DE2510087C2 - Use of a cold-deformable aluminum-magnesium-zinc alloy - Google Patents

Description

The invention relates to the use of a cold-formable aluminum-magnesium-zinc alloy with the composition defined in the main claim.

In general, Al-Mg type corrosion-resistant aluminum alloys have excellent mechanical properties and corrosion resistance. They were therefore used for large structures such. B. od for buildings, ships or bridges. Like. Used. However, these alloys have the disadvantage that they are particularly easily subject to stress corrosion cracking because the intermetallic compound Mg ₂ Al _{3 is} easily deposited at the grain boundaries, so that corrosion occurs at the grain boundaries. For this reason, the magnesium content of conventional high-strength cold-forged alloys of the Al-Mg type has been reduced in order to overcome the disadvantages mentioned. This is e.g. B. the case with the aluminum alloy according to JIS H 4000 and 5083. However, these conventional alloys have insufficient mechanical strength for large structures. They have the disadvantage of low elongation (according to Table 1). Ternary alloys of the Al-Zn-Mg type are age-hardenable and have high strength, in particular excellent mechanical strength. They are weldable. However, these alloys have the disadvantage of poor resistance to corrosion and poor resistance to stress corrosion cracking. The German patent application 40d, 1/50, W 3774 describes a method for improving the stress corrosion cracking resistance of an aluminum-magnesium-zinc alloy with 5 to 12% magnesium, 0.05 to 1% manganese, 0.01 to 0.596 chromium, 0.01 to 0.396 titanium, 0.01 to 0.396 zirconium and 0.1 to 296 zinc are known. A stress corrosion-resistant, heterogeneous structure is formed by hot deformation. The process is carried out in such a way that a completely homogenized, ie excretion-free, structural condition is avoided.

From DE-PS 9 40 324 it is known that kneadable aluminum-magnesium alloys with 2 to 696 zinc, 3.4 to 1296 magnesium, 0.05 to \% chromium, up to 1% manganese and with small amounts of silicon and iron in the homogeneous, ie precipitation-free state, show good resistance to both intergranular and stress corrosion cracking. In the case of alloys with a zinc content of more than 296, however, the workability becomes poorer and precipitation is also observed during the aging process. Therefore, these alloys are not suitable for construction purposes.

It is the object of the present invention to provide a cold-formable aluminum-magnesium-zinc alloy for To provide workpieces with excellent corrosion resistance and stress corrosion resistance and excellent mechanical properties are required.

According to the invention, this object is achieved by using a cold-deformable aluminum-magnesium-zinc alloy from 4 to 7% by weight of magnesium, 0.5 to 2% by weight of zinc, one or more of the Elements from the group of 0.05 to 0.5 wt. 96 chromium, 0.1 to 0.6 wt. 96 manganese, 0.05 to 0.25 wt. 96 titanium and 0.05 to 0.25% by weight of zirconium and aluminum as the remainder with less than 0.5% by weight of impurities,

which is not artificially aged, for workpieces with high resistance to internal crystalline corrosion and Stress corrosion cracking and at the same time good tensile strength and elongation.

The impurities mentioned consist mainly of iron and silicon. the Said amount of impurity can rub off Fe and Si still from small amounts of other impurities exist, which preferably make up less than 0.1% by weight based on the total alloy.

In the subclaims are preferred alloy compositions for use for the invention Purpose stated.

The aluminum alloy used is cold deformable. The aluminum alloy is produced without artificial aging. There is no elimination effect during production. If the magnesium content is increased, the mechanical strength is improved, but the processability and the corrosion resistance are worsened. Accordingly, the magnesium content of 4 to 7 wt ¹ V should, and are preferably from 4.5 to 6.5 wt cent, based on the Gesamtlegiftrung. The mechanical strength of the alloy is not affected by the zinc content. The zinc is added to improve the workability and to prevent corrosion at the grain boundaries due to the precipitation of Mg ₂ Ah at the grain boundaries. With more than 2% by weight zinc, a deterioration in corrosion resistance and hardenability is observed. Accordingly, the zinc content should be 0.5 to 2% by weight and preferably 0.5 to 1.5% by weight. The addition of chromium and manganese increases the mechanical properties, in particular strength and elongation, as well as corrosion resistance and Stress corrosion cracking resistance significantly improved. The alloy contains 0.05 to 0.5% by weight and from 0.1 to 0.3% by weight of Cr or 0.1 to 0.6% by weight of Cr or 0.1 to 0.6% by weight and preferably 0 , 2 to 0A% by weight of Mn or 0.3 to 0.5% by weight, a total of Cr + Mn. In the case of an excessive content of Cr and / or Mn, coarse intermetallic compounds are formed, as a result of which the mechanical properties and the cold workability as well as the corrosion resistance are impaired. By adding titanium and / or zirconium instead of or in addition to chromium and / or manganese, the mechanical strength, the corrosion resistance and the stress corrosion cracking resistance can be significantly improved. The content of titanium and zirconium is 0.05 to 0.25% by weight, and preferably 0.07 to 0.15% by weight. By adding Mn on the one hand and Ti or Zr on the other hand, alloys with excellent elongation, good corrosion resistance and excellent stress corrosion cracking resistance can be obtained. The values achieved thereby correspond to an addition of Mn. On the other hand, however, the mechanical strength can be significantly improved so that it is higher than the mechanical strength of an alloy with Mn. The aluminum alloy used can contain small amounts of impurities, e.g. B. contain iron and / or silicon, as is the case with conventional aluminum alloys. However, the corrosion resistance and the mechanical properties of the alloy are adversely affected by an excessive content of impurities. It is therefore preferred to keep the content of impurities to less than 0.5% by weight and in particular less than 0.4% by weight. The content of other impurities, apart from iron and silicon, is less than 0.01% by weight for each individual impurity and less than 0.1% by weight for all impurities together. Thus, apart from Al, Mg, Zn, Cr, Mn, Ti, Zr, Fe and Si, the aluminum alloys used according to the invention contain essentially no other components. The invention is explained in more detail below with the aid of exemplary embodiments.

example

One aluminum leg at a time is made by casting a molten aluminum alloy of the composition manufactured according to Table 1 at a casting temperature of 750 ° C. A permanent form is used with the Internal dimensions 150 mm 110 mm 30 mm used. The blocks are freed from the casting skin and then homogenized for 24 h at 430 ° C. and then hot-rolled at the same temperature. Thereafter the product is cold rolled after washing the surface (treating the surface with water), whereby a rolled product with a thickness of 1.5 to 2 mm is obtained. This Walzpiodukl is then Soft annealed for 5 h at about 370 ° C. The annealed product is used for various tests. The soft annealed product is then treated by cold rolling, giving it a hardness of 1/4 H. the The hardened alloy obtained in this way is used for various tests. It uses the following test procedures applied:

(a) Tensile strength, 0.2 limit and elongation:
JlS Z 2201

(b) Corrosion resistance:
JlS D 0201

(Partial immersion in artificial sea water for 6 months) The test samples are checked for signs of corrosion on the surface after the corrosion treatment examined and tested for their mechanical strength.

(c) Stress corrosion cracking test:

Corrosive solution: aqueous solution of 5 "» NaCl + 0.3 ¹ O H> O.

Load: 70% weight for 0.2 "., - limit c

Duration: time to break (h). If no break occurs: 4000 to 5000 h.

The results are compiled in the tables below. In these tables means

○: the soft alloy and

II: the popular alloy (corresponding to 1/4 II).

With sample no. 1! up to 15 are comparison alloys. Sample No. 15 is around the alloy 5083.

Tabel

At- composition (%)

play _M " _Zn

Type mechanical properties

Mn Cr tensile strength- 0.2 limit elongation

speed N / mm ² N / mm ² %

Tabel

5.0 1.1 0.44 0.26 O
H 5.0 1.0 0.19 - O
H 5.4 1.4 - 0.16 O
H 6.3 1.1 0.44 0.45 O
H 6.2 1.0 0.20 - O
H 6.5 0.72 0.20 0.15 O
H 6.4 1.3 0.22 0.14 O
H 6.6 1.6 0.34 0.15 O
H 5.5 1.1 0.34 - O
H 5.6 1.0 - - O
H 5.1 1.0 - - O
H 5.0 1.0 - - O
H 5.0 1.0 - - O
H 6.2 1.0 0.54 - O
H 4.5 - 0.17 O
H

300.1
310.9 148.1
208.9 29.9
25.1 301.1
327.6 140.2
239.3 31.0
18.9 310.9
339.4 150.0
248.2 33.6
20.5 318.8
355.1 161.8
257.0 29.5
20.0 332.5
361.9 156.9
260.9 30.0
21.0 324.7
357.0 155.9
246.2 32.1
23.4 323.7
363.9 149.1
255.0 31.5
22.8 340.4
378.6 155.9
280.5 29.8
18.9 338.4
352.1 191.2
273.7 25.0
16.8 387.4
419.8 237.4
334.5 19.8
15.3 299.2
329.6 151.0
244.2 32.3
20.3 326.6
354.1 183.4
273.7 23.0
15.8 262.9
325.6 120.6
274.6 30.1
12.3 287.4
354.1 130.4
302.1 32.8
14.6 388.4
358.0 154.0
323.7 22.5
9.0

Example No. Composition (%) Mg Zn

Mn

Cr

Type figure of merit of the duration up to

Corrosion stress cracking resistance corrosion (h)

5.0

5.0

5.4

6.3

1.0

1.0

1.4

1.1

0.44

0.19

0.26

0.16

0.45

O 9 H 9 O 9 H 9 O 9 H 9 O 9 H 9

> 4000> 4000

> 4000> 4000

> 5000> 5000

> 4000> 4000

continuation

Example No. Composition (%) Mg Zn

Mn

Type figure of merit of the duration up to

Corrosion stress cracking resistance corrosion (h)

6.2 6.5 6.4 6.6 5.5 5.6 5.1 5.0 5.0 6.2 4.5

1.0

0.72

1.3

1.6

1.1

1.0

1.0

1.0

1.0

1.0

0.44 0.20 0.20 0.22 0.34 0.34

0.54

O 8th H 7th O 9 H 9 O 9 H 9 O 8th H S. O 9 H 9 O 8th H 8th O 9 H 9 O 8th H 8th O 8th H 8th O 7th H 7th O 8th H 7th

> 4000> 4000

> 5000> 5000

> 5000> 5000

> 5000> 5000

> 4000> 4000

> 4000> 4000

2000 1000

1000 800

2000 1000

? M

As Table 1 shows, the 0.2 limit of the soft alloy containing Cr or Mn or both is essential higher than that of the comparison alloys. The elongation of the work-hardened alloy is due to Addition of Cr or Mn or both is greatly improved, more than twice that of the conventional one Alloy No. 5083. The tensile strength of an alloy containing about 696 Mg is particularly high. The aluminum alloys used according to the invention have remarkably good mechanical properties Properties on. Compared to conventional stress-resistant alloys, they are quite ductile, so that they are ideal for a wide variety of construction purposes. The mechanical strength of the alloy can be changed by changing the Mg content. Therefore, aluminum alloys can be used for various uses are produced. The corrosion resistance and the stress corrosion cracking resistance can be significantly improved by adding Cr or Mn or Cr and Mn. Typical Examples are given in Table 2. As the comparative samples show, Al-Mg-Zn type alloys have without Cr and without Mn, a corrosion resistance and a stress corrosion cracking resistance which are the same is or less than the corrosion resistance of the conventional alloy No. 5083. By adding Cr and / or Mn, corrosion resistance and stress corrosion cracking resistance are significantly improved. Alloys containing more than 296 Zn have inferior workability and exhibit lower corrosion resistance. The workability and corrosion resistance are no better than that of Alloy No. 5083 even if Mn or Cr is added. In addition, one observes with alloys With a content of more than 296 Zn, precipitates during the aging process. Therefore these alloys are suitable not for construction purposes. By adding 0.05-0.2596 Ti and / or Zr instead of Cr or Mn becomes mechanical strength, corrosion resistance and stress corrosion cracking resistance improved.

The aluminum alloys used according to the invention are outstandingly suitable as extrudable alloys, and indeed much better than the comparison alloys. This can be shown by measuring the resistance to plastic deformation. The results are shown in FIG. Resistance to plastic deformation (N / mm ² ) is plotted on the ordinate, and the reduction in cross-sectional area (96) is plotted on the abscissa. The upper graph relates to samples made by casting and the lower graph relates to samples made by forging (5096). The samples have the following composition:

ο Mg: 5.496, Zn: 1.1%, Mn: 0.1896, Cr: 0.14% D Mg: 6.396, Zn: 1.1%, Mn: 0.19%, Cr: 0.15% χ 5056 alloy

45

50

55

65

Il alloy no. 5056 containing 5.4% Mg. To perform the test, the following test methods were used. The alloys were each cast in a cylindrical permanent mold, which has an inner diameter of 60 mm and a height of 200 mm. From the center of the cast product, a cylindrical

^: see sample cut with a diameter of 15 mm and a height of 18 mm. The results are in

shown in the diagram above. On the other hand, the molded product was thermoformed by 50%, and then

.;.: 'a cylindrical sample with a diameter of 15 mm and a

Cut out a height of 18 mm. The results are shown in the graph below. The compression tests were carried out for each group of samples at 430 ° C. It can be seen that the aluminum alloys used according to the invention have a significantly better processability than alloy No. 5056. ¹ ■ The one for extrusion of an alloy with 6.1% Mg, 1.0% Zn, 0.13% Cr and 0.13 % Mn required pressure is less than that required for alloy No. 5083.

. '; In addition, the increase is less than with alloy 5083. In the case of two-stage heating

B (4 to 5 h at 430 ⁰ C and then at 530 ⁰ C) is evident in the implementation of the Strangpreßtests at 530 ° C a

fc extrusion speed in the alloy used according to the invention, which is more than twice the

¹ x extrusion speed for alloy 5083. Thus, that used in the present invention is suitable

\ k Aluminum alloy is an excellent extrusion alloy. In addition, the one used in the present invention

I alloy with excellent weldability. The joint effectiveness in the sweat test is 85%. The comparative

$ alloys have the following composition:

I '"■ Alloy No. 5056 Alloy No. 5083

'' A Mg 5.4% by weight Mg 4.5% by weight

I Mn 0.09% by weight Mn 0.54% by weight

_(Tj Cr 0.1 wt .-% Cr 0.17 wt -.%

If Al rest Al rest

1 sheet of drawings

Claims (1)

Patent claims: 1. Use of a cold-deformable aluminum-magnesium-zinc alloy composed of 4 to 7% by weight of magnesium, 0.5 to 2% by weight of zinc, one or more of the elements from the group of 0.05 to 0.5% by weight. -% chromium, 0.1 to 0.6% by weight manganese, 0.05 to 0.25% by weight T'tan and 0.05 to 0.25% by weight zirconium and aluminum as the remainder with less than 0.5% by weight of impurities that are not artificially aged for workpieces with high resistance to intergranular corrosion and stress corrosion cracking and at the same time good tensile strength and elongation.
S 2. Use of the alloy according to claim 1 with 0.1 to 0.3% by weight of chromium and 0.2 to 0.4 % by weight ä: ·· Manganese, the total amount of chromium and manganese being 0.3 to 0.5% by weight and less than 0.5 jb % by weight of impurities consisting mainly of iron and silicon for the purpose || Claim 1. , fs 3. Use of the alloy according to claim 1 with 0.1 to 0.6% by weight manganese and 0.05 to 0.25% by weight || Titanium and / or 0.05 to 0.25 wt% zirconium and less than 0.5 wt% impurities contained in the Ijj mainly consist of iron and silicon, for the purpose of claim 1. ff 4. Use of the alloy according to claim 3 with 0.1 to 0.6% by weight of manganese and 0.07 to 0.15% by weight Ii titanium and / or 0.07 to 0.15 wt. 96 zirconium and less than 0.4 wt. 96 impurities contained in the % Mainly consist of iron and silicon, for the purpose according to claim '. $ 5. Use of the alloy according to claim 1 with 4.5 to 6.5 parts by weight 96 magnesium, 0.5 to 1.5 parts by weight fti f | Zinc and 0.1 to 0.3 wt .-% chromium and less than 0.4 wt .- * impurities, the main ones j! $ consist of iron and silicon for the purpose of claim 1. S; 6. Use of the alloy according to claim 1 with 4.5 to 6.5 wt. 96 magnesium, 0.5 to 1.5 wt. 9b p zinc, 0.2 to 0.4 wt. -96 manganese and less than 0.4 wt. 96 impurities, which are mainly composed i | Iron and silicon consist for the purpose of claim 1. |; 7. Use of the alloy according to claim 1 with 4.5 to 6.5% by weight of magnesium, 0.5 to 1.5% by weight j: S zinc, 0.1 to 0.3 wt. 96 chromium and 0.2 to 0.4 wt. 96 manganese, the total amount of chromium and % Manganese is 0.3 to 0.5 wt .-% and less than 0.5 wt .-% impurities, which are mainly made up ;! Iron and silicon consist for the purpose of claim 1. ö 8. Use of the alloy according to claim 1 with 4.5 to <5.5 wt .-% magnesium, 0.5 to 1.5 wt .-% y ■. Zinc, 0.2 to 0.4% by weight of manganese and 0.07 to 0.17% by weight of titanium and / or 0.07 to 0.15% by weight of zirconium μ> and less than 0.4% by weight of impurities, which mainly consist of iron and silicon, for '! ■ *, the purpose of claim 1.