JP2006522872A - High strength Al-Zn alloy and method for producing such an alloy product - Google Patents

Abstract

The present invention relates to high-strength Al-Zn alloy products having a combination of improved corrosion resistance and toughness, the alloy being substantially (by weight) Zn 6.0-9.5, Cu 1.3-2.4. Mg1.5-2.6, Mn and Zr <0.25, preferably 0.05-0.15 for high Zn content, less than 0.05 each for other elements, 0.25 in total Less than, with the balance being aluminum, in which case 0.1% [Cu] +1.3 <[Mg] <0.2 [Cu] +2.15, preferably 0.2% [Cu] +1.3 <[Mg] <0.1 [Cu] +2.15. The invention also relates to a method of manufacturing these alloy products and some preferred applications thereof, for example upper wing applications in aerospace.

Description

Field of Invention

  The present invention provides a forged high-strength Al-Zn alloy having a combination of improved corrosion resistance and toughness according to claim 1, and having an improved combination of corrosion resistance and toughness according to claim 9. The present invention relates to a method for producing a forged high-strength Al-Zn alloy and, if desired, a plate product of such an alloy produced by the method. More particularly, the present invention relates to a forged high-strength Al—Zn alloy, referred to as the AA7000 series in the International Association of Aluminum Association for Structural Aviation Applications. More particularly, the present invention relates to a novel chemistry window that does not require special aging or tempering to obtain an Al-Zn alloy with an improved combination of strength, toughness and corrosion resistance.

  It is known in the art to use heat treatable aluminum alloys for many applications involving relatively high strength, high toughness and corrosion resistance, such as aircraft fuselage, vehicle components, and other applications. Aluminum alloys AA7050 and AA7150 exhibit high strength with T6 tempering (see US Pat. No. 6,315,842). The precipitation-hardened AA7x75 and AA7x55 alloy products also show high strength values by T6 tempering. T6 tempering is known to increase the strength of alloys, where the above AA7x50, AA7x75 and AA7x55 alloy products containing large amounts of zinc, copper and magnesium have a high strength-to-weight ratio. And is therefore used especially in the aircraft industry. However, as these applications are exposed to a wide variety of weather conditions, the work and aging conditions need to be carefully managed to provide sufficient strength and resistance to corrosion, including both stress corrosion and delamination.

  It is known to artificially overage these AA7000 series aluminum alloys to increase resistance to stress corrosion and delamination and fracture toughness. When artificially aged to T79, T76, T74 or T73 type tempering, their resistance to stress corrosion, exfoliation corrosion and fracture toughness are improved in the above order, but at a cost / strength compared to T6 tempering conditions. (T73 is the best and T79 is close to T6). A reasonable tempering condition is T74 type tempering, which is a limited overaging between T73 and T76 to obtain reasonable levels of tensile strength, stress corrosion resistance, exfoliation corrosion resistance and fracture toughness. . Such T74 tempering is performed by overaging the aluminum product at a temperature of 121 ° C. for 6-24 hours and at 171 ° C. for about 14 hours.

  Depending on the design criteria for a particular aircraft component, even minor improvements in strength, toughness or corrosion resistance can reduce weight and lead to improved fuel economy over the entire useful life of the aircraft. Other 7000 series alloys have been developed to meet these requirements.

EP 037779 is a method for the production of sheet or sheet applications with high toughness and good corrosion properties, for example upper wing members, in the aerospace field, Zn 7.6-8.4% by weight.
Cu 2.2-2.6
Mg 1.8-2.1,
And Zr 0.5-0.2
Mn 0.05-0.4
V 0.03-0.2
Hf 0.03-0.5
One or more elements selected from the above (the total of these elements does not exceed 0.6% by weight), the process of processing a substrate having a composition comprising aluminum constituting the remaining part and inevitable impurities, Heat treatment and quenching step, and the product is sequentially heat-treated three times at one or more temperatures from 79 ° C. to 163 ° C. Disclosed is a method comprising the step of subjecting to artificial aging by heating above or heating the product to one or more temperatures between 148 ° C and 174 ° C. These products exhibit improved exfoliation corrosion resistance, “EB” or better, and about 15% greater yield strength than similarly sized AA7 × 50 products in T76 tempering conditions. These products also exhibit a strength that is at least about 5% greater than similarly sized 7x50-T77 products (AA7150-T77 is used below as a reference alloy).

  U.S. Pat. No. 5,312,498 provides a method for producing aluminum-based alloy products having improved levels of peel resistance and fracture toughness and balanced zinc, copper and magnesium levels so that there is no excess copper and magnesium. Is disclosed. In this method for producing an aluminum-based alloy product, one or two aging treatments are performed, and copper, magnesium and zinc are stoichiometrically balanced. In the disclosed two-step aging sequence, the alloy is first aged at about 121 ° C. for about 9 hours, followed by a second aging step at about 157 ° C. for about 10-16 hours, followed by air cooling. Such an aging method is directed to a thin plate or sheet used for a lower wing skin or for a body skin.

U.S. Pat. No. 4,954,188 discloses the following alloying elements: Zn 5.9-8.2% by weight.
Cu 1.5-3.0
Mg 1.5-4.0
Cr <0.04
Using an alloy consisting of other elements less than a total of 0.5, such as zirconium, manganese, iron, silicon and titanium, and the rest of aluminum, processing the alloy into a product of a predetermined shape; The molded product is subjected to solution heat treatment, quenched, and subjected to aging at a temperature of 132 ° C. to 140 ° C. for 6 to 30 hours. A method for producing a strength aluminum alloy is disclosed. The desired properties of high strength, high toughness and high corrosion resistance make this alloy high in aging temperature as previously disclosed, for example, by US Pat. Nos. 3,881,966 or 3,794,531. It was achieved by lowering rather than doing it.

  Known precipitation hardened aluminum alloys AA7075 and other AA7000 series alloys are reported to fail to provide sufficient corrosion resistance under certain conditions under T6 tempering conditions. However, T7 tempering, which improves the resistance to stress corrosion cracking of the alloy, greatly reduces the strength compared to the T6 condition.

  Thus, U.S. Pat. No. 5,221,377 is substantially about 7.6-8.4 wt.% Zn, about 1.8-2.2 wt.% Mg and about 2.0-2.6. An alloy product comprising weight percent Cu is disclosed. Such an alloy product exhibits a yield strength about 10% higher than its 7x50-T6 product with good toughness and corrosion resistance. This yield strength is reported to exceed 579 MPa and the peel resistance (EXCO) level is “EC” or better.

  U.S. Pat. No. 5,496,426 is an alloy as disclosed in U.S. Pat. No. 5,221,377, and the hot rolling, annealing and cold shrinkage ranges are preferably within 20% to 70%. Disclosed is a method of making an alloy that includes some cold rolling, followed by preferably controlled annealing, which exhibits properties superior to the AA7075-T6 properties. AA7075-T6 fails the stress corrosion resistance test (SCC resistance 40 days in 35% NaCl alternating immersion test) at 138 MPa, but the disclosed processed alloy has a SCC resistance of 241 MPa.

  U.S. Pat. Nos. 5,108,520 and 4,477,292 describe (1) that alloys are substantially below peak yield strength at one or more temperatures significantly above room temperature but below 163 ° C. Aging, (2) subsequently aging the alloy at one or more temperatures of about 190 ° C. to increase the corrosion resistance of the alloy, and (3) the alloy is significantly above room temperature but below 163 ° C. Disclosed is a solution heat treatment aging method for precipitation hardened alloys, including a three-step aging comprising aging at one or more temperatures to increase yield strength. The resulting product showed good strength properties and good corrosion performance. However, the three-step aging procedure is labor intensive and difficult to perform, increasing the manufacturing cost of such alloys.

Detailed description of the invention

  Accordingly, an object of the present invention is to provide an improved Al-Zn alloy having high strength and improved balance between toughness and corrosion performance, preferably for plate products. More particularly, it is an object of the present invention to provide an alloy with improved compressive yield strength that can be used for upper wing applications in aerospace and has properties superior to those of conventional AA7055 alloys in T77 tempering. is there.

  Another object of the present invention is to obtain an AA7000 series aluminum alloy that exhibits strength in the range of T6 type temper and toughness and corrosion resistance in the range of T73 type temper.

  Yet another object of the present invention is to provide an alloy that can be used in an aging-creep forming process and does not require complicated and time-consuming aging treatments.

  The present invention has many preferred purposes.

  The above object of the invention can be achieved by using the features of claim 1. Other preferred embodiments are described and defined in the dependent claims. A preferred method for producing such an alloy is defined in claim 9 and each plate product is claimed and described in claim 14 and the corresponding dependent claims.

  As noted below, unless otherwise indicated, the names of alloys and tempered names are from the Aluminum Association name in the Aluminum Standards and Data and the Regislation Records published by the US Aluminum Association. All percentages are by weight unless otherwise indicated.

The above objective of the present invention is achieved by using a high strength Al-Zn alloy product having an improved combination of corrosion resistance and toughness, the alloy being substantially (in weight percent).
Zn about 6.0 to 9.5
Cu about 1.3 to 2.4
Mg about 1.5 to 2.6
Mn <0.12
Zr <0.20, preferably 0.05-0.15
Cr <0.10
Fe <0.25, preferably <0.12
Si <0.25, preferably <0.12
Ti <0.10
Hf and / or V <0.25, and optionally Ce and / or Sc <0.20, in particular 0.05 to 0.15,
Comprising a plurality of other elements each less than 0.05 and less than 0.25 in total, the balance aluminum (in weight percent)
0.1 [Cu] +1.3 <[Mg] <0.2 [Cu] +2.15,
Preferably 0.2 [Cu] +1.3 <[Mg] <0.1 [Cu] +2.15
It is.

  Such component ranges for AA7000 series alloys exhibit excellent properties when manufactured into thin plate products that can preferably be used in aerospace upper wing applications.

  The alloys defined above have the same or better properties as the existing AA7x50 or AA7x55 series alloys in T77 tempering without using the complex T77 aging cycle described above. Aluminum products obtained from this chemical composition are not only excellent in terms of cost, but are also easy to manufacture because they require fewer processing steps. In addition, this chemical composition allows for novel manufacturing techniques that are not applicable when using T77 tempered alloys, such as age creep forming. The chemical composition defined above can also be aged in T77 tempering, in which case the corrosion resistance is further improved as compared to the two-step aging process, and in particular the exfoliation corrosion performance is enhanced. .

  The selected range of elements using a large amount of Zn and a special range of Mg and Cu combinations of the present invention will greatly enhance strength, toughness and corrosion performance, such as exfoliation corrosion resistance and stress corrosion cracking resistance. It has been found that an excellent combination is obtained.

  It has been reported that copper content should be kept high to improve exfoliation and stress corrosion cracking performance, while a better combination of strength and density is achieved with relatively low zinc content It has been reported that it can be done.

  However, according to the present invention, by increasing the amount of zinc and optimizing the ratio of magnesium to copper, it has better strength while maintaining good corrosion performance and better toughness than conventional T77 tempered alloys. Was found to be obtained. Accordingly, the combined content of zinc, magnesium and copper is within the range of about 11.50 to 12.50 (wt%) when no manganese is contained, preferably 0.06 to 0.12 (wt%). ) Is advantageously less than 11.00 in the presence of manganese.

  The preferred amount of magnesium is 0.2 [Cu] +1.3 <[Mg] <0.1 [Cu] +2.15, most preferably 0.2 [Cu] +1.4 <[Mg] <0.1. [Cu] +1.9. The copper is about 1.5 to 2.1, more preferably less than 1.5 to 2.0. The balance of magnesium and copper is important for the chemistry of the present invention.

  Copper and magnesium are important elements for imparting strength to the alloy. If the amount of magnesium and copper is too low, the strength will decrease, and if the amount of magnesium and copper is too high, the corrosion performance will be poor and problems with the weldability of the alloy product will occur. The prior art uses small amounts of magnesium and copper to improve strength using special aging procedures and achieve good corrosion performance. It has been found that a good balance can be obtained with thick alloy products by adjusting the amount of copper and magnesium (wt%) to about 1.5-2.3 to balance strength, toughness and corrosion performance. However, since corrosion performance is an indispensable parameter for thin alloy products, it is necessary to reduce the amount of copper and magnesium used, thereby reducing strength. The chemical composition claimed in the present invention can achieve strength levels in the region of T6 tempered alloys while maintaining corrosion performance similar to that of T74 tempered alloys.

  Apart from the amount of magnesium and copper, the present invention discloses a balance of magnesium and copper to zinc, in particular the balance of magnesium to zinc, which gives the alloy these performance characteristics. The improved corrosion resistance of the alloys of the present invention has a peel resistance (“EXCO”) greater than EB, preferably greater than EA.

  These peel properties, along with the typical performance of T6, include the stress corrosion cracking ("SCC") and peel resistance ("SCC") resistance currently required for AA7075, AA7050 and AA7150 products aged to T73, T74 and T76 tempering. EXCO ")). To determine whether a commercially available alloy meets the SCC standard, a particular test sample is subjected to pre-defined test conditions. The rod-shaped sample is immersed in a 3.5% NaCl aqueous solution for 10 minutes, and then subjected to a cycle of air drying for 50 minutes while pulling from both ends with a constant strain (stress level). Such testing is typically performed for a minimum of 20 days (or a shorter time if the sample is broken or cracked before 20 days have passed). This test is the ASTM standard G47 (G47-98) test.

  Another preferred SCC test performed according to ASTM standard G47 (G38-73) is used for extruded alloy products including thin plate products. This test consists of compressing the opposite ends of the C-ring using a constant strain level and alternating dipping conditions substantially similar to those described above. AA7075, AA7050 or AA7150-T6 tempered alloys fail the SCC test in less than 20 days, the peel properties are EC or ED, and the corrosion resistance is improved by tempering T76-, T74-, T73. The peel properties of T73 are EA or better. Specific examples are described below.

  The alloy of the present invention has a preferred amount of magnesium and copper of about 1.93 when the amount of zinc (wt%) is about 8.1. However, when manganese is less than 0.05, preferably less than 0.02, the amount (wt%) of zinc is 6.1-8.3, more preferably 6.1-7.0. Some preferred embodiments of the present invention are illustrated in the following examples.

  When the amount of zinc (wt%) is greater than about 7.6, the amount of magnesium is preferably about 0.06-0.12. Manganese contributes to or facilitates grain size adjustment during operations that can cause recrystallization of the alloy microstructure. The preferred manganese level is lower than in conventional AA7000 series alloys, but can be increased if more zinc is used.

  The amount of additional alloying element Ce and / or Sc is less than 0.20, preferably 0.05 to 0.15, most preferably about 0.10.

A preferred method for producing a high strength Al-Zn alloy product having a combination of improved corrosion resistance and toughness is:
a) The following composition (in weight percent): Zn about 6.0 to 9.5
Cu about 1.3 to 2.4
Mg about 1.5 to 2.6
Mn <0.12
Zr <0.20, preferably 0.05-0.15
Cr <0.10
Fe <0.25
Si <0.25
Ti <0.10
Hf and / or V <0.25, optionally Ce and / or Sc <0.20
A plurality of other elements each less than 0.05 and in total less than 0.25, with the balance aluminum composition (in weight percent)
0.1 [Cu] +1.3 <[Mg] <0.2 [Cu] +2.15
A process of casting an ingot,
b) homogenizing and / or preheating the ingot after casting;
c) a step of hot-working the ingot, cold-working if desired, and forming a processed product;
d) a solution heat treatment for a sufficient time at a temperature sufficient to bring substantially all of the soluble constituents in the alloy into solid solution; and e) the solution heat treated product is water or other rapid cooling. Using a medium and comprising quenching by either spray quenching or immersion quenching.

  The properties of the present invention can be further achieved by a preferred method including artificially aging processed, solution heat treated products, wherein the aging treatment step is performed at a temperature of 105 ° C to 135 ° C, Preferably, the first heat treatment is carried out at about 120 ° C. for 2 to 20 hours, preferably about 8 hours, and the temperature is higher than 135 ° C. but less than 210 ° C., preferably about 155 ° C. Second heat treatment.

  Through such a two-step aging treatment, a corrosion performance equivalent to that of the T76 tempered alloy is achieved. However, the processed and heat-treated product can also be artificially aged, and in this case, the aging treatment is performed at a temperature of 105 ° C. to 135 ° C. for more than 20 hours and less than 30 hours. Comprising. This T77 tempering aging procedure is well known and further improves performance characteristics compared to a two-step aging procedure. However, the two-step aging procedure results in a thin aluminum alloy product that is partially comparable to and partially superior to the T77 tempered product.

  Furthermore, the processed and heat-treated product can be artificially aged to T79- or T76-temper in a two-step aging procedure. After homogenizing and / or preheating the ingot after casting, the ingot is preferably hot worked, and if desired, the hot worked product is cold worked into a 15 mm to 45 mm processed product to obtain a thin plate Can be recommended.

  Such a plate product of high strength Al-Zn alloy can be obtained by an alloy having the above composition or manufactured by the above method. Such plate products can preferably be used as thin aircraft members, more preferably as elongated structural shaped members. Further preferred are plate products for use as upper wing members, preferably aircraft upper wings or stringer thin skin members.

  The above and other features and advantages of the alloys of the present invention can be readily understood from the following detailed description of the preferred embodiments.

Example 1
A test was performed comparing the alloy of the present invention and the AA7150-T77 alloy. It has been found that the example alloy of the present invention is an improvement over the conventional AA7150-T77 tempered alloy.

  On an industrial scale, four different aluminum alloys were cast into ingots, homogenized, preheated at 410 ° C. for over 6 hours, and hot rolled into 30 mm plates. Thereafter, the plate was solution heat treated at 475 ° C. and quenched with water. Thereafter, the rapidly cooled product was subjected to an aging treatment by a two-step T79-T76 aging treatment procedure. The chemical composition is shown in Table 1.

Table 1
Chemical composition of thin plate alloy (wt%), the rest is aluminum and inevitable impurities, alloys 1-4 are Mn ≦ 0.02

SiFeCuMnMgCrZnTiZr
Alloy 1 0.03 0.06 2.23 0.00 2.08 0.00 6.24 0.03 0.10
(7050)
Alloy 2 0.05 0.08 2.05 0.01 2.04 0.01 6.18 0.04 0.11
Alloy 3 0.05 0.09 2.20 0.01 2.30 0.01 7.03 0.04 0.10
Alloy 4 0.04 0.07 1.91 0.02 2.13 0.00 6.94 0.03 0.11

  The aged alloy was then tested under the following test conditions.

  Tensile yield strength is measured according to EN10.002, peel resistance ("EXCO") is measured according to ASTM G-34-97, and stress corrosion cracking ("SCC") is all in the ST direction, ASTM G-47. The Kahn-tear (toughness) was measured by ASTM E-399, and the compressive yield strength (“CYS”) was measured by ASTM E-9.

  Table 2a shows the results of T79-T76 aging plate products of the four types of alloys shown in Table 1 in comparison with the conventional AA7150-T77 tempered alloy, and Table 2b shows the conventional AA7150-T76 / T74. / T6 compared with tempered alloy.

Table 2a
Overview of strength and toughness of alloys (30 mm plate) in Table 1 compared to three reference alloys (AA7150-T77), Alloys 1-4 are aged to T79-T76

Rp-L CYS-LT EXCO K _1C -LT
(MPa) (MPa) (MPa√m)
Alloy 1 555 565 EC 35.1
Alloy 2 561 604 EA / B 34.5
Alloy 3 565 590 EB 29.1
Alloy 4 591 632 EB 28.9
AA7150-T77 586-EB 28.6
AA7150-T77 579-EB 29.2
AA7150-T77 537-EA 33.2
NF = no damage after 40 days

Table 2b
An overview of the corrosion performance of the alloys (30 mm plate) in Table 1 compared to three reference alloys (AA7150-T76, AA7150-T74, AA7150-T6), Alloys 1-4 are aged to T79-T76

SCC threshold
Alloy 1 NF at 172 MPa
Alloy 2 NF at 240 MPa
Alloy 3 NF at 240 MPa
Alloy 4 NF at 240 MPa
AA7150-T76 117-172 MPa
AA7150-T74 240 MPa
AA7150-T6 <48MPa
NF = no damage after 40 days

  As can be seen from Tables 2a, b, Alloys 1, 2 and 4 show better strength / toughness combinations. Alloys 2, 3 and 4 all have reasonable EXCO performance, and Alloys 2, 3 and 4 are alloy no. 1 (AA 7050 alloy) has a significantly higher pressure yield strength. Alloys 2 and 4 exhibit a property balance that is very suitable for upper wing applications in aerospace, and a property balance superior to that of the conventional 7150-T77 alloy. However, as shown in Table 3, it is also possible to use T77 tempering for the alloys of the present invention.

Table 3
Overview of alloys 2 and 4 tempered under T77 tempering conditions, strength, toughness and corrosion performance

Rp-L CYS-LT EXCO K _1C -LT SCC threshold
(MPa) (MPa) (MPa√m)
Alloy 2 585 613 EA 32.2 NF at 240MPa
Alloy 4 607 641 EA 26.4 NF at 240MPa

  Promising alloy no. 4 where a sample of Alloy 4 was prepared according to the procedure described in ASTM G-47-98 (a standard test method for measuring the susceptibility of AA7000 series aluminum alloy products to stress corrosion cracking). Corrosivity as defined and prepared according to ASTM G-44-94 (alternating immersion according to standard methods for assessing stress corrosion cracking resistance of metals and alloys by alternating immersion in 3.5% NaCl solution) Exposed to the atmosphere.

  As shown in Table 4, four stress levels were selected for the alloy 4 samples. For each stress level, three samples were exposed to the test environment (ASTM G-44). One was removed after one week and the other two were exposed for 40 days. When no cracks occurred during exposure, the tensile properties were measured as shown in Table 4.

Table 4
The tensile strength characteristics and prestress of sample 4 after exposure to four different stress levels were acting in the LT direction.

Alloy 4 prestress tensile strength [MPa]
[MPa] 1 week 40 days
300 524.3 428.0
340 513.1 416.9
380 503.1 424.5
420 515.5 425.1

  As can be seen from FIG. 4, no decrease in residual strength with increasing load was measured, ie, as far as tensile strength properties were concerned, no measurable stress corrosion appeared after 40 days.

Example 2
Where higher strength levels are required and toughness is less important, conventional AA7055-T77 alloy is preferred for upper wing applications instead of AA7150-T77 alloy. Accordingly, the present invention discloses optimal copper and magnesium ranges that exhibit properties that are equal to or better than conventional AA7055-T77 alloys.

  Eleven different aluminum alloys having chemical compositions as shown in Table 5 were cast into ingots.

Table 5
The chemical composition (% by weight) of 11 types of alloys, the remainder being aluminum and inevitable impurities, Zr = 0.08, Si = 0.05, Fe = 0.08.

Alloy Cu Mg Mg Zn Mn
1 2.40 2.20 8.2 0.00
2 1.94 2.33 8.2 0.00
3 1.26 2.32 8.1 0.00
4 2.36 1.94 8.1 0.00
5 1.94 1.92 8.1 0.00
6 1.30 2.09 8.2 0.00
7 1.92 1.54 8.1 0.00
8 1.27 1.57 8.1 0.00
9 2.34 2.25 8.1 0.07
10 2.38 2.09 8.1 0.00
11 2.35 1.53 8.2 0.00

  Strength and toughness were measured after pre-heating the cast alloy at 410 ° C. for 6 hours and then hot rolling the alloy to 28 mm gauge. Thereafter, solution heat treatment was performed at 475 ° C. and quenched with water. The aging treatment was performed at 120 ° C. for 8 hours and at 155 ° C. for 8 to 10 hours (T79-T76 tempering). The results are shown in Table 6.

Table 6
An overview of the strength and toughness of the 11 alloys shown in Table 5 in the specified direction.

Rp Rm Kq
Alloy L LT L LT L-T
1 628 596 651 633 28.9
2 614 561 642 604 29.3
3 566 544 596 582 39.0
4 614 568 638 604 33.0
5 595 556 620 590 37.1
6 562 513 590 552 38.6
7 549 509 573 542 41.7
8 530 484 556 522 41.9
9 628 584 644 618 26.6
10 614 575 631 606 28.1
11 568 529 594 568 36.6

Alloys 3-8 and 11 showed good toughness, while alloys 1-5, 9 and 10 showed good strength properties. Therefore, Alloys 3, 4 and 5 show a good balance between strength and toughness, so that when zinc is present in an amount of 8.1, the copper content exceeds 1.3 and the magnesium content is 1.6. It is clear that it exceeds (in weight percent). Such an amount is the lower limit of the copper and magnesium ranges. As can be seen from Table 6, if the copper and magnesium levels are too high (alloys 1, 2, 9 and 10), the toughness drops to an unacceptably low level.

Example 3
The effect of manganese on the properties of the alloy of the present invention was investigated. The optimum manganese level was found to be 0.05 to 0.12 for alloys with high zinc content. These results are shown in Tables 7 and 8. All chemical properties and processing parameters not listed are equivalent to those of Example 2.

Table 7
Chemical composition (% by weight) of three types of alloys (Mn-0, Mn-1 and Mn-2), the rest being aluminum and inevitable impurities, Zr = 0.08, Si = 0.05, Fe = 0.08

Alloy Cu Mg Mg Zn Mn
Mn-0 1.94 2.33 8.2 0.00
Mn-1 1.94 2.27 8.1 0.06
Mn-2 1.96 2.29 8.2 0.12

Table 8
An overview of strength and toughness in the specified direction for the three alloys shown in Table 7.

Alloy Rp Rm Kq
L LT L LT L-T
Mn-0 614 561 642 604 29.3
Mn-1 612 562 635 602 31.9
Mn-2 612 560 639 596 29.9

  As shown in Table 8, as the strength properties increase, the toughness decreases. For alloys with a high zinc content, the optimum manganese level is 0.05 to 0.12.

Example 4
Where higher strength levels are required and toughness is less important, the conventional AA7055-T77 alloy is preferred as the alloy for upper wing applications instead of the AA7150-T77 alloy. Thus, the present invention discloses an optimal range of copper and magnesium that exhibits properties that are equal to or better than conventional AA7055-T77 alloys.

  Two different aluminum alloys were cast into ingots having the chemical compositions shown in Table 9.

Table 9
Chemical composition of 3 types of alloys (% by weight), the rest are aluminum and inevitable impurities, Zr = 0.08, Si = 0.05, Fe = 0.08, (Ref = AA7055 alloy)

Alloy Si Fe Cu Cu Mn Mg Cr Zn Ti Zr
1 0.05 0.09 2.24 0.01 2.37 0.01 7.89 0.04 0.10
2 0.04 0.07 1.82 0.08 2.18 0.00 8.04 0.03 0.10
Ref. 2.1- 1.8- 7.6-
2.6 2.2 8.4

  Alloys 1 and 2 were tested for their strength properties. These characteristics are shown in Table 10. Alloy 2 was tempered under two tempering conditions (T79-T76 and T77). Reference alloy AA7055 is measured by T77 tempering (M-Ref) and also shows technical data of AA7055 reference alloy in T77 tempering (by Ref).

Table 10
The alloy nos. 2 is an overview of strength under two tempering conditions, a standard alloy (AA7055) measurement (M-Ref), and a technical sheet (Ref).

Alloy Tempering Rp-L Rp-LT Rp-ST Rm-L Rm-LT Rm-ST
1 T79-T76 604 593 559 634 631 613
2 T79-T76 612 598 571 645 634 618
2 T77 619 606 569 640 631 610
Ref T77 614 614-634 641-
M-Ref T77 621 611 537 638 634 599

  Table 11 shows the toughness in the LT and TL directions and the compressive yield strength and corrosion performance characteristics in the L and LT directions.

Table 11
The toughness and CYS properties of the two alloys of the present invention shown in Table 9 in different tempering conditions and in different test directions, NF = no damage after 40 days at the specified stress level, others indicate the day the sample broke .

Alloy Tempering K _IC K _IC CYS-L CYS-LT EXCO SCC
(LT) (TL)
1 T79-T76 21.0-596 621 EC 2,3,8
2 T79-T76 28.9 27.1 630 660 EB at 172MPa
NF
2 T77 28.8 26.5 628 656 EA at 210MPa
NF
Ref T77 28.6 26.4 621 648 EB at 103MPa
NF
M-Ref T77----EB 103MPa
NF

  The alloy of the present invention has tensile properties equivalent to the conventional AA7055-T77 alloy. However, the characteristics in the ST direction are superior to those of the conventional AA7055-T77 alloy. Stress corrosion performance is also superior to AA055-T77 alloy. Therefore, the alloy of the present invention can be used as an inexpensive alternative to the AA7055-T77 tempered alloy, and can also be used for aging creep forming, showing excellent compressive yield strength and corrosion resistance.

  Although the present invention has been fully described above, many variations and modifications can be made without departing from the spirit or scope of the invention described herein, as will be apparent to those skilled in the art. The invention is defined by the appended claims.

Claims (30)

A forged high-strength Al-Zn alloy product having a combination of improved corrosion resistance and toughness, substantially (in weight percent)
Zn 6.0-9.5
Cu 1.3-2.4
Mg 1.5-2.6
Mn <0.12
Zr <0.20
Cr <0.10
Fe <0.25
Si <0.25
Ti <0.10
Hf and / or V <0.25,
Ce and / or Sc <0.20 as desired
Comprising a plurality of other elements each less than 0.05 and less than 0.25 in total, the balance aluminum (in weight percent)
0.1 [Cu] +1.3 <[Mg] <0.2 [Cu] +2.15
Is an alloy. The amount of Mg (wt%)
0.2 [Cu] +1.3 <[Mg] <0.1 [Cu] +2.15
The alloy of claim 1 in the range of The amount of Mg (wt%)
0.2 [Cu] +1.4 <[Mg] <0.1 [Cu] +1.9
The alloy of claim 1 in the range of   The alloy of claim 1, wherein the alloy product has EB or better exfoliation corrosion resistance (“EXCO”).   The alloy of claim 1, wherein the alloy product has EA or better exfoliation corrosion resistance (“EXCO”).   The alloy according to claim 1, wherein the amount (% by weight) of Cu is 1.5 to 2.1.   The alloy according to claim 1, wherein the amount (% by weight) of Cu is 1.5 to 2.0.   The alloy according to claim 1, wherein the amount (% by weight) of Zr is 0.05 to 0.15.   The alloy of claim 1 wherein the amount of Mg and Cu (wt%) is about 1.93 when the amount of Zn (wt%) is about 8.1.   The alloy according to claim 1, wherein when Mn is less than 0.05, the amount (wt%) of Zn is 6.1-8.3, preferably 6.1-7.0.   The alloy according to claim 1, wherein when Mn is less than 0.02, the amount (wt%) of Zn is 6.1-8.3, preferably 6.1-7.0.   The alloy according to claim 1, wherein when the amount (wt%) of Zn exceeds 7.6, the amount (wt%) of Mn is 0.06 to 0.12.   The alloy according to claim 1, wherein the amount (% by weight) of Fe is less than 0.12.   The alloy according to claim 1, wherein the amount (wt%) of Si is less than 0.12.   The alloy of claim 1, wherein the alloy is artificially aged to T79 or T76 temper in a two-step aging procedure.   The two-step aging treatment procedure comprises a first heat treatment at a temperature of 105 ° C to 135 ° C for 2 to 20 hours and a second heat treatment at a temperature higher than 135 ° C but less than 210 ° C for 4 to 12 hours. 15. The alloy according to 15.   The alloy of claim 1, wherein the product is a plate product.   The alloy according to claim 1, wherein the product is a plate product having a thickness of 15 to 45 mm.   The alloy of claim 18, wherein the plate product is a thin aircraft member.   The alloy of claim 18, wherein the plate product is an elongated structurally shaped aircraft member.   The alloy of claim 18, wherein the plate product is an aircraft upper wing member.   The alloy of claim 18, wherein the plate product is a thin skin member of an aircraft upper wing.   The alloy of claim 18, wherein the plate product is an aircraft stringer.   The alloy of claim 18, wherein the plate product is an aircraft upper wing stringer. A method for producing a forged high-strength Al-Zn alloy product having improved corrosion resistance and toughness combination according to claim 1 comprising:
a) The following composition (in wt%): Zn 6.0-9.5
Cu 1.3-2.4
Mg 1.5-2.6
Mn <0.12
Zr <0.20, preferably 0.05-0.15
Cr <0.10
Fe <0.25
Si <0.25
Ti <0.10
Hf and / or V <0.25, optionally Ce and / or Sc <0.20
A plurality of other elements each less than 0.05 and in total less than 0.25, with the balance aluminum composition (in weight percent)
0.1 [Cu] +1.3 <[Mg] <0.2 [Cu] +2.15
A process of casting an ingot,
b) a step of homogenizing and / or preheating the ingot after casting;
c) Hot working the ingot, cold working as desired to form a processed product;
d) a solution heat treatment step; and e) a step of rapidly cooling the solution heat treated product.   The processed, solution heat-treated product is artificially aged, and the aging treatment step is a first heat treatment at a temperature of 105 ° C. to 135 ° C. for 2 to 20 hours, and higher than 135 ° C. but less than 210 ° C. 25. The method of claim 24, comprising a second heat treatment at a temperature for 4-12 hours.   26. Artificial aging treatment of the processed, solution heat treated product, wherein the aging treatment step comprises a third heat treatment at a temperature of 105 ° C. to 135 ° C. for more than 20 hours and less than 30 hours. The method described in 1.   The processed, solution heat-treated product is artificially aged, and the aging treatment step is a first heat treatment at a temperature of 105 ° C. to 135 ° C. for 2 to 20 hours, and higher than 135 ° C. but less than 210 ° C. 26. The method of claim 25, comprising a second heat treatment at temperature for 4-12 hours.   25. The method of claim 24, wherein the processed solution heat treated product is artificially aged to T79 or T76 temper in a two-step aging procedure.   25. The method of claim 24, wherein after the casting ingot is homogenized and / or preheated, the ingot is hot worked and optionally cold worked into a 15 mm to 45 mm thick work product.