CH617228A5 - Aluminium based alloy and its use - Google Patents

Abstract

This alloy contains 1.80 to 3 % of copper, 1.20 to 2.70 % of magnesium, 0.01 to 0.25 % of titanium, up to 0.30 % of silicon, 0.10 to 0.40 % of iron and at least one element from the nickel and cobalt group. The total nickel and cobalt content is between 0.10 and 0.40 % and its ratio to the iron content is close to one. This makes it possible to improve the toughness of the alloy when compared with the known alloys of similar composition, while retaining the good mechanical characteristics when hot of the latter. This alloy can be employed for the manufacture of moulded bodies, of forged or stamped articles and of rolled sheets, which have high mechanical characteristics that are suitable especially for aeronautical construction.

Description

The present invention relates to an aluminum-based alloy containing copper between 1.80 and 3.00%, magnesium between 1.20 and 2.70%, titanium between 0.01 and 0.25%, iron and at least one element from the nickel and cobalt group.

It also relates to the use of this alloy.

Alloys of this type with structural hardening have high mechanical properties, high hot properties and good creep behavior.

It is well known that the aeronautical industry uses several varieties of this type of alloys which their high hot characteristics are intended in particular for the construction of supersonic devices. Among these alloys, A-U2GN, described in particular in French patent 978 805 filed on January 10, 1949, in the name of Rolls Royce Limited and High Duty Alloys Limited, has experienced remarkable development in recent years.

Its composition is as follows:

Copper 1.8 to 2.5%

1.2 to 2% magnesium

Nickel 0.3 to 1.5% with Fe + Ni included

Iron 0.85 to 1.5% f between 1.5% and 2.75%

Silicon 0 to 0.4% ^

Titanium 0.02 to 0.2%

The proportions of copper and magnesium in this alloy allow structural hardening by submicroscopic precipitation of the S'Al-Cu-Mg phase.

It is well known that additions of iron and nickel are made to obtain good hot characteristics and in particular good creep resistance, due to the existence of an Al-Fe-Ni phase which impedes the propagation of dislocations. However, this alloy has the characteristics of toughness, appreciated by the stress intensity factor KiC, and resistance to the propagation of cracks which, without being insufficient, do not classify it among the best in these fields.

The KiC factor, which characterizes the toughness of an alloy, is measured according to the ASTM E-399-72 method.

The object of the invention is to produce an aluminum alloy which, compared with the previous FAU2GN, has a higher toughness in particular in the short-cross direction, a better KiC factor and a better resistance to the propagation of fatigue cracks while keeping the good hot properties and the good corrosion resistance under tension of this alloy.

The licensee discovered, with surprise, that the action of the Al-Fe-Ni phase as well as that of other intermetallic compounds Al-Cu-Ni and Al-Cu-Fe present in the known prior alloy, is not not only beneficial. Each of these three compounds has, in fact, a relatively significant harmful action on the resistance to the propagation of fatigue cracks and on the stress intensity factor KiC.

The licensee also discovered that, contrary to generally accepted opinion regarding the action on the hot characteristics of the Al-Fe-Ni compound, a significant reduction in the iron and nickel contents does not substantially modify the characteristics at alloy hot. On the other hand and on condition that the Ni / Fe weight ratio close to 1 is maintained, the toughness, in particular in the cross-short direction, the stress intensity factor KiC and the resistance to the propagation of cracks fatigue are significantly improved.

The present invention is characterized in that the iron content is between 0.10 and 0.40%, that the total nickel plus cobalt content is between 0.10 and 0.40% and that the ratio of the content in nickel increased from the cobalt content to the iron content is close to 1.

The alloy defined above, in which the copper content is between 2.10 and 2.90%, that of magnesium between 1.40 and 2.00% and that of titanium between 0.15 and 0.25 % may also contain between 0.10 and 0.35% iron and between 0.10 and 0.35% nickel plus cobalt.

The ratio of the nickel content increased by the cobalt content to the iron content is preferably between 0.9 and 1.3.

It is possible to add to the composition of the alloy at least one of the elements Zr, Mn, Cr, V, Mo, each of these elements having a content ranging up to 0.4%.

It is also possible to add to the composition of the alloy at least one of the elements Cd, In, Sn, Be, each of these elements having a content of up to 0.2%.

Finally we can add at least one of the following two elements: Silver up to 1%, Zinc up to 8%.

s

10

15

20

25

30

35

40

45

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55

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65

3

617228

The present invention also relates to the use of this aluminum-based alloy for the manufacture of molded bodies.

According to one embodiment, the bodies manufactured from molded articles are plates and billets intended for forging, spinning, rolling and any other mode of plastic deformation.

These molded articles can also be in the form of thick sheets intended for aeronautical construction and obtained by rolling the plates. They can be in the form of forged, stamped, stamped, stamped or flow-turned parts, or in the form of extruded products made from plates and billets. These parts and these products preferably undergo a structural hardening heat treatment comprising dissolution in a temperature higher than the starting melting temperature of the alloy, followed by quenching and tempering.

The composition of the present aluminum alloy is as follows:

Copper Magnesium Nickel Iron

Titanium Silicon

1.80% to 3.00% preferably 2.10% to 2.70% 1.20% to 2.70% preferably 1.40% to 2.00% 0.10% to 0.40% of preferably 0.10% to 0.35% 0.10% to 0.40% preferably 0.10% to 0.35% with Ni from 0.9 to 1.3

Fe

0.01% to 0.25%

0% to 0.30% preferably 0.15% to 0.25%

Cobalt can be partially or completely substituted for nickel.

Other elements, for example zirconium, manganese, chromium, vanadium, molybdenum can be added at contents of between 0 and 0.4%.

It is also possible to add cadmium, indium and tin at levels between 0 and 0.2% as well as beryllium at levels between 1 and 2000 ppm.

Finally, additions of silver from 0 to 1% and of zinc from 0 to 8% can also be made.

The heat treatment of this type of alloy does not differ from that of conventional A-U2GN, that is to say that it comprises:

- dissolving at a temperature between 520 ° C and 535 ° C

- soaking in cold, lukewarm or boiling water

- tempering at a temperature between 150 ° C and 230 ° C.

Work hardening between quenching and tempering can also be practiced. It has the advantage of loosening and standardizing the internal tensions due to quenching and of increasing the mechanical characteristics of the alloy, in particular its elastic limit.

A heat treatment as claimed in the French patent filed on 7/1/1974 under No. 7,400,399 can also be practiced: it consists in dissolving at a temperature higher than that of the beginning melting of the alloy . This dissolution must last long enough for the liquid phases which appear to be practically completely absorbed at the time of quenching. Quenching and tempering are carried out under conditions identical to those indicated above. For example a solution made to

Alloy 2

555 ° C (instead of 520 ° to 535 °) improves the mechanical characteristics:

one gains 1 to 2 hbar on the breaking load.

In order to facilitate understanding of the present invention, the measurement method and the meaning of the KiC factor as well as the measurement of the speed of propagation of fatigue cracks are briefly recalled below.

The stress concentration factor KiC is measured according to the method described in standard ASTM-E-398-72. 10 Without going into the detail of the coefficient calculation, it is useful to know, to understand its meaning, what is the principle of this method.

A sample is taken from the product as shown in FIG. 1. The line joining the centers of the two holes is in the short-cross direction; the edge of the bow produced by machining is in the cross-long direction.

The test piece is then subjected to a series of wavy tensile cycles by fixing it to a fatigue machine by means of pins passing through the holes. The wavy traction cycles are stopped when a fatigue crack of approximately 1.3 mm (1/20 inch) in length has been measured, measured at the surface of the test piece from the end of the notch. The test piece is then, still by means of pins passing through the holes, mounted on a traction machine. An increasing force is then exerted until rupture by recording the tensile force as a function of the spacing of the lips of the test piece measured using a sensor. We obtain a curve such as that shown in fig. 2.

A graphical method makes it possible to determine the load Pq 30, the application of which caused the propagation of the crack produced by fatigue of a length equal to 2% of its initial value. The coefficient KiC is proportional to Pq, the proportionality factor being calculated as a function of the geometric dimensions of the test piece and the length of the crack 35 initiated beforehand by fatigue. This coefficient is expressed in hbarVmm.

The higher the KiC factor for a given specimen, the higher Pq, therefore the greater the force to be exerted to advance the crack by 2%.

40 The speed of propagation of fatigue cracks is measured as follows:

A central hole 2 mm in diameter is drilled in the center of a rectangular test tube 250 mm long, 100 mm wide and 1.6 mm thick. This test piece 45 is subjected to fatigue cycles in wavy traction and the length of the cracks is measured on photographic images taken at regular intervals. The curve of the length of the crack is then plotted as a function of the number of cycles, which makes it possible to measure the speed of propagation of the cracks.

The examples given below are given purely by way of illustration. They relate to a series of treatments and characteristic measurements on five alloys, the compositions of which are as follows:

50

ss Alloy 0

Cu

= 2.65% Alloy 1

Cu

= 2.63%

witness

Mg

= 1.64%

Mg

= 1.60%

Fe

= 1.07%

Fe

= 0.30%

Or

= 1.19%

Or

= 0.35%

Yes

= 0.22%

Yes

= 0.22%

60

Ti

= 0.10%

Ti

= 0.10%

Cu

= 2.63% Alloy 3

Cu

= 2.65% Alloy 4

Cu

= 2.65%

Mg

= 1.60%

Mg

= 1.64%

Mg

= 2.04%

Fe

= 0.15%

Fe

= 0.29%

Fe

= 0.15%

Or

= 0.17%

Or

= 0.36%

Or

= 0.17%

Yes

= 0.22%

Yes

= 0.22%

Yes

= 0.23%

Ti

= 0.10%

Ti

= 0.10%

Ti

= 0.11%

Zr

= 0.12%

617,228

4

Alloy O is the control alloy of composition in accordance with French patent 978 805. The other alloys are different compositions all coming within the scope of the invention.

1st Example

Alloys 0,1, 2 and 3 are cast semi-continuously, in the form of plates with a cross-section of 120 X 380 mm, then homogenized for 20 h at 520 ° C.

After debitage and peeling of the surfaces, the plates are heated to 480 ° C and rolled in 10 mm passes to a thickness of 45 mm. The treatment of thick sheets thus obtained then comprises the following phases:

- 10 h solution treatment at 530 ° C,

- water quenching,

- traction between quenching and tempering corresponding to a permanent elongation of 2%,

s - final income from 8 p.m. at 190 ° C.

Tensile specimens in the long-direction and in the short-direction, test specimens for measuring the KiC coefficient, specimens for the rate of crack propagation and io specimens for creep were taken from the sheets obtained from the 4 alloy plates.

The mechanical characteristics as well as the KiC factor appearing in the table below:

Alloys Mechanical tensile properties K, C Sens

Long traverse direction

Short-cut direction

through-short

Rp 0.2

Rm

AT %

Rp0.2

Rm

AT %

hbar Vmm

hbar hbar

hbar hbar

0

41.6

45.9

8.5

40.8

46.3

8.7

71.4

1

41

45

8.4

40.2

45.1

7.9

84

2

40.5

44.6

7.9

39.1

44.3

7.1

98.6

3

41.2

45.2

8.9

40.1

45.2

7.8

86.9

It can be seen that the KiC coefficients of the alloys 1, 2 and 3 (new composition) are significantly higher (by 38% in the best case) than that of the control alloy (old composition) without the tensile characteristics being lowered so significant.

The fatigue cracking rates expressed in mm, for 1000 cycles, measured between 5 and 20 mm are as follows:

Alloys

Average speed of propagation

mm / 1000 cycles

0

0.87

î

0.69

2

0.64

3

0.79

It can therefore be seen that the alloys 1, 2 and 3 according to the invention have crack propagation speeds lower than those of the alloy 0 taken as a control.

Creep constraints

100 ° 0.1

in the cross-short direction were also determined;

100 ° 0.1

represents the stress causing a creep extension of 0.1% in 100 h of temperature maintenance.

The creep results at temperatures of 130 ° C and 175 ° C are shown in the table below:

Alloys

100 "0.1

At 130 ° C hbar

At 175 ° C hbar

0

27.5

17.6

1

27.0

17.9

2

26.4

17.3

3

27.2

18.0

The creep resistance of alloys 1, 2 and 3 which is the subject of our invention is therefore quite comparable to that of alloy 0 taken as a basis for comparison.

40

2nd Example

The alloys of composition 0.2 and 4 were cast semi-continuously in the form of plates of 120 × 380 mm and then homogenized for 20 h at 520 ° C.

45 After peeling the surfaces, the plates are heated to 480 ° C and rolled in 10 mm passes to a thickness of 45 mm.

The thick sheets are then subjected to a solution treatment at 530 ° C for 10 h, then quenching in cold water, n / a Then, and this time without drawing by traction between quenching and tempering, an income of 20 h at 203 ° in order to obtain a T6 state which is generally used in the case of forged and stamped products.

The traction characteristics were measured in the cross-long and cross-short direction.

The results obtained are shown in the table below:

Alloys

Long traverse direction

Short-cut direction

Rp0.2

Rm

AT %

Rp0.2

Rm

AT %

hbar hbar

5.65 V§ô

hbar hbar

5.65 V§ô

0

37.3

42.8

6.9

38.3

43.5

6.8

2

38.3

42.5

6.6

38.2

42.2

5.3

4

40.3

44.3

6.2

40.2

44

5

In the T6 state (quenching-tempering), alloy 2 has characteristics 65 65 The KiC factor goes from a value of 82 hbar Vmm in the mechanical tensile ques comparable to those of the alloy case of the alloy 0 to 102 hbar Vmm for alloy 2 and 103 hbar

0. Alloy 4 reaches an elastic limit and a load of Vmra for alloy 4.

rupture greater than that of the witness.

B

1 Blatt Zeichnungen

Claims (12)

617,228 1. Aluminum-based alloy containing copper between 1.80 and 3.00%, magnesium between 1.20 and 2.70%, titanium between 0.01 and 0.25%, iron and at least an element from the nickel and cobalt group, characterized in that the iron content is between 0.10 and 0.40%, that the total nickel plus cobalt content is between 0.10 and 0.40% and that the ratio of the nickel content increased by the cobalt content to the iron content is close to 1. 2. Alloy according to claim 1, characterized in that it also contains silicon with a content of up to 0.30%. 2 3. An alloy according to claim 1 or claim 2, in which the copper content is between 2.10 and 2.70%, that of magnesium between 1.40 and 2.00%, and that of titanium between 0, 15 and 0.25%, characterized in that the iron content is between 0.10 and 0.35% and that the nickel plus cobalt content is between 0.10 and 0.35%. 4. Alloy according to one of claims 1 to 3, characterized in that the ratio of the nickel content increased by the cobalt content to the iron content is between 0.9 and 1.3. 5. Alloy according to claim 3, characterized by the additional presence in the alloy composition of at least one of the elements Zr, Mn, Cr, V, Mo, each of the elements having a content of up to 0.4 %. 6. Alloy according to claim 5, characterized by the additional presence in the composition of the alloy of at least one of the elements Cd, In, Sn, Be, each of the elements having a content ranging up to 0.2%. 7. Alloy according to one of claims 1 to 6, characterized by the presence of at least one of the following elements: Silver up to 1%, zinc up to 8%. 8. Use of the alloy according to claim 1 for the manufacture of formed bodies. 9. Use according to claim 8, characterized in that the bodies formed are bodies molded in the form of plates or billets. 10. Use according to claim 9, characterized in that the molded bodies are subjected to plastic deformation, for example by forging, spinning, rolling, stamping, stamping, stamping or flow forming. 11. Use according to claim 10, characterized in that one obtains by rolling, from plates, thick sheets usable in aeronautical construction. 12. Use according to claim 10, characterized in that the parts obtained by plastic deformation are subjected to a structural hardening treatment comprising dissolving at a temperature above the starting melting temperature of the alloy, followed by 'quenching and income.