RU2691826C1 - Method of producing casts from dispersed-hard alloys based on aluminum or magnesium - Google Patents

Abstract

FIELD: metallurgy.SUBSTANCE: invention relates to metallurgy of light alloys, particularly, to methods of casting of alloys based on aluminum and magnesium. Method of producing casts from dispersed-hardened alloys based on aluminum or magnesium involves preliminary heating of a sealed cylindrical chamber, on side walls and upper cover of which a heat-insulating coating is made, immersion of the lower end of the branch pipe, installed in the chamber bottom, into the crucible of the melting furnace with melt, creation of vacuum for filling of the tight chamber by melt, tight chamber with melt movement to the mold, introduction of the lower end of the sealed chamber branch pipe into the mold metal container and melt pouring into it by supplying inert gas into the sealed chamber under pressure, wherein sealed chamber preliminary heating is carried out to temperature not lower than (450÷500) °C by means of conductive and radiant heat exchange with molten metal in crucible of melting furnace, heated to temperature not lower than 700 °C, wherein sealed chamber tube nozzle is made of titanium alloy with titanium nitride coating on outer side walls, during filling of tight chamber by melt, there is continuously fed a refractory compound powder with simultaneous mechanical stirring, and after filling the sealed chamber with molten metal it is additionally stirred for at least 60 s.EFFECT: higher quality of castings from hardened aluminum and magnesium alloys and reduced power consumption during their production.1 cl, 4 dwg, 1 ex

Description

The invention relates to the field of metallurgy of light alloys, in particular to methods for producing and casting alloys based on aluminum and magnesium with increased strength due to the introduction of reinforcing disperse refractory modifiers into them. Dispersion-strengthened light alloys are used for the manufacture by injection molding of individual parts with high performance characteristics with low weight in a number of industries (rocket and aerospace, aviation, automotive, etc.).

One of the promising ways to increase the strength characteristics of alloys based on aluminum and magnesium is the introduction of dispersed additives from refractory compounds (oxides, carbides, borides of various metals) into their composition.

Known methods for producing hardened alloys based on aluminum and magnesium, based on the introduction into the molten metal of fine powders or briquettes from high-strength ceramic particles (modifiers). To ensure uniform distribution of the modifier particles in the volume of the melt, which increases the strength characteristics of the alloys, they carry out the activation of the metal melt by mechanical agitation, ultrasound or electromagnetic field [1-3].

The ultimate goal of the technological process is to obtain specific products by pouring the melt into molds. With traditionally used methods of casting alloys from the crucible of a smelting furnace using buckets or metering devices, it is possible to oxidize reactive aluminum and magnesium alloys upon contact with ambient air. To obtain high-quality products, various methods are used for pouring molten metal into molds.

A known method of casting under the action of pressure drop [4], in which a gas-permeable form containing a corrugated tube for filling metal, sealed to the lower end of the gate channel, is immersed in the lower molten bath to fill a plurality of mold cavities during casting. When the mold cavities are filled with liquid metal from the melt bath located at the bottom, the metal filling tube closes in the corrugated position during its immersion in the molten bath to prevent leakage of the molten metal upon its subsequent removal from the molten bath.

There is a method of casting by vacuum suction of chemically active metals [5], which includes placing a gas-permeable form with risers and a metal pipe in a sealed chamber, feeding the metal into a crucible with a casing filled with an inert gas, immersing the lower end of the metal metatrovod into a crucible with liquid metal through the hole in the casing cover , creating a vacuum in a sealed chamber to fill the mold with molten metal. At the same time, in order to prevent air from entering the casing, the pressure of the inert gas in it is maintained above atmospheric pressure.

Closest to the claimed method is a method implemented using a device for pouring a liquid metal into molds [6]. The method includes preheating the sealed chamber with an electro-coil connected to a voltage source, filling the chamber with molten metal from the crucible of the smelting furnace through the nozzle by evacuating the chamber. After filling the chamber, the nozzle is removed from the crucible and injected into the mold, the molten metal is poured into the mold by feeding an inert gas into the chamber under pressure.

The disadvantages of the method include the high cost of electricity for heating and maintaining a high temperature of the chamber. In addition, the hardening of aluminum and magnesium alloy is preliminarily carried out in a crucible melting furnace, which, as a rule, has a large volume. In the process of repeatedly introducing the melt into the chamber and pouring it into the casting molds, gravitational separation of reinforcing particles in the melt matrix, which have been in the crucible for a long time, is possible. This may lead to a deterioration of the strength characteristics of the alloy.

The technical result of the present invention is to improve the quality and reduction of energy consumption in the preparation of castings of specific products from hardened aluminum and magnesium alloys.

To achieve this technical result, a method has been developed for producing castings from dispersion-hardened alloys based on aluminum or magnesium, including preheating of a sealed cylindrical chamber, on the side walls and upper lid of which a heat-shielding coating was made, immersing the lower end of the nozzle installed in the bottom of the chamber into a crucible melting furnace with a melt, creating a vacuum for filling the sealed chamber with melt, moving the sealed chamber with melt to the mold, introducing the bottom the end of the nozzle of the sealed chamber into the metal receiver of the casting mold and pouring melt into it by feeding an inert gas under pressure into the sealed chamber. Pre-heating of the sealed chamber is carried out to a temperature not lower than (450 ÷ 500) ° C by conductive and radiant heat exchange with the molten metal in the crucible of the melting furnace, heated to a temperature not lower than 700 ° C. The pipe of the sealed chamber is made of titanium alloy with a coating of titanium nitride on the outer side walls. In the process of filling the sealed chamber with the melt, the refractory compound powder is continuously fed into it with simultaneous mechanical stirring, and after the sealed chamber is filled with the melt, it is additionally mixed for at least 60 s.

The positive effect of the invention is due to the following factors.

1. The execution of the heat-shielding coating on the side walls and the upper lid of the sealed chamber makes it possible to reduce heat losses during its preheating, filling with molten metal and pouring the melt into molds. In this case, the absence of a heat-shielding coating on the bottom of the chamber provides for an intense heating of the chamber due to radiant heat exchange with the molten metal in the crucible of the melting furnace (Fig. 1).

2. Preheating of the sealed chamber prevents cooling and crystallization of the melt in the process of filling the chamber. The preheating temperature (not lower than (450 ÷ 500) ° C) was determined experimentally and ensures the preservation of the metal in the chamber in the molten state, taking into account the melting point of aluminum (658 ° C) and magnesium (651 ° C) and the temperature of the molten metal in the crucible melting furnace (not below 700 ° C).

3. The implementation of a titanium alloy nozzle with a titanium nitride coating applied to its inner walls ensures non-wettability of the nozzle with molten metal, which increases the reliability of the closure element (ball valve).

4. The heating temperature of the molten metal in the crucible of the melting furnace (not lower than 700 ° C) was determined experimentally and prevents the melt from cooling down below the melting temperature in a sealed chamber during its filling.

5. Hardening aluminum and magnesium alloys directly in a sealed chamber in the process of filling the chamber with molten metal by introducing a refractory compound powder into the chamber with simultaneous mechanical agitation makes it possible to clear the molten metal from gas inclusions, effectively use refractory powder modifying particles, and ensure conditions for the generation of a large number evenly located nuclei (nuclei) of crystallization, which allows, ultimately, to obtain in the casting fine-grained steel ukturu.

6. Additional mixing of the molten metal after filling the sealed chamber allows to increase the uniformity of distribution of reinforcing particles in the volume of the melt. The time of additional mixing (not less than 60 s.) Was determined experimentally taking into account the results of metallographic analysis of the obtained samples of hardened alloys.

The invention is illustrated by drawings.

FIG. 1. - Diagram of the device for implementing the method (the stage of filling the chamber with molten metal).

FIG. 2. - Diagram of the device for implementing the method (stage of filling the mold).

FIG. 3. - General view of the device for implementing the method.

FIG. 4. - The structure of the resulting alloy: without hardening (Fig. 4a) and hardened alloy (Fig. 4b).

An example implementation of the method

The essence of the proposed method is illustrated by diagrams (Fig. 1, Fig. 2). In the bottom of the sealed cylindrical chamber 1, a nozzle 2 is installed with a ball valve 3. On the side walls and the top cover of the chamber 1, a heat-shielding coating 4 is made. On the axis of symmetry of the chamber 1 there is a rotating mixer 5 with electric drive 6. In the upper part of the chamber 1 there is a fitting 7 for input powder of refractory compounds, fitting 8 with valve 9 for connecting chamber 1 to the vacuum system and fitting 10 with valve 11 for supplying inert gas to chamber 1.

The inventive method is implemented as follows. The hermetic chamber is transferred to the crucible 12 of the melting furnace with molten metal 13, the lower end of the nozzle 2 is immersed in the molten metal 13 (Fig. 1) and the chamber 1 is preheated due to conductive and radiant heat exchange of the chamber 1 with the molten metal 13 heated to a temperature not below 700 ° C. The heating of the chamber 1 is controlled by a temperature sensor placed in it (not shown in Fig. 1). After heating the chamber 1 to a temperature not lower than (450 ÷ 500) ° C, the ball valve 3 and the valve 9 are opened with the valve 11 closed. Due to the vacuum created in the chamber 1, it is filled with metal melt through nozzle 2. At the same time, the rotating mixer 6 is switched on and powder of refractory compounds is fed into chamber 1 through nozzle 7. In the process of filling chamber 1 with molten metal, uniform mixing is carried out by the mixer 5 of the melt with the powder of refractory compounds, which provides hardening of aluminum or magnesium sp Av. After filling the sealed cylindrical chamber 1 with molten metal to a predetermined level controlled by the melt level sensor (not shown in Fig. 1), the ball valve 3 and valve 9 are closed, shut off the powder supply nipple 7 and perform additional mixing by the melt mixer 5 in chamber 1 for not less than 60 s.

After additional mixing, the hermetic cylindrical chamber 1 is moved to the mold 14 and the lower end of the nozzle 2 is introduced into the metal receptacle 15 of the mold 14 (Fig. 2). A photograph of the device for moving the camera 1 is shown in FIG. 3. To fill the mold, the ball valve 3 and the valve 11 are opened. Inert gas through the nozzle 10 enters the upper part of the sealed cylindrical chamber 1 and displaces the hardened melt through the metal receiver 15 into the mold 14.

The effectiveness of the proposed method is confirmed by conducting experiments on the hardening of aluminum alloy AK7 nanoparticles of aluminum oxide (0.2 wt.%) In a sealed cylindrical chamber (pouring tank) with a volume of 10 liters. Metallographic analysis showed a uniform fine-grained structure of the obtained hardened alloy. FIG. 4 shows photographs of the structure of an alloy without reinforcing particles (Fig. 4a) and a hardened alloy (Fig. 4b).

Thus, from the above example, it follows that the proposed method ensures the achievement of the technical result of the invention — an increase in quality and a decrease in energy consumption in the production of castings from hardened aluminum and magnesium alloys through the use of the heat of metal melt in a smelting furnace.

LITERATURE

1. RF patent №1797218, IPC B22F 9/04, С22С 1/05. A method of producing dispersion-strengthened aluminum alloys / F.G. Lovshenko, G.F. Lovshenko; publ. 09/10/1996.

2. RF patent №2323991, IPC С22С 1/10, С22С 1/00, D22F 3/02, B22F 3/26, В82В 3/00. Cast composite material based on aluminum alloy and method for its production / A.V. Panfilov, D.N. Branchukov, A.A. Panfilov [et al.]; publ. 05/10/2008

3. RF patent №25777779, IPC С22С 1/10, С22С 21/00, B82Y 30/00. The method of obtaining modified aluminum alloys / V.A. Arkhipov, V.Kh. Dummer, A.B. Vorozhtsov [and others]; publ. 11/10/2015 Bull. №31.

4. US Patent No. 4589466, IPC B22D 37/00, B22D 18/04, B22D 18/06. Metal casting / George D. Chandley, Eugene W. Thomas; publ. 05/20/1986.

5. Patent of the USSR No. 1722218, IPC B22D 18/06. The method of casting by vacuum suction in a gas-permeable form and device for its implementation / George D. Chandley; publ. 23.03.92 Bull. №11.

6. RF Certificate for Utility Model No. 1449, IPC B22D 39/06, B22D 35/04. A device for pouring liquid metal into molds / V.H. Dummer, A.S. Kapanets, V.V. Soldatenko; publ. 01/16/1996 Bull. №1.

Claims (1)

The method of producing castings from dispersion-hardened alloys based on aluminum or magnesium, including preheating of an airtight cylindrical chamber, on the side walls and upper lid of which a heat-shielding coating was made, immersion of the lower end of the nozzle installed in the bottom of the chamber, into the crucible of a melting melting furnace, creating vacuum for filling the sealed chamber with melt, moving the sealed chamber with the melt to the mold, inserting the lower end of the pipe of the sealed chamber into the metal reservoir cast form and pour the melt into it by supplying an inert gas under pressure into a sealed chamber, characterized in that the sealed chamber is preheated to a temperature not lower than (450 ÷ 500) ° C by conductive and radiant heat exchange with the metal melt in the crucible of the melting furnace, heated to a temperature not lower than 700 ° C, while the nozzle of the sealed chamber is made of titanium alloy with a coating of titanium nitride on the outer side walls, in the process of filling the sealed chamber with a melt it is continuously fed refractory compound powder with simultaneous mechanical agitation, and sealed after filling of the melt chamber it is further stirred for at least 60 seconds.

Images