BRPI0617699A2 - al-cu-mg alloy suitable for aerospace application - Google Patents

Abstract

<B> AI-Cu-Mg ALLOY SUITABLE FOR AEROSPACE APPLICATION <D> The present invention relates to a worked product of aluminum alloy having high resistance and high fracture toughness and high resistance to intergranular corrosion, the alloy including weight: Or 4.1% - 5.5%; Mg 0.30% - 1.6%; Mn 0.15% - 0.8%; Ti 0.03% - 0.4%; Cr 0.05% - 0.4%; Ag <0.7%; Zr <0.2%; Fe <0.20%, preferably <0.15%, more preferably <0.1%; Si <0.20%, preferably <0.15%, more preferably <0.1%; and the balance being aluminum and other impurities or incidental elements, each <0.05%, total <0.15%.

Description

Descriptive Report of the Invention Patent for "Al-Cu-Mg Alloy Suitable for Aerospace Application".

Field of the invention

The present invention relates to a worked aluminum alloy, particularly an Al-Cu-Mg type alloy (or A-A2000 series aluminum alloy as designated by the Aluminum Association). More specifically, the present invention relates to an aluminum alloy product having high strength, high fracture toughness exhibiting low detrimental propagation and high resistance to intergranular corrosion. Products made of aluminum alloy according to the invention are very suitable for aerospace applications, but not limited thereto. The alloy may be processed into various product shapes such as sheet, thin plate or an extruded product, a forged product, or a welded product. The aluminum alloy product may be uncoated or coated or plated with another aluminum alloy in order to further enhance the desired properties.

Background of the invention

Designers and manufacturers particularly in the aerospace industry are constantly trying to improve fuel efficiency, product performance and constantly trying to reduce manufacturing, maintenance and service costs. One way to achieve these goals is to improve the relevant properties of the aluminum alloys used, so that a structure made of a particular alloy can be designed more effectively or will have better overall performance. By improving material-relevant properties for a particular application, service costs can also be significantly reduced by longer frame inspection intervals such as an airplane.

The main application of AA2000 series aluminum alloys on airplanes is as a fuselage or cladding plate, for which purpose typically alloy AA2024 is used in tempering T351, or as a lower plate, for which purpose typically alloys are used. AA2024 on T351 revival and AA2324 on T39 tempering. For these applications high tensile strength and toughness are required. It is known that these properties of an AA2000 series aluminum alloy can be improved by higher levels of alloying elements such as Cu, Mg and Ag.

However, by increasing the concentration of the alloying elements, the resistance to corrosion, particularly also to intergranular corrosion, is reduced to levels that may limit the applicability of the alloy.

Intergranular corrosion of an aluminum alloy does not only affect the integrity of the structure in which it is used, in which corroded grain contours can act as a crack core that propagates under the influence of alternating load during operation of the structure. Therefore, the occurrence of intergranular corrosion sets limits for the use of AA2000 series aluminum alloys with high levels of the mentioned alloying elements.

The most commonly used aluminum alloys that form the AA2000 series for aerospace application are AA2024, AA2024HDT ("High Damage Tolerance") and AA2324.

For newly designed aircraft, there is a desire for even better properties of aluminum alloys than known alloys have in order to design aircraft that is more cost-effective to manufacture and operate. Thus, there is a need for an aluminum alloy capable of achieving an improved balance of aluminum alloy properties to a relevant extent.

Summary of the invention

The present invention relates to an A-A2000 series aluminum alloy having the ability to achieve a property balance on any relevant product made of the alloy which is better than the balance of properties of the commercially available AA2000 series aluminum alloy variety used. nowadays for a product like this or AA2000 series aluminum alloy product described so far.

An object of the present invention is to provide a worked aluminum alloy product particularly suited for aerospace application within the AA20Q0 series of alloys having an improved balance of high strength and fracture toughness and high resistance to intergranular corrosion.

Another object of the present invention is to provide an aluminum alloy work product as previously mentioned which has a high resistance to exfoliation corrosion and stress cracking.

A further object of the present invention is to provide a worked aluminum alloy product as mentioned above which is tolerant to the usual variation in process parameters during its manufacturing process.

Also another object of the present invention is to provide a worked aluminum alloy product as above which is weldable and suitable for use in welded constructions.

Also another object of the present invention is to provide a worked aluminum alloy product as referred to above in a form that is suitable for use in an aerospace structure.

A further object of the present invention is to provide a method of fabricating a worked aluminum alloy product as mentioned above.

One or more of the objectives and other objectives and advantages are achieved with an aluminum alloy worked product having high strength and high fracture toughness and high resistance to intergranular corrosion, the aluminum alloy comprising by weight: Cu 4.1% - 5.5% Mg 0.30% - 1.6% Mn 0.15% -0.8%

Ti 0.03% -0.4% Cr0.05% -0.4% Ag <0.7% Zr <0.2%

Fe <0.20%, preferably <0.15%, more preferably <0.1%

Si <0.20%, preferably <0.15%, more preferably <0.1%,

and the balance being aluminum and other impurities or incidental elements, each <0.05%, total <0.15%.

Unless stated otherwise in this document all percentages are weight percentages (% by weight). Summary Description of DrawingsIn the drawings:

Figure 1 shows a Cr-Ti diagram specifying the Cr-Ti range for the invention along with narrower preferred ranges.

Figures 2a, 2b show micrographs of a cross section of a sample of an alloy according to the invention in tempering T3e of a comparative alloy after corrosion testing.

Figures 3a, 3b show cross-sectional micrographs of a sample of an alloy according to the invention in tempering T6e of a comparative alloy after corrosion testing. Detailed description of preferred embodiments

The present invention provides a crafted aluminum alloy product having high strength and high fracture toughness and high resistance to intergranular corrosion, the aluminum alloy comprising by weight: Cu 4.1% -5.5%

Mg 0.30% -1.6% Mn 0.15% -0.8% Ti 0.03% -0.4% Cr 0.05% -0.4% Ag <0.7% Zr <0, 2% Fe <0.20%, preferably <0.15%, more preferably <0.1% Si <0.20%, preferably <0.15%, more preferably <0.1%,

and the balance being aluminum and other impurities or incidental elements, each <0.05%, total <0.15%. Unless otherwise stated herein all percentages are weight percentages (weight percent).

It has been found that the composition of the aluminum alloy according to our invention leads to the alloy product having a high resistance to intergranular rosin while maintaining a higher strength and higher toughness when compared to conventional AA2024 alloys. tional. The alloy product of the invention also has a high resistance to exfoliation corrosion and stress corrosion cracking.

Good results are also obtained in a preferred embodiment of the invention wherein 0.03% <Ti <0.3%, preferably 0.05% <Ti <0.2%. According to this embodiment good properties can also be achieved with a lower Ti concentration.

Another embodiment has the range wherein 0.05% <Cr <0.3%, preferably 0.05% <Cr <0.15%. In this embodiment particularly good properties of intergranular corrosion are maintained although the alloy product is at the same time less susceptible to tempering.

An additional embodiment has the range wherein 0.1% <Ti + Cr <0.4%. It has been found that within the given range Ti and Cr can be substituted for each other while maintaining good resistance against intergranular corrosion and good mechanical properties.

Preferably 0.1% <Ti + Cr <0.3%. In this embodiment of the invention good properties are still achieved with reduced addition of Ti and Cr alloy elements.

In a preferred embodiment the Cu level is selected from the range wherein 4.4% <Cu <5.5%, more preferably 4.7% <Cu <5.3%.

In a further preferred embodiment the Mg level is selected in the range of 0.3% <Mg <1.2%, more preferably 0.4% <Mg <0.75%.

Iron may be present in the range of up to 0.20% and preferably is maintained at a maximum of 0.15%, more preferably at a maximum of 0.1%. A typical preferred iron level would be in the range of 0.03% to 0.08%. Silicon may be present in a range of up to 0.20% and preferably is maintained at a maximum of 0.15%, more preferably at a maximum of 0,1%. A typical preferred silicon level would be as low as possible and would typically be for practical reasons within a range of 0.02% to 0.07%.

Zirconium may be present in the alloy product according to the invention in an amount of up to 0.20%. An appropriate level of Zr is a range of 0.04% to 0.15%. A more preferred upper limit for the level of Zr is 0.13%, and even more preferably no more than 0.11%.

Manganese may be added alone or in combination with other dispersoid formers. A preferred maximum level for Min is 0.80% and a preferred minimum level is 0.15%. A preferred range for the Mn level is in the range where 0.2% <Mn <0.5%.

In the prior art, it has been proposed to add Ag to an AA2000 alloy to improve intergranular corrosion resistance. However, there are disadvantages associated with the addition of Ag. One disadvantage is that Ag is a costly element and its addition increases the price of the alloy. A second disadvantage is that, also with respect to the price of Ag, any scrap of Alloy must be carefully handled and recycled to recover Ag.

Therefore, in another preferred embodiment of the aluminum alloy product according to the invention, the alloy is Ag free. In practical terms this would mean that Ag is present at the level of an impurity or incidental element, thus at a level. <0.05%. More preferably, the alloy is substantially free of Ag. With "substantially free" it is intended that no intentional addition of Ag has not been made to the chemical composition, but that because of impurities and / or leakage from contact with equipment. In manufacturing, minimal amounts of Ag can, however, find their way into the aluminum alloy product.

In a preferred embodiment of the aluminum alloy product according to the invention, the alloy has a composition consisting of, by weight percent: Cu 4.1% -5.5%

Mg 0.30% -1.6%

Mn 0.15% - 0.8%

Ti 0.03% - 0.4%

Cr 0.05% -0.4%

Zr <0.2%

Fe <0.15%, preferably <0.1%

Si <0.15%, preferably <0.1%,

and the balance being aluminum and other impurities or incidental elements, each <0.05%, total <0.15%, and is substantially free of Ag.

More narrow preferred ranges for the various alloying elements are set forth in this specification and claims.

Preferably, the aluminum alloy product according to the invention is in tempering T3x, T6x or T8x. Depending on the intended field of application of the alloy the appropriate tempering is selected to give the alloy product the desired properties. Resale assignments are in accordance with the Aluminum Association.

Because of the increased resistance to intergranular corrosion at high strength and fatigue levels, the product is preferably supplied in the form of a sheet, plate, forged or extruded for use in an aerospace structure.

The aluminum alloy product according to the invention has an excellent balance of properties for application as a plate in a wide range of thicknesses, preferably in the form of a plate having a thickness in the range of 0.7 to 80 mm. In the plate thickness range of 0.6 to 1.5 mm the aluminum alloy product is also of particular interest as automotive body sheet.

In the thickness range up to 40 mm the aluminum alloy product properties will be excellent for fuselage sheet and preferably the thickness is up to 25 mm.

In the range of thicknesses from 20 to 80 mm the properties are excellent for wing plates, eg lower wing plate, when properties of tensile strength and fatigue are of great importance. In this range of thickness aluminum alloy products can also be used for beams or to form an integral wing and beam panel for use with an airplane wing structure.

The aluminum alloy product according to the invention may also be used as a tooling plate or molding plate, for example for molds to make products formed of plastic, for example by means of die casting or molding. by injection. In this application higher Fe and Si levels of up to 0.4% for each of these elements are acceptable.

The invention is also embodied in a method for the manufacture of an aluminum alloy product having high strength and high fracture toughness and high intergranular corrosion resistance comprising the steps of:

The. shaping an ingot having a composition according to the invention;

B. homogenize and / or preheat the ingot after molding;

ç. hot working the ingot for a product worked by one or more methods selected from the group consisting of lamination, extrusion and forging;

d. optionally reheat the worked product, and

and. working hotter optionally and / or working cold for a desired workpiece shape;

f. heat treat by solubilizing said shaped workpiece at a temperature and time sufficient to invert substantially all soluble constituents in the alloy for solid solutions;

g. tempering the heat-treated workpiece by solubilization by spray quenching or water quenching or other quenching means;

H. optionally stretching or compressing the tempered workpiece;

i. naturally or artificially aging the tempered and optionally stretched or compressed workpiece to achieve the desired temperature.

The method according to the invention produces an aluminum alloy product having excellent intergranular corrosion resistance and high strength and excellent fatigue properties.

The alloy products of the present invention are prepared regularly by melting and bonding an aluminum alloy product and may be by direct cooling ("C.C") casting into ingots or other suitable casting techniques. Homogenization treatment is typically carried out in one or more steps, each step having a temperature preferably in the range of 460 ° C to 535 ° C. Preheating temperature involves heating the ingot to the hot working temperature which is typically in a temperature range of 400 ° C to 480 ° C. Working of the alloying product may be done by one or more selected methods. group consisting of rolling, extrusion and forging. For the present alloy product, hot rolling is preferred. Solubilization heat treatment is typically performed in the same temperature range as that used for homogenization, although slightly shorter soaking times may be selected.

In one embodiment of the method according to the invention, artificial aging preferably comprises an aging step at a temperature in the range of from 135 ° C to 210 ° C, preferably for 5 to 20 hours.

In another embodiment of the invention natural aging preferably comprises an ambient temperature aging step for 1 to 10 days.

Preferably, the aluminum alloy product is aged to a tempering selected from the group comprising T3, T351, T39, T6, T651 and T87.

In one embodiment the aluminum alloy product is processed to the fuselage sheet, preferably to the fuselage sheet having a thickness of less than 30 mm.

In another embodiment the aluminum alloy product is processed for the lower wing plate.

In an additional embodiment the aluminum alloy product is processed for upper wing plate.

In still a further embodiment the aluminum alloy product is processed into an extruded product.

Also in an additional embodiment the aluminum alloy product is processed into a forged product.

Also in another embodiment the aluminum alloy product is processed to a thin plate having a thickness in the range of 15 to 40 mm.

In yet another embodiment the aluminum alloy product is processed to a thick plate having a thickness of up to 300 mm.

Examples

In the following, the invention will be further illustrated with reference to the drawings and laboratory test results.

Figure 1 shows a Cr-Ti diagram specifying the Cr-Ti range for the invention along with narrower preferred ranges.

Figure 1 shows schematically the bands for Cr and Ti content for the alloy according to the invention. The widest range is identified by a rectangular figure with vertices A, B, C and D.

Figure 1 also schematically shows a preferred range of a balanced content of both Cr and Ti. The widest range itself is identified by a quadrangular figure with vertices E, F, G and H.

Point P indicates the Cr and Ti content of a sample of an alloy according to the invention that was used for testing (also referred to as alloy 3 in the following examples).

The letter Q indicates the Cr and Ti content of two comparative alloys, also used for testing and also referred to as alloys 1 and 2. The alloys 1 and 2 are outside the invention.

Alloy 2 has, with the exception of the Cr and Ti1 content, the same chemical composition as Alloy 3 according to the invention. Alloy 1 has a typical chemical composition for a conventional AA2024 alloy.

On a laboratory scale three ingots were molded and processed to a plate to prove the principle of the present invention.

Alloy compositions of the three alloys are listed in Table 1.

Table 1. Composition of alloys (weight percent), aluminum

<table> table see original document page 12 </column> </row> <table>

The alloys listed in Table 1 were processed as follows:

- Ingot molding;

- For alloy 1: Ingot homogenization at a heating rate from 30 ° C / h to 465 ° C, soaking at that temperature for 2 hours, followed by additional heating at a rate of 15 ° C / h to 495 ° C soaking at this temperature for 24 hours, followed by air cooling to room temperature.

- for alloys 2 and 3; homogenization of the ingot at a heating rate of 30 ° C / h to 525 ° C, soaking at this temperature for 24 hours, followed by air cooling to room temperature.

- Preheating up to 420 ° C.

- Hot rolling from 80 mm to 8 mm.

- Cold rolling from 8 mm to 2 mm for a cold rolled plate.

- Heat treatment of solubilization of cold rolled plate.

° For alloy 1 at 495 ° C for 30 min.

° For alloys 2 and 3 at 525 ° C for 30 min.

- Cold-rolled plate quench by either direct water quenching or water quenching after retaining for 10 seconds at noon.

- Cold rolled plate storage for 4 hours at room temperature.

- Stretching and aging of cold rolled plate both

per:

° Stretching and natural aging for 5 days at room temperature for T3x tempering (ie T3, T351 and T39); how much for

° stretching and artificial aging for 12 hours at 175 ° C for T6x and T8x tempering (ie T6, T651 and T87).

Samples taken from cold-rolled plates processed as described above were subjected to an inter-granular corrosion test according to ASTM G110.

Corrosion test results are shown in Tables 2, 3, 4 and 5.

In the tables, (i) indicates only localized corrosion and that no intergranular corrosion was not observed, (ii) indicates localized corrosion with slight intergranular corrosion at the bottom of the pite that was observed, and (iii) indicates local intergranular corrosion. was observed.

Table 2. Maximum corrosion depth and type of T3x alloys

<table> table see original document page 13 </column> </row> <table>

Table 2 shows that a balanced addition of Cr and Ti according to one embodiment of the invention causes considerable intergranular corrosion-free properties in T3x tempering with a noticeably lower pitting depth compared to other alloys.

Table 3. Maximum corrosion depth and type of T3x standard alloys with a 10 second hardening delay after solubilization heat treatment. <table> table see original document page 14 </column> </row> <table>

This table shows that also after a hardening delay of up to 10 seconds the stressed corrosion properties are maintained with the alloy according to the invention. Table 4. Maximum corrosion depth and type of alloys in

T6x tempering and T8x tempering.

<table> table see original document page 14 </column> </row> <table>

As can be seen from this table, improved rosin properties are achieved by the balanced addition of Cr and Ti. Only pitting has been discovered with very little intergranular corrosion at the bottom of the pite.

Table 5. Maximum Corrosion Depth and Type of T6x and T8x Clad Alloys with a 10-second Quenching Delay

after solubilization heat treatment.

<table> table see original document page 14 </column> </row> <table>

For long quenching delays of up to 10 seconds the intergranular corrosion resistance decreases slightly, but the performance is still noticeably superior to the performance of comparative alloys, as with no quenching.

Corrosion test results are also shown in Figures 2a, 2b, 3a and 3b. Figures 2a, 2b show micrographs of a cross section of a sample of an alloy according to the invention in tempering T3e of a comparative alloy after the corrosion test.

Particularly, Figure 2a shows a micrograph of a cross section of a sample of comparative alloy 1 (Ref. AA2024) in T3 after the corrosion test. The micrograph clearly shows localized corrosion and intergranular corrosion to a depth too deep of 150 pm.

Figure 2b shows a cross-sectional micrograph of a sample of an alloy according to the invention (alloy 3) also in revetment T3 after corrosion testing. The sample has only a small pit with a maximum depth of 60 μητι and no intergranular corrosion.

Figures 3a, 3b show a cross-sectional micrograph of an alloy sample according to the invention in tempering T6 and a comparative alloy after the corrosion test. In particular, Figure 3a shows a cross-sectional micrograph of an alloy sample 1 (ReferenceAA2024) on tempering T6 after the corrosion test. The micrograph clearly shows local intergranular corrosion extending to a depth of about 220 pm.

Figure 3b shows a cross-sectional micrograph of a sample of an alloy according to the invention (alloy 3) also in retention T6 after the corrosion test. The sample shows pits only with minor intergranular corrosion to a depth of less than 160 μm.

In both T3 and T6 tempering, the corrosion performance of the alloy according to the invention is considerably better than the corrosion performance of benchmark AA2024 comparative alloy.

Mechanical properties of the alloys, cast and processed as described above, were also measured and the results were collected in Tables 6 and 7.

Table 6. Tensile properties (L direction) of the revealing T3 alloys. <table> table see original document page 16 </column> </row> <table>

From Table 6 it can be seen that in tempering T3 comparable mechanical properties can be achieved with an alloy according to the invention as for reference alloys 1 (Reference A-A2024) and 2.

Table 7. Fracture toughness (L-T direction) of tempering alloys T3.

<table> table see original document page 16 </column> </row> <table>

From Table 7 it can be seen that significantly higher toughness is maintained with an alloy of the present invention as compared to comparative AA2024 alloy.

Although the present invention has been described with reference to some specific examples, those skilled in the art will certainly be able to achieve many other embodiments within the spirit and scope of the invention. Thus, the invention is not limited by the above-listed embodiments, but is instead defined by the claims appended hereto.

Claims (23)

1. Worked aluminum alloy product having high strength and high fracture toughness and high resistance to intergranular corrosion, the worked aluminum alloy diode product made of an alloy comprising weight: Cu 4.1% -5.5% Mg 0.30 % -1.6% Mn 0.15% -0.8% Ti 0.03% - 0.4% Cr 0.05% -0.4% Ag <0.7% Zr <0.2% Fe < 0.20%, preferably <0.15% Si <0.20%, preferably <0.15%, and the balance being aluminum and other impurities or incidental elements, each <0.05%, total <0.15% . Aluminum alloy product according to claim 1, wherein 0.03% <Ti <0.3%, preferably 0.05% <Ti <0.2%. Aluminum alloy product according to claim 1 or claim 2, wherein 0.05% <Cr <0.3%, preferably 0.05% <Cr <0.15%. Aluminum alloy product according to one or more of the preceding claims, wherein 0.1% <Ti + Cr <0.4%. Aluminum alloy product according to one or more of the preceding claims, wherein 0.1% <Ti + Cr <0.3%. Aluminum alloy product according to one or more of the preceding claims, wherein 4.4% <Cu <5.5%, preferably 4.7% <Cu <5.3%. Aluminum alloy product according to one or more of the preceding claims, wherein 0.3% <Mg <1.2%, preferably 0.4% <Mg <0.75%. Aluminum alloy product according to one or more of the preceding claims, wherein 0,2% <Mn <0,5%. Aluminum alloy product according to one or more of the preceding claims, wherein Ag is present at the level of an impurity or incidental element. Aluminum alloy product according to claim 9, which is substantially free of Ag. Aluminum alloy product according to one or more of the preceding claims, wherein the product is in T3x, T6x or T8x tempering. Aluminum alloy product according to one or more of the preceding claims, wherein the product is in the form of a sheet, plate, forged or extruded for use in an aerospace structure. Aluminum alloy product according to one or more of the preceding claims, wherein the product is in the form of a plate having a thickness in the range of 0.7 to 80 mm. A method for the manufacture of an aluminum alloy product having high strength and high fracture toughness and high resistance to intergranular corrosion comprising the steps of: a. shaping an ingot having an alloy composition as defined in one or more of claims 1 to 10; homogenize and / or preheat the ingot after casting c. hot working the ingot for a pre-worked product by one or more methods selected from the group consisting of mining, extrusion and forging d. optionally reheating the pre-worked product, ee. working hotter optionally and / or working cold for a desired workpiece shape; heat treat by solubilizing said shaped workpiece at a temperature and time sufficient to invert substantially all soluble constituents in the alloy for solid solutions; tempering the heat treated workpiece by solubilization by spray quenching or water quenching or other quenching means; optionally stretching or compressing the tempered workpiece; naturally or artificially aging the tempered and optionally stretched or compressed workpiece to achieve the desired temperature. A method according to claim 14, wherein the aluminum alloy product is aged to a tempering selected from the group comprising T3, T351, T39, T6, T651 and T87. A method of manufacture according to claim 14 or -15, wherein the aluminum alloy product is processed to fuselage sheet. A method of manufacture according to any one of claims 14 to 16, wherein the aluminum alloy product is processed to the fuselage sheet having a thickness of less than 30 mm. A manufacturing method according to any one of claims 14 to 16, wherein the aluminum alloy product is processed to the lower wing plate. A method of manufacture according to any one of claims 14 to 16, wherein the aluminum alloy product is processed to the upper wing plate. A method of manufacture according to any one of claims 14 to 16, wherein the aluminum alloy product is processed into an extruded product. A method of manufacture according to any one of claims 14 to 16, wherein the aluminum alloy product is processed into a forged product. A method of manufacture according to any one of claims 14 to 16, wherein the aluminum alloy product is processed to a thin plate having a thickness in the range of 15 to 40 mm. A method of manufacture according to any one of claims 14 to 16, wherein the aluminum alloy product is processed to a thick plate having a thickness of up to 300 mm.