RU2767091C1 - Method of producing heat-resistant wire from aluminum-calcium alloy - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy of light alloys, in particular to aluminum-based alloys, and can be used in production of wire from aluminum-calcium alloy, including with diameter less than 0.3 mm. Method of producing wire from an aluminum-calcium alloy involves obtaining an aluminum-based melt containing the following, wt%: calcium 0.8–1.8, zirconium 0.3–0.7, iron 0.1–0.64, silicon 0.05–0.4, aluminum — the rest; obtaining a cast workpiece with diameter of 8 to 12 mm by crystallization of melt in electromagnetic crystallizer, deformation of the cast workpiece by cold drawing and stabilizing annealing of the obtained wire at temperature of 420–460 °C for 1–10 hours. Besides, the wire diameter is less than 3.1 mm, in particular, less than 0.3 mm.

EFFECT: obtaining heat-resistant wire from aluminum-calcium alloy with the following characteristics: density less than 2_7 g/cm³, high deformation processability, after 1-hour heating at 450 °C: tensile strength (σ_B) — not less than 180 MPa, conventional yield strength (σ_{0_2}) — not less than 170 MPa, relative elongation after fracture (δ) — not less than 8 %, electrical conductivity — not less than 54 % IACS.

3 cl, 6 dwg, 3 tbl, 2 ex

Description

The invention relates to the field of metallurgy of light alloys, in particular to alloys based on aluminum, and can be used in the production of wire from an aluminum-calcium alloy, including wires with a diameter of less than 0.3 mm.

Currently, there are many inventions to achieve the best combination of electrical conductivity, strength and heat resistance in the wire. In particular, alloy 01417 alloyed with cerium, lanthanum and other rare earth metals (REM) is known [Dobatkin V.I., Elagin V.I., Fedorov V.M. Rapidly crystallized aluminum alloys. M.: VILS, 1995, 341 p.]. Alloy 01417 is intended for the manufacture of wire that operates for a long time at temperatures up to 250°C. Currently, it is used to make airliners' flight lines instead of copper wires, while reducing the weight of the product from 100 to 300 kg. The gain in weight in terms of electrical conductivity compared to copper wire is up to 30%.

The main disadvantage of the 01417 alloy is that it focuses on a complex and costly process involving pellet casting followed by powder metallurgy (known as RS/PM). Other disadvantages of the alloy are limited operating temperatures (up to 250°C) and increased density (2.828 g/cm ³ ) compared to pure aluminum. This is due to the high content of REM in the composition of the alloy.

A method for producing a conductive aluminum alloy is known (RU 2667271, published on September 18, 2018). This method includes obtaining an alloy billet containing (wt.%) 0.2-0.8% magnesium, 0.2-0.5% zirconium and impurities, annealing the billet in the temperature range of 300-450°C for a duration of 30 to 350 hours and deformation by the method of severe plastic deformation at a pressure of 0.1-6.0 GPa, in the range of homological temperatures of 0.3-0.5 Tm to the value of the true accumulated deformation e≥4. The invention is aimed at improving the mechanical strength, electrical conductivity and heat resistance of an aluminum alloy.

The disadvantage of this method is limited heat resistance (up to 180°C) and excessively long annealing (more than 30 hours).

A method for producing a conductive ultrafine-grained aluminum alloy is known (RU 2616316, published on April 14, 2017). This method includes obtaining an alloy containing at least one alloying component selected from the group of rare-earth metals (La, Ce, Nd, Pr) in an amount of 7.0-9.0%, iron and silicon in an amount of 0.05- 0.1% (wt.%), severe plastic deformation with a true accumulated degree of deformation e≥4 when applying a pressure of 0.5-6.0 GPa in the range of homologous temperatures of 0.3-0.5 Tmelt, and annealing in a temperature range of 280-400°C for at least 1 hour . The technical result is to increase the mechanical strength and heat resistance with satisfactory electrical conductivity in the alloy.

The disadvantages of this method are limited heat resistance (up to 310°) and increased density (2.847 g/cm ³ ) compared to pure aluminum.

Closest to the proposed one is a method for obtaining deformed semi-finished products from an aluminum-calcium alloy (RU 2716566, publ. 12.03.2020). The claimed method includes the preparation of a melt containing calcium, zirconium, iron, silicon and scandium, obtaining an ingot, hot deformation at a temperature in the range from 390 to 450°C, cold deformation and stabilizing annealing at a temperature in the range from 300 to 400°C for a time from 1 to 10 hours, providing the formation of a composite structure consisting of an aluminum matrix containing nanoparticles of the Al ₃ (Zr,Sc)-L1 ₂ phase with a size of not more than 20 nm in an amount of not less than 0.4 vol.%, and evenly distributed in the aluminum a matrix of calcium-containing particles with a size of not more than 1 μm in an amount of not less than 16 vol.%. The technical result is the creation of a method for producing various deformed semi-finished products (including wires with a diameter of less than 0.3 mm) from an aluminum-calcium composite alloy. The materials obtained in this way have a high level of physical and mechanical properties (tensile strength of at least 250 MPa, elongation of at least 3.5% and specific electrical conductivity of at least 46.0% IACS), heat resistance (350 ° C) and density (less than 2. ⁷ g/cm3).

The disadvantage of this method is that it includes hot deformation and does not allow for direct cold drawing of a cast billet (ingot). Another disadvantage of this method is that, due to the high calcium content, the electrical conductivity of the wire does not exceed 46.0% IACS. Another disadvantage of this method is the need to introduce expensive scandium into the melt.

The technical result of the invention is to obtain a heat-resistant aluminum-calcium alloy wire with the following characteristics:

density less than 2.7 g/cm ³ (lower than that of pure aluminum), high deformation workability (no need for hot deformation) and the following set of physical and mechanical properties after 1 hour heating at 450°C: tensile strength at break (σ _C ) not less than 180 MPa, conditional yield strength (σ _0.2 ) not less than 170 MPa, relative elongation after rupture (δ) - not less than 8%, electrical conductivity - not less than 54% IACS.

The technical result is achieved as follows.

A method for producing wire from an aluminum-calcium alloy includes obtaining an aluminum-based melt containing components with the following composition % (wt):

calcium 0.8-1.8 zirconium 0.3-0.7 iron 0.1-0.64 silicon 0.05-0.4 aluminum rest,

obtaining a cast billet with a diameter of 8 to 12 mm by melt crystallization in an electromagnetic mold, deformation of the cast billet by cold drawing and stabilizing annealing of the resulting wire at a temperature of 420-460°C for 1-10 hours.

Moreover, the wire diameter is less than 3.1mm.

Also, the wire diameter is less than 0.3mm.

When the calcium content is below 0.8 wt. %, the heat resistance of the wire decreases (strength properties after 1 hour exposure at 450°C), with a calcium content of more than 1.8 wt. %, the electrical conductivity and deformation processability are reduced.

When the zirconium content is below 0.3 wt. %, the heat resistance of the wire decreases (strength properties after 1 hour exposure at 450°C), with a zirconium content of more than 0.7 wt. %, primary crystals of the stable phase Al ₃ Zr-D023 are formed and, as a result, the nanoparticles of the metastable phase Al ₃ Zr-L1 ₂ are reduced, which leads to a decrease in strength.

When the content of iron and silicon is below 0.1 wt. % and 0.05 wt. %, respectively, excludes the possibility of preparing alloys based on technical purity aluminum. When the content of iron and silicon is above 0.6 wt. % and 0.5 wt. %, respectively, the technological plasticity of the alloy deteriorates due to the coarsening of the structure.

When the diameter of the cast billet is less than 8 mm, it is difficult to obtain the necessary compression during wire production and, as a result, to achieve the required strength properties. With a cast billet diameter of more than 12 mm, the structure coarsens due to a decrease in the cooling rate during crystallization.

The annealing temperature below 420°C and holding time less than 1 hour do not allow to fully stabilize the structure and realize the required level of thermal stability. The annealing temperature above 460°С and holding time of more than 10 hours lead to coarsening of the structure (in particular, an increase in the particle size of Zr- and Ca-containing phases and the formation of recrystallized grains) and, as a consequence, to a decrease in strength properties.

The proposed modes provide the formation of a composite structure consisting of an aluminum matrix containing nanoparticles of the Al ₃ Zr-L1 ₂ phase with a size of not more than 20 nm in an amount of not less than 0.4 vol.% and eutectic calcium-containing particles of submicron size uniformly distributed in the aluminum matrix. In this case, the total concentration of alloying elements in the aluminum solid solution does not exceed 0.1 wt. %.

In private versions, the method may include obtaining a wire with a diameter of less than 3.1 mm or a diameter of less than 0.3 mm.

The invention is illustrated by the drawing, where: in Fig. 1 shows a cast billet of aluminum alloy, obtained by crystallization of the melt in an electromagnetic mold, in Fig. 2 shows a wire obtained by cold drawing from a cast billet of aluminum alloy (Fig. 1), in fig. 3 shows the microstructure of a cast aluminum alloy billet obtained by melt crystallization in an electromagnetic mold (scanning electron microscopy (SEM)), FIG. 4 nanoparticles of the Al ₃ Zr-L1 ₂ phase in an annealed wire structure (transmission electron microscopy (TEM)), FIG. 5 shows calcium-containing particles in an annealed wire (FEM) structure, FIG. 6 shows the fracture of the annealed wire after tensile testing (SEM).

The figures show: image 1 obtained in a bright field, dark field image 2 and diffraction pattern, image 3 obtained by a back-scattered electron detector, image 4 obtained by a secondary electron detector.

The choice of calcium as the main eutectic-forming component is due to the fact that in terms of the volume fraction of the second phase, the aluminum-calcium eutectic is almost 3 times higher than the aluminum-silicon eutectic. A large amount of the calcium phase of eutectic origin makes it possible to realize, with a relatively small amount of alloying elements, a high volume fraction of intermetallic compounds, commensurate with alloys of the 01417 type, containing more than 7 wt. % REM.

Eutectic alloys with calcium, in contrast to alloys with a high content of silicon, as well as alloys with a high content of rare earth metals, can be strengthened by additional alloying with the addition of zirconium. Due to the high cooling rate under the conditions of melt crystallization in an electromagnetic crystallizer, zirconium completely transforms into an aluminum solid solution, which decomposes during subsequent annealing to form nanoparticles of the Al ₃ Zr-L1 ₂ phase (Fig. 4). Retaining high dispersity in a wide temperature range (up to 450°C inclusive), these nanoparticles act as effective antirecrystallizers, which can additionally provide an increase in the strength of the deformed semi-finished product.

The combination of calcium, iron and silicon ensures the formation of a highly dispersed structure under the conditions of melt crystallization in an electromagnetic mold (Fig. 3). The relatively high plasticity of calcium-containing intermetallic compounds favors the formation of submicron particles during cold drawing. These particles also prevent the occurrence of recrystallization when heated at temperatures up to 450°C inclusive (Fig. 5).

EXAMPLE 1

Under laboratory conditions, 5 variants of the method for producing aluminum-calcium alloy wire were tested. The melt was prepared on the basis of aluminum grade A99 (GOST 11069-2001). Melting was carried out in the following sequence. After the melting of aluminum, alloys containing iron, silicon, and zirconium were introduced. After the alloys were dissolved and the furnace reached the set temperature, calcium was introduced under the melt mirror and actively mixed. The melt was poured into an electromagnetic mold, obtaining bar stock of various diameters (Fig. 1). The casting temperature was obviously higher than the liquidus temperature.

Bar blanks were subjected to cold drawing to a diameter of 3 mm. After that, the wire was subjected to multistage annealing, the last stage of which served as a stabilizing annealing. The concentrations of calcium, zirconium, iron and silicon, the diameter of the bar stock, the temperature of the stabilizing annealing and its duration varied according to the values indicated in table. 1. On the annealed (at 450°C for 1 hour) wire (Fig. 2), the mechanical tensile properties were determined (ultimate strength at break (σ _В ), conditional yield strength (σ _0.2 ), relative elongation after rupture (δ )) and electrical conductivity (SEC).

As can be seen from Table. 1, with a low content of alloying components in the melt (option 1), the technological parameters of stabilizing annealing do not allow providing a sufficient amount of calcium-containing phases of eutectic origin and zirconium nanoparticles in the structure. The consequence of this is reduced strength and increased containing density (Table 2). The content of iron and silicon in the case of option 1 also does not allow the use of technical purity aluminum.

With a high content of alloying components in the melt (option 5), the volume fraction of calcium-containing phases (in the ingot) is too high. In addition, primary crystals of the aluminum-zirconium phase are present in the structure of the cast billet. All this does not provide sufficient plasticity during cold drawing (Table 2).

When the diameter of the cast billet is more than 12 mm, the annealing temperature is higher than 460°C, and the exposure time is more than 10 hours (option 6), the structure coarsens due to a decrease in the cooling rate during crystallization and an increase in the particle size of the Zr- and Ca-containing phases, as a result, decrease in strength properties.

Thus, it can be concluded that only options 2, 3 and 4, in which the content of the alloy components, the annealing temperature and holding time, as well as the diameter of the cast billet, are within the stated limits, allow the claimed method of producing aluminum-calcium alloy wire to be implemented. The claimed variants of the method for producing wire provide the implementation of the required structure, containing nanoparticles of the Al ₃ Zr-L1 ₂ phase (Fig. 4) and calcium-containing particles of submicron size (Fig. 5). The uniform distribution of these particles ensures the viscous nature of the destruction of the wire, which manifests itself in the presence of evenly distributed pits in the fracture, the size of which does not exceed 2 μm (Fig. 6).

EXAMPLE 2

Under laboratory conditions, a wire with a diameter of 260 μm was obtained from 3 mm wire obtained according to option 3 (see example 1) (Fig. 4). The wire was annealed at 450°C for 1 hour. Properties given in table. 3 show that they correspond to the given values.

Claims (5)

1. A method for producing wire from an aluminum-calcium alloy, including obtaining an aluminum-based melt containing components, wt.%: calcium 0.8-1.8 zirconium 0.3-0.7 iron 0.1-0.64 silicon 0.05-0.4 aluminum rest, obtaining a cast billet with a diameter of 8 to 12 mm by melt crystallization in an electromagnetic mold, deformation of the cast billet by cold drawing and stabilizing annealing of the resulting wire at a temperature of 420-460°C for 1-10 hours. 2. Method according to claim 1, characterized in that the wire diameter is less than 3.1 mm. 3. Method according to claim 1, characterized in that the wire diameter is less than 0.3 mm.

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