RU2849509C1 - Composition of pelleted modifier for aluminium alloys - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy of light alloys, specifically to modifiers for aluminium alloys. Pelletized modifier for aluminium alloys contains the following, wt. %: K₂TiF₆ 20-30, H₃BO₃ 20-30, Fe₂O₃ 7-12, AlF₃ 7-12, aluminium powder 10-20, red iron red lead 5-10, nitrogen-phosphorus compound 5-12.

EFFECT: providing high and stable mechanical properties (tensile strength, Brinell hardness and relative elongation) of cast aluminium alloys at maintaining the time of modifier action on melt from 5 to 180 minutes, as well as excluding formation of reaction products in the melt.

1 cl, 2 tbl, 3 ex

Description

The invention relates to the field of light alloy metallurgy and can be used in the production of cast aluminum alloys, namely for their modification (structure refinement) and refining in order to improve their mechanical, technological and corrosion properties.

Currently, there are several directions for improving aluminum alloys:

- adsorption methods of refining and degassing, as well as modification of the melt, thanks to which the required level of quality indicators and guaranteed operational reliability of the products are achieved;

- physical methods of influencing the crystallization process: electromagnetic and mechanical stirring, exposure to vibrations, ultrasonic treatment of the melt, etc.;

- optimization of the alloy composition by combining metallographic and technological approaches, which allows us to determine the required alloy structure and the method for achieving it.

The modification effect depends on the degree of component absorption and the ability to interact with melt components, impurities, and refining additives. The probability of reactions, their sequence, the selective nature of element interactions, and the reaction limits under various temperature conditions for aluminum alloys play a significant role.

A complex modifier for aluminum-silicon hypereutectic alloys ( RU2287604C1, 20.11.2006) is known, containing, in mass%: aluminum phosphate 19-20, potassium chloride 65-68.5, hexachloroethane 11-13, sulfur 1-2. This modifier has a stable effect immediately after the reaction is complete and maintains long-term modifying capacity, grinding primary crystals. Aluminum phosphate and potassium chloride form a low-melting mixture, and phosphorus is released during the chemical reaction. Hexachloroethane is the main refining element, and sulfur dries the slag. When sulfur is used, degassing occurs due to the formation of a significant number of gaseous sulfur bubbles in the melt. Gaseous sulfur, in a vapor state, is released to the surface. In this process, hydrogen and solid non-metallic inclusions are adsorbed on the gaseous sulfur bubbles. It has been proven that treating 500 kg of melt with sulfur at a rate of 0.05% of its mass produces a volume of gaseous sulfur 1.5 to 2.0 times greater than the volume of argon blown through the same amount of metal for 7 to 10 minutes. Since refining efficiency is determined by the duration of gas bubble existence and their total surface area, treating the melt with sulfur is more effective.

The use of this modifier requires its increased consumption – 1.5% of the melt mass, which leads to increased emissions of reaction products into the atmosphere.

A modifying composition for aluminum alloys is known (CN109439945A, 08.03.2019), including powders of the following salts (in parts by weight) mixed in a ball mill: 60-70 KF, 50-60 NaCl, 40-60 LiCl, 20-25 cryolite, 10-25 AlF ₃ , 10-15 CaF ₂ , 5-10 light calcium carbonate, 15-20 graphite powder, 10-20 talc, 20-30 MgCl ₂ and 10-30 rare earth acid salts. This refining composition promotes effective slag removal and is a good degasser. Salts containing rare earth elements (La, Er), due to their state, are evenly distributed in the aluminum melt and act as centers for the formation of crystal nuclei, which leads to a modifying effect.

Additional grinding of this composition in a ball mill leads to its hygroscopicity and, consequently, to a decrease in the refining efficiency of the modifier, which ultimately leads to a decrease in the alloy quality. Furthermore, the use of non-compacted modifiers for large-volume melts is a more labor-intensive operation.

The closest analogue of the proposed invention is a compounded refiner for hypoeutectic aluminum-silicon alloy (CN100460535 C, 11.02.2009), containing, by weight: 10-30 NaCl, 10-15 KCl, 10-20 NaF, 1-30 KBF ₄ , 1-20 K ₂ TiF ₆ , 1-20 SrCO ₃ , 1-15 CeF ₃ , 5-20 granulated mixture of rare earth metals enriched with lanthanum, and 1-5 C ₂ Cl ₆ . The components are dried at a temperature of 100 to 150 °C, mixed in a certain proportion and compacted in the form of tablets. The refining effect is achieved during the use of the modifier.

A disadvantage of the prototype is the presence of sodium salts and chlorine compounds. Sodium in the melt promotes hydrogenation, which leads to increased porosity in the final product. High levels of chlorine compounds during melt processing lead to reduced corrosion resistance of the final alloy. The presence of rare earth elements also increases the cost of the modifier.

The technical objective of the proposed invention is to develop a composition of tableted modifiers for cast aluminum alloys in order to improve their mechanical, technological and corrosion properties.

The technical result is to ensure high and stable mechanical properties (tensile strength, Brinell hardness and relative elongation) of cast aluminum alloys while maintaining the time of action of the modifier on the melt from 5 to 180 minutes, as well as eliminating the formation of reaction products in the melt.

To achieve the desired technical result, a composition of a tableted modifier for aluminum alloys is proposed, containing, in wt.%:

K ₂ TiF ₆ 20-30;

H ₃ BO ₃ 20-30;

Fe ₂ O ₃ 7-12;

AlF ₃ 7-12;

aluminum powder 10-20;

iron red lead 5-10;

nitrogen-phosphorus compound 5-12.

The _K2TiF6 modifier component decomposes in the melt and forms the _Al3Ti compound with aluminum, which acts as crystallization centers and effectively refines α-Al grains. _{The Fe2O3} , red iron _oxide , nitrogen-phosphorus compound, and aluminum powder components act synergistically, raising the decomposition temperature to improve the yield of boron from _H3BO3 and titanium from _K2TiF6 . Lower contents of all of the above _components in _the modifier reduce its effectiveness. Excessive contents saturate the melts with intermetallic compounds and dispersed particles, which impair the mechanical properties of the alloys. During the decomposition of fluorine-containing components, the released fluorine refines the melt, purifying it of dissolved hydrogen. It should be noted that the reaction products of the modifier components are absent in the melt volume, which eliminates alloy contamination, thereby improving the mechanical properties and their stability.

Thus, it was established that the proposed modifier contributes to the achievement of the technical result, namely, by grinding the structure and refining the alloy, it provides high and stable mechanical properties - tensile strength, Brinell hardness and relative elongation.

The proposed modifier contains components that contain elements of two types simultaneously. The first type includes elements (K), which are surface-active substances that adsorb onto nuclei in the central crystallization region and inhibit their growth. This results in the formation of numerous new nuclei, which actively grow due to the decrease in the overall modifier concentration relative to the number of grains.

The second type includes so-called inoculators (Ti, B). When introduced into the melt, inoculator particles accelerate the cooling and solidification process, which facilitates the emergence of numerous new crystallization sites, forming numerous small grains of the main phase or tiny inclusions of other phases. This results in the desired change in the overall structure, with the addition of new structural components to the existing ones.

The complex effect on the melt of the multi-component composition of the proposed modifier with components of the 1st and 2nd types simultaneously ensures that the modifier's action time is maintained from 5 to 180 minutes.

By producing the modifier in the form of tablets, the method of introducing it into the melt is simplified and the processing efficiency is increased.

Examples of the invention

All starting components, except aluminum powder, boric acid, and the nitrogen-phosphorus compound, were heated in a drying oven at a temperature of 150 to 180°C. After mixing in a paddle mixer, the samples, weighing 40 to 250 g, were placed in pressing fixtures with a diameter of 45 to 55 mm. Pressing was performed using a hydraulic press.

The compositions of the proposed modifier options are given in Table 1.

Examples 1-3

The prepared modifier of compositions A, B, and C, weighing 40 g, was added subcutaneously to 30 kg of AK7pch alloy at a temperature no higher than 800°C. After the reaction ceased, the alloy was left to stand for 5 to 180 minutes and then poured into cold-hardening molds.

The compositions of the proposed modifier are given in Table 1.

The test results of separately cast samples are presented in Table 2.

As the test results have shown, the proposed invention ensures high and stable mechanical properties of cast aluminum alloys: superiority quotas for tensile strength range from 4 to 25%, relative elongation from 33 to 64%, and Brinell hardness from 33 to 56%, which will allow them to be used for the manufacture of critical parts of aircraft equipment.

Maintaining the modifier's action time on the melt from 5 to 180 minutes allows for long-term pouring of melts into casting molds, which eliminates the need for repeated modification.

Table 1.

Component content, mass% Composition number K ₂ TiF ₆ H ₃ BO ₃ Fe ₂ O ₃ AlF ₃ aluminum powder iron red lead nitrogen-phosphorus compound A 20 30 7 11 17 10 5 b 25 25 10 10 15 7 8 V 30 21 12 8 12 5 12

Table 2.

Composition, alloy grade Maintenance mode Mechanical properties (average value) Excellence quotas, % σ _in , MPa δ, % NV σ _in δ NV Composition a,
AK7pch T4 230 7.0 75 17 40 50 T5 245 5.9 80 4 48 33 Composition b,
AK7pch T4 245 7.4 78 25 48 56 T5 255 5.7 82 9 43 37 Composition in,
AK7pch T4 210 8.2 74 7 64 48 T5 245 5.3 81 4 33 35 AK7pch
GOST 1583-93 T4 196 5.0 50 - - - T5 235 4.0 60 - - -

Claims (8)

The composition of a tableted modifier for aluminum alloys containing potassium fluorotitanate K ₂ TiF ₆ , characterized in that it additionally contains boric acid H ₃ BO ₃ , iron oxide (III) Fe ₂ O ₃ , aluminum fluoride AlF ₃ , aluminum powder, iron red lead, a nitrogen-phosphorus compound in the following ratio of components, wt.%: K ₂ TiF ₆ 20-30; H ₃ BO ₃ 20-30; Fe ₂ O ₃ 7-12; AlF ₃ 7-12; aluminum powder 10-20; iron red lead 5-10; nitrogen-phosphorus compound 5-12.