RU2478136C2 - Ultra fine-grained aluminium alloys for electric hardware and method of their products (versions) - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: Al-Mg-Si- system aluminium alloys incorporates two types of ultra fine-grained structures with grain size not exceeding 400 nm and 400 nm-1000 nm produced by water quenching at 520-565°C, intensive plastic forming with total true accumulated strain e≥8 and forming temperature not exceeding 200°C, in compliance with first version, and e≥4 and forming temperature not exceeding 300°C in compliance with second version whereby artificial ageing is performed. Produced alloys feature structure containing, at least, 60% of grains with great-angle boundaries off-oriented relative to adjacent grains by 10 degrees and greater, and aluminium matrix depleted of main alloying elements Mg and Si. Besides it comprises nano-sized precipitations of hardening phase Mg₂Si of modification (β) uniformly distributed in grain volume or those of modification (β) located at grain boundary area, and those of needle-shape modifications (β", β') located at grain center.

EFFECT: higher strength and electric conductivity.

14 cl, 2 dwg, 2 tbl, 2 ex

Description

The invention relates to the field of UFG aluminum alloys with increased mechanical strength and electrical conductivity, intended for the manufacture of billets for electrical purposes, such as wire rods of round and square cross-section, wire, wire for overhead power lines, conductive tires and profiles, as well as to a method for processing these alloys.

It is known that in electrical engineering the use of technically pure aluminum, which has the highest electrical conductivity among aluminum materials, is limited due to its low strength [IB Peshkov. Status and prospects of the use of aluminum in the cable industry // Cables and wires (2009) No. 1. 314. C.7-9.]. An increase in the strength characteristics of aluminum is achieved by introducing certain alloying additives, such as, for example, magnesium (Mg) and silicon (Si), i.e. creating alloys of the Al-Mg-Si system. Because of good processability and high corrosion resistance, Al-Mg-Si alloys are widely used as materials for electrical products [Aluminum and aluminum alloys in electrical products / L.A. Vorontsova, V.V. Maslov, I. B. Peshkov Publishing House . "Energy", Moscow, 1971 - 224 p .; M.B. Altman, Yu.P. Arbuzov, B. I. Babichev and others. Aluminum alloys. The use of aluminum alloys. Reference guide. M.: Metallurgy, 1972 - 408 s]. Studies of the optimal content of Mg and Si, with the aim of improving the mechanical properties, as well as minimizing the electrical conductivity, showed that the best combination of mechanical and electrical characteristics is demonstrated by alloys having a Mg and Si ratio corresponding to Mg ₂ Si. It was found that Mg and Si in aluminum form the hardening phase of Mg ₂ Si, and the solubility of this compound with increasing temperature allows thermal and thermomechanical treatment to be applied to such alloys.

Several methods are known for processing aluminum alloys of the Al-Mg-Si system, which make it possible to increase their mechanical strength and electrical conductivity by forming special structures. For example, in the work of [L.A. Vorontsova, V.V. Maslov, I. B. Peshkov, Aluminum and aluminum alloys in electrical products. "Energy" 1971 - 224 pp.] Describes a method of heat treatment (TH) of billets of aluminum alloys Al-Mg-Si, which includes: hardening from 520 ... 550 ° C into water and artificial aging at 150 ... 160 ° C for 12 ... 10 hours.

In the invention [US 3770151 148 / 11.5, IPC C22f 1/04, publ. November 6, 1973] a method is described for thermomechanical processing (TMT) of an aluminum alloy Al-Mg-Si, which includes successively quenching from a temperature of 621 ° C into water and cold rolling to a degree of deformation of 99.6%.

There is a method of TMT blanks from aluminum alloys Al-Mg-Si [M.B. Altman, Yu.P. Arbuzov, B. I. Babichev and other Aluminum alloys. The use of aluminum alloys. Reference guide. M .: Metallurgy, 1972 - 408 pp.], Including successively quenching from 525 ... 565 ° C into water, drawing during natural aging with a degree of deformation of more than 85%, artificial aging at a temperature of 140 ... 180 ° C for 2 ... 12 hours. This method, as the closest, is selected as a prototype for the claimed technical solution.

After the implementation of this TMT method, the structure of the alloys is characterized by large elongated, mainly unrecrystallized grains, with a transverse size of more than 50 microns. The grains contain a developed cellular dislocation structure and nano-sized precipitates in the form of needles of reinforcing particles of Mg ₂ Si metastable modification β "and β '. Moreover, the content of Mg and Si in the aluminum matrix is at least 0.2 and 0.3 at.%, Respectively.

The disadvantage of the structure of aluminum alloys formed by the known TMT method is that it contains mainly small-angle dislocation boundaries and it contains nanosized particles of Mg ₂ Si phases of only metastable modification. Such a structural state and the method for its preparation do not provide sufficient strength and do not allow electrical conductivity in aluminum alloys to be close to that of technically pure aluminum. For example, if a wire made of electrotechnical aluminum of the AE grade (99.5 Al) demonstrates a level of temporary resistance (σ _B ) of 100 ... 150 MPa with a specific electrical resistance (ρ) of 0.0283 Ohm * mm ² / m (about 61% IACS), then the wire made of ABE grade Al-Mg-Si alloy obtained by the known TMT method has σ _B 280 ... 300 MPa, at which ρ is only 0.0325 ... 0.0335 Ohm * mm ² / m (53 ... 51.5% IACS) [GOST 839-80 . Wires not insulated for overhead power lines; M.B. Altman, Yu.P. Arbuzov, B. I. Babichev and others. Aluminum alloys. The use of aluminum alloys. Reference guide. M.: Metallurgy, 1972 - 408 p.].

The technical result of the invention is to increase the mechanical strength and electrical conductivity of aluminum alloys of the Al-Mg-Si system by creating an ultrafine-grained (UFG) structure in them obtained by the proposed processing methods.

The specified technical result is achieved by an aluminum alloy of the Al-Mg-Si system, characterized by a structure having an average grain size of not more than 400 nm, with at least 60% of the grains having high-angle boundaries misoriented from neighboring grains by angles of 10 degrees or more, and consisting of aluminum matrix containing magnesium and silicon no higher than 0.06 and 0.09 at.%, respectively, and precipitates of Mg ₂ Si particles of the hardening phase of a stable modification (β) of globular shape uniformly distributed in the grain volume.

The indicated technical result is also achieved by an aluminum alloy of the Al-Mg-Si system, characterized by a structure having an average grain size in the range from 400 to 1000 nm, while at least 60% of the grains have high-angle boundaries, misoriented from neighboring grains by angles of 10 degrees or more consisting of an aluminum matrix containing magnesium and silicon no higher than 0.08 and 0.10 at.%, respectively, and precipitates of Mg ₂ Si particles of the hardening phase of a stable modification (β) of globular shape located in the boundary region of grains, and metastable modifications β ", β 'in the form of a needle located in the Central region of the grains.

The technical result is also achieved by the method of obtaining UFG aluminum alloy system Al-Mg-Si, including quenching from 520 ... 565 ° C in water and plastic deformation, in which, unlike the prototype, plastic deformation is carried out with a true cumulative deformation e ≥ 8 by the method of intensive plastic deformation (SPD) at a temperature not exceeding 200 ° C to obtain a structure with an average grain size of not more than 400 nm.

According to the invention, the SPD is carried out by torsion (IPDK), equal channel angular pressing (ECAP), equal channel angular pressing in parallel channels (ECAP-PC) and equal channel angular pressing according to the Conform scheme (ECAP-K).

According to the invention, after the IPD, drawing is carried out.

According to the invention, after SPD rolling is carried out.

According to the invention, after drawing or rolling, artificial aging is carried out at a temperature of 100 ... 180 ° C for 0.5 ... 24 hours.

The technical result is also achieved by the method of obtaining UFG aluminum alloy system Al-Mg-Si, including quenching from 520 ... 565 ° C in water, plastic deformation and artificial aging, in which, unlike the prototype, plastic deformation is carried out with the true accumulated deformation e ≥ 4 method severe plastic deformation at a temperature not exceeding 300 ° C and artificial aging at a temperature of 100 ... 180 ° C with a holding time of 0.5 ... 24 hours to obtain a structure with an average grain size of 400 ... 1000 nm.

According to the invention, intense plastic deformation is carried out by torsion, or equal channel angular pressing, or equal channel angular pressing in parallel channels, or equal channel angular pressing according to the Conform scheme.

According to the invention, after intensive plastic deformation, drawing is carried out.

According to the invention, after intensive plastic deformation, rolling is carried out.

According to the invention, after drawing, the workpiece is artificially aged at a temperature of 100 ... 180 ° C with a holding time of 0.5 ... 12 hours.

According to the invention, after rolling, the workpiece is artificially aged at a temperature of 100 ... 180 ° C with a holding time of 0.5 ... 12 hours.

The proposed UMP structures and methods for their preparation provide a higher level of mechanical strength and electrical conductivity of aluminum alloys of the Al-Mg-Si system used in electrical products.

The specified technical result is achieved due to the following.

It is known that the formation of an UFG structure containing mainly high-angle boundaries allows one to achieve unusually high strength in metallic materials [R.Z. Valiev, I.V. Aleksandrov. Volumetric nanostructured metallic materials. - M.: IKC "Akademkniga", 2007 - 308 p.]. It is also known that for the formation of UMP structures use such treatment as IPDK, ECAP, ECAP-PK and ECAP-K. In this case, the true accumulated deformation should reach a value of e ≥ 4. Simultaneously with the formation of the UFG structure during SPD in alloys of the Al-Mg-Si system, a significant decrease in the concentration of alloying elements in the aluminum matrix occurs due to the development of deformation dynamic aging (DDS), which is accompanied by the release of nanoscale particles of hardening phases. The process of depletion of the aluminum matrix by the main alloying elements in the IPD process is much more intensive than in the implementation of traditional TO and TMT methods [Y. Estrin, M. Murashkin and RZValiev Ultra-fine aluminum alloys: processes, structural features and properties pp.468-503 in Fundamentals of aluminum metallurgy. Production, processing and applications. Ed. by Roger Lumley, Woodhead Publishing limited, 2011, p.843].

It is known that the increase in the strength of aluminum alloys subjected to SPD is due, firstly, to a small average grain size (≤1000 nm) and predominantly higher-angle grain boundaries, which ensures an increase in flow stress during plastic deformation, according to the Hall-Petch relation [Hall E. ABOUT. // Proc. Phys. Soc. London 1951. V.64 B.381. P.747-753; Petch N.J. // J. Iron Steel Inst. 1953. V.174.1. P.25-28; R.Z. Valiev, I.V. Aleksandrov. Bulk nanostructured metallic materials: production, structure and properties. - M .: Academic book, 2007 - 398 p.]. Secondly, the regulated release in the UFG structure of the hardening nanoscale particles of phases stable (β) and in particular metastable modification (β ", β ') also provides the hardening effect from the implementation of the dispersion hardening mechanism [IN Fridlyander Aluminum deformable structural alloys. - M .: Metallurgy, 1979 - 208 p.].

Simultaneously with hardening, the regulated release of nanosized particles leads to the depletion of the UFG of the aluminum matrix by the main alloying elements (Mg and Si), which ensures an increase in the electrical conductivity of the alloys, since it is the alloying elements that are responsible for electron scattering [B. Livshits, BC Kraposhin, Y. Lipetskiy. L. Physical properties of metals and alloys. - M .: Metallurgy, 1973 - 311 p .; Aluminum and aluminum alloys in electrical products / L.A. Vorontsova, V.V. Maslov, I.B. Peshkov Izd. "Energy", Moscow 1971 - 224 p.].

In General, the formation of the above UFG structures in aluminum alloys of the Al-Mg-Si system in the proposed combination of features of the invention leads to a simultaneous increase in their mechanical strength and electrical conductivity.

Structural changes in aluminum alloys are implemented by the proposed processing methods, subject to the specified conditions for their implementation.

The invention is illustrated by illustrations, where figure 1 shows the UFG structure with a grain size of less than 400 nm (a - electron microscopic photograph of the structure, b - schematic representation of the structure); figure 2 - UFG structure with a grain size of more than 400 nm (a - electron microscopic photograph of a General view of the structure, b - electron microscopic photograph of the grain, c - electron microscopic photograph of a fragment of the Central region of the grain, d - schematic image of the structure).

Figure 1a shows that the structure consists of grains (1) with a size of less than 400 nm and contains nanoscale precipitates of particles of the reinforcing phase Mg ₂ Si (2) of stable modification (β) having a globular shape and uniformly distributed in the volume of grains.

On figa shows that the structure consists of grains (3) with sizes greater than 400 nm, and fig.2b shows that in the boundary region of the grain there are precipitates of particles of the strengthening phase Mg ₂ Si (2) stable modification (β) having globular shape. It is also seen that inside the grain (Fig.2b) is located the region (4), shown in enlarged view in Fig.2c, containing nanoscale precipitates of particles of the hardening phase of metastable modification (β ', β ") in the form of a needle (5).

The invention is implemented as follows.

To form an UFG structure with an average grain size of not more than 400 nm, an initial billet of an Al-Mg-Si alloy with a standard chemical composition is used. At the first stage, the billet is subjected to heat treatment — quenching, which includes heating the billet to a temperature of 520 ... 565 ° C, holding it under given temperature conditions for up to 2 hours, and subsequent cooling in room temperature water.

At the second stage, the hardened billet is subjected to SPD processing at a temperature not exceeding 200 ° С with a true accumulated deformation of e ≥ 8. This treatment can be carried out with SPDK or ECAP, or ECAP-PK, or ECAP-K. At this stage, the microstructure is crushed in the bulk of the workpiece without changing its size. Due to the evolution of the structure during the SPD process under specified conditions, an UFG structure with an average grain size of not more than 400 nm is formed in aluminum alloys. At least 60% of the grains have large-angle boundaries misoriented relative to neighboring grains by angles of 10 degrees or more. Simultaneously with the formation of the UFG structure during SPD, DDS occurs in the aluminum matrix, as a result of which nanodimensional precipitates of particles of the hardening β phase (Mg ₂ Si) of stable modification are formed in it, having a globular shape uniformly located in the grain volume. The selection of particles of the β phase leads to a significant depletion of the aluminum matrix by the main alloying components (Mg and Si), which ensures an increase in the electrical conductivity of the material.

To form an UFG structure with a grain size in the range from 400 to 1000 nm, an initial billet of an alloy of the Al-Mg-Si system with a standard chemical composition is used. At the first stage, the billet is subjected to heat treatment - hardening, including heating the billet to a temperature of 520 ... 565 ° C, holding it under given temperature conditions for up to 2 hours and then cooling it in water at room temperature.

At the second stage, the hardened billet is subjected to SPD processing at a temperature not exceeding 300 ° С with a true accumulated deformation of e ≥ 4. This treatment can be carried out by the IPDK method or ECAP, or ECAP-PK, or ECAP-K. After processing the SPD with the true accumulated strain e = 1 in the alloy billet, the initial structure is transformed into a subgrain, which has a clearly defined orientation relative to the shear plane. The transverse size of the formed subgrains is 600 nm, and the longitudinal size is 1200 nm, respectively. The resulting structural state is characterized by a high density of lattice dislocations.

As a result of processing the SPD with the true accumulated deformation e = 2-3 in the subgrains, fragmentation develops due to the formation of transverse subboundaries in them. Along with fragmentation, separate sections are formed in the alloy (the volume fraction of which in the structure is ~ 30%) of equiaxed grains with an average size of 500 nm. The achievement of e ≥ 4 during SPD leads to the formation of a homogeneous UFG structure in the alloy billet with a grain size in the range from 400 to 1000 nm.

Thus, as a result of the evolution of the structure during the SPD process, an UFG structure is formed in an aluminum alloy with a grain size in the range 400 ... 1000 nm, of which more than 60% of the grains have high-angle boundaries misoriented from neighboring grains by angles of 10 degrees or more. Simultaneously with the formation of the UFG structure during the SPD according to the proposed method, DDS passes in the aluminum matrix, as a result of which nanodimensional precipitates of particles of the strengthening phase (Mg ₂ Si) of a stable modification (β) of a globular shape are formed. After completion of the SPD, the formed β phase particles are predominantly located in regions adjacent to the grain boundaries.

At the third stage, the UFG billet is subjected to artificial aging at a temperature of 100 ... 180 ° C with a holding time of 0.5 ... 24 hours. Artificial aging according to the indicated mode leads to further evolution of the structure obtained after SPD, which consists in the formation of a metastable modification (β ', β ") having the shape of a needle in the central region of grains of particles of strengthening phases of Mg ₂ Si phases that provide an additional increase in material strength .

The depletion of the aluminum matrix by the main alloying elements (Mg and Si) at the second stage of processing — during the DDS, and at the third stage of processing — during artificial aging, ensures an increase in the electrical conductivity of the material.

To obtain UFG billets in the form of wire rod, wire or profile after SPD, additional plastic deformation is carried out by drawing or rolling.

Examples of specific implementation of the invention

Example No. 1

As the initial billet, a hot-pressed rod of alloy 6060 of the Al-Mg-Si system, a standard chemical composition with a diameter of 20 mm, was used. From this rod, a billet in the form of a disk with a diameter of 20 mm and a thickness of 1.5 mm was made by machining. This billet was subjected to heat treatment — quenching, including heating to a temperature of 540 ° C, holding at a given temperature for 1 hour, and subsequent cooling to room temperature water. The time interval between the heat treatment operation and the IPD was no more than 1 hour.

After quenching, the workpiece was subjected to IPDK at a temperature of 180 ° C, at an applied pressure of 6 GPa, with a true accumulated deformation of e = 10. Then the workpiece was removed from the tool / tool, cooled in air to room temperature.

Samples for studying the microstructure, mechanical properties, and electrical conductivity were made from the obtained preform.

Microstructure analysis was performed by transmission electron microscopy (TEM) using a Jeol 2100 EX microscope.

Using X-ray diffraction analysis (XRD) on a Rigaku diffractometer and spatial atomic tomography on a Cames installation, an analysis was made of the concentration changes in the aluminum matrix of the main alloying elements.

Mechanical testing of the samples was carried out in accordance with the requirements of GOST 1497-84.

The obtained UFG structure in the alloy preform (Fig. 1a), which was formed during the implementation of the proposed processing method, has an average grain size (1) of 350 nm. Inside the grains, the globular precipitates of the secondary reinforcing β phase (Mg ₂ Si) (2) with an average size of 30 nm are visible, uniformly distributed in the aluminum matrix.

Table 1 presents the results of structural studies, mechanical tests and measurements of the electrical conductivity of the obtained samples. As a comparison, the results of studies of alloy samples subjected to the TMT method according to the prototype are given.

From table 1 it is seen that the content of alloying elements in the aluminum matrix after processing by the proposed method decreased by almost an order of magnitude. The achieved decrease in the concentration of alloying elements in the aluminum matrix in combination with the UFG structure made it possible to significantly increase the value of temporary resistance (σ _B ), lower the electrical resistivity (ρ) and, accordingly, increase the electrical conductivity of the 6060 aluminum alloy in comparison with the corresponding values achieved in the material subjected to standard TMT method.

Example No. 2

A hot-pressed rod of alloy AD31 of the Al-Mg-Si system of standard chemical composition with a diameter of 12 mm and a length of 500 mm was used as the initial billet. This billet was subjected to heat treatment — quenching, including heating to a temperature of 540 ° C, holding at a given temperature for 1 hour, and subsequent cooling to room temperature water. The interval between the heat treatment operation and the IPD was no more than 1 hour.

After quenching, the billet was subjected to ECAP-K processing to the true accumulated strain e = 4.8 under isothermal conditions at a temperature of 100 ° C. The channel angle in the instrument was 110 degrees. Then the workpiece was removed from the tool / tool, cooled in air to room temperature, and then subjected to drawing at room temperature with a total degree of deformation of 50%. As a result of this treatment, a bar with a diameter of 6 mm and a length of more than 1 m was obtained. After drawing, the billet was subjected to heat treatment - artificial aging at a temperature of 130 ° C and a holding time of 12 hours.

Samples for studying the microstructure, mechanical properties, and electrical conductivity were made from the obtained preform.

Microstructure analysis was performed by transmission electron microscopy (TEM) using a Jeol 2100 EX microscope.

Using X-ray diffraction analysis (XRD) on a Rigaku diffractometer and spatial atomic tomography on a Cames installation, an analysis was made of the concentration changes in the aluminum matrix of the main alloying elements.

Mechanical testing of the samples was carried out in accordance with the requirements of GOST 1497-84. The electrical resistivity of the samples was determined in accordance with GOST 7229-76 and GOST 12177-79.

The obtained UFG structure in the alloy preform (Fig. 2a), which was formed during the implementation of the proposed processing method, has an average grain size (3) of 600 nm. Inside the grain (FIG. 2b), there are visible precipitates of globular particles of the secondary reinforcing β phase (Mg ₂ Si) (2) of stable modification with an average size of 20 nm, located in the border region, and precipitated particles of the reinforcing phases (β ', β ") metastable modifications in the form of needles (5) (Fig. 2c) with a diameter of 2 nm and a length of up to 40 nm, located in the central region of the grains (4) (Fig. 2b).

Table 2 presents the results of structural studies, mechanical tests and measurements of electrical resistivity of the obtained samples. As a comparison, the results of studies of alloy samples subjected to the TMT method according to the prototype.

From table 2 it is seen that the content of alloying elements in the aluminum matrix after processing by the proposed method decreased by almost an order of magnitude. The decrease in the concentration of alloying elements in the aluminum matrix in combination with the UFG structure achieved by the proposed method made it possible to significantly increase the value of temporary resistance (σ _B ), the conditional yield strength (σ _0.2 ), lower the electrical resistivity (ρ) and, accordingly, increase the electrical conductivity of the AD31 aluminum alloy, comparing with the corresponding values achieved in the material subjected to the TMT method.

Thus, the proposed invention allows to form in aluminum alloys UFG structure that provides the material with increased mechanical strength and electrical conductivity.

Claims (14)

1. An ultrafine-grained aluminum alloy of the Al-Mg-Si system, characterized by a structure having an average grain size of not more than 400 nm, with at least 60% of the grains having high-angle boundaries misoriented from neighboring grains by angles of 10 ° or more, and consisting of aluminum matrix containing magnesium and silicon not higher than 0.06 and 0.09 at.%, respectively, and precipitates of Mg ₂ Si particles of the hardening phase of a stable modification (β) of globular shape uniformly distributed in the grain volume. 2. An ultrafine-grained aluminum alloy of the Al-Mg-Si system, characterized by a structure having an average grain size in the range of 400 to 1000 nm, with at least 60% of the grains having high-angle boundaries misoriented from neighboring grains by angles of 10 ° or more, and consisting of an aluminum matrix containing magnesium and silicon no higher than 0.08 and 0.10 at.%, respectively, and precipitates of Mg ₂ Si particles of the hardening phase of a stable modification (β) of a globular shape located in the boundary region of grains, and a metastable modification of β " , β 'in the form of a needle, p memory location in the central region of the grains. 3. A method of obtaining ultrafine-grained aluminum alloy of the Al-Mg-Si system, comprising quenching from 520-565 ° C in water and plastic deformation, characterized in that the plastic deformation is carried out with a true accumulated deformation e≥8 by the method of intensive plastic deformation at a temperature not higher than 200 ° C to obtain a structure with an average grain size of not more than 400 nm. 4. The method according to claim 3, characterized in that the intense plastic deformation is carried out by torsion, or equal channel angular pressing, or equal channel angular pressing in parallel channels, or equal channel angular pressing according to the Conform scheme. 5. The method according to claim 4, characterized in that after intense plastic deformation carry out drawing. 6. The method according to claim 4, characterized in that after intense plastic deformation, rolling is carried out. 7. The method according to claim 5, characterized in that after drawing carry out the artificial aging of the workpiece at a temperature of 100-180 ° C with a holding time of 0.5-12 hours 8. The method according to claim 6, characterized in that after rolling, the workpiece is artificially aged at a temperature of 100-180 ° C with a holding time of 0.5-12 hours. 9. A method of producing an ultrafine-grained aluminum alloy of the Al-Mg-Si system, comprising quenching from 520-565 ° C in water, plastic deformation and artificial aging, characterized in that the plastic deformation is carried out with true accumulated deformation e≥4 by the method of intensive plastic deformation at temperature not higher than 300 ° C and artificial aging at a temperature of 100-180 ° C with a holding time of 0.5-24 hours to obtain a structure with an average grain size of 400-1000 nm. 10. The method according to claim 9, characterized in that the intense plastic deformation is carried out by torsion, or equal channel angular pressing, or equal channel angular pressing in parallel channels, or equal channel angular pressing according to the Conform scheme. 11. The method according to claim 10, characterized in that after intense plastic deformation carry out drawing. 12. The method according to claim 10, characterized in that after intense plastic deformation, rolling is carried out. 13. The method according to claim 11, characterized in that after drawing, the workpiece is artificially aged at a temperature of 100-180 ° C with a holding time of 0.5-12 hours. 14. The method according to p. 12, characterized in that after rolling, the workpiece is artificially aged at a temperature of 100-180 ° C with a holding time of 0.5-12 hours.

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