RU2725496C1 - Sintered ligature from powder materials for alloying aluminum alloys - Google Patents

Abstract

FIELD: metallurgy.SUBSTANCE: invention relates to powder metallurgy of metals and alloys, namely, to production of ligatures based on aluminum for alloying of aluminum-based alloys. Sintered ligature of powder materials for alloying aluminum alloys contains, wt%: chrome 40–50, copper 4.0–4.5 and aluminum – the rest.EFFECT: improved distribution and increased rate of dissolution of alloying components in melt, high stability of compositions of molten alloys, elimination or significant reduction of amount of iron in ligature.1 cl, 4 tbl, 3 ex

Description

The invention relates to the field of powder metallurgy of metals and alloys, in particular to the production of aluminum alloys for alloying aluminum-based alloys, as well as to obtain the exact content of components in castings.

The alloying process is designed to facilitate the introduction of various components (including refractory) into the melt to provide the necessary chemical composition of the alloy. When alloying, double or multicomponent ligatures are widely used as raw materials. Ligature is an auxiliary alloy that is added to molten metals and alloys in order to give them certain properties, for example, fluidity, increased mechanical strength, improved antifriction and other properties.

The use of ligatures for alloying is due to the fact that the process of assimilation of the alloying element from the ligature is more reliable and efficient than when it is introduced in pure form. In addition, the use of ligatures allows the introduction of chemical elements into the melt, which it is practically impossible to introduce into the melt in its pure form, and also provides a more uniform distribution of the alloying element in the melt volume. The chemical composition and structure of ligatures have a significant impact on the structure and properties of ingots and products obtained from them.

In the production of various metals and alloys, for example, titanium, magnesium, nickel, copper, aluminum and others containing refractory components, such as chromium, cast alloys based on aluminum are often used to introduce it into the melt. One of the disadvantages of cast Al-Cr alloys is their low chromium content. Despite this, the use of such cast aluminum alloys turned out to be so effective that state and international standards were established that regulate the content of components in them.

Known aluminum alloy Alcr5 (B), obtained by melting, for alloying and modification in the production of wrought and cast aluminum alloys. This ligature contains silicon, iron, copper, manganese, magnesium, chromium, nickel, zinc, titanium, inevitable impurities and aluminum in the following ratio of components, wt. %: silicon 0.5, iron 0.7, copper 0.2, manganese 0.4, magnesium 0.5, chromium 4.5-5.5, nickel 0.2, zinc 0.2, titanium 0.1 , inevitable impurities of 0.1 and aluminum - the rest (GOST R 53777-2010, Aluminum alloys. Specifications. Table 1, page 3).

The disadvantage of this ligature is the low chromium content, which leads to its high consumption to achieve the desired content of the alloying element in the melt. In turn, this leads to a long alloy smelting process and high energy costs. In addition, the presence of iron and manganese is the reason for limiting the use of this ligature in aluminum antifriction alloys, since these elements are harmful impurities and must be disposed of.

Closest to the technical nature of the present invention is selected as a prototype aluminum alloy AlСr20 (A), obtained by melting, for alloying and modification in the production of wrought and cast aluminum alloys. This ligature contains silicon, iron, chromium, inevitable impurities and aluminum in the following ratio of components, wt. %: silicon 0.3, iron 0.3, chromium 18-20, inevitable impurities 0.1 and aluminum - the rest (GOST R 53777-2010, Aluminum alloys. Specifications. Table 1, page 3).

The advantage of this ligature is that the chromium content in it can be significantly increased to 20 wt. %, which increases the efficiency of using ligatures. This saves energy consumption with a significant reduction in the melting time of the base alloy compared to the analogue. In addition, the presence of harmful impurities of manganese and other components such as copper, manganese, magnesium, nickel, zinc and titanium was completely eliminated in the AlСr20 ligature, and the iron level was reduced to 0.3 wt. %

The disadvantages of the known solutions, including technical problems, are the limited chromium content of up to 20 wt. % in the ligature, the difficulty in its production, as well as the limitation of its use in aluminum antifriction alloys due to the presence of iron, the level of which cannot be reduced to zero, since its introduction occurs involuntarily in the manufacture of the melt. In addition, the use of this cast ligature does not guarantee the uniform distribution of alloying components in the finished ingot and the stability of the compositions of melted alloys in different melts, which creates certain technical problems when alloying aluminum alloys.

The proposed technical solution aims at eliminating the specified technical problems and allows to obtain a technical result — the technical expansion of the operational capabilities of the ligature for use in aluminum alloys, including antifriction aluminum alloys by improving the distribution and increasing the dissolution rate of alloying components in the melt, increasing stability compositions of smelted alloys in different melts in order to obtain a more accurate and homogeneous content in the entire volume of the melt and the finished ingot by increasing the chromium content in the ligature, completely eliminating or significantly reducing the amount of iron in the ligature, and using spark plasma sintering technology to consolidate the ligature component powders with the addition of copper.

The technical result is achieved by a sintered alloy of powder materials for alloying aluminum alloys, including chromium and aluminum, additionally containing copper in the following ratio of the above components, wt. %: chromium 40-50, copper 4.0-4.5 and aluminum - the rest.

The invention is characterized as follows.

Sintered alloy of powder materials for alloying aluminum alloys includes, by weight. %:

chrome 40-50;

copper 4.0-4.5;

aluminum - the rest.

The use of chromium, copper and aluminum powders as starting materials makes it possible to produce sintered ligatures with the exact content of components, as well as to eliminate or reduce the presence of a significant amount of iron in it. Since iron is a harmful impurity for aluminum antifriction alloys, its elimination from the ligature allows us to expand its operational capabilities for use in antifriction alloys.

The consolidation of the powdered components of the ligature is carried out using spark plasma sintering technology (Spark Plasma Sintering). This technology allows you to control the grain size during sintering, to preserve the structure of the initial powders, to obtain uniform microstructures in the ligature, to apply low values of pressure during sintering in comparison with other similar methods, which significantly increases the porosity and surface area of the ligature. Thus, the use of this sintering technology to consolidate the initial powders makes it possible to obtain a sintered ligature with a homogeneous distribution of components in its entire volume and with a large contact surface with the melt, accelerating the dissolution of the ligature in the melt, which, in turn, reduces the alloy smelting process , increasing the stability of the chemical compositions of the alloy in different melts and reducing energy costs.

Addition to the main components (chromium and aluminum) of copper powder in an amount of 4.0-4.5 wt. % increases the mechanical strength of the sintered ligature due to improved adhesion between particles of copper, aluminum and chromium while maintaining increased porosity. In addition, the indicated mass of copper will complement the required amount of this element, which is present in most anti-friction aluminum alloys.

The combined use of the powder components of the ligature and the technology of spark plasma sintering makes it possible to produce sintered ligature that does not have a limitation on the chromium content in aluminum, as is the case when obtaining cast ligatures. Due to this, it is possible to produce a ligature sintered from powder materials containing a large amount of chromium (40-50 wt.%) In an aluminum matrix, which increases the efficiency of using the ligature by reducing its consumption to achieve the required chromium content in the melt. In addition, the use of one Al-Cr-Cu ligature allows replacing the use of two double cast ligatures Al-Cu and Al-Cr.

The industrial applicability of the invention is confirmed by the following examples of specific performance.

As an example, we consider the manufacture of two sintered powder alloys and the use of the well-known commercial cast alloy AlСr20 (А) (GOST R 53777-2010) for casting cylindrical ingots with a diameter of 100 mm and a height of 500 mm from Al-1Cr alloy. To obtain these ingots, it is required to melt 12 kg of an alloy containing 120 g of Cr in an open high-frequency induction furnace.

The following ligatures were used: 1 - sintered AlСr40Сu4 ligature; 2 - sintered AlCr50Cu4.5 ligature; 3 - cast ligature (prototype) AlСr20 (A).

In order to determine the stability of alloying for each example, three ingots were cast, differing in the melt holding time after dissolution of the ligature: two of them were aged for 10 minutes, and the third - 22 minutes.

Example 1

To prepare the sintered AlCr40Cu4 alloy, the following powder materials were used in the following ratio of components, wt. %: chromium 40, copper 4.0 and aluminum - the rest.

The powders of the components are mixed in a ball mill in isopropyl alcohol together with hard alloy balls until they are completely mechanically activated, followed by drying in a vacuum oven at a temperature of 90 ° C to obtain a powder mass - a mixture. Next, the resulting mixture is sieved through a sieve with a mesh size of 100 μm, then 20 g of the obtained mass are loaded into a graphite matrix for spark plasma sintering in order to obtain a disk with a diameter of 40 mm and a height of ~ 4 mm The sintering process is carried out at a temperature of 400 ° C without exposure and a pressure of 48 MPa.

The results of determining the chemical composition of the obtained sintered alloys are shown in table 1, and the porosity and tensile strength of the sintered discs are given in table 2.

Then, the obtained disks from sintered alloys were used in casting cylindrical ingots from Al-1Cr alloy. For casting one ingot, 300 grams of sintered AlСr40Сu4 ligature per 11.7 kg of molten aluminum will be required.

Tests showed that the dissolution of the required mass of AlCr40Cu4 ligature occurs 6 minutes after it is introduced into the melt, table 3. After that, the melt was poured into the mold.

Next, a chemical analysis was carried out in three places of the ingot at a distance of 50, 250 and 450 mm from its bottom. The results on the distribution of chromium in the sections of the ingot are given in table 4. The distribution of iron over the ingot was relatively uniform and is in the range of 0.07 - 0.1 wt. %

Example 2

By analogy with example 1, a mixture was prepared for the preparation of sintered AlCr50Cu4.5 ligature. For this, the following powder materials were used in the following ratio of components, wt. %: chrome 50, copper 4.5 and aluminum - the rest.

Next, the resulting mixture is sieved through a 100 μm sieve, then 20 g of the resulting mass are loaded into a graphite matrix for spark plasma sintering to obtain a disk with a diameter of 40 mm and a height of ~ 4 mm. The sintering process is carried out at a temperature of 400 ° C without exposure and a pressure of 48 MPa.

The results of determining the chemical composition of the obtained sintered alloys are shown in table 1, and the porosity and tensile strength of the sintered discs are given in table 2.

Then, the obtained disks from sintered alloys were used in casting cylindrical ingots from Al-1Cr alloy. For casting one ingot, 240 grams of sintered AlСr50Сu4.5 ligature per 11.76 kg of molten aluminum will be required. Tests have shown that the dissolution of the required mass of AlCr50Cu4.5 ligature occurs 8 minutes after it is introduced into the melt, table 3. After that, the melt was poured into the mold.

After hardening, a chemical analysis was carried out in three places of the ingot at a distance of 50, 250 and 450 mm from its bottom. The results on the distribution of chromium in the sections of the ingot are given in table 4. The distribution of iron over the ingot was relatively uniform and is in the range of 0.07 - 0.1 wt. %

Example 3

To compare the obtained sintered ligatures, it was necessary to make castings of cylindrical ingots from Al-1Cr alloy using cast ligatures. For the implementation of this example, a commercial cast alloy Alcr20 (A) was used (GOST R 53777-2010). The results of determining the chemical composition of this ligature are shown in table 1.

For casting one ingot, 600 grams of AlCr20 (A) master alloy per 11.39 kg of molten aluminum will be required. Tests showed that the dissolution of the required mass of AlCr20 (A) ligature occurs 28 minutes after it was introduced into the melt, table 3. After that, the melt was poured into the mold.

After hardening, a chemical analysis was carried out in three places of the ingot at a distance of 50, 250 and 450 mm from its bottom. The results of the distribution of chromium in the cross sections of the ingot are given in table 4. The distribution of iron over the ingot was relatively uniform, and is in the range of 0.14-0.17 wt. %

The results of the study of ligatures and ingots showed that the use of the invention allows to increase the chromium content in the ligature to 40-50 wt. %, increase the dissolution rate of alloying components in the melt, increase the stability of the compositions of the alloyed alloys in different melts, obtain a more accurate and homogeneous content of the alloying component in the entire volume of the finished ingot, completely eliminate the amount of iron in the ligature and, thereby, significantly reduce the amount of iron in the ingots up to 0.07-0.1 wt. %

Thus, the claimed combination of essential features, reflected in the independent claim, ensures the achievement of the claimed technical result - technical expansion of the operational capabilities of the ligature for use in aluminum alloys, including for antifriction aluminum alloys due to improved distribution and increased dissolution rate of alloying components in the melt, to increase the stability of the compositions of melted alloys in different melts in order to obtain a more accurate and homogeneous content in the entire volume of the melt and the finished ingot by increasing the chromium content in the ligature, completely eliminating or significantly reducing the amount of iron in the ligature, and using spark plasma sintering technology for the consolidation of powders of ligature components with the addition of copper.

The analysis of the claimed technical solution for compliance with the conditions of patentability showed that the characteristics indicated in the formula are essential and interconnected with the formation of a stable set of necessary characteristics, unknown at the priority date from the prior art and sufficient to obtain the required synergistic (super-total) technical result.

Thus, the above information indicates the fulfillment of the following set of conditions when using the claimed technical solution:

- the object embodying the claimed technical solution in its implementation is intended for the production of aluminum alloys for alloying aluminum-based alloys, as well as to obtain the exact content of the components in the castings;

- for the claimed object in the form described in the formula, the possibility of its implementation using the methods and methods described above or known from the prior art on the priority date is confirmed;

- the object embodying the claimed technical solution, when implemented, is able to ensure the achievement of the technical result perceived by the applicant.

Therefore, the claimed subject matter meets the patentability criteria of “novelty”, “inventive step” and “industrial applicability” under applicable law.

Claims (1)

Sintered alloy of powder materials for alloying aluminum alloys, containing chromium and aluminum, characterized in that it additionally contains copper in the following ratio of the above components, wt. %: chromium 40-50; copper 4.0-4.5; aluminum - the rest.