absorb shock energy, as well as fluctuations in acoustic and electromagnetic waves.

 A known method of producing products from foam aluminum, including mixing powders of aluminum alloy with porophore, filling the mixture into a container, hot pressing the mixture into a dense workpiece, hot deformation of the workpiece, followed by heat treatment in the mold (RF patent 2085339, class B 22 F, 1997 )

 The main disadvantages of this method are low productivity, high cost, as well as the potential explosion and fire hazard of the process during technological operations of filling, mixing and pouring mixtures into a container due to the pyrophoricity of aluminum powders.

 The closest analogue of the invention is the method described in the copyright certificate of the USSR 491715, publ. 02/10/1976, C 22 C 1/08. The description of the indicated copyright certificate provides information on the method for producing foam aluminum products, including the preparation of an aluminum-based melt, the introduction of a foaming reagent, TC porophore into the melt, the melt feeding into the slip crystallizer during continuous casting and drawing of the ingot at a rate that ensures the foamed melt solidifies on the basis of aluminum. The melt is mixed with the porophore and foamed before it is introduced into the crystallizer, thus the already foamed mass enters the crystallizer.

 The disadvantage of this method is the narrow range of products from foam aluminum both in size and configuration. In this way, products can only be obtained in the form of round or flat ingots. Obtaining another type of product (sheet, profile, stamping, etc.) is not possible, because a foamed ingot cannot be subjected to pressure treatment like ingots from wrought aluminum alloys.

 The invention is aimed at solving the problem of manufacturing products from molded foam aluminum according to the nomenclature close to the nomenclature of products from wrought aluminum alloys.

 The technical result of the proposed method is to expand the range of products from foam, as well as increasing their operational properties (wear resistance, stiffness), which can significantly expand the scope of this material.

 In the proposed method, an unfoamed ingot is obtained from a homogeneous mixture of aluminum melt with porophore particles, which, like ingots from wrought aluminum alloys, can be subjected to various types of hot pressure treatment (pressing, rolling, stamping, etc.) with the aim of making dense blanks of the required configuration and subsequent foaming to obtain a wide range of foam products (sheet, plate, profile, pipe, stamping, etc.) of various sizes and weights.

 The use of aluminum alloys reinforced with particles of refractory compounds in the proposed method can increase the wear resistance and stiffness of foam aluminum products and increase their service life.

 The proposed method for producing products from foam aluminum includes the preparation of an aluminum-based melt, the introduction of porophore into the melt, foaming, casting into a slip mold during continuous casting and cooling. The proposed method is characterized in that the porophore is introduced into the melt stream when casting it into the crystallizer, the ingot is drawn at a rate that solidifies the aluminum-based melt with the porophore introduced before its active decomposition, the obtained ingot is subjected to hot deformation to form a dense workpiece with the configuration the finished product, and foaming is carried out during the subsequent high-temperature heat treatment of a dense workpiece placed in the mold.

 In this case, the melt is prepared from alloys selected from the group consisting of aluminum alloys with a wide crystallization interval and aluminum alloys reinforced with particles of refractory compounds with a dispersion of not more than 20 μm, inert with respect to the melt of the matrix alloy and insoluble in water, with a content of particles of refractory compounds in the volume of the melt in an amount of 5-15 vol.%. Porophore is selected from the group of materials that are actively decomposed with gas evolution at a temperature above the solidus of an aluminum alloy.

 High-temperature heat treatment in the form of a dense billet of aluminum alloy with a wide crystallization interval with a porophore introduced into it is carried out in the solidus-liquidus temperature range of this aluminum alloy.

 High-temperature heat treatment in the form of a dense billet of aluminum alloy reinforced with particles of refractory compounds with a porophore introduced is carried out at a temperature not lower than the liquidus temperature of this aluminum alloy.

 The proposed method produces products from foam aluminum with a density of 0.2-0.9 g / cm with closed porosity.

 In the proposed method, increasing the viscosity of the melt based on an aluminum alloy with a wide crystallization interval and controlling the degree of thickening when foaming a solid billet from it is achieved by maintaining the solid phase of this alloy in the melt during high-temperature heat treatment in the solidus-liquidus temperature range of the used aluminum alloy.

 When using aluminum alloys reinforced with particles of refractory compounds, increasing the viscosity of the melt and controlling the degree of its thickening during foaming during high-temperature heat treatment of a solid billet at a temperature above the liquidus matrix aluminum alloy temperature is achieved by varying the volume fraction of particles with a dispersion of not more than 20 μm in the range of 5 15 vol.%. When the content of particles in an amount of less than 5 vol.%, The melt viscosity remains practically unchanged, when the content of particles is more than 15 vol.%, The melt becomes very viscous and does not allow to obtain the product with the required density. When using reinforcing particles with a fineness of more than 20 microns, technological difficulties arise associated with the gravitational settling of particles in the melt and in the processing of cutting products from foam aluminum.

 The use of aluminum alloys reinforced with solid particles of refractory compounds such as corundum, silicon carbide, etc. in the proposed method, characterized by higher values of hardness and elastic modulus, allows to increase the service life by increasing the wear resistance of foam aluminum and the rigidity of products made from it. The use of porophore with an active decomposition temperature below the solidus temperature of the aluminum alloy according to the proposed method does not make it possible to obtain a product with the necessary density, since in this case the workpiece is solid and has sufficient strength, therefore, the gas released from the porophore does not form internal pores, but diffuses along the grain boundaries particles and goes into the surrounding atmosphere.

 During continuous casting of an aluminum-based melt with a porophore introduced into it at a rate that does not solidify before the porophore is actively decomposed, the melt foams, preventing the formation of a high-quality ingot suitable for deformation.

 The proposed method for producing products from foam aluminum has been tested on aluminum alloys of two compositions using various porophores.

 Example 1

In the chamber of the melting furnace, 500 kg of melt was prepared from an aluminum alloy of grade D16 (T _S = 502 ^o C, T _L = 638 ^o C), calculated by the average chemical composition of the alloy in accordance with GOST 4784-74. The resulting melt, superheated to 690 ^o C, was poured into a slip mold with a diameter of 294 mm, a height of 100 mm. Titanium hydride powder was introduced in an argon stream into the melt stream coming from the notch of the furnace into the funnel of the casting ladle at a temperature of 650 ^° С during continuous casting and drawing of the ingot at a speed of 12 cm / min, which solidified the aluminum melt with the porophore introduced into it before it started active decomposition. The ratio of the mass of the melt and porophore was kept constant and amounted to 99: 1.

 The result was a cylindrical ingot with a density of 90%, a length of 2.0 m, a mass of 374 kg from alloy D16 with 1 wt.% Titanium hydride. After turning to a diameter of 290 mm and cutting the bottom and gating parts, the ingot was cut into two billets 900 mm long each and six pieces of billets 30 mm high.

Then, one billet 900 mm long, heated to 380 ^° C, was pressed on a horizontal hydraulic press with a force of 5,000 tf at a container temperature of 420 ^° C to obtain a strip with a cross section of 220 x 40 mm and a length of 3.6 m. The strip was cut into measuring billets 700 mm long and rolled at a temperature of 450 ^o C. As a result, sheets of size 6x700x1100 mm with a density of 99% were obtained. Each sheet was placed in a rectangular tray and heat treated in a resistance furnace when heated to 620 ^o C and holding at this temperature for five minutes. Then the tray with a foam sheet was taken out of the oven and cooled. The resulting foamed aluminum sheets had a thickness of 25 mm at a density of 0.5 g / cm ³ . Sheets were used in the manufacture of screens to protect special rooms from electromagnetic radiation.

The die was changed on the same press and the second workpiece, 900 mm long, was pressed under the same heating conditions to obtain a profile with a density of 95% in the form of a channel 240005 with a size of 105x120 mm with shelves 7 mm thick and 55 mm long. The total length of the profile was 5.2 m. The profile was cut into measuring blanks with a length of 500 mm and foamed in the appropriate form when heated to 600 ^° C with holding at this temperature for 7.5 minutes. After foaming and cooling of the profile, its density was 0.65 g / cm ³ . The obtained profile was used as a fragment of the design of the heat-insulating block.

Workpieces with a height of 30 mm were subjected to isothermal stamping to obtain blanks with a density of 95%, a diameter of 290 mm, a height of 60 mm and a wall thickness along the generatrix of the cylinder of 3.5 mm. The thickness of the bottom is 6.0 mm. Each preform was placed in a demountable form and heat treated at T = 620 ^° C with holding at this temperature for 5 minutes. The result was a product in the form of a cylindrical glass with a diameter of 290 mm and a height of 60 mm with a wall thickness along the generatrix of the cylinder of 15 mm (density - 0.45 g / cm ³ ) and a bottom thickness of 20 mm (density - 0.8 g / cm ³ ) Such a product is intended to certify it as a structural element of noise-absorbing covers of devices and assemblies.

 Example 2

In the same furnace as in example 1, a melt weighing 150 kg was prepared from pigs of an aluminum alloy of grade AD33 (T _S = 582 ^° C, T _L = 652 ^° C) reinforced with silicon carbide grinding powder particles with a dispersion of 10-14 μm , with the content of the latter in an amount of 12 vol.% of the volume of the matrix aluminum alloy. The obtained melt was superheated to 720 ^{° C.} and poured into a hollow mold with an outer diameter of 178 mm and an inner diameter of 58 mm, a height of 100 mm. Zirconium hydride powder was used as a porophore. Zirconium hydride was introduced into the melt stream. The casting speed was 15 cm / min; the ratio of melt and porophore was 98.5: 1.5.

As a result, a 2-meter-long tube billet with a mass of 106 kg and a density of 88% was obtained. After cutting to the measure (500 mm), the hollow billets were pressed on a press with a force of 1650 tf at T = 430 ^{° C.} to obtain a pipe with an outer diameter of 60 mm and a wall thickness of 2.0 mm. As a result, 4 pipes were obtained with a length of 6 m and a density of 96%. The pipes were cut into 1 meter long billets and each was placed in a split mold, which is a steel pipe with an inner diameter of 78 mm with a cylinder inserted with an outer diameter of 54 mm. After heat treatment at T = 700 ^o C for 3 minutes and cooling, a pipe with a density of 0.4 g / cm ³ with an outer diameter of 78 mm and a wall thickness of 12 mm was obtained. The pipes were used as thermal insulation for the supply of hot liquids and steam.

 Below are the comparative properties of the foams obtained by the proposed method in comparison with the prototype (the prototype is made of aluminum) (see table).

 Thus, the proposed method allows to expand the range of products from foam aluminum both in geometric shape (round, rectangular and complex configuration), and in weight and size, and also to improve their operational properties - to increase wear resistance and stiffness by 1.5-3 times .

Claims (5)

 1. A method of producing products from foam aluminum, including the preparation of an aluminum-based melt, introducing porophore into the melt, foaming, casting into a slip mold during continuous casting and cooling, characterized in that the porophore is introduced into the melt stream when casting it into the mold, drawing an ingot carried out at a rate that solidifies the aluminum-based melt with the porophore introduced before its active decomposition begins; the obtained ingot is subjected to hot deformation to form a dense billet with the configuration of the finished product, and foaming is carried out during subsequent high-temperature heat treatment of a dense billet placed in a mold.  2. The method according to p. 1, characterized in that the melt is prepared from alloys selected from the group comprising aluminum alloys with a wide crystallization interval and aluminum alloys reinforced with particles of refractory compounds with a dispersion of not more than 20 microns, inert with respect to the molten matrix alloy and insoluble in water, with a particle content of refractory compounds in the melt volume of 5-15 vol. %  3. The method according to any one of paragraphs. 1 and 2, characterized in that the porophore is selected from the group of materials that are actively decomposed with evolution of gas at a temperature above the solidus of an aluminum alloy.  4. The method according to any one of paragraphs. 1-3, characterized in that the high-temperature heat treatment of a dense billet of aluminum alloy with a wide crystallization interval with a porophore introduced into it is carried out in the temperature range solidus - liquidus of this aluminum alloy.  5. The method according to any one of paragraphs. 1-3, characterized in that the high-temperature heat treatment of a dense billet of aluminum alloy reinforced with particles of refractory compounds is carried out at a temperature not lower than the liquidus temperature of the aluminum alloy.

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