RU2683176C1 - Method of obtaining silumin - Google Patents

Abstract

FIELD: metallurgy.SUBSTANCE: invention relates to the metallurgy of non-ferrous metals, namely to the production of silumin using amorphous silica fume as a source of silicon. Method of obtaining silumin includes the introduction of silicon-containing oxide raw materials in the aluminum melt, mixing the melt and casting the resulting alloy, moreover, amorphous silica fume is used as a silicon-containing oxide raw material, which prior to its introduction into the melt is subjected to heat treatment at a temperature of 200–300 °C, the introduction of amorphous microsilica is carried out in a stream of inert gas with stirring, ensuring that the silica fume particles are drawn into the vortex funnel formed in liquid aluminum, and after mixing the melt is alloyed with magnesium in an amount up to 1 % wt.EFFECT: method allows efficiently and with minimal cost to obtain alloys that meet the requirements of GOST 1583-93 93 in chemical composition and mechanical properties.4 cl, 5 ex, 1 tbl, 3 dwg

Description

The invention relates to the metallurgy of non-ferrous metals, and in particular to the production of silumins using amorphous silica fume as a source of silicon.

The most common foundry aluminum alloys are silumins [Belov N.A. Phase composition of aluminum alloys: monograph. - M.: Publishing. House MISiS, 2009. - 398 p.]. Silumins are a group of aluminum alloys, the main alloying element of which is silicon. The demand for silumins is ensured by a unique combination of a number of their basic properties: low density, high fluidity, relatively low shrinkage, low tendency to form stresses and cracks, high values of strength properties, wear resistance and heat resistance.

Various methods for producing silumins are known from the prior art, the use of which depends on the purpose of the alloys, their composition, the ability to provide the necessary purity for non-metallic inclusions and gases, the type of feedstock, volume and production conditions, as well as economic considerations. So there are six main ways:

1) A carbothermic (ore-thermal) method, in which silumins are obtained by reducing natural aluminum-silicon minerals (kaolinite, kyanite, sillimanite, etc.) in electrothermal furnaces (RU No. 2010881, RU 2484165). The disadvantages of this method are its high energy intensity, the complexity of the preparation of charge materials, as well as a high degree of contamination of the alloy with impurities and non-metallic inclusions (mainly carbon, which is the main reducing agent).

2) A metallothermic method based on the reaction of reduction of silicon from its compounds (oxygen, halide) with aluminum [Belyaev AI, Bochvar OS, Bunov NN Aluminum alloys. Metallurgy of aluminum and its alloys. M .: Metallurgy, 1983]. The method consists in introducing onto the surface of the aluminum melt a mixture of aluminum and silica powders, local heating of the mixture to a temperature of 1100-1200 ° C and the subsequent production of aluminum-silicon alloys. The disadvantage of this method is the need to use aluminum and silica in a powder state, the need for significant overheating of the melt, the difficulty of obtaining an alloy of a given composition, as well as contamination of the resulting alloy with an admixture of iron.

3) The electrolytic method, which consists in the joint reduction on the cathode of aluminum and silicon (patent RU 2556188, copyright certificate SU No. 1826998, patent RU 2030487) [Melting and casting of aluminum alloys. Reference, ed. / M.B. Altman [et al.] - 2nd ed. - M.: Metallurgy, 1983. - 352 p.]. This method is distinguished by the possibility of using relatively cheap compounds as feedstock and producing alloys with a low content of non-metallic and gas inclusions. The main disadvantages of the method are the high energy costs of its implementation, as well as the difficulty of maintaining the optimum silicon concentration in the electrolyte, resulting in an increase in the process temperature and a decrease in current efficiency.

4) Dissolution of crystalline silicon in aluminum melt (patent RU 2010881). This method is the main industrial method for producing foundry silumins, which is used in aluminum plants. The main advantage of the method is its high productivity and the ability to obtain alloys with a given silicon content. However, this method has a number of significant drawbacks - large irretrievable loss of metal due to fumes, low absorption of silicon of small fractions (less than 5-6 mm), high energy costs.

5) A method for producing alloys using a “liquid” Al-Si ligature, which consists in pouring molten silicon into a vacuum ladle with aluminum melt inside it (patents RU 93010136, RU 2432411, RU 2215803). Despite the high quality of the obtained alloys, for the implementation of this method, the close territorial location of aluminum and silicon manufacturing enterprises is necessary.

6) Liquid-phase technologies for producing aluminum-silicon alloys, which consist in the direct reduction of silicon from its oxides by aluminum directly in the melt with relatively little overheating (670-900 ° C).

Among the existing methods for producing silumins, analogues of the claimed technical solution are methods based on the reduction of silicon from aluminum oxide by aluminum, as well as methods in which amorphous silica fume is used as a source of silicon.

From the existing level of technology there is known "A method of producing an aluminum-silicon alloy in an electrolyzer for aluminum production" (patent RU 2599475, IPC С25С 3/06, publ. 10.10.2016), according to which silumins are produced in an electrolyzer for aluminum production using amorphous silicon-containing oxide raw materials. As an amorphous silicon-containing oxide raw material, silica fume is used, obtained in the process of purification of technological gases in the production of silicon and silicon-containing alloys, which is loaded into the molten electrolyte using automatic electrolysis units.

A common feature of the analogue with the claimed invention is the use as a silicon-containing raw material of amorphous silica fume obtained during the processing of dust from gas treatment systems of ore-thermal furnaces for the production of silicon.

The disadvantage of this method is that a prerequisite for its implementation is the need for preliminary mixing of silica fume with alumina and fluoride salts, since otherwise there is the formation of silica fume agglomerates in the electrolyte melt, which reduce the dissolution rate of SiO ₂ and can lead to the formation of a precipitate on the bottom of the cell. Moreover, the introduction of quartzite (5 ^ 40% (mass.)) Into the electrolyzer can lead to a decrease in the electrolyzer productivity and current efficiency.

Closest to the claimed technical solution is "Aluminum alloy and method for its production" (US patent 9657377 B2, IPC B22D 21/04, C22C 21/08, C22C 1/026, C22C 21/02, C22C 21/12, C22C 21 / 14, C22C 21/16, C22F 1/043, C22F 1/047, C22F 1/057, publ. 05.23.2017), according to which silumins are produced by introducing silicon dioxide onto the surface of an aluminum melt and its subsequent mechanical or electromagnetic mixing. In this method, a one-time or batch introduction of silica into an aluminum melt is carried out. During mixing of the surface part of the melt (10-20% of the total metal volume in the crucible), silicon dioxide is reduced. By-products of the reaction pass into slag, after the removal of which the resulting alloy is poured.

The main disadvantages of this method are that, firstly, the method does not provide for the application of coating fluxes during the alloy production, which can lead to increased oxidation of aluminum and loss of metal with slag, and secondly, the mixing of silicon dioxide into the aluminum melt is carried out only in its near-surface zone (10-20% of the total metal volume in the crucible), which significantly reduces the degree of involvement of silicon dioxide particles in the “mirror” of the melt, limits the contact surface in the Al-SiO _{2 system} and, as a result, thye reduces its performance of the presented method.

The objective of the invention is to obtain silumins using as a source of silicon amorphous silica fume obtained from waste from silicon production.

The technical result of the invention is:

- utilization and effective use as a source of silicon dust of gas treatment systems of electrothermal furnaces, which has a very low cost and contains up to 95% (mass.) of amorphous silica fume;

- acceleration of the reaction in the Al (g) -SiO _{2 system} due to pre-treatment of amorphous silica fume, as well as alloying of the aluminum melt with magnesium;

- obtaining pre-eutectic and eutectic silumins that meet the requirements of GOST 1583-93 in chemical composition and mechanical properties.

The technical result is achieved in that in a method for producing silumins, comprising introducing a silicon-containing oxide raw material into an aluminum melt, mixing the melt and casting the obtained alloy, according to the claimed invention, amorphous silica fume is used as a silicon-containing oxide raw material, which is subjected to heat treatment at a temperature before being introduced into the melt 200-300 ° C, the introduction of amorphous silica fume is carried out in a stream of inert gas with stirring, providing retraction frequently microsilica silica into a vortex funnel formed in liquid aluminum, and after mixing, the melt is alloyed with magnesium in an amount of up to 1% of the mass.

The invention is supplemented by the following distinctive features:

Amorphous silica fume obtained from dust from gas treatment systems of electrothermal furnaces is used.

To average the particles in the melt, magnetohydrodynamic and / or mechanical mixing of the melt is carried out.

Before casting the alloy, it is processed using a coating-refining flux to obtain alloys of the required quality (removal of the reaction products of silicon reduction with aluminum and cleaning of its surface).

To increase the wettability of dispersed particles of amorphous silica fume along with alloying of aluminum melt with magnesium and preliminary heat treatment of particles, hydraulic, heat treatment, treatment with solutions of weak acids, and their mechanical activation can be used.

The difference from the prototype is that before the introduction of particles of amorphous silica fume in aluminum melt, they are subjected to heat treatment at a temperature of 200-300 ° C; the introduction of silica fume is carried out by blowing it into an aluminum melt together with a stream of inert gas; mixing of the melt is carried out mechanically and / or by a magnetohydrodynamic method, ensuring the retraction of silica fume particles into a vortex funnel formed under the influence of an electromagnetic field; alloying of the aluminum melt with magnesium (up to 1% (mass.)) is carried out in order to reduce the surface tension of the melt, to reduce the energy of interfacial interaction between the solid and liquid phase, as well as to accelerate the process of reduction of silicon from its oxide; Before casting, in order to remove the reaction products of silicon reduction with aluminum and to clean its surface, it is processed using a coating-refining flux.

The presence of distinctive features allows us to conclude that the claimed invention meets the condition of patentability "novelty".

Comparison of the claimed technical solution not only with the prototype, but also with other technical solutions in this and related fields did not allow to identify sources containing information about the popularity of the totality of all the distinguishing features of the claimed technical solution.

A new set of features of the proposed method for producing silumins, namely:

1) the dust of gas treatment systems of electrothermal furnaces containing up to 95% (mass.) Of amorphous silica fume is used as a silicon source;

2) the introduction of amorphous silica fume is carried out in conjunction with an inert gas flow, which allows dispersed particles to enter directly under the “mirror” of the aluminum melt, their uniform distribution in the melt volume, as well as the concomitant removal of non-metallic inclusions and gases from the melt;

3) the melt is mixed mechanically and / or by the magnetohydrodynamic method, which ensures that the particles of silica fume are drawn into a vortex funnel formed by the action of an electromagnetic field;

4) as the main factor affecting the production of alloys of the required quality, preliminary heat treatment of amorphous silica is used, which allows gas films to be removed from the surface of its particles, as well as alloying of the aluminum melt with magnesium in an amount of up to 1% (mass.), Which reduces surface tension melt, reducing the energy of interfacial interaction between the solid and liquid phase, as well as accelerating the process of recovery of silicon from its oxide.

Based on the foregoing, we can conclude that the claimed invention meets the condition of patentability "inventive step".

The method is illustrated in the graphic and photo materials shown in FIG. 1, FIG. 2 and FIG. 3.

In FIG. Figure 1 shows a photograph of silica particles with an average size of 60 μm, which can provide silumins with a fine-grained structure and enhanced mechanical properties.

In FIG. Figure 2 shows the dependence of the change in the Gibbs energy of the reaction of the interaction of silicon oxide with aluminum as a function of temperature.

In FIG. Figure 3 shows the distribution maps of aluminum (a, c) and silicon (b, d) of samples of the starting aluminum and the obtained alloy, where the bright regions in the images correspond to Al and Si atoms.

The essence of the claimed technical solution is to restore silicon from amorphous silica fume in aluminum melt in the temperature range 670-900 ° C.

In a crucible with a volume of 900 ml made of borosilicon graphite, aluminum weighing 1000 g was immersed, containing impurities in the amount,% (mass): Fe - 0.12, Si - 0.10, Cu - 0.015, Mn - 0.02, Mg - 0.02, Zn - 0.03, Ga - 0.01, Ti - 0.01, V - 0.0013, Cr - 0.002. Melting was carried out in an IPP-5S induction melting furnace. The metal was heated to a temperature of 670-900 ° C, melted, after which amorphous silica fume (previously subjected to heat treatment at a temperature of 200-300 ° C) was introduced into it together with a stream of inert gas. Due to the low wettability of silica fume particles, its introduction into the aluminum melt was carried out in excess. So, to obtain a 12% eutectic Al-Si alloy, 300 g of SiO ₂ was introduced into the melt (against the required 257 g). The average particle size of silica fume is 60 μm (Fig. 1).

Mixing of amorphous silica fume particles in the melt was carried out for 10-15 minutes by the magnetohydrodynamic method using an electromagnetic inductor, and also using a laboratory mixer with a rotation speed range of 1-530 rpm. The use of intensive mixing of amorphous silica fume particles into aluminum melt is due to the need to ensure effective interaction in the Al (g) -SiO _{2 system} by involving amorphous silica fume particles under the “mirror” of molten metal and to prevent their further ascent.

There are a number of factors that complicate the preparation of silumins using amorphous silica fume by simply introducing it into an aluminum melt (similar to dissolving crystalline silicon in an aluminum melt):

1) the low contact area of the silica fume powder with the melt [Pai B.C., Geetha Ramani, Pillai R.M., Satyanarayana KG. Role of magnesium in cast aluminum alloy matrix composites // Journal of Materials Science. - 1995. - Vol. 30.-P. 1903-1911];

2) the presence of gas films on the surface of silica fume particles that impede effective interaction at the interface between liquid and solid phases [Gowri Shankar M.C. and Jayashree, R.K. and Kini, Achutha U and Sharma SS Effect of silicon oxide (SiO ₂ ) reinforced particles on aging behavior of Al-2024 Alloy // International Journal of Mechanical Engineering and Technology. - 2014 .-- Vol. 5 (9). - P. 15-21];

3) the presence in the powder of 40-50% (vol.) Of air, reducing its density, heat capacity and thermal conductivity.

To solve these problems, along with preliminary heat treatment of silica fume (as well as possible hydraulic treatment, treatment with solutions of weak acids and mechanical activation), mechanical and magnetohydrodynamic mixing of the melt was carried out by doping with magnesium. Magnesium was introduced into the melt in the form of magnesium ligature MG-90.

The use of an alloying element of magnesium in the proposed technical solution is due to the fact that magnesium can act as a surfactant that allows you to remove gas films from the surface of dispersed particles, reduce the surface tension of aluminum melt, and also reduce the energy of interfacial interaction between solid and liquid phase [Pai BC, Geetha Ramani, Pillai RM, Satyanarayana KG. Role of magnesium in cast aluminum alloy matrix composites // Journal of Materials Science. - 1995. - Vol. 30. - P. 1903-1911]. Moreover, magnesium is also involved in the process of reducing silicon from its oxide.

To determine the melt temperature, a chromel-alumel thermocouple connected to an electronic recorder was used. To increase the accuracy of temperature measurement, the thermocouple readings were checked against the readings of a digital small-sized thermometer.

To obtain alloys of the required quality (removal of the reaction products of silicon reduction with aluminum and cleaning of its surface), it is processed using a coating-refining flux before casting the metal.

The silicon and alloying elements in aluminum before and after the experiments were determined using an optical emission spectrometer with a spark source for spectrum excitation.

The microstructure of the samples was studied in the mode of secondary and retroreflected electrons using a scanning electron microscope equipped with an energy dispersive detector.

Example 1

In a crucible with a volume of 900 ml made of borosilicon graphite, aluminum weighing 1000 g is loaded, containing impurities in the amount,% (mass): Fe - 0.12, Si - 0.10, Cu - 0.015, Mn - 0.02, Mg - 0.02, Zn - 0.03, Ga - 0.01, Ti - 0.01, V - 0.0013, Cr - 0.002. Then the metal is melted in an IPP-5C induction melting furnace. To control the temperature of the melt, the DTPK 015-011.200 chromel-alumel thermocouple is immersed in it, connected to the PARAGRAF-PL20 electronic recorder. The melt temperature is brought to 670 ° C. Then, amorphous silica fume (pre-heat treated at a temperature of 200-300 ° C) in an amount of 300 g is introduced into the metal together with a stream of inert gas. Alloying the fumed silica with magnesium (0.5% (mass)) is carried out simultaneously. Mixing of the melt is carried out using a laboratory mixer IKA EUROSTAR 200 Control P4 at a speed of 120 rpm for 15 minutes After obtaining the alloy of the required chemical composition, it is processed using the FPR-23 flux preparation in order to remove the reaction products of silicon reduction with aluminum, which have passed into slag and clean its surface.

Example 2

The process conditions are similar to example 1, however, the working temperature for producing silumins is 900 ° C.

Example 3

The process conditions are similar to example 1, however, the melt is mixed using an electromagnetic inductor at a speed of 90 rpm.

Example 4

The process conditions are similar to example 1, however, preliminary heat treatment of amorphous silica fume, and alloying of the aluminum melt with magnesium are not performed.

Example 5

The process conditions are similar to example 1, however, preliminary heat treatment of amorphous silica fume, and alloying of the aluminum melt with magnesium are not performed. Moreover, the mechanical mixing of the dispersed particles into the melt is carried out at a speed of 30 rpm

The results for each example are shown in table 1.

As can be seen from the table, the greatest influence on the process of recovery of silicon from amorphous silica fume has a preliminary heat treatment of particles, alloying of the melt with magnesium, and intensive mixing of the melt (mechanical or magnetohydrodynamic) (examples 1, 3). In example 2, there is also a good degree of transition of silicon to aluminum melt, however, due to an increase in the process temperature to 900 ° C, the viscosity of the melt decreases, which somewhat reduces the rate of reduction of silicon by aluminum. This is consistent with the data obtained in assessing the thermodynamic possibility of the process of reduction of silicon by aluminum from amorphous silica (4Al + 3SiO ₂ → 2Al ₂ About ₃ + 3Si) in the temperature range 298-1600 K (25-1327 ° C) (Fig. 2 )

The obtained AG-T dependence indicates a decrease in the intensity of the process of reduction of silicon by aluminum with increasing temperature.

Moreover, due to an increase in temperature in the obtained alloy, an increase in the iron content is observed in comparison with the starting metal.

Example 3 shows the high efficiency of electromagnetic mixing of amorphous silica particles in an aluminum melt, which allows to obtain an alloy of the required chemical composition with a low content of iron impurity when the mixing speed is reduced.

Thus, with an initial silicon content of 0.10% (mass.) As a result of applying the inventive method, silumins can be obtained that meet the requirements of GOST 1583-93 in chemical composition and mechanical properties.

The study of the microstructure of the samples of the starting aluminum and alloy obtained during the implementation of the process conditions according to example 1, allowed to obtain their two-dimensional "map" of the distribution of aluminum and silicon (Fig. 3, a-d). The distribution map of silicon of the obtained alloy clearly demonstrates the presence of silicon inclusions along the grain boundaries of aluminum (Fig. 3, d), which are practically absent in the starting metal (Fig. 3, b). This confirms the results obtained during spectral analysis of the samples.

The presented method for producing silumins using amorphous silica fume as a source of silicon is promising, since it allows efficiently and with minimal costs to obtain alloys that meet the requirements of GOST 1583-93 in chemical composition and mechanical properties.

When creating an industrial design, this method can be introduced into the production process of cast aluminum alloys. The use of silicon production dust as a silicon source will increase the efficiency of the existing technological process for producing silumins by partially eliminating the energy-consuming stage of metallurgical silicon production from it.

Claims (4)

1. A method of producing silumins, comprising introducing a silicon-containing oxide raw material into an aluminum melt, mixing the melt and casting the resulting alloy, characterized in that amorphous silica fume is used as a silicon-containing oxide raw material, which is subjected to heat treatment at a temperature of 200-300 ° C before being introduced into the melt. , the introduction of amorphous silica fume is carried out in a stream of inert gas with stirring, ensuring the retraction of particles of silica fume in a vortex funnel formed in a liquid lump of aluminum, and after mixing, the melt is alloyed with magnesium in an amount of up to 1% of the mass. 2. The method according to p. 1, characterized in that they use amorphous silica fume obtained from dust from gas treatment systems of electrothermal furnaces. 3. The method according to p. 1, characterized in that for averaging the particles in the melt carry out magnetohydrodynamic and / or mechanical mixing of the melt. 4. The method according to p. 1, characterized in that before casting the alloy is treated with a coating-refining flux.

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