RU2804669C1 - HIGH-STRENGTH ALUMINIUM ALLOY OF Al-Zn-Mg-Cu SYSTEM AND PRODUCTS MADE OF IT - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: deformable thermally hardened high-strength aluminium alloys used as a structural material for highly loaded elements. A deformable and thermally hardenable high-strength aluminium-based alloy contains, wt.%: zinc – 8.5-10.5, magnesium – 2.2-3.7, copper – 1.2-2.8, zirconium – 0.10-0.14, iron – 0.10-0.30, silicon – 0.05-0.15, manganese – 0.15-0.60, at least one element from the group: nickel – 0.15-0.30, – niobium 0.01- 0.05, and cobalt – 0.10-0.30, if necessary, at least one element from the group: scandium – 0.05-0.25, titanium – up to 0.05, and beryllium – 0.0001-0.002, the balance is aluminium.

EFFECT: increased short-term strength at temperatures of 20-70°C, as well as long-term strength of the alloy at a temperature of 60°C at high voltages.

7 cl, 3 tbl, 9 ex

Description

The invention relates to the field of metallurgy, namely to deformable thermally strengthened high-strength aluminum alloys of the Al-Zn-Mg-Cu system, intended for use in mechanical engineering and other industries as a structural material for highly loaded elements, in particular for nuclear engineering products, including number of gas centrifuge parts.

There is a known series of modern common high-strength aluminum alloys of the Al-Zn-Mg-Cu system for various purposes, additionally alloyed with microadditives of various transition metals to increase strength, ductility, and manufacturability.

These include the aluminum alloy of the Al-Zn-Mg-Cu system (RU 2553781 C1, 06/20/2015), having the following composition, wt.%:

zinc 8-10 magnesium 2.0-3.0 copper 1.6-2.6 scandium 0.12-0.25 zirconium 0.06-0.20 beryllium 0.0001-0.005 cobalt 0.05-0.15 nickel 0.5-1.0 iron 0.45-0.95 aluminum rest

while the ratio of zinc content to magnesium content is in the range of 3.1-4.1.

The alloy does not have high enough structural strength and reliability characteristics, which are necessary for highly loaded parts of gas centrifuges operating for a long time at constantly operating high voltages.

An aluminum alloy of the Al-Zn-Mg-Cu system is known (RU 2514748 C1, 05/10/2014), having the following composition, wt.%:

zinc 6.0-8.0 magnesium 3.4-4.2 copper 0.8-1.3 scandium 0.07-0.15 ironium 0.08-0.12 beryllium 0.0005-0.004 cerium 0.01-0.15 titanium 0.02-0.08 silicon 0.01-0.15 iron 0.01-0.15 hydrogen 0.05-0.35 cm ³ /100 g metal

inevitable impurities from the group Mn, Cr, V, Mo, Li, Ag, K, Na, O not more than 0.1 aluminum the rest, while the ratio between the content of magnesium and zinc is from 0.53 to 0.57.

The disadvantage of this alloy is a significant decrease in the level of mechanical properties at elevated temperatures.

A wrought aluminum-based alloy is known (RU 2394113 C1, 07/10/2010), containing, wt.%:

zinc 2.5-4.0 magnesium 4.1-6.5 copper 0.2-1.0 iron up to 0.25 silicon up to 0.15 scandium 0.005-0.3 zirconium 0.005-0.25 nickel and/or cobalt up to 0.1 titanium up to 0.15 boron and/or carbon up to 0.05

at least one element from the group:

hafnium up to 0.15 molybdenum up to 0.15 cerium up to 0.15 manganese up to 0.5 chromium up to 0.28 yttrium up to 0.15 vanadium up to 0.15 niobium up to 0.15 aluminum and inevitable impurities rest

wherein the ratio of Mg content to Zn content is greater than or equal to 1.1.

The disadvantage of this alloy is the low level of strength characteristics (tensile strength σ _in not higher than 580 MPa, proof strength σ _0.1 not higher than 520 MPa), which is due to the selected range of content of elements such as magnesium, zinc, copper. Also, the composition contains boron, which is not allowed in materials for gas centrifuges.

The closest analogue is a high-strength aluminum alloy of the Al-Zn-Mg-Cu system (RU 2164541 C2, 03/27/2001), having the following composition, wt.%: zinc 8.0-9.0

magnesium 2.3-3.0 copper 2.0-2.6 zirconium 0.1-0.2 iron 0.05-0.3 silicon 0.03-0.15 beryllium 0.0001-0.002 hydrogen (0.9-3.6) × 10 ^-5 aluminum rest

with Fe/Si ratio≥0.5.

The alloy has high strength characteristics, high creep resistance at moderately elevated temperatures and has been successfully used in gas centrifuges for many years, however, it has limitations in terms of creep resistance and long-term strength at temperatures above 40°C, which does not allow its use in parts of new generation gas centrifuges (9+).

The objective of the proposed invention is to develop a new high-strength aluminum alloy of the Al-Zn-Mg-Cu system for highly loaded structural elements of nuclear engineering products, including parts of gas centrifuges, ensuring an increase in their productivity and reliability during long-term operation.

The technical result of the claimed invention is an increase in short-term strength (temporary strength σ _B , proof strength σ _0.2 ) at temperatures of 20-70°C, as well as long-term strength of the alloy at a temperature of 60°C at high stresses (560-600 MPa).

The technical result is achieved due to the fact that the proposed deformable and thermally hardenable high-strength aluminum-based alloy contains zinc, magnesium, copper, zirconium, iron, silicon, manganese, at least one element from the group containing nickel, niobium and cobalt, if necessary , at least one element from the group including scandium, titanium and beryllium, with the following component ratio, wt.%:

zinc 8.5-10.5 magnesium 2.2-3.7 copper 1.2-2.8 zirconium 0.10-0.14 iron 0.10-0.30 silicon 0.05-0.15 manganese 0.15-0.60

at least one element from the group:

nickel 0.15-0.30 niobium 0.01-0.05 and cobalt 0.10-0.30

if necessary, at least one element from the group consisting of scandium, titanium and beryllium:

scandium 0.05-0.25 titanium up to 0.05 and beryllium 0.0001-0.002 aluminum rest

The preferred zinc to magnesium ratio is >2.5. The preferred iron to silicon ratio is ≥1.5. Preferably, the alloy contains both niobium and cobalt, the preferred total content of which is not less than 0.15 wt.%. Preferably, the alloy contains both nickel and scandium.

A product made from this deformable and thermally hardenable high-strength aluminum-based alloy is also proposed.

Due to the high content of zinc and magnesium in the structure of the alloy, during artificial aging the main strengthening phase -η(MgZn ₂ ) is released, which provides high strength characteristics (tensile strength and yield), while the preferred ratio of zinc to magnesium is more than 2.5.

Additional strengthening of the alloy is achieved by alloying with copper, which is included both in the solid solution and in the composition of the phase (Al ₂ CuMg).

Zirconium is introduced as an anti-recrystallizer and forms semi-coherent ZrAb dispersoids, thereby providing increased strength, ductility and cyclic durability. The amount of zirconium should be limited (to 0.14 wt.%) due to the appearance of undesirable coarse particles of intermetallic compounds.

Alloying the proposed alloy with manganese provides additional both solid solution strengthening and dispersion (MgZr)Al ₆ ), which helps to increase strength.

A beryllium additive from 0.0001 to 0.002 wt.% provides increased manufacturability during casting due to the formation of a protective film that prevents oxidation and burnout of magnesium and other low-melting elements during the process of melting and casting ingots.

The introduction of at least one element from the group including cobalt, niobium, nickel leads to an increase in short-term and long-term strength characteristics at elevated temperatures. Joint introduction of niobium and cobalt with a total content of at least 0.15 wt. % allows you to provide the best combination of high strength while maintaining ductility due to solid solution strengthening and the formation of Co ₂ Al ₉ phases in the structure. In addition, nickel, in the presence of iron, ensures the formation of insoluble refractory secondary phases FeNiAl ₂ , and also in the presence of manganese, the formation of the Mn ₃ NiAl ₆ phase, which leads to an increase in long-term strength characteristics due to the inhibition of dislocation movement processes.

In order to modify the structure of the ingots and ensure a non-recrystallized structure in semi-finished products after deformation, scandium can be additionally introduced into it, which forms compounds with aluminum that are centers of crystallization during casting, providing a fine-grained structure in the ingots.

With the joint introduction of scandium with zirconium during homogenization and hardening, dispersed particles of Al ₃ (ScZr) are formed and due to dispersion hardening, as well as due to the formation of a non-recrystallized structure, additional strengthening of the alloy occurs, while the tensile strength and fluidity increase, and ductility increases.

Also, titanium (no more than 0.05 wt%) can be additionally introduced into the alloy as a modifier of the ingot structure in order to increase the technological ductility of the ingot during deformation.

Implementation example

Under pilot production conditions, round ingots with a diameter of 110 mm of various chemical compositions (shown in Table 1) were cast using the semi-continuous casting method, and their homogenization annealing was carried out. Then the ingots were cut, turned and pressed with a draw ratio >15 onto a strip measuring 8x45 mm. After pressing, hardening and artificial aging were carried out according to the T1 mode.

The tensile mechanical properties of pressed strips (minimum and maximum values) in the longitudinal and transverse directions at test temperatures of 20°C, 60°C and 70°C are given in Table 2. Tensile tests were carried out on round samples at a temperature of 20°C according to GOST 1497, and at elevated temperatures in accordance with GOST 9651. The long-term strength of the alloys was determined according to GOST 10145 on cylindrical samples No. 20K, cut in the transverse direction, at a temperature of 60 ° C at different stresses in the range of 560-600 MPa (Table 3).

As can be seen from a comparison of the mechanical characteristics of the strips presented in Table 2, the proposed alloy at test temperatures of 20°C and 60-70°C has a -5-10% increased tensile strength and yield strength in comparison with the prototype. With the additional introduction of scandium into the alloy, the strength characteristics at 20-70°C in the transverse direction increase by 20-40 MPa.

From Table 3 it can be seen that when tested for long-term strength at a temperature of 60°C, samples from the proposed alloy withstood 1000 hours at stresses of 580-590 MPa, in contrast to the prototype, the long-term strength of which was 325-530 hours at these stresses.

Claims (12)

1. A deformable and thermally hardenable high-strength aluminum-based alloy containing zinc, magnesium, copper, zirconium, iron, silicon, manganese, at least one element from the group containing nickel, niobium and cobalt, if necessary, at least one element from the group including scandium, titanium and beryllium, with the following ratio of components, wt.%: zinc 8.5-10.5 magnesium 2.2-3.7 copper 1.2-2.8 zirconium 0.10-0.14 iron 0.10-0.30 silicon 0.05-0.15 manganese 0.15-0.60 at least one element from the group: nickel 0.15-0.30 niobium 0.01-0.05 and cobalt 0.10-0.30 if necessary, at least one element from the group consisting of scandium, titanium and beryllium: scandium 0.05-0.25 titanium up to 0.05 and beryllium 0.0001-0.002 aluminum rest 2. The alloy according to claim 1, characterized in that the ratio of zinc to magnesium content is >2.5. 3. The alloy according to claim 1, characterized in that the ratio of iron to silicon content is ≥1.5. 4. The alloy according to claim 1, characterized in that it simultaneously contains niobium and cobalt. 5. The alloy according to claim 4, characterized in that the total content of niobium and cobalt is at least 0.15 wt.%. 6. The alloy according to claim 1, characterized in that it simultaneously contains nickel and scandium. 7. A product made of a deformable and thermally hardenable high-strength aluminum-based alloy, characterized in that it is made of an alloy according to any one of claims. 1-6.