RU2808313C1 - Flux for modifying aluminum alloys - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: fluxes for melting cast aluminum-based alloys, used to modify the grain of aluminum alloys when producing shaped castings using various casting methods, including low-pressure casting. The flux contains, wt.%: potassium hexafluorotitanate 15-25, potassium tetrafluoroborate 7-15, potassium chloride and inevitable impurities - the rest.

EFFECT: providing possibility to grind the grain to a size of no more than 500 microns at a flux consumption of no more than 1 kg per ton of melt.

1 cl, 1 dwg, 4 tbl, 2 ex

Description

Field of technology to which the invention relates

The invention relates to the field of metallurgy, namely to fluxes for melting cast aluminum-based alloys, and can be used to modify the grain of aluminum alloys when producing shaped castings using various casting methods, including low-pressure casting.

State of the art

In the production of aluminum castings, various modifiers are widely used for grain refinement. The most widely used alloy is Al-5%Ti-1%B, which in its structure is an aluminum matrix with inclusions of titanium borides distributed in it. When this master alloy is introduced into an aluminum melt, it dissolves and releases borides, which serve as nuclei for the formation of grains during the crystallization of aluminum alloys in the casting mold. Moreover, the more dispersed the borides are in the alloy, the greater their quantity and the stronger the modifying effect. In this regard, the best option is the use of Al-5%Ti-1%B alloy in the form of wire rod. Thus, with this production method, dispersed borides are formed due to the high rate of crystallization during casting of wire rod and its subsequent compression. However, there is a problem associated with the presence of boride segregations in such a master alloy, which worsens the modifying effect, and in some cases can impair the ductility of aluminum alloys in castings. The use of modifying fluxes makes it possible to ensure the formation of nuclei directly in the processed melt itself, which is especially effective for conditions of out-of-furnace melt processing in ladles on rotary degassing units.

The material reflected in the invention “Flux for refining and modifying aluminum alloys” is known (author’s certificate SU No. 569633, C22C1/06, published on August 25, 1977). The proposed composition contains, by weight. %: potassium chloride 15-42, calcium chloride 10-30, potassium fluorozirconate 5-15, calcium 0.5-2, hexachloroethane - the rest. The material can be used in the production of aluminum alloys.

Among the disadvantages of the proposed material, the presence of toxic hexachloroethane in the flux should be noted. In addition, it should be noted that the presence of calcium in the composition, the admixture of which is limited in cast alloys of the Al-Si system, since its presence in the alloy impairs the adhesion of paint and varnish coatings.

Another material is known, reflected in the invention “Flux for processing cast aluminum alloys” (author’s certificate SU No. 311975, C22C21/04, 08/19/1971). The proposed composition contains, by weight. %: cadmium chloride 45-50, potassium fluorozirconate 40-45, boric acid 5-10.

The main disadvantage of this composition is the presence of highly toxic cadmium chloride in the flux. Also, boric acid, which is part of the flux, when it interacts with the aluminum melt, will saturate the alloy with hydrogen, which creates the danger of the formation of hydrogen porosity.

The closest to the proposed invention is the material disclosed in the invention “Method for modifying aluminum-silicon alloys” (RU patent No. 2623966, S22S1/06, S22S21/02, 06/29/2017). The essence of the invention is the introduction into the melt of a flux containing carbon-containing material, titanium-containing material and barium carbonate, characterized in that the titanium-containing material is used in the form of a salt of potassium fluorotitanate, and on the surface of the aluminum-silicon melt at a temperature of 760-770°C in the amount of 2 -3% of the weight of the melt, pour flux in an even layer, leave for 2-3 minutes, and then mix into the melt to a depth of 10-20 cm. The proposed composition contains, by weight. %: barium carbonate 27-35, potassium fluorotitanate 50-57, carbon-containing material - the rest.

Among the disadvantages of the proposed material, it should be noted the increased melt processing temperature, which is 760-770 ℃, and its extremely high consumption, at the level of 2-3% of the mass of the processed melt.

Disclosure of the invention

The objective of the invention is to create a new modifying flux intended for modifying the grain of aluminum casting alloys. The main application is the modification of aluminum alloys for shaped castings.

The technical result is to ensure effective grain refinement in castings made of aluminum foundry alloys, no more than 500 microns at a flux consumption of no more than 1 kg per ton of melt.

The technical result is achieved due to the fact that a flux containing potassium hexafluorotitanate, potassium tetrafluoroborate and potassium chloride is used, with the following ratio of components, mass. %:

potassium hexafluorotitanate 15 – 25 potassium tetrafluoroborate 7 – 15 potassium chloride and inevitable impurities rest.

Brief description of drawings

Figure 1 shows a typical structure of a modified wheel.

Carrying out the invention

When potassium hexafluorotitanate interacts with an aluminum melt, titanium is reduced from it at the flux-melt interface, which reacts with boron, which in turn is formed during the interaction of potassium tetrafluoroborate with an aluminum melt. When titanium interacts with boron, dispersed particles of titanium diboride are formed at the flux-melt interface, serving as crystallization centers for the aluminum solid solution grain. Potassium chloride reduces the melting point of the flux, which increases the reactivity of the proposed flux composition.

The contents (wt.%) of potassium hexafluorotitanate (15-25), potassium tetrafluoroborate (7-15), potassium chloride (the rest) are limited to the declared limit, which ensures melting of the flux at a temperature not exceeding 670 ℃ and ensures grain grinding to a size not more than 500 microns at a consumption of 1 kg of flux per ton of alloy. At other concentrations, the melting point of the flux increases, and its reactivity sharply deteriorates, which leads to grain enlargement.

The flux is made in the form of a mechanical mixture of components.

Various modifications and improvements are permitted, not exceeding the scope of the invention as defined by the claims.

Example of a specific implementation

EXAMPLE 1

To determine the modifying ability of the flux, the AK12pch alloy was melted in an induction furnace and processed by applying flux to the surface and mixing it with a graphite mixer, flux consumption was 0.1% of the melt weight, the melt temperature during processing was 690-700 ℃, processing time 10-15 minutes. Crystallization of the alloy was carried out in a metal die to produce a blank for cutting samples in accordance with GOST 1583 with a die temperature of 400-450 °C. The grain size was assessed after etching using an optical microscope on a transverse macrosection.

To confirm the declared composition, the flux compositions given in Table 1 were prepared in laboratory conditions. The melting temperatures of the fluxes are given in Table 2, the grain sizes are given in Table 3.

Table 1 - Composition of fluxes, %wt.

No. Potassium hexafluorotitanate Potassium tetrafluoroborate Potassium chloride Prototype 50-57 27-35 BaCO ₃ Carbon-rest 10.0 5.0 Rest 15.0 7.0 Rest 20.0 10.0 Rest 25.0 15.0 Rest 30.0 18.0 Rest

Table 2 – Melting temperature of flux

No. _Tpl , ℃ Prototype 750-770 718 670 660 657 711

Table 3 - Grain size

No. Grain size, microns Prototype 1761 No processing 3751 930 500 452 391 1142

From the analysis of the results presented in tables 2 and 3, it is clear that compositions 2-4, according to the stated range, provide the required modification efficiency with grain refinement to a size of no more than 500 microns, due to the presence of a titanium-containing additive in the form of potassium hexafluorotitanate, a boron-containing additive in the form of potassium tetrafluoroborate and potassium chloride in the required amount with a decrease in the melting point of the flux, which ensures its high reactivity.

EXAMPLE 2

To confirm the suitability of the flux for alloys used in low-pressure casting, automobile wheels were cast from the AlSi11 alloy, treated with an Al-5%Ti-1%B rod alloy with a consumption of 1.7 kg per ton of melt and treated with the proposed flux (composition 3) with a consumption of 0.8 kg per ton. The resulting grain sizes are shown in Table 4.

Table 4 - Grain size

Modification method Grain size in different zones of the wheel, microns Spoke-rim transition Spoke Spoke-hub transition Al-5%Ti-1%B 891 1350 1408 Composition 3 443 412 451

From the analysis of the results presented in Table 4, it is clear that the flux has a high modifying ability in comparison with the Al-5%Ti-1%B rod alloy when producing castings using low pressure casting. A typical structure of a modified wheel is shown in Fig. 1.

Claims (2)

Flux for modifying aluminum alloys, characterized in that it contains potassium hexafluorotitanate, potassium tetrafluoroborate, potassium chloride and inevitable impurities in the following ratio of components, wt.%: potassium hexafluorotitanate 15-25 potassium tetrafluoroborate 7-15 potassium chloride and inevitable impurities rest