RU2696794C1 - Method for production of rod from heat-resistant aluminium alloy - Google Patents

Abstract

FIELD: metallurgy.SUBSTANCE: invention relates to metallurgy, namely to methods for production of aluminum-based electrotechnical products, used for production of electrotechnical wire and wires of high-voltage power transmission lines. Method involves preparation of a melt containing the following in wt. %: 0.2–0.4 Zr, 0.2–0.4 Si, 0.6–0.8 Fe, Al is rest, at temperature 800–900 °C, crystallisation at rate of 5 °C/s, production of wire by hot deformation of cast billet, winding of rolled wire into coils, thermal treatment of rolled coils at temperature of 200–600 °C for not more than 24 hours with subsequent cooling in air.EFFECT: technical result is improved conductivity of wire rod without loss of optimum level of heat resistance and mechanical properties.1 cl, 3 ex, 3 tbl

Description

The invention relates to the field of metallurgy, and in particular to methods for producing aluminum-based electrical products used for the manufacture of wire rod and wires of high voltage power lines.

At present, low-alloyed aluminum alloys of the Al-Fe-Si system (alloys of the 1XXX series in the international classification) are widely used in electrical products due to their high electrical conductivity and corrosion resistance. The optimal combination of light weight and moderate electrical conductivity makes these alloys preferable for the production of wires of high voltage overhead power lines (power lines) compared to copper alloys.

The tensile properties of aluminum alloys of the Al-Fe-Si system are low. Currently, there is GOST R IEC 62004-014, which displays the requirements for improving the strength and thermal stability of aluminum alloys used for power transmission lines. Traditional wires made of technical aluminum of the A5E and ABE brands do not meet these requirements, since they significantly soften even after short-term heating to 100 ° C. To solve this problem, the most promising is the creation of a wire made of low alloy aluminum alloy with the addition of zirconium.

Zirconium alloying is used to increase the strength characteristics at room temperature and to ensure the stability of the structure and improve the mechanical properties under tension at elevated temperatures due to the formation of Al ₃ Zr particles.

The initial billet for the aluminum wire from which the wires are made is wire rod, which is obtained by continuous casting and rolling. The achievement of the required characteristics, electrical resistivity and strength (after heating to 250 ° C) is determined by the microstructure of the wire rod. The heat resistance of aluminum wire depends on the concentration of zirconium in the alloy, as well as on the technological modes of melting, casting and heat treatment. The effect of zirconium on heat resistance is due to Al ₃ Zr particles with a L1 ₂ crystal lattice, which are formed in the wire rod during annealing. The solubility of zirconium in the aluminum matrix is negligible, due to which Al-Zr alloys can exhibit high strength, thermal stability and electrical conductivity at the same time.

A known conductor aluminum alloy is disclosed in patent FR 2996951 from 04/18/2014, which contains 0.05-0.5 wt.% Zr and impurities. A method of manufacturing a wire includes the following steps: preparing a melt containing aluminum, zirconium and inevitable impurities; obtaining cast billets from the melt; rolling the workpiece and subsequent annealing at a temperature of from 400 to 450 ° C for 100 to 500 hours.

The disadvantages of this method include too long the duration of the heat treatment (more than 100 hours), which is impractical in an industrial environment, as there is an extension of the technological process of wire production.

Known heat-resistant high-strength aluminum alloy disclosed in patent EP 0787811 A1 from 6.08.1997. According to this patent, an aluminum-based alloy contains: 0.28-0.8 wt.% Zr; 0.1-0.8% Mn; 0.1-0.4% Cu; 0.16-0.3% Si. The method for producing aluminum alloy wire includes the following stages: preparation of the melt at a temperature not lower than 750 + 227 × (Z-0.28) ° С (where Z is the concentration of zirconium in the alloy, wt.%); cooling at a rate not lower than 0.1 ° C / s; obtaining the primary (cast) billet with subsequent hot deformation; heat treatment at a temperature of 320-390 ° C for 30-200 hours and cold deformation.

The disadvantages of this method include:

1. Insufficient electrical conductivity (below 53% IACS);

2. Long duration of heat treatment (more than 100 hours);

3. In the method there is additional cold processing, which complicates the process of obtaining the desired level of performance.

The closest in technical essence to the proposed invention is the method described in patent RU 2657678 C1, publ. 06/14/2018, including the production of wire rod from a heat-resistant alloy based on aluminum, characterized by an electrical conductivity of at least 60% IACS, containing zirconium in an amount of 0.20-0.52 wt.% And inevitable impurities. The method includes the following operations: obtaining a cast billet of unlimited length by crystallizing the melt at a temperature of 5 ° C above the liquidus temperature of the alloy, producing wire rod of unlimited length by hot deformation of the cast billet, winding the wire rod in bays of measured length, heat treating the bays of wire rod at maximum temperature heating 415 ° C for no more than 144 hours, while the heating rate in the temperature range 300-400 ° C is not higher than 15 ° C / h.

The disadvantages of this method include:

1. Along with high electrical conductivity, low values of strength properties are observed, which does not allow the use of material for the manufacture of electrical wire rod and power line wires;

2. The insufficient casting temperature leads to the formation of primary crystals of the Al ₃ Zr phase with a lattice of type D0 ₂₃ in the structure of the cast billet, which negatively affect the mechanical properties.

The objective of the invention is to provide a method for producing wire rod from a heat-resistant aluminum alloy doped with zirconium, silicon and iron, while achieving high values of electrical conductivity and a high level of mechanical properties.

The technical result is to solve the problem, in particular, to increase the electrical conductivity of the alloy without losing the optimum level of heat resistance and mechanical properties, after high-temperature heating without the use of long time exposures.

To solve this problem, a method for producing wire rod from a heat-resistant aluminum alloy containing 0.2-0.4 wt.% Zr, 0.2-0.4% Si, 0.6-0.8% Fe, Al - the rest, including the preparation of the melt, the preparation of the cast billet with subsequent crystallization, the production of wire rod by hot deformation of the cast billet, the winding of the wire rod in the bays, the heat treatment of the bays, moreover, the preparation of the melt is carried out at a temperature of 800-900 ° C, followed by crystallization at a rate of 5 ° C / s getting wire rod is carried out by hot deformation Ita preform at a temperature of 300 ° C with a reduction ratio of 70% and heat treating coils of wire rod is performed at a temperature of 200-600 ° C for no longer than 24 hours, followed by cooling in air.

To ensure the optimal combination of electrical conductivity, mechanical properties and heat resistance, even after high-temperature heating, the structure of the conductive material should be an undoped aluminum solid solution with Al ₃ Zr particles uniformly distributed in it with a crystal lattice L1 ₂ and an average size of not more than 25 nm.

Overheating of the melt by 5 ° C above the liquidus temperature of the aluminum alloy and crystallization rate of 40 K / s (° C / s) can lead to the formation of coarse primary Al ₃ Zr particles with a crystal lattice D0 ₂₃ and a decrease in the concentration of zirconium in the solid solution, which will lead to loss of strength properties during further processing.

The temperature range of casting from 800 to 900 ° C allows you to achieve the desired structure of the cast billet. The content of zirconium in excess of 0.3 wt.% Leads to the release of coarse primary particles of Al ₃ Zr with a crystal lattice D0 ₂₃ , which reduce the properties of wire rod. However, a low zirconium content will not be sufficient for hardening during the separation of secondary Al ₃ Zr particles with a L1 ₂ crystal lattice. Therefore, for the complete dissolution of zirconium in the melt, it is necessary to increase the casting temperature and increase the crystallization rate. When hardening is not fast enough, coarse primary crystals of the Al ₃ Zr phase can form, which is accompanied by a decrease in the concentration of zirconium in Al, therefore, the recommended crystallization rate is at least 5 ° C / s (N. Belov. Phase composition of industrial and promising aluminum alloys. - 2010) . With an increase in the crystallization rate, the concentration region of the aluminum solid solution expands, which makes it possible to obtain a structure without primary particles of Al ₃ Zr. Solidification in this concentration region is carried out according to the principle of solid solutions, while the transition of the primary crystallization region of the Al ₃ Zr phase directly to the crystallization region of the aluminum solid solution is observed.

According to patent RU 2657678, hot deformation at temperatures above 300 ° C can lead to uneven decomposition of the aluminum solid solution with the formation of secondary precipitates of the Al ₃ Zr phase with the L1 ₂ crystal lattice, which negatively affects the mechanical properties.

Doping with iron and silicon is necessary for a significant increase in strength characteristics while maintaining electrical conductivity at an acceptable level (Zolotorevsky V. S., Belov N. A. Metal science of cast aluminum alloys. - MISiS, 2005). In this case, the silicon / iron ratio = 0.3-0.5 ensures the formation of spherical Al ₈ Fe ₂ Si and Al ₅ FeSi particles after annealing with a size of less than 3 μm. Particles are obstacles to the movement of dislocations at elevated temperatures and prevent softening of the alloy during heating. In addition, doping with silicon leads to increased diffusion of zirconium, accelerates the release of Al ₃ Zr particles and thereby reduces the heat treatment time (Alabin, AN, Belov, NA, Korotkova, NO, Samoshinal, ME Effect of Annealing on the Electrical Resistivity and Strengthening of Low-Alloy Alloys of the Al – Zr – Si System // Metal Science and Heat Treatment. - 2017. - V. 58. - No. 9-10. - S. 527-531), which allows to optimize the process, reduce energy costs and reduce the cost of the finished product. The absence of Si leads to the formation of harmful needle particles of Al ₃ Fe in the microstructure of the aluminum alloy after annealing, which reduce ductility. Therefore, the optimum amount of silicon should be 0.25-0.50 wt.% Due to the formation of the Al ₈ Fe ₂ Si phase with a preferred plate morphology. Doping with silicon and iron above the stated limits entails a strong decrease in the conductive properties.

Examples of implementation.

Example 1. To confirm the concentration range in which the alloy structure is presented in the form of an aluminum solid solution of zirconium and a certain amount of iron-containing phases of eutectic origin, 3 alloy compositions were cast (Table 1). The casting temperature of the billets was measured immediately before pouring into the mold, providing a crystallization rate of 5 ° C / s. The chemical composition of the alloys, casting temperature and structure parameters of the alloys are given in table 1.

Using scanning electron microscopy, the microstructure of the aluminum alloy was analyzed for the presence or absence of primary particles of Al ₃ Zr with a crystal lattice of D0 ₂₃ .

Table 1.

The presence / absence of Al ₃ Zr particles with a crystal lattice D0 ₂₃ for experimental alloys at a casting temperature of 800-900 ° C

where "-" the absence in the structure of the alloy of Al ₃ Zr particles with a crystal lattice D0 _23,

"+" The presence in the structure of the alloy of Al ₃ Zr particles with a crystal lattice D0 ₂₃ .

From the results presented in table 1, it follows that at a casting temperature in the range of 800-900 ° C and a crystallization rate of 5 ° C / s, a structure without primary particles is formed in Al ₃ Zr with a crystal lattice of D0 ₂₃ .

This cast billet structure is acceptable for subsequent thermomechanical processing.

Example 2. From an alloy of composition 2 (Table 1), a cast billet was obtained by continuous casting at a temperature of 840 ° C and a crystallization rate of 5 ° C / s. Hot deformation of the cast billet is carried out at a temperature of 300 ° C on a rolling mill, which leads to a wire rod with a final diameter of 9.5 mm Heat treatment of wire rod coils is carried out in the temperature range 200-600 ° C for 3 hours, followed by cooling in air.

As can be seen from table 2, only at an annealing temperature of 400 ° C is it possible to simultaneously achieve high electrical conductivity (IACS) and a high level of mechanical properties (σ _B , δ) of an aluminum alloy wire rod.

Table 2.

Properties of heat-resistant aluminum alloy after heat treatment at a temperature of 200-600 ° C for 3 hours.

Example 3. From a heat-resistant aluminum alloy with a chemical composition 2 proposed in Example 1, a cast billet was obtained by continuous casting at a temperature of 840 ° C and a crystallization rate of 5 ° C / s. Hot deformation of the cast billet is carried out at a temperature of 300 ° C on a rolling mill, which leads to a wire rod with a final diameter of 9.5 mm Heat treatment of wire rod coils is carried out in the temperature range 200-600 ° C for 24 hours, followed by cooling in air.

Table 3.

Properties of heat-resistant aluminum alloy after heat treatment at a temperature of 200-600 ° C for 24 hours.

As can be seen from table 3, only at an annealing temperature of 400-450 ° C, a given electrical conductivity is maintained while maintaining a set of high performance characteristics, namely high strength and heat resistance.

The proposed method for producing wire rod is economically feasible in an industrial environment compared to the methods proposed in patents FR 2996951 and EP 0787811. The data in the table show that the developed method for the production of wire rod from heat-resistant aluminum alloy provides a complex of high performance properties that exceed the properties in patent RU 2657678 .

The physicomechanical characteristics of the developed method meet the requirements of GOST R IEC 62004-014; therefore, the production of wire rod from this material can be realized not only as part of the import substitution program, but also as part of the expansion of export deliveries of domestic products abroad.

Claims (1)

The method of obtaining wire rod from a heat-resistant aluminum alloy containing, wt.%: 0.2-0.4 Zr, 0.2-0.4 Si, 0.6-0.8 Fe, Al - the rest, including the preparation of the melt, obtaining cast billets with subsequent crystallization, obtaining wire rod by hot deformation of the cast billet, winding wire rod into coils, heat treatment of coils, characterized in that the melt is prepared at a temperature of 800-900 ° C with a crystallization rate of 5 ° C / s, heat treatment of coils of wire rod carried out at a temperature of 200-600 ° C for no more than 24 hours with next cooling in air.