RU2542191C1 - Method of alloys manufacturing for aluminium alloys production - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: exothermic mixture of aluminium and titanium powders is prepared, then it is subjected to mechanical activation. Simultaneously briquettes of the pressed titanium chips are made. Mixture of powders and briquettes of the pressed titanium chips are simultaneously added to aluminium melt, its surface has cryolite, the melt is held for at least 30 minutes with periodic agitation. Ratio of stoichiometric mixture of powders and briquette of titanium chips is selected as 1/3 of powders mixture to 2/3 of titanium chips.

EFFECT: invention increases quality of the alloy, improves its structure and uniformity of titanium distribution in the alloy volume, excludes slug inclusions and segregation zones combined by intermetallic compounds Al₃Ti.

2 cl, 3 tbl, 11 dwg

Description

The invention relates to the production of non-ferrous metal alloys, in particular to the production of aluminum-titanium alloys, and can be used in the aviation, automotive and other industries manufacturing wrought and cast aluminum alloys.

Modifying and simultaneously alloying elements in aluminum alloys, as a rule, are introduced in the form of alloys - intermediate alloys of aluminum with one of the metals - titanium, zirconium, vanadium, chromium and others. Ligatures should dissolve well in liquid aluminum, have a uniform chemical composition and sufficiently dispersed inclusions of primary intermetallic compounds.

One way to solve this problem is to modify, i.e. grain refinement of the alloy structure, for the implementation of which mainly ligatures are used, more than 70% of the alloys used as a modifying additive contain titanium. The most popular, due to their high efficiency and relatively low cost, are Al-Ti and Al-Ti-B ligatures. As a result of numerous studies of their structure, it was found that in order to obtain the maximum modifying effect, TiAl ₃ and TiB ₂ particles should be spherical and possibly have a size: the first no more than 130 microns, and the second 1-2 microns. To get rid of harmful impurities, multicomponent fluxes of various compositions in amounts up to 0.3% are often added to ligatures, which contain sodium cryolite as one of the components. In addition, in all traditional technologies for producing modifying ligatures, in addition to the problem of high energy and labor costs, the issue of intense gas saturation is acute, which leads to a coarsening of the structure of primary intermetallic compounds (see Luts Alfiya Rasimovna. Self-propagating high-temperature synthesis of modifying ligatures and composite alloys in molten aluminum from aluminum application of fluxes: the dissertation of the candidate of technical sciences: 01.04.17. - Samara, 2006. - 225 pp., ill. RSL OD, 61 07-5 / 433).

Several methods are known for producing aluminum-titanium alloys. The most common of these is direct fusion of aluminum with titanium.

However, this method is characterized by significant fumes of aluminum and titanium.

The method of thermal reduction of halide compounds by aluminum, which is characterized by a significant loss of titanium and aluminum with slags and fluxes, is also widely known, and also requires a significant expenditure of energy on the melting of the charge; moreover, the formation of harmful sublimates is observed in it.

Many of these disadvantages are eliminated by the electrolytic preparation of the ligature by introducing a titanium-containing material into the electrolyte of the baths to produce aluminum. In this case, usually titanium dioxide is used as titanium-containing material.

However, this method has inherent disadvantages associated with the use of titanium dioxide, which is expensive and significant losses of titanium are observed in its production. The solubility and dissolution rate of titanium dioxide in the cryolite-alumina melt is limited and part of the injected dioxide forms a precipitate on the surface of the electrolyzer, which leads to a breakdown in the technological regime of the bath, overheating of the electrolyte, an increase in metal loss, and the need to reduce the current density at the electrodes.

A known method of producing aluminum-titanium alloys by introducing titanium into an aluminum-titanium melt with an initial titanium concentration of 4-5 wt.% At a melt temperature of 150-350 ° C below the liquidus temperature to bring its concentration in the melt to 7.2-13, 7 wt.%, After which the melt is diluted with aluminum to the initial titanium concentration, and when casting the ligature, a part of the melt equal to 0.33-0.54 of its total volume is left, which is used as an aluminum-titanium melt for introducing titanium (analogue - author's USSR certificate No. 1836471, C22C 1/03, 08/23/1993). The resulting ligature has a titanium concentration of 4-5 wt.%.

The disadvantage of this method is the high cost of the ligature due to the use of expensive pure components, as well as its multi-stage.

A known method of producing aluminum-titanium alloys by aluminothermic reduction of titanium oxide in the presence of alkali metal bifluoride (sodium or potassium) and alkali metal chloride, in particular potassium chloride as a flux at a ratio of alkali metal bifluoride to titanium oxide from 4: 1 to 2: 1 ( US patent analogue No. 2955935, IPC C22C 21/00, 10/11/1960).

The disadvantages of the described method include the receipt of ligatures with large up to 300 microns intermetallic compounds, as well as a high percentage of irretrievable losses of titanium.

Known traditional methods for producing titanium aluminides (furnace metallurgy) have a number of difficulties caused by the high chemical activity of the starting components at elevated temperatures, the difference in the melting, evaporation and density of the starting components. The existing technology for their production is very complex and multi-stage (Kim Y.-W., Froes F. Physical Metallurgy of Titanium Aluminides. Warrendale. PA., 1990, p.451-465).

Therefore, the development of new, low-cost technologies for the production of Ti aluminides is an urgent task.

One of the most advanced methods for the synthesis of Al ₃ Ti intermetallic compounds, at the moment, is self-propagating high-temperature synthesis (SHS), which is due to the simplicity of the processing equipment, the efficiency of the process, and the acceptable time to obtain products.

As is known (see Merzhanov A.G. Combustion processes in chemical technology and metallurgy. Chernogolovka, 1975), the synthesis of materials by the SHS method refers to solid-phase combustion processes, and it can be carried out in two different technological regimes: in the layered mode burning an exothermic mixture and in the mode of thermal self-ignition (explosion), each of which has a number of advantages. However, the need for the correct selection of the optimal exothermic mixture of the starting reagents is an urgent task for both methods. Based on the foregoing, structure formation in the Al-Ti binary system becomes an important issue.

A known method of producing alloys for the production of aluminum alloys, including melting aluminum, introducing into the melt a transition metal, for example titanium, mixed in stoichiometric ratio with aluminum to form intermetallic compounds as a result of self-propagating high-temperature synthesis, mixing and crystallization, and the mixture of metal powders is pre-briquetted (prototype - AS USSR No. 1759930 dated 08/15/90, IPC C22C 1/03, C22C 1/04).

The disadvantage of this method is the high cost of the powder components and the large sizes of intermetallic Al ₃ Ti.

The objective of the invention is to obtain a homogeneous melt Al ₃ Ti with sizes of intermetallic compounds up to 1-2 microns, reducing irreversible losses of titanium.

The technical result of the invention is to improve the quality of the obtained alloys based on aluminum while reducing the quantity and price of the alloy.

The technical result is achieved by the fact that in the method for producing Al ₃ Ti alloys for the production of modified aluminum alloys, including melting aluminum, introducing a transition metal in the form of a powder, for example titanium, mixed in stoichiometric ratio with aluminum powder to form Al ₃ Ti intermetallics in the aluminum melt as a result of self-propagating high-temperature synthesis, mixing and crystallization according to the invention, cryolite is preliminarily placed as a flux on the melt mirror technical artificial, a mixture of Al and Ti powders is subjected to preliminary mechanical activation, pressed molten titanium shavings are introduced into the melt simultaneously with a mechanically activated mixture of titanium and aluminum powders and the melt is held for at least 30 minutes with periodic stirring.

The ratio of powder and shavings is selected in a ratio of 1/3: 2/3.

The technical result from the use of all the essential features of the claimed invention is to improve the quality of the ligature, improve its structure and uniform distribution of titanium in the volume of the ligature. In addition, slag inclusions and segregation zones depleted in Al ₃ Ti intermetallic compounds are excluded.

Due to the preliminary preparation of the powder mixture, the SHS process improves, which allows for the active interaction of aluminum with pressed titanium chips introduced into the aluminum melt simultaneously with the powder, which ensures the SHS process, thereby improving the structure and quality of the ligature.

The introduction into the melt simultaneously with a mechanically activated mixture of titanium and aluminum powders of pressed titanium shavings and keeping the melt for at least 30 minutes with periodic stirring can improve the quality of the ligature, improve its structure and ensure uniform distribution of titanium in the volume of the ligature. In addition, the addition of pressed chips allows eliminating slag inclusions and segregation zones depleted in Al ₃ Ti intermetallic compounds. The presence of titanium briquette briquettes and its melting on the aluminum molten mirror absorbs a large amount of heat, preventing the temperature of the SHS reaction between titanium and aluminum powders from rising above the critical temperature, from which an undesired AlTi phase is formed.

The use of ligatures obtained by the proposed method in the manufacture of aluminum alloys provides higher quality alloys (for example, reduced grain size AK12M2 alloy).

The chemical composition and dispersion of titanium powder must comply with the technical specifications for porous titanium powder TPP-7, TU 1715-449-05785388.

The chemical composition and dispersion of aluminum powder must comply with the requirements of GOST 6058-73 for PA-4 aluminum powder.

The description of the method is accompanied by a schematic diagram of a device for implementing the inventive method.

As applications, photographs of the microstructure of ligature samples obtained in various ways are provided.

Photo 1 - the microstructure of the slice of the alloy AK12M2, modified by the ligature obtained by the claimed method.

Photo 2 - the microstructure of the ligature obtained by the claimed method, taken at individual points of the sample.

Photo 3 - the microstructure of the ligature obtained by the claimed method, magnification × 100.

Photo 4 - the microstructure of the ligature obtained by the claimed method, magnification × 200.

Photo 5 - microstructure of a slice of AK12M2 alloy modified by a ligature obtained by a furnace method.

Photo 6 - microstructure of the ligature obtained by the furnace method, magnification × 100.

Photo 7 - microstructure of the ligature obtained by the furnace method, magnification × 200.

Photo 8 - microstructure of a slice of AK12M2 alloy modified by a ligature obtained by the classical SHS method.

Photo 9 - the microstructure of the ligature obtained by the classical SHS method, magnification × 100.

Photo 10 - microstructure of the ligature obtained by the classical SHS method, magnification × 200.

The proposed method is as follows.

An exothermic mixture of powders of aluminum and titanium 1 (see drawing) is prepared in a proportion of 3Al: Ti, then it is subjected to mechanical activation in a ball mill. Uniform mixing in a ball mill is carried out to increase the contact of particles, the rolling and sliding modes are combined. Mixing mechanically activated powder is performed within 2 hours. In this case, particles of a titanium powder having a higher specific surface are surrounded by smaller particles of aluminum powder. At the same time, briquettes of pressed titanium chips are prepared 2. The chemical composition of titanium chips is shown in Table 1. Titanium chips are waste products from the enterprise, which are usually disposed of.

A mixture of powders and briquettes from pressed titanium shavings is introduced into the aluminum melt located in the graphite crucible 3. On the surface of the aluminum melt in the crucible 3 there is technical artificial cryolite 4 (Na ₃ AlF ₆ ) in an amount of 0.1% by weight of the smelting. The presence on the surface of the molten aluminum heated to 900 ° C, flux from technical artificial cryolite increases the activity of the SHS reaction due to the removal of oxides Al ₂ O ₃ and TiO ₂ . For a more complete passage of the SHS reaction, a stoichiometric mixture of powdered reagents (Ti + 3Al) can be placed between two briquettes of pressed titanium chips. The ratio of the amount of the stohemetric mixture of powders and the briquette of titanium chips is preferably selected in the ratio of 1/3 of the powder: 2/3 of the titanium chips. Ignition, combustion of the mixture and the formation of Al ₃ Ti intermetallic compounds as a result of self-propagating high-temperature synthesis occurs inside the aluminum melt. In the diagram, arrows 5 show the direction of propagation of the SHS reaction. The stoichiometric proportion of the powders is the most reactionary, the SHS wave propagates faster along it, and a large amount of energy is released that is sufficient to melt the briquetted titanium shavings.

During melting of pressed titanium shavings during SHS synthesis, on the surface of the aluminum melt, under the layer of cryolite flux, the refractory Al ₃ Ti phase is synthesized (position 6 in the diagram). At this moment, the melt temperature increases by 50-60 ° C, because reagents of aluminum and titanium react with each other on a mirror of aluminum melt, heated to a temperature of 900 ° C. The end of synthesis is determined by the cessation of gas evolution on the surface of the melt. Then, the target Al ₃ Ti phase, with active stirring of the melt, diffuses into the aluminum melt for 30 minutes (arrows, position 7).

As a result of diffusion, the refractory Al ₃ Ti phase from the surface of the melt is evenly distributed in the ligature melt.

The spill of the ligature melt is carried out with a measuring spoon, in one step. The casting mass is 2.5-3 kg. Chill casting. The filling is carried out manually in a separate mold.

The prototype of the proposed combined SHS and furnace synthesis is the classic SHS synthesis and the method of direct fusion of aluminum with titanium (furnace). Upon receipt of the AlTi-3 ligature by direct fusion (furnace synthesis), Al ₃ Ti intermetallics with a size of 16-18 μm are formed of a large-needle shape (see photo 1). During the classical SHS synthesis of (Ti + 3Al) + Q, Al ₃ Ti intermetallics with a size of 16–18 μm of globular-block morphology are formed (see photo 2).

Refractory intermetallic Al ₃ Ti ligatures obtained by the claimed combined method (SHS and foundry technology) have a globular-block morphology of 1-2 microns in size (see photo 2, 3, 4) under the following conditions:

- mechanical activation of the powder mixture;

- the introduction simultaneously with the powder mixture of a briquette of titanium chips;

- observing the mixing ratio of 1/3 (Ti + 3Al) powder + 2/3 Ti shavings.

The use of the ligature obtained by the inventive combined method when modifying the AK12M2 alloy allows one to form a more dispersed eutectic (Al) + (Si) in the alloy and increase its share in the microstructure of the alloy (see photo 1).

The chemical composition of AlTi-3 ligature, obtained in three ways, is the same, corresponds to GOST TTM 4.79.1058-2006 and is shown in Table 2.

The mechanical properties of the AK12M2 alloy, depending on the type of AGP-3 modifying alloy used, are shown in Table 3.

The ligature obtained by the claimed method has favorable macro and micro composition, good adhesion between the aluminum matrix and the hardening phase Al ₃ Ti, uniform distribution of structural components in the structure of the AK12M2 alloy.

The AlTi-3 ligature, smelted by the claimed method, obtained a structurally homogeneous kink of silver color, absent: non-metallic slag inclusions, impurities, gas porosity, segregation zones, areas depleted of intermetallic compounds. The hardening phase is synthesized directly in the aluminum matrix, Al ₃ Ti titanides of globular-block morphology are uniformly dissolved in the volume of the aluminum melt.

Thus, the proposed method for producing AlTi-3 ligatures with Al ₃ Ti intermetallic sizes up to 1-2 μm, allows to reduce the cost of producing ligatures by using waste from our own production - titanium chips, and also to increase the modifying ability of the ligature, which is reflected in a change in the main structural components and improving the mechanical properties of the AK12M2 alloy.

The use of a stoichiometric mixture of mechanically activated powders (Ti + 3Al) and pressed titanium chips in the ratio 1/3 (Ti + 3Al) powder when receiving AlTi-3 ligatures: 2/3 Ti chips, along with the disposal of titanium metal waste, eliminates overheating in the exothermic zone reaction and is the main factor ensuring the production of dispersed and reinforcing phases of Al ₃ Ti globular-block morphology with a particle size of 1-2 microns.

When implementing the proposed method can be used known technological equipment.

Table 1 Chemical composition in% titanium shavings Sn Cd Ag Ru Mo Nb Pb W Zn Cu Ni Fe Mn Cr V Ti Al Si Mg up to 0.002 up to 0.002 up to 0.008 up to 0.001 up to 0.004 up to 0.007 0.003 0.005 until 0.04 up to 0.01 up to 0.003 up to 1.14 until 0.02 up to 0.01 until 0.09 up to 97.88 up to 1.26 0.002 0.002

table 2 Al Ti Fe Si Impurities DOS 3,1 0.15 0.1 0.3

Table 3 The method of preparation and composition of the ligature Mechanical properties and parameters of α-Al dendrides of AK12M2 alloy Strength σ _in [MPa] Elongation δ [%] The average size of dendrides (α-Al), microns Furnace synthesis (direct fusion of Al and Ti) 150 2.2 24.8 Classic SHS Ti + 3Al + Q 162 2,5 21.5 The inventive method is a combined SHS and furnace synthesis 1/3 (Ti + 3Al) powder + 2/3 Ti shavings + O 186 2.9 19.1

Claims (2)

1. A method of obtaining a ligature for the production of aluminum alloys, comprising melting aluminum, introducing a transition metal in the form of a titanium powder mixed in stoichiometric ratio with aluminum powder to form intermetallic compounds as a result of self-propagating high-temperature synthesis, mixing the obtained melt and its crystallization, characterized in that previously cryolite is placed as a flux on the aluminum melt mirror, a mixture of aluminum and titanium powders subjected After preliminary mechanical activation, in the melt, simultaneously with a mechanically activated mixture of titanium and aluminum powders, extruded titanium shavings are introduced and the melt is held for at least 30 minutes with periodic stirring. 2. The method according to claim 1, characterized in that the ratio of the mixture of powders of titanium and aluminum and titanium shavings is selected in a ratio of 1/3: 2/3, respectively.

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