RU2299256C1 - Aluminum-based alloy and article made therefrom - Google Patents

Abstract

FIELD: nonferrous metallurgy.

SUBSTANCE: invention, in particular, relates to aluminum-copper-magnesium system and provides alloy for manufacturing aerospace-destination welded articles capable of working under loadings not only at ambient temperatures but also at short and long-term elevated temperature action. Alloy has following chemical analysis, wt %: copper 4.5-7.0, magnesium 1.75-4.5, manganese 0.25-0.8, titanium 0.05-0.45, iron 0.05-0.45, silicon 0.02-0.2, beryllium 0.001-0.07, hydrogen 1.8·10-6-3.1·10-5, calcium 0.0001-0.08, cobalt 0.02-0.45; at least one of the following elements: nickel 0.001-0.05, chromium 0.001-0.05, or zinc 0.001-0.05; one of the following elements: zirconium 0.0555-0.45 or vanadium 0.055-0.45; and aluminum - the balance.

EFFECT: enabled preparation of deformable aluminum-based alloy and article therefrom showing good weldability, little hot brittleness, and high strength of welded joint at ambient and elevated temperatures.

4 cl, 2 tbl

Description

The invention relates to the field of non-ferrous metallurgy, and in particular to alloys based on aluminum of the aluminum-copper-magnesium system. The proposed alloy is intended for the manufacture of various engineering structures, including for welded products of aerospace engineering, capable of working under the influence of loads not only at room temperature, but also under short-term and very long-term effects of elevated temperatures, exhibiting increased heat resistance and maintaining high corrosion resistance.

Known aluminum weldable alloys of the following chemical composition (wt.%):

1. Cu 4.9-6.5

Mg 1.8-2.9

Mn 0.05-0.65

Co 0.05-0.65

Ti 0.05-0.45

Zr 0.05-0.45

Fe 0.1-0.45

Be 0.001-0.005

Al - the rest

(RF patent No. 668363)

2. Cu 4.9-6.5

Mg 1.7-3.0

Mn 0.15-0.7

Co 0.05-0.5

Ti 0.05-0.45

V 0.05-0.45

Fe 0.1-0.45

Be 0.001-0.005

Al - the rest

(RF patent No. 923216)

These alloys during application in structures showed increased (compared with previously mastered industrial alloys of Al-Cu-Mn and Al-Cu-Mg systems) heat resistance, corrosion resistance and weldability. However, the increased requirements for heat resistance and corrosion resistance of aluminum alloys necessitate an increase in thermal stability (i.e., a decrease in the rate of softening under the influence of temperature and time) and corrosion resistance.

The disadvantages of these alloys must also include a negative combination of an increased value of the index of heat resistance (17-20 mm) and a lower index of fluidity (275-295 mm) in casting samples, which negatively affects the casting of ingots (especially large diameters), weldability and leads to an increase defective percentage on products made from these alloys.

Known alloy system Al-Cu-Mg-Si-Zr, containing (wt.%):

3. Cu 1.5-7.0

Mg 0.3-2.5

Si 0.1-1.0

Zr 0.3-0.8

optionally containing at least one of the elements:

Fe 0.5-1.5

Ni 0.8-3.0

and / or containing one or two elements from:

Mn 0.05-0.6

V 0.05-0.5

Ti 0.001-0.5

Al is the rest.

(Japan Patent No. 1290740).

The specified alloy is heat-resistant, but not welded, intended only for the manufacture of engine parts operating at elevated temperatures. Also, a drawback of the alloy, in addition to a narrow scope, is the limited range of manufactured semi-finished products, for example, there is no information on the manufacture of rolled semi-finished products, which are the basis of various engineering structures.

For the prototype adopted the closest in chemical composition to the proposed alloy based on aluminum system Al-Cu-Mg, containing (wt.%):

Cu 3.8-4.9

Mg 0.4-2.5

Mn 0.3-1.2

Ti 0.01-0.1

at least one element from the group:

B 0.0001-0.05

C 0.00001-0.008

at least one element from the group containing at most:

Fe 0.4

Si 0.3

Ni 0.08

Be 0.08

V 0.05

Cr 0.1

Zn 0,1

H 2.5 · 10 ^-5

S 0,0004

Al - the rest

(RF patent No. 2209844)

The disadvantages of the alloy include the relatively low strength of the welded joint (σ _{in sv} = 32.5-34.0; σ _{in sv} / σ _{in the base} = 0.65-0.69), low value of the fluidity index L = 200 mm combined with a very high tendency to heat resistance K _Tr = 27-38 mm (for casting samples) and K _Tr = 30-50% (for a welded sample). The alloy does not weld well and, therefore, cannot be used in welded structures. The alloy and the product made from it are not intended for use in elevated temperatures.

An object of the present invention is to provide a wrought alloy based on aluminum of the aluminum-copper-magnesium system and articles thereof with good weldability, low tendency to heat resistance, increased fluidity, increased values of heat resistance and corrosion resistance, high strength of the welded joint at 20 ° C and elevated temperatures, high manufacturability.

To achieve this, an alloy based on aluminum is proposed: containing copper, magnesium, manganese, titanium, iron, silicon, beryllium, hydrogen, at least one element from the group: nickel, chromium, zinc, characterized in that it additionally contains cobalt , calcium and one element from the group: zirconium, vanadium in the following ratio of components (wt.%):

Cu 4,5-7,0

Mg 1.75-4.5

Mn 0.25-0.8

Ti 0.05-0.45

Fe 0.05-0.45

Si 0.02-0.2

Be 0.001-0.07

N 1.8 · 10 ^-6 -3.1 · 10 ^-5

Ca 0.0001-0.08

From 0.02-0.45

at least one element from the group:

N10.001-0.05

Cr 0.001-0.05

Zn 0.001-0.05

one item from the group:

Zr 0.055-0.45

V 0.055-0.45

Al - the rest

and an article made from it.

In the case of using the proposed alloy as a structural material, the total content of copper and magnesium should be at least 6.25 wt.%. In this case, there is an increase (by 10-15%) in the values of strength characteristics at 20 ° C and heat resistance (for example, in the range of 200-350 ° C), a decrease in the rate of softening when exposed to heat due to an increase in the thermal stability of a solid solution supersaturated during quenching; ensuring good weldability: lowering the heat resistance K≤12% (in the cast sample), K≤6-7% (in the welded sample), increasing the fluidity to 310-350 mm, with σ _in cb / σ _{, the base is} ≥0.75 (at 20-250 ° С) and up to 1.0 (at t> 250 ° С).

In addition, to obtain high values of the strength of the welded joint, it is not necessary to strengthen the welded edges of the parts, heat treatment or cold rolling of welded joints.

The alloy can be successfully used as a filler material in welding. If the proposed alloy is used as a filler material, the total content of magnesium and copper should be at least 8.2 wt.%. In this case, the alloy has a significant decrease in the tendency to heat resistance by a factor of ~ 2 (up to 7.0% for the cast sample and K≤5% for the welded sample) and an increase in the fluidity index (up to 370-450 mm). However, in this case, the alloy is slightly inferior in strength values at 20 ° C and elevated temperatures (by 10-15%), while the absolute values of these characteristics (especially welded joints) remain higher than that of existing mass-produced aluminum alloys.

The ability of industrial alloys of the Al-Cu-Mn and Al-Cu-Mg systems to natural aging, the process of "return" (for fast heating up to 200-250 ° C), low corrosion resistance and relatively fast softening rate when exposed to elevated temperatures (especially for alloys of the Al-Cu-Mn system) is due to the high copper content in Al-Cu-Mn alloys or, for Al-Cu-Mg alloys, its excess content compared to the magnesium content and, consequently, the formation of the phase θ (Al ₂ Cu). All this is a consequence of a specific change in the energy of the aluminum crystal lattice under the influence of the nature of the dissolved copper atoms. The introduction of the optimal calculated magnesium content into Al-Cu-Mg alloys binds copper atoms to the S phase (Al ₂ CuMg), as a result, the corrosion resistance, heat resistance, weldability and processability of the Al-Cu-Mg system alloys increase significantly.

However, under industrial conditions, in the manufacture of alloys of the Al-Cu-Mg system, magnesium losses are inevitable, therefore, maintaining the calculated optimal ratio of the contents of copper and magnesium in the alloy and, therefore, eliminating the effect of excess copper is very problematic.

The introduction of small calcium additives into the alloy helps to remove the negative effect of excess copper on the alloy characteristics: due to the binding of a certain number of copper atoms in the CaCu ₅ compounds, as well as by changing the energy of the alloy solid solution: inhibiting the diffusion of vacancies and neutralizing stress in the crystalline lattice (r _Cu <r _Al ~ by 10%, r _Ca > r _Al ~ by 30%). Thus, the calcium atom is able to neutralize the effect of 3-5 copper atoms on the energy of the solid solution. Enough small additions of calcium to the alloy to practically reduce the effect of a small excess (with respect to the magnesium content) presence of copper in industrial smelting.

The appearance of small intermetallic compounds (CaCu ₅ ) in the melt to some extent prevents the growth of large branched dendritic formations, having a positive effect on fluidity and resistance to hot cracking, which is especially noticeable during crystallization of small volumes of the alloy during welding.

Since the proposed alloy contains a complex of transition metal additives, some of which also have a modifying effect on the structure, a certain calculated cobalt content is introduced into the alloy to obtain optimal sizes of structural components and balanced values of viscosity and heat resistance.

The use of zirconium or vanadium in the proposed alloy is necessary to increase the strength characteristics in the temperature range of 20-400 ° C.

Implementation example

Ingots were cast into a water-cooled mold by continuous casting (melt temperature: 700–740 ° C), some of which, after homogenizing annealing (at 485–495 ° C for 6 and 50–60 h), were forged at a temperature of 400–440 ° C until the dimensions of the blank for rolling sheets with a thickness of 2.0 mm, and part pressed at 400 ° C to obtain a strip. The resulting sheets and pressed strips were quenched from a temperature of 500 ^{± 3} ° C in water at 20 ° C. The chemical composition of the alloys is shown in table 1, where examples 1-4 of the proposed alloy (of which examples 1-2 are applicable mainly as a filler material in welding; examples 3-4 as structural), example 5 is a prototype alloy.

Subsequently, standard samples were made from heat-treated sheets and a pressed strip to determine the values of mechanical properties (tension) at 20 ° C and elevated temperatures (GOST 1497, GOST 9657). The tendency of the alloy to heat resistance was determined using a standard casting test (OST 1-90020) and a standard welding cross test, and fluidity by a test according to OST 1-90008. Corrosion resistance was determined accordingly: resistance to intergranular corrosion - GOST 9.021, delaminating corrosion - GOST 9.04 and stress corrosion cracking - GOST 9.019.

Table 2 presents the mechanical properties of the proposed alloy and prototype alloy.

As can be seen from table 2, the proposed alloy as a filler material (examples 1, 2) has superiority in the following characteristics: the heat resistance index (K _tr - in casting and welded samples) is 5-6 times lower, the fluidity index (L _W ) is greater 43-66%, increased resistance to various types of corrosive effects (KR by 11%; RSK by 1.7-2.0 times; MKK by 4 times). At the same time, the values of the strength of the welded joint (σ _{in sv} ) at 20 ° C and the base material (σ in; σ _0.2 ) at 250 ° C also have some excess (by 4-6%).

As a structural material, the proposed alloy (examples 3, 4) has the following advantages: increased values of strength characteristics at 20 ° C of the base material (σ _in ; σ _0.2 ) by 6-7%, welded joint (σ _{in st} ) - by 23% 15-18% higher values of heat-resistant characteristics at 250 ° C; significantly reduced indicators of heat capacity in the casting sample - 2.4 times and in the welded sample - 2.85-3.3 times; increased resistance to various types of corrosive effects: KR by 20%, RSK 1.7-2.5 times, MKK more than 4 times.

The indicated advantages of the alloy can significantly reduce rejects when casting large-sized flat and round ingots and thereby increase the yield, lower costs in the manufacture of various types of semi-finished products. The proposed alloy can be used in the manufacture of various welded structures of mechanical engineering (including aerospace, subject to operational heating). The use of the proposed alloy in welded structures will reduce costs, weight, increase the tightness and reliability of structures under conditions of increased loads, temperatures and corrosion.

Table 1
The content of elements in alloys (wt.%) Alloy Cu Mg Mn Ti Fe Si Be H Ca Co Ni Cr Zn Zr V FROM B Al Suggested 1 7.0 4,5 0.25 0.05 0.45 0.2 0,07 1.8 · 10 ^-6 0,03 0.02 0.001 - 0.05 - 0.45 - - Ost. 2 4.8 3.4 0.35 0.2 0.3 0.15 0,03 1.6 · 10 ^-5 0.01 0.15 - 0.02 - 0,055 - - - Ost. 3 5.8 2,3 0.55 0.12 0.2 0.08 0.004 2.0 · 10 ^-5 0.0001 0.25 0.05 0.001 0.001 0.45 - - - Ost. four 4,5 1.75 0.8 0.45 0.05 0.02 0.001 3.1 · 10 ^-5 0.08 0.45 - 0.05 - - 0,055 - - Ost. Prototype 5 4.2 1,6 0.7 0.05 0.18 0.08 - 1,0 · 10 ^-5 - - 0.008 - - - 0.01 0.0001 0.008 Ost.

Claims (4)

1. An aluminum-based alloy containing copper, magnesium, manganese, titanium, iron, silicon, beryllium, hydrogen, at least one element from the group: nickel, chromium, zinc, characterized in that it additionally contains cobalt, calcium and one element from the group: zirconium, vanadium in the following ratio of components wt.%: Cu 4,5-7,0 Mg 1.75-4.5 Mn 0.25-0.8 Ti 0.05-0.45 Fe 0.05-0.45 Si 0.02-0.2 Be 0.001-0.07 H 1.8 ÷ 10 ^-6 -3.1 · 10 ^-5 Ca 0.0001-0.08 From 0.02-0.45 at least one element from the group: Ni 0.001-0.05 Cr 0.001-0.05 Zn 0.001-0.05 one item from the group: Zr 0.055-0.45 V 0.055-0.45 Al - The rest. 2. The aluminum-based alloy according to claim 1, characterized in that the total content of copper and magnesium is not less than 6.25% wt.%. 3. The aluminum-based alloy according to claim 1, characterized in that the total content of copper and magnesium is at least 8.2% wt.%. 4. An aluminum alloy product, characterized in that it is made of an alloy according to any one of claims 1 to 3.