Al—Zn—Mg—Cu alloy with improved damage tolerance-strength combination properties

Abstract

An AlZnMgCu alloy with improved damage tolerance-strength combination properties. The present invention relates to an aluminum alloy product comprising or consisting essentially of, in weight %, about 6.5 to 9.5 zinc (Zn), about 1.2 to 2.2% magnesium (Mg), about 1.0 to 1.9% copper (Cu), preferable (0.9 Mg0.6)Cu(0.9 Mg+0.05), about 0 to 0.5% zirconium (Zr), about 0 to 0.7% scandium (Sc), about 0 to 0.4% chromium (Cr), about 0 to 0.3% hafnium (Hf), about 0 to 0.4% titanium (Ti), about 0 to 0.8% manganese (Mn), the balance being aluminum (Al) and other incidental elements. The invention relates also to a method of manufacturing such as alloy.

Claims

1. Method of producing a high-strength, high-toughness AA7xxx-series alloy product having a good corrosion resistance, comprising the processing steps of: a) casting an ingot having a composition comprising, in wt. %: Zn 6.9 to 7.9 Mg 1.4 to 2.1 Cu 1.43 to 1.90 Zr up to 0.15 Ti<0.05 Fe<0.05 Si<0.07 Mn 0.15 to 0.30, Cr 0.15 to 0.20 and other impurities or incidental elements each <0.05, total <0.15, and the balance being aluminium; b) homogenizing the ingot after casting in a range of 460 C. to 490 C., then cooling the homogenized ingot, and then homogenizing the cooled ingot to a temperature in a range of 460 C. to 490 C.; c) hot working the homogenized ingot by hot rolling to a desired workpiece form, wherein said hot working the homogenized ingot is by said hot rolling with an absence of forging and an absence of extrusion; d) solution heat treating said formed workpiece at a temperature and time sufficient to place into solid solution essentially all soluble constituents in the alloy; e) quenching the solution heat treated workpiece by one of spray quenching or immersion quenching in water or other quenching media; f) stretching of the quenched workpiece at most 8%; i) artificially ageing the quenched and stretched workpiece in a two step ageing procedure to achieve a temper selected from the group consisting of T74, T76, T751, T7451, T7651, T77 and T79, wherein the artificial ageing comprises a first ageing step at a temperature in a range of 105 C. to 135 C. for 2 to 20 hours and a second ageing step at a temperature in a range of 135 C. to 210 C. for 4 to 20 hours, wherein the product has a thickness of 2.5 to 11 inches.

2. The method according to claim 1, wherein the alloy has 7.2 to 7.9% Zn, 1.4 to 1.90% Mg, 1.43 to 1.80% Cu, and 0.15-0.20% Cr.

3. The method according to claim 2, wherein the Zr-content in the ingot is 0.06 to 0.15%.

4. The method according to claim 2, wherein the alloy Ti-content is in a range of 0.03-0.05%.

5. The method according to claim 2, wherein the alloy product is artificially aged to a T74 or T76 temper.

6. The method according to claim 5, wherein the alloy has 0.04 to 0.11% Zr.

7. The method according to claim 2, wherein the alloy product is artificially aged to a T7451 or T7651 temper.

8. The method according to claim 2, wherein the Zn-content in the ingot is in a range of 7.2 to 7.7%.

9. The method according to claim 8, wherein the Zn-content in the ingot is in a range of 7.43% to 7.7%.

10. The method of according to claim 2, wherein the Zr-content in the ingot is 0.06 to 0.15%.

11. The method according to claim 2, wherein the alloy has 0.04 to 0.11% Zr.

12. The method according to claim 1, wherein the Zr-content in the ingot is at least 0.06 to 0.13%.

13. The method according to claim 1, wherein the Zr-content in the ingot is in a range of 0.04 to 0.15%.

14. The method according to claim 1, wherein the Zr-content in the ingot is in a range of 0.04 to 0.11%.

15. The method according to claim 1, wherein the product has an EXCO corrosion resistance of EB or better.

16. The method according to claim 1, wherein the product has an EXCO corrosion resistance of EA or better.

17. The method according to claim 1, wherein the method comprises: a) the casting of the ingot; b) the homogenizing of the cast ingot; c) the hot working of the homogenized ingot by hot rolling to a desired workpiece form; d) the solution heat treating of said workpiece at temperature in a range of 460 C. to 490 C. for time sufficient to place into solid solution essentially all soluble constituents in the alloy; e) the quenching of the solution heat treated workpiece by one of spray quenching or immersion quenching in water to a temperature lower than 95 C.; f) the stretching of the quenched workpiece about 1 to 3%; g) the artificially ageing of the quenched and stretched workpiece to achieve the temper.

18. The method according to claim 17, wherein the product has the following properties: exfoliation corrosion resistance (EXCO) when measured according to ASTM G34-97 is at least EA or better; tensile yield strength of at least 510 MPa, an ultimate strength of at least 560 MPa, a notch toughness of at least 1.5 and a UPE of at least 200 kJ/m.sup.2; wherein Mg/Zn is 0.27 or lower.

19. The method according to claim 1, wherein the ingot composition comprises, in wt. %: Zn 7.2 to 7.7 Mg 1.4 to 1.79 Cu 1.43 to 1.80 Zr 0.06 to 0.15 Ti<0.05 Fe<0.05 Si<0.07 Mn 0.15 to 0.30, Cr 0.15 to 0.20 and other impurities or incidental elements each <0.05, total <0.15, and the balance being aluminium.

20. The method according to claim 19, wherein the method comprises: a) the casting of the ingot; b) the homogenizing of the cast ingot; c) the hot working of the homogenized ingot by a first hot rolling into a pre-worked product; d) optionally the reheating of the pre-worked product, e) then hot working the pre-worked product by a second hot rolling to the desired workpiece form; f) the solution heat treating of said formed workpiece at temperature in a range of 460 C. to 490 C. for time sufficient to place into solid solution essentially all soluble constituents in the alloy; g) then quenching the solution heat treated workpiece with water; h) then cold stretching of the quenched workpiece about 1 to 3%; i) the artificially ageing of the quenched and stretched workpiece in the two step ageing procedure to achieve a desired temper, wherein the artificial ageing comprises a first ageing step at a temperature in a range of 105 C. to 135 C. for 2 to 20 hours and a second ageing step at a temperature in a range of 135 C. to 210 C. for 4 to 20 hours.

21. The method according to claim 20, wherein the product has the following properties: exfoliation corrosion resistance (EXCO) when measured according to ASTM G34-97 is at least EA or better; tensile yield strength of at least 472 MPa, an ultimate tensile strength of at least 512 MPa, inter-granular corrosion resistance of at most 70 m, and wherein Mg/Zn is 0.27 or lower.

22. The method according to claim 19, wherein first hot rolling hot rolls the pre-worked product in a first direction 90 to a second direction in which the second hot rolling hot works the pre-heated ingot.

23. The method of according to claim 19, wherein the Zr-content in the ingot is 0.06 to 0.13%.

24. The method of according to claim 23, wherein the Cu-content in the ingot is 1.52 to 1.80%.

25. The method according to claim 24, wherein the Zn-content in the ingot is 7.43 to 7.7%, the Mg-content in the ingot is 1.4 to 1.79%, the Mn-content in the ingot is 0.19 to 0.3%.

26. The method of according to claim 1, wherein the Cr-content in the ingot is 0.15%.

27. The method of according to claim 1, wherein the Cr-content in the ingot is 0.20%.

28. The method according to claim 1, wherein the ingot composition consists of, in wt. %: Zn 7.43 to 7.7 Mg 1.4 to 1.79 Cu 1.52 to 1.80 Zr 0.06 to 0.13 Ti 0.03-0.05 Fe<0.05 Si<0.07 Mn 0.19 to 0.30, Cr 0.15 to 0.20 and other impurities or incidental elements each <0.05, total <0.15, and the balance being aluminium, wherein the method consists of: a) the casting of the ingot; b) the homogenizing of the cast ingot in the range of 460 C. to 490 C., then cooling the homogenized ingot, and then homogenizing the cooled ingot to a temperature in a range of 460 C. to 490 C.; c) the hot working of the homogenized ingot by a first hot rolling into a pre-worked product; d) optionally the reheating of the pre-worked product, e) then hot working the pre-worked product by a second hot rolling to the desired workpiece form; f) the solution heat treating of said formed workpiece at temperature in a range of 460 C. to 490 C. for time sufficient to place into solid solution essentially all soluble constituents in the alloy; g) then quenching the solution heat treated workpiece with water; h) then cold stretching of the quenched workpiece about 1 to 3%; i) the artificially ageing of the quenched and stretched workpiece in the two step ageing procedure to achieve a desired temper, wherein the artificial ageing consists of a first ageing step at a temperature in a range of 105 C. to 135 C. for 2 to 20 hours and a second ageing step at a temperature in a range of 135 C. to 210 C. for 4 to 20 hours.

29. The method according to claim 28, wherein first hot rolling hot rolls the pre-worked product in a first direction 90 to a second direction in which the second hot rolling hot works the pre-heated ingot.

30. The method according to claim 29, wherein the product has the following properties: exfoliation corrosion resistance (EXCO) when measured according to ASTM G34-97 is at least EA or better; tensile yield strength of at least 472 MPa, an ultimate tensile strength of at least 512 MPa, inter-granular corrosion resistance of at most 70 m, and wherein Mg/Zn is 0.27 or lower.

31. The method of according to claim 28, wherein the Cr-content in the ingot is 0.15%.

32. The method of according to claim 28, wherein the Cr-content in the ingot is 0.20%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an MgCu diagram setting out the CuMg range for the alloy according to this invention, together with narrower preferred ranges;

(2) FIG. 2 is a diagram comparing the fracture toughness vs. the tensile yield strength for the alloy product according to the invention against several references;

(3) FIG. 3 is a diagram comparing the fracture toughness vs. the tensile yield strength for the alloy product according to this invention in a 30 mm gauge against two references;

(4) FIG. 4 is a diagram comparing the plane strain fracture toughness vs. the tensile yield strength for the alloy products according to the invention using different processing routes.

(5) FIG. 1 shows schematically the ranges for the Cu and Mg for the alloy according to the present invention in their preferred embodiments as set out in dependent claims 2 to 4. Also shown are two narrower more preferred ranges. The ranges can also be identified by using the corner-points A, B, C, D, E, and F of a hexagon box. Preferred ranges are identified by A to F, and more preferred ranges by A to F. The coordinates are listed in Table 1. In FIG. 1 also the alloy composition according to this invention as mentioned in the examples hereinafter are illustrated as individual points.

(6) TABLE-US-00001 TABLE 1 Coordinates (in wt. %) for the corner-points of the CuMg ranges for the preferred ranges of the alloy product according to the invention. (Mg, Cu) (Mg, Cu) (Mg, Cu) more Corner wide Corner preferred Corner preferred point range point range point range A 1.20, 1.00 A 1.40, 1.10 A 1.40, 1.10 B 1.20, 1.13 B 1.40, 1.26 B 1.40, 1.16 C 2.05, 1.90 C 2.05, 1.80 C 2.05, 1.75 D 2.20, 1.90 D 2.10, 1.80 D 2.10, 1.75 E 2.20, 1.40 E 2.10, 1.40 E 2.10, 1.40 F 1.77, 1.00 F 1.78, 1.10 F 1.87, 1.10

EXAMPLES

Example 1

(7) On a laboratory scale alloys were cast to prove the principle of the current invention and processed to 4.0 mm sheet or 30 mm plate. The alloy compositions are listed in Table 2, for all ingots Fe<0.06, Si<0.04, Ti 0.01, balance aluminium. Rolling blocks of approximately 80 by 80 by 100 mm (heightwidthlength) were sawn from round lab cast ingots of about 12 kg. The ingots were homogenised at 4605 C. for about 12 hrs and consequently at 4755 C. for about 24 hrs and consequently slowly air cooled to mimic an industrial homogenisation process. The rolling ingots were pre-heated for about 6 hrs at 4105 C. At an intermediate thickness range of about 40 to 50 mm the blocks were re-heated at 4105 C. Some blocks were hot rolled to the final gauge of 30 mm, others were hot rolled to a final gauge of 4.0 mm. During the whole hot-rolling process, care was taken to mimic an industrial scale hot rolling. The hot-rolled products were solution heat treated and quenched. Most were quenched in water, but some were also quenched in oil to mimic the mid and quarter-thickness quenching-rate of a 6-inch thick plate. The products were cold stretched by about 1.5% to relieve the residual stresses. The ageing behaviour of the alloys was investigated. The final products were over-aged to a near peak aged strength (e.g. T76 or T77 temper).

(8) Tensile properties have been tested according EN10.002. The tensile specimens from the 4 mm thick sheet were flat EURO-NORM specimen with 4 mm thickness. The tensile specimens from the 30 mm plate were round tensile specimens taken from mid-thickness. The tensile test results in Table 1 are from the L-direction. The Kahn-tear toughness is tested according to ASTM B871-96. The test direction of the results on Table 2 is the T-L direction. The so-called notch-toughness can be obtained by dividing the tear-strength, obtained by the Kahn-tear test, by the tensile yield strength (TS/Rp). This typical result from the Kahn-tear test is known in the art to be a good indicator for true fracture toughness. The unit propagation energy (UPE), also obtained by the Kahn-tear test, is the energy needed for crack growth. It is believed that the higher the UPE, the more difficult to grow the crack, which is a desired feature of the material.

(9) To qualify for a good corrosion performance, the exfoliation corrosion resistance (EXCO) when measured according to ASTM G34-97 must be at least EA or better. The inter-granular corrosion (IGC) when measured according MIL-H-6088 is preferable absent. Some pitting is acceptable, but preferably should be absent also.

(10) In order to have a promising candidate alloy suitable for a variety of products, it had to fulfil the following requirements on lab-scale: A tensile yield strength of at least 510 MPa, an ultimate strength of at least 560 MPa, a notch toughness of at least 1.5 and a UPE of at least 200 kJ/m.sup.2. The results for the various alloys as function of some processing are listed in Table 2 also.

(11) In order to meet all those desired material properties, the chemistry of the alloy has to be carefully balanced. According to the present results, too high values for Cu, Mg and Zn contents were found to be detrimental to toughness and corrosion resistance. Whereas too low values were found to be detrimental for high strength levels.

(12) TABLE-US-00002 TABLE 2 Invention Specimen Alloy Thickness Mg Cu Zn Zr Others Rp Rm UPE No. (Y/N) (mm) Temper (wt %) (wt %) (wt %) (wt %) (wt %) (MPa) (MPa) (kJ/m.sup.2) Ts/Rp 1 yes 30 T77 1.84 1.47 7.4 0.10 587 627 312 1.53 2 yes 30 T76 1.66 1.27 8.1 0.09 530 556 259 1.76 3 yes 4 T76 2.00 1.54 6.8 0.11 517 563 297 1.62 4 no 4 T76 2.00 1.52 5.6 0.01 0.16 Cr 473 528 232 1.45 5 no 4 T76 2.00 1.53 5.6 0.06 0.08 Cr 464 529 212 1.59 6 yes 4 T76 1.82 1.68 7.4 0.10 594 617 224 1.44 7 yes 30 T76 2.09 1.30 8.2 0.09 562 590 304 1.64 8 yes 4 T77 2.20 1.70 8.7 0.11 614 626 115 1.38 9 yes 4 T77 1.81 1.69 8.7 0.10 574 594 200 1.47 10 no 4 T76 2.10 1.54 5.6 0.07 490 535 245 1.53 11 no 4 T76 2.20 1.90 6.7 0.10 563 608 1.07 12 no 4 T76 1.98 1.90 6.8 0.09 559 592 1.32 13 no 4 T77 2.10 2.10 8.6 0.10 623 639 159 1.31 14 no 4 T77 2.50 1.70 8.7 0.10 627 643 117 1.33 15 no 4 T77 1.70 2.10 8.6 0.12 584 605 139 1.44 16 no 4 T77 1.70 2.40 8.6 0.11 598 619 151 1.42 17 no 4 T76 2.40 1.54 5.6 0.01 476 530 64 1.42 18 no 4 T76 2.30 1.54 5.6 0.07 488 542 52 1.54 19 no 4 T76 2.30 1.52 5.5 0.14 496 543 155 1.66 20 yes 4 T76 2.19 1.54 6.7 0.11 0.16 Mn 521 571 241 1.65 21 no 4 T76 2.12 1.51 5.6 0.12 471 516 178 1.42

(13) But, very surprisingly, a higher Zn-level is increasing the toughness and crack growth resistance. Therefore, it is desirable to use higher Zn level and combine these with lower Mg and Cu levels. It has been found that the Zn-content should not be below 6.5%, and preferably not below 6.7%, and more preferably not below 6.9%.

(14) Mg is required to have acceptable strength levels. It has been found that a ratio of Mg/Zn of about 0.27 or lower seems to give the best strength-toughness combination. However, Mg levels should not exceed 2.2%, and preferably not exceed 2.1%, and even more preferably not exceed 1.97%, with a more preferred upper level of 1.95%. This upper-limit is lower than in the conventional AA-windows or ranges of presently used commercial aerospace alloys like AA7050, AA7010 and AA7075.

(15) In order to have a desirably very high crack growth resistance (or UPE) Mg levels must be carefully balanced and should preferably be in the same order or slightly more than the Cu levels, and preferably (0.9Mg0.6)Cu(0.9Mg+0.05). The Cu-content should not be too high. It has been found that the Cu-content should not be higher than 1.9%, and preferably should not exceed 1.80%, and more preferably not exceed 1.75%.

(16) The dispersoid formers used in AA7xxx-series alloys are typically Cr, as in e.g. AA775, or Zr, as in e.g. AA750 and AA710. Conventionally, Mn is believed to be detrimental for toughness, but much to our surprise, a combination of Mn and Zr shows still a very good strength-toughness balance.

Example 2

(17) A batch of full-size rolling ingots with a thickness of 440 mm thick on an industrial scale were produced by a DC-casting and having the chemical composition (in wt. %): 7.43% Zn, 1.83% Mg, 1.48% Cu, 0.08% Zr, 0.02% Si and 0.04% Fe, balance aluminium and unavoidable impurities. One of these ingots was scalped, homogenised at 12 hrs/470 C.+24 hrs/475 C.+air cooled to ambient temperature. This ingot was pre-heated at 8 hrs/410 C. and then hot rolled to about 65 mm. The rolling block was then turned 90 degrees and further hot rolled to about 10 mm. Finally the rolling block was cold rolled to a gauge of 5.0 mm. The obtained sheet was solution heat treated at 475 C. for about 40 minutes, followed by water-spray quenching. The resultant sheets were stress relieved by a cold stretching operation of about 1.8%. Two ageing variants have been produced, variant A: for 5 hrs/120 C.+9 hrs/155 C., and variant B: for 5 hrs/120 C.+9 hrs/165 C.

(18) The tensile results have been measured according to EN 10.002. The compression yield strength (CYS) has been measured according to ASTM E9-89a. The shear strength has been measured according to ASTM B831-93. The fracture toughness, Kapp, has been measured according to ASTM E561-98 on 16-inch wide centre cracked panels [M(T) or CC(T)]. The Kapp has been measured at ambient room temperature (RT) and at 65 F. As reference material a high damage tolerant (HDT) AA224-T351 has been tested as well. The results are listed in Table 3.

(19) TABLE-US-00003 TABLE 3 L-TYS LT-TYS L-UTS LT-UTS L-T CYS T-L CYS Ageing (MPa) (MPa) (MPa) (MPa) (MPa) (MPa) INV Variant A 544 534 562 559 554 553 INV Variant A 489 472 526 512 492 500 HDT- T351 360 332 471 452 329 339 2x24 L-T T-L RT RT 65 F. 65 F. Shear Shear L-T Kapp T-L Kapp L-T Kapp L-T Kapp Ageing (MPa) (MPa) MPa .Math. m MPa .Math. m.sup.0.5 MPa .Math. m.sup.0.5 MPa .Math. m.sup.0.5 INV Variant A 372 373 103 100 INV Variant B 340 338 132 127 102 103 HDT- T351 328 312 101 103 2x24

(20) The exfoliation corrosion resistance has been measured according ASTM G34-97. Both variant A and B showed EA rating.

(21) The inter-granular corrosion measured according to MIL-H-6088 for variant A was about 70 m and for variant B about 45 m. Both are significantly lower than the typical 200 m as measured for the reference AA224-T351.

(22) From Table 3 it can be seen that there is a significant improvement with the alloy according to the invention. A significant increase in strength at comparable or even higher fracture toughness levels. Also the alloy according to the invention at a low temperature of minus 65 F., outperforms the nowadays standard high damage tolerant fuselage alloy AA224-T351. Note that also the corrosion resistance of the inventive alloy is significant better than the AA224-T351.

(23) The fatigue crack growth rate (FCGR) has been measured according to ASTM E647-99 on 4-inch wide compact tension panels [C(T)] with an R-ratio of 0.1. In Table 3 the da/dn per cycle at a stress range of K=27.5 ksi.Math.in.sup.0.5 (=about 30 MPa.Math.m.sup.0.5) of the inventive alloy has been compared with the reference high damage tolerant AA224-T351.

(24) It can be clearly seen from the results in Table 4 that the crack growth of the inventive alloy is better than that of the high damage tolerant AA224-T351.

(25) TABLE-US-00004 TABLE 4 Crack growth per cycle at a stress range of deltaK = 27.5 ksi in.sup.0.5 INV Variant A L-T 96% INV Variant A T-L 84% INV Variant B L-T 73% INV Variant B T-L 74% HDT-2x24 T351 L-T 100%

Example 3

(26) Another full-scale ingot taken from the batch DC-cast from Example 2 was produced into a plate of 6-inch thickness. Also this ingot was scalped, homogenised at 12 hrs/470 C.+24 hrs/475 C.+air cooled to ambient temperature. The ingot was pre-heated at 8 hrs/410 C. and then hot rolled to about 152 mm. The obtained hot-rolled plate was solution heat treated at 475 C. for about 7 hours followed by water-spray quenching. The plates were stress relieved by a cold stretching operation of about 2.0%. Several different two-step ageing processes have been applied.

(27) The tensile results have been measured according to EN 10.002. The specimens were taken from the T/4-position. The plane strain fracture toughness, Kq, has been measured according to ASTM E399-90. If the validity requirements as given in ASTM E399-90 are met, these Kq values are a real material property and called K.sub.1C. The K.sub.1C has been measured at ambient room temperature (RT). The exfoliation corrosion resistance has been measured according to ASTM G34-97. The results are listed in Table 5. All ageing variants as shown in Table 5 showed EA rating.

(28) In FIG. 2 a comparison is given versus results presented in US-2002/0150498-A1, Table 2, incorporated herein by reference. In this US patent application an example (example 1) is given of a similar product, but with a different chemistry that is stated to be optimised for quench sensitivity. In our inventive alloy we have obtained a similar tensile versus toughness balance as in this US patent application. However, our inventive alloys shows at least superior EXCO resistance.

(29) Furthermore, also the elongation of our inventive alloy is superior to that disclosed in US2002/0150498-A1, Table 2. The overall property balance of alloy according to the present invention when processed to 6-inch thick plate is better than that disclosed in US-2002/0150498-A1. In FIG. 2 also documented data for thick gauges of 75 to 220 mm are shown for the AA7050/7010 alloy (see AIMS03-02-022, December 2001), the AA7050/7040 alloy (see AIMS03-02-019, September 2001), and the AA7085 alloy (see AIMS03-02-025, September 2002).

(30) TABLE-US-00005 TABLE 5 L-TYS L-UTS L-A50 L-T K1C Ageing process (MPa) (MPa) (%) (MPa .Math. m.sup.0.5) EXCO 5 hrs/120 C. + 453 497 9.9 EA 11 hrs/165 C..sup. 5 hrs/120 C. + 444 492 12.5 44.4 EA 13 hrs/165 C..sup. 5 hrs/120 C. + 434 485 13.0 45.0 EA 15 hrs/165 C..sup. 5 hrs/120 C. + 494 523 10.5 39.1 EA 12 hrs/160 C..sup. 5 hrs/120 C. + 479 213 8.3 EA 14 hrs/160 C..sup.

Example 4

(31) Another full-scale ingot taken from the batch DC-cast from Example 2 was produced to plates of respectively 63.5 mm and 30 mm thickness. The cast ingot was scalped, homogenised at 12 hrs/470 C.+24 hrs/475 C.+air cooled to ambient temperature. The ingot was pre-heated at 8 hrs/410 C. and then hot rolled to respectively 63.5 and 30 mm. The obtained hot-rolled plates were solution heat treated (SHT) at 475 C. for about 2 to 4 hrs followed by water-spray quenching. The plates were stress relieved by a cold stretching operation of respectively 1.7% and 2.1% for the 63.5 mm and 30 mm plates. Several different two-step ageing processes have been applied.

(32) The tensile results have been measured according to EN 10.002. The plane strain fracture toughness, Kq, has been measured according to ASTM E399-90 on CT-specimens. If the validity requirements as given in ASTM E399-90 are met, these Kq values are a real material property and called K.sub.1C. The K.sub.1C has been measured at ambient room temperature (RT). The EXCO exfoliation corrosion resistance has been measured according to ASTM G34-97. The results are listed in Table 6. All ageing variants as shown in Table 6 showed EA-rating.

(33) TABLE-US-00006 TABLE 6 TYS UTS A50 TYS UTS A50 Thickness Ageing MPa MPa (%) L-T K1C (MPa) (MPa) (%) T-L K1C (mm) ( C.-hrs) L-direction MPa .Math. vm LT-direction MPa .Math. m.sup.0.5 63.5 120-5/ 566 594 10.7 42.4 532 572 9.8 32.8 150-12 63.5 120-5/ 566 599 11.9 40.7 521 561 11.2 33.0 155-12 63.5 120-5/ 528 569 13.0 51.6 497 516 11.6 40.2 160-12 30 120-5/ 565 590 14.2 46.9 558 582 13.9 36.3 150-12 30 120-5/ 557 589 14.4 51.0 547 572 13.6 39.2 155-12 30 120-5/ 501 548 15.1 65.0 493 539 14.3 46.8 160-12

(34) In Table 7 the values are given of nowadays state of the art commercial upper wing alloys, and are typical data according to the supplier of that material (Alloy 7150-T7751 plate & 7150-T77511 extrusions, Alcoa Mill products, Inc., ACRP-069-B).

(35) TABLE-US-00007 TABLE 7 Typical values from ALCOA tech sheet on AA7150-T77 and AA7055-T77, both plates of 25 mm. TYS UTS A50 TYS UTS A50 Thickness MPa MPa (%) L-T KIC (MPa) (MPa) (%) T-L KIC (mm) Ageing L-direction MPa .Math. m.sup.0.5 LT-direction MPa .Math. m.sup.0.5 25 7150- 572 607 12.0 29.7 565 607 11.0 26.4 T77 25 7055- 614 634 11.0 28.6 614 641 10.0 26.4 T77

(36) In FIG. 3 a comparison is given of the inventive alloy versus AA7150-T77 and AA7055-T77. From FIG. 3 it can be clearly seen that the tensile versus toughness balance of the current inventive alloy is superior to commercial available AA7150-T77 and also to AA7055-T77.

Example 5

(37) Another full-scale ingot taken from the batch DC-cast from Example 2 (hereinafter in Example 5 Alloy A) was produced to plates of 20 mm thickness. Also one other casting was made (designated Alloy B for this example) with a chemical composition (in wt. %): 7.39% Zn, 1.66% Mg, 1.59% Cu, 0.08% Zr, 0.03% Si and 0.04% Fe, balance aluminium and unavoidable impurities. These ingots were scalped, homogenised at 12 hrs/470 C.+24 hrs/475 C.+air cooled to ambient temperature. For further processing, three different routes were used.

(38) Route 1: The ingots of alloy A and B were pre-heated at 6 hrs/420 C. and then hot rolled to about 20 mm.

(39) Route 2: Ingot of alloy A were pre-heated at 6 hrs/460 C. and then hot rolled to about 20 mm.

(40) Route 3: Ingot of alloy B were pre-heated at 6 hrs/420 C. and then hot rolled to about 24 mm, subsequently these plates were cold rolled to 20 mm.

(41) Thus, four variants were produced and identified as: A1, A2, B1 and B3. The resultant plates were solution heat treated at 475 C. for about 2 to 4 hrs followed by water-spray quenching. The plates were stress relieved by a cold stretching operation of about 2.1%. Several different two-step ageing processes have been applied, whereby for example 120-5/150-10 means 5 hrs at 120 C. followed by 10 hrs at 150 C.

(42) The tensile results have been measured according to EN 10.002. The plane strain fracture toughness, Kq, has been measured according to ASTM E399-90 on CT specimens. If the validity requirements as given in ASTM E399-90 are met, these Kq values are a real material property and called K.sub.1C or KIC. Note that most of the fracture toughness measurement in this example failed the meet the validity criteria on specimen thickness. The reported Kq values are a conservative with respect to K.sub.1C, in other words, the reported Kq values are in fact generally lower than the standard K.sub.1C values obtained when specimen size related validity criteria of ASTM E399-90 are satisfied. The exfoliation corrosion resistance has been measured according to ASTM G34-97. The results are listed in Table 8. All ageing variants as shown in Table 8 showed EA-rating for the EXCO resistance.

(43) The results of Table 8 have are shown graphically in FIG. 4. In FIG. 4 lines have been fitted through the data to get an impression of the differences between A1, A2, B1 and B3. From that graph it can be clearly seen that alloy A and B, when comparing A1 and B1, have a similar strength versus toughness behaviour. The best strength versus toughness could be obtained by either B3 (i.e. cold rolling to final thickness) or by A2 (i.e. pre-heat at a higher temperature). Also note that the results of Table 8 show a significant better strength versus toughness balance than AA7150-T77 and AA7055-T77 as listed in Table 7.

(44) TABLE-US-00008 TABLE 8 Ageing TYS UTS A50 TYS UTS A50 Al- ( C.- MPa (MPa) (%) MPa MPa (%) T-L KIC loy hrs) L-direction LT-direction MPa .Math. m.sup.0.5 B3 120-5/ 563 586 13.7 548 581 12.5 38.4 150-10 B3 120-5/ 558 581 14.4 538 575 13.1 38.7 155-12 B3 120-5/ 529 563 14.6 517 537 13.7 40.3 160-10 B1 120-5/ 571 595 13.4 549 581 13.4 36.5 150-10 B1 120-5/ 552 582 14.3 528 568 13.9 37.1 155-12 B1 120-5/ 510 552 15.1 493 542 14.5 39.4 160-12 A1 120-5/ 574 597 13.7 555 590 14.0 33.7 150-10 A1 120-5/ 562 594 14.4 548 586 13.9 37.1 155-12 A1 120-5/ 511 556 15.0 502 550 14.3 37.6 160-12 A2 120-5/ 574 600 14.0 555 595 13.9 36.7 150-10 A2 120-5/ 552 584 14.3 541 582 13.1 38.0 155-12 A2 120-5/ 532 572 14.8 527 545 12.4 39.8 160-12

Example 6

(45) On an industrial scale two alloys have been cast via DC-casting with a thickness of 440 mm and processed into sheet product of 4 mm. The alloy compositions are listed in Table 9, whereby alloy B represents an alloy composition according to a preferred embodiment of the invention when the alloy product is in the form of a sheet product.

(46) The ingots were scalped, homogenized at 12 hrs/470 C.+24 hrs/475 C. and then hot rolled to an intermediate gauge of 65 mm and final hot rolled to about 9 mm. Finally the hot rolled intermediate products have been cold rolled to a gauge of 4 mm. The obtained sheet products were solution heat treated at 475 C. for about 20 minutes, followed by water-spray quenching. The resultant sheets were stress relieved by a cold stretching operation of about 2%. The stretched sheets have been aged thereafter for 5 hrs/120 C.+8 hrs/165 C. Mechanical properties have tested analogue to Example 1 and the results are listed in Table 10.

(47) The results of this full-scale trial confirm the results of Example 1 that the positive addition of Mn in the defined range significantly improves the toughness (both UPE and Ts/Rp) of the sheet product resulting in a very good and desirable strength-toughness balance.

(48) TABLE-US-00009 TABLE 9 Chemical composition of the alloys tested, balance impurities and aluminium Alloy Si Fe Cu Mn Mg Zn Ti Zr A 0.03 0.08 1.61 1.86 7.4 0.03 0.08 B 0.03 0.06 1.59 0.07 1.96 7.36 0.03 0.09

(49) TABLE-US-00010 TABLE 10 Mechanical properties of the alloy products tested for two testing directions. L-direction LT-direction Rp Rm A50 Ts/ Rp A50 Ts/ Alloy MPa MPa (%) TS UPE Rp MPa Rm (%) TS UPE Rp A 497 534 11.0 694 90 1.40 479 526 12.0 712 134 1.49 B 480 527 12.9 756 152 1.58 477 525 12.8 712 145 1.49

Example 7

(50) On an industrial scale two alloys have been cast via DC-casting with a thickness of 440 mm and processed into a plate product having a thickness of 152 mm. The alloy compositions are listed in Table 11, whereby alloy C represents a typical alloy falling within the AA7050-series range and alloy D represents an alloy composition according to a preferred embodiment of the invention when the alloy product is in the form of plate, e.g. thick plate.

(51) The ingots were scalped, homogenized in a two-step cycle of 12 hrs/470 C.+24 hrs/475 C. and air cooled to ambient temperature. The ingot was pre-heated at 8 hrs/410 C. and then hot rolled to final gauge. The obtained plate products were solution heat treated at 475 C. for about 6 hours, followed by water-spray quenching. The resultant plates were stretched by a cold stretching operation for about 2%. The stretched plates have been aged using a two-step ageing practice of first 5 hrs/120 C. followed by 12 hrs/165 C. Mechanical properties have been tested analogue to Example 3 in three test directions and the results are listed in Table 12 and 13. The specimens were taken from S/4 position from the plate for the L- and LT-testing direction and at S/2 for the ST-testing direction The Kapp has been measured at S/2 and S/4 locations in the L-T direction using panels having a width of 160 mm centre cracked panels and having a thickness of 6.3 mm after milling. These Kapp measurements have been carried out at room temperature in accordance with ASTM E561. The designation ok for the SCC means that no failure occurred at 180 MPa/45 days.

(52) From the results of Tables 12 and 13 it can be seen that the alloy according to the invention in comparison with AA7050 has similar corrosion performance, the strength (yield strength and tensile strength) are comparable or slightly better than AA7050, in particular in the ST-direction. But more importantly the alloy of the present invention shown significantly better results in elongation (or A50) in the ST-direction. The elongation (or A50), in particular the elongation in ST-direction, is an important engineering parameter of amongst others ribs for use in an aircraft wing structure. The alloy product according to the invention further shows a significant improvement in fracture toughness (both K.sub.1C and Kapp).

(53) TABLE-US-00011 TABLE 11 Chemical composition of the alloys tested, balance impurities and aluminium. Alloy Si Fe Cu Mn Mg Zn Ti Zr C 0.02 0.04 2.14 2.04 6.12 0.02 0.09 D 0.03 0.05 1.58 0.07 1.96 7.35 0.03 0.09

(54) TABLE-US-00012 TABLE 12 Tensile test results of the plate products for three testing directions. TYS TYS TYS UTS UTS UTS Elong Elong Elong. (MPa) (MPa) (MPa) (MPa) (MPa) (MPa) (%) (%) (%) Alloy L LT ST L LT ST L LT ST C 483 472 440 528 537 513 9.0 7.3 3.3 D 496 486 460 531 542 526 9.2 8.0 5.8

(55) TABLE-US-00013 TABLE 13 Further properties of the plate products tested. L-T KIC T-L KIC S-L KIC L-T Kapp Alloy (MPa .Math. m.sup.0.5) (MPa .Math. m.sup.0.5) (MPa .Math. m.sup.0.5) (MPa .Math. m.sup.0.5) EXCO SCC C 27.8 26.3 26.2 45.8 (s/4) 52 (s/2) EA ok D 30.3 29.4 29.1 62.6 (s/4) 78.1 (s/2) EA ok

Example 8

(56) On an industrial scale two alloys have been cast via DC-casting with a thickness of 440 mm and processed into a plate product having a thickness of 63.5 mm. The alloy compositions are listed in Table 14, whereby alloy F represents an alloy composition according to a preferred embodiment of the invention when the alloy product is in the form of plate for wings.

(57) The ingots were scalped, homogenized in a two-step cycle of 12 hrs/470 C.+24 hrs/475 C. and air cooled to ambient temperature. The ingot was pre-heated at 8 hrs/410 C. and then hot rolled to final gauge. The obtained plate products were solution heat treated at 475 C. for about 4 hours, followed by water-spray quenching. The resultant plates were stretched by a cold stretching operation for about 2%. The stretched plates have been aged using a two-step ageing practice of first 5 hrs/120 C. followed by 10 hrs/155 C.

(58) Mechanical properties have been tested analogue to Example 3 in three test directions are listed in Table 15. The specimens were taken from T/2 position. Both alloys had a EXCO test result of EB.

(59) From the results of Table 15 it can be seen that the positive addition of Mn results in an increase of the tensile properties. But most importantly the properties, and in particular the elongation (or A50), in the ST-direction are significantly improved. The elongation (or A50) in the ST-direction is an important engineering parameter for structural parts of an aircraft, e.g. wing plate material.

(60) TABLE-US-00014 TABLE 14 Chemical composition of the alloys tested, balance impurities and aluminium. Alloy Si Fe Cu Mn Mg Zn Ti Zr E 0.02 0.04 1.49 1.81 7.4 0.03 0.08 F 0.03 0.05 1.58 0.07 1.95 7.4 0.03 0.09

(61) TABLE-US-00015 TABLE 15 Mechanical properties of the products tested for three testing directions. L-direction LT-direction ST-direction TYS UTS Elong. TYS UTS Elong. TYS UTS Elong. Alloy (MPa) (MPa) (%) (MPa) (MPa) (%) (MPa) (MPa) (%) E 566 599 12 521 561 11 493 565 5.3 F 569 602 13 536 573 9.5 520 586 8.1

(62) Having now fully described the invention, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made without departing from the spirit or scope of the invention as hereon described.