RU2528598C1 - Production of modifier for aluminium alloys - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: proposed method comprises mixing of carrier powder with superfine modifying powder in planetary-type mill and compaction of obtained composition. Said superfine modifying powder represents the composition of powders of silicon carbide (SiC) - 50÷70%, silicon nitride (Si₃N₄) - 20÷30%, sodium hexafluoraluminate (Na₃AlF₆) - 10÷20% produced by azide process of self-propagating high-temperature synthesis with particle size of 70-100 nm Note here that silicon carbide features β-modification. Said superfine modifying powder carrier represents the copper powder with particle size not over 180 mcm at copper-to-superfine powder ratio of 9:1.

EFFECT: application of modifier of aluminium alloys allows making of dendrites 2,4 time smaller to up the alloy mechanical properties.

1 tbl, 1 dwg

Description

The invention relates to foundry and metallurgical production, in particular to the production of a modifier for processing aluminum alloys.

The following method is known from the prior art for the manufacture of aluminum-based alloys (patent No. 2190682 of the Russian Federation, publ. 10.10.2002). In the manufacture of alloys with an aluminum matrix containing 40-80% of refractory particles, the particles are placed in an impregnation mold and filled with liquid aluminum. In this case, the particles and aluminum are heated to different temperatures. Aluminum is heated to a temperature exceeding its melting point by no more than 5-10 ° C, and particles in the form are heated to a threshold temperature significantly higher than the temperature of liquid aluminum and depending on the specific surface of the particles and the surface tension of aluminum. Exceeding the heating temperature of particles over the heating temperature of aluminum allows one to overcome capillary backpressure, improve the wettability of all particles and, as a result, prevents the formation of a ligature containing a significant amount of impregnated particles that float to the surface and go to slag.

This method involves the use of additional energy-intensive equipment for heating refractory particles of silicon carbide (SiC). It is impossible to obtain ligatures with a calculated content of refractory particles due to oxidation and ascent of impregnated particles into the slag.

The well-known "Method for producing rod alloys aluminum-titanium-boron" (patent No. 2110597 of the Russian Federation, publ. 05/10/1998). The proposed method for producing rod-shaped alloys aluminum-titanium-boron involves loading ingot aluminum, its melting and heated to a temperature of 770 ° C, then boron is introduced based on the calculation of 1% boron content in the ligature. After the introduction and completion of the boron reduction reaction, sponge titanium is introduced at the rate of obtaining 5% in the ligature, then the melt is mixed to average the chemical composition, the slag is removed and cast. From ligature ingots by pressing, a bar with a diameter of 9-10 mm is obtained.

The disadvantage of this method is the use of additional pressing operations to obtain a bar, the uneven distribution of borides over the cross section of the bar. This ligature does not have a significant modifying effect when introduced into foundry silumins.

Closest to the claimed technical solution is the "Method of obtaining a modifier for pre-eutectic aluminum-silicon alloys" (patent No. 2475334 of the Russian Federation, publ. 02.20.2013), which includes obtaining a modifier in the form of a rod by mixing aluminum powder with a particle size of 0.5-0 , 7 mm and an ultrafine titanium nitride powder with an average particle size of about 40 nm, obtained by plasma chemical synthesis in a planetary mill for 5 minutes at 400 rpm and pressing the resulting composition into a bar.

The disadvantages of this technical solution are: high energy intensity of the method for producing titanium nitride powder; expensive and sophisticated equipment; special storage conditions of the powder due to its ability to oxidize in air.

The technical result consists in developing a method for producing a modifier at the lowest cost with a high content of ultrafine powder, increasing the modifier's action time (survivability) and in increasing the physicomechanical properties of aluminum alloys.

The technical result is achieved by mixing the carrier powder and the ultrafine modifying powder in a planetary mill and pressing the resulting composition, while the composition of silicon carbide (SiC) powders is 50 ÷ 70%, silicon nitride (Si ₃ N ₄ ) - 20 ÷ 30%, sodium hexafluoroaluminate (Na ₃ AlF ₆ ) - 10 ÷ 20%, obtained by the azide technology of self-propagating high-temperature synthesis with particle sizes of 70-100 nm, while silicon carbide has a β-modification, and Copper with a particle size of less than 180 microns in a ratio of Cu: ultrafine powder of 9: 1 is used as a carrier of ultrafine powder.

A composition of powders of silicon carbide, silicon nitride and sodium hexafluoroaluminate with an average particle size of 70-100 nm, obtained by the azide technology of self-propagating high-temperature synthesis (SHS-A ₃ ), was chosen as an ultrafine modifier. This method of producing powders allows to obtain β-modification silicon carbide, which is supposed to be well wetted by aluminum melt.

The composition of the powder composition is selected based on the following data. Silicon carbide according to the Dankov-Konobeyevsky rule (principle of dimensional-structural correspondence) has the type and parameters of the crystal lattice close to the α-A1 crystal lattice. The crystal lattices of β-modification silicon carbide and aluminum are of the same type (face-centered cubic), and the crystal lattice parameters of β-modification silicon (a = 4.3596 Å) and aluminum (a = 4.0413 Å) are quite close. The differences in the crystal lattice parameters are ~ 7.9%. Included in the composition of Na ₃ AlF ₆ is a long-known and generally accepted affinity-modifying reagent for aluminum alloys.

Copper, which is part of the modifier (pseudo-ligature), is selected taking into account its high density (8.2 g / cm ³ ) with respect to aluminum melt (~ 2.4 g / cm ³ ) and serves as the carrier of the composition of powders based on silicon carbide. In addition, copper, which is part of the modifier, serves as a microalloying component for an aluminum alloy.

An example of the method.

Obtained by the azide technology of self-propagating high-temperature synthesis, the composition of ultrafine powders of silicon carbide, silicon nitride, and sodium hexafluoroaluminate of size 70-100 nm was preliminarily mixed with copper powder smaller than 180 microns in a ratio of 9: 1, loaded into a glass of a planetary mill and put it into action for 2 min at 1500 rpm The resulting composition was pressed into rods with a diameter of 10 mm with a pressing force of 4.84 tons (40 atm). The result was bars containing 8-12% of an ultrafine modifying composition.

The effectiveness of the modifier was evaluated when modifying the industrial aluminum alloy AK6M2 according to GOST 1583-2003 (table 1).

Figure 1 - Microstructure of AK6M2 alloy: a, b - without modification; c, d — modification with CuSiC ₁₀ ligature at the rate of 0.02% (SiC + Si ₃ N ₄ + Na ₃ AlF ₆ ) of the smelting mass.

Table 1 Dimensions of phase components of the AK6M2 alloy Type of processing Parameters α-A1 Parameters Si _e The average size, microns Quantity, pcs / mm ² The average size, microns Quantity pcs / mm ² Without modification 54.1 367 13.6 1240 Modification with pseudo-ligature CuSiC ₁₀ (0.02% (SiC + Si ₃ N ₄ + Na ₃ AlF ₆ )) 22.1 1805 3.9 9360

Claims (1)

A method for producing a modifier for aluminum alloys, comprising mixing a carrier powder and an ultrafine modifying powder in a planetary mill and compressing the resulting composition, characterized in that the composition of silicon carbide (SiC) powders is 50 ÷ 70%, silicon nitride (Si ₃ N ₄₎ - 20 ÷ 30%, geksaftoralyuminata sodium (Na ₃ AlF ₆₎ - 10 ÷ 20%, obtained by azide SHS technology, a 70-100 nm particle size, and the carbide to emniya has β-modification and as carrier ultrafine powder is used copper powder having a particle size less than 180 microns in a ratio copper: ultrafine powder = 9: 1.

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