2XXX series aluminum lithium alloys having low strength differential

Abstract

The present application discloses wrought 2xxx AlLi alloy products that are work insensitive. The wrought aluminum alloy products generally include from about 2.75 wt. % to about 5.0 wt. % Cu, from about 0.2 wt. % to about 0.8 wt. % Mg, where the ratio of copper-to-magnesium ratio (Cu/Mg) in the aluminum alloy is in the range of from about 6.1 to about 17, from about 0.1 wt. % to 1.10 wt. % Li, from about 0.3 wt. % to about 2.0 wt. % Ag, from 0.50 wt. % to about 1.5 wt. % Zn, up to about 1.0 wt. % Mn, the balance being aluminum, optional incidental elements, and impurities. The wrought aluminum alloy products may realize a low strength differential and in a short aging time due to their work insensitive nature.

Claims

1. A method comprising: (a) casting an ingot consisting of: from 2.75 wt. % to 5.0 wt. % Cu; from 0.2 wt. % to 0.8 wt. % Mg; wherein the ratio of copper-to-magnesium ratio (Cu/Mg) in the wrought aluminum alloy product is in the range of from 8.0 to 17; from 0.1 wt. % to 1.10 wt. % Li; from 0.30 wt. % to 2.0 wt. % Ag; from 0.4 wt. % to 1.5 wt. % Zn; wherein wt. % Ag+wt. % Zn in the wrought aluminum alloy product is at least 0.89 wt. %; up to 1.0 wt. % Mn; and the balance being aluminum, optional incidental elements, and impurities; (b) hot working the ingot into an intermediate alloy product, optionally followed by pre-SHT cold working; (c) after the hot working step (b), solution heating treating (SHT) and quenching the intermediate alloy product; (d) after the solution heat treating step (c), post-SHT cold working the intermediate aluminum alloy product into an end product; (I) wherein the post-SHT cold working step (d) results in a first portion of the end product having a first amount of cold work and a second portion of the end product having a second amount of cold work, wherein the difference between the first amount of cold work and the second amount of cold work is at least 3.0%; (e) artificially aging the end product for not greater than 64 hours at a temperature of 310 F., or a substantially equivalent artificial aging practice; wherein, after the artificially aging step (e), the first portion and the second portion realizes a strength differential of not greater than 3 ksi.

2. The method of claim 1, wherein the post-SHT cold working step (d) results in the second portion receiving substantially no cold work and the first portion receiving at least 3% cold work.

3. The method of claim 1, wherein the end product is one of a stepped-extruded product, a forging product, and a stretch-formed product.

4. The method of claim 1, wherein, after the artificially aging step (e), the strength differential is not greater than 2 ksi.

5. The method of claim 1, wherein, after the artificially aging step (e), the strength differential is greater than 1 ksi.

6. The method of claim 1, wherein the difference between the first amount of cold work and the second amount of cold work is at least 5%.

7. The method of claim 1, wherein the difference between the first amount of cold work and the second amount of cold work is at least 7%.

8. The method of claim 1, wherein the difference between the first amount of cold work and the second amount of cold work is at least 10%.

9. The method of claim 1, wherein the wrought product realizes a longitudinal tensile yield strength of at least 60 ksi and an K.sub.IC fracture toughness L-T of at least 20 ksiin.

10. The method of claim 9, wherein the wrought product realizes a longitudinal tensile yield strength of at least 70 ksi.

11. The method of claim 1, wherein the artificially aging comprises artificially aging the end product for not greater than 40 hours at a temperature of 310 F., or a substantially equivalent artificial aging practice.

12. The method of claim 1, wherein the artificially aging comprises artificially aging the end product for not greater than 30 hours at a temperature of 310 F., or a substantially equivalent artificial aging practice.

13. A method comprising: (a) selecting an amount of Cu, Mg, Li, Ag and Zn to be included in a wrought aluminum alloy product having a variable amount of cold work to achieve no more than a 3 ksi longitudinal strength differential across the wrought aluminum alloy product having the variable amount of cold work, wherein the amounts of Cu, Mg, Li, Ag an Zn are selected from the following ranges: from 2.75 wt. % to 5.0 wt. % Cu; from 0.2 wt. % to 0.8 wt. % Mg; wherein the ratio of copper-to-magnesium ratio (Cu/Mg) in the aluminum alloy is in the range of from 6.1 to 17; from 0.1 wt. % to 1.10 wt. % Li, from 0.3 wt. % to 2.0 wt. % Ag; from 0.40 wt. % to 1.5 wt. % Zn; optionally up to 1.0 wt. % Mn; and optionally up to 1.0 wt. % in incidental elements; (b) casting an ingot having the selected composition, the balance being aluminum and impurities; and (c) preparing the wrought aluminum alloy product from the ingot, wherein, after the preparing, the wrought aluminum alloy product realizes at least 3% differential in cold work and no more than a 3 ksi longitudinal strength differential across the wrought product.

14. The method of claim 13, wherein the preparing step comprises: (a) hot working the ingot into an intermediate alloy product, optionally followed by pre-SHT cold working; (b) after the hot working step (a), solution heating treating (SHT) and quenching the intermediate alloy product; (c) after the solution heat treating step (b), post-SHT cold working the intermediate aluminum alloy product into a substantially final form representative of the wrought aluminum alloy product, wherein the post-SHT cold working introduces the variable amount of cold work; and (d) artificially aging the wrought aluminum alloy product.

15. The method of claim 14, wherein the post-SHT cold working comprises one of stepped-extruding, forging and stretch-forming.

16. The method of claim 14, wherein the post-SHT cold working comprises stretching.

17. The method of claim 14, wherein the post-SHT cold working comprises compressing.

18. The method of claim 14, wherein the post-SHT cold working comprises rolling.

19. The method of claim 13, wherein the selecting step comprises selecting the amount of Cu, Mg, Li, Ag and Zn such that the no more than a 3 ksi longitudinal strength differential across the wrought aluminum alloy product is realized with an artificial aging comprising not greater than 64 hours at a temperature of 310 F., or a substantially equivalent artificial aging practice.

20. The method of claim 14, wherein the artificial aging step (d) occurs for not greater than 64 hours at a temperature of 310 F., or a substantially equivalent artificial aging practice.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates a prior art cold worked, forged 2xxx aluminum lithium alloy product.

(2) FIGS. 2-9 are aging curves corresponding with Example 1 alloys.

(3) FIG. 10 is a graph illustrating the T8-T6 strength difference for various Example 1 alloys.

(4) FIGS. 11-31 are aging curves corresponding with Example 2 alloys.

(5) FIG. 32 is a graph illustrating the effect of the Cu/Mg ratio for various alloys.

(6) FIG. 33 is a graph illustrating the T8-T6 strength differential relative to Example 1 and Example 2 alloys.

(7) FIG. 34 is a graph illustrating the effect of Zn for various alloys.

(8) FIG. 35 is a graph illustrating the effect of Ag for various alloys.

(9) FIGS. 36a-36c are graphs illustrating the effect of Cu and Mg levels for various alloys.

(10) FIGS. 37-49 are aging curves corresponding with Example 3 alloys.

(11) FIGS. 50-51 are graphs illustrating the effect of Ag for various Example 3 alloys.

(12) FIGS. 52-53 are graphs illustrating the effect of Li for various Example 3 alloys.

(13) FIGS. 54-55 are graphs illustrating the effect of Zn for various Example 3 alloys.

(14) FIG. 56 is an aging curve corresponding with Example 4 alloys.

(15) FIGS. 57-62 are aging curves corresponding with Example 5 alloys.

(16) FIGS. 63-65 are flow charts illustrating various methods for producing wrought aluminum alloy products in accordance with the present patent application.

DETAILED DESCRIPTION

(17) Reference will now be made in detail to the accompanying drawings, which at least assist in illustrating various pertinent embodiments of the new technology provided for by the present disclosure.

Example 1Bookmold Testing of 2xxx Alloys Having Li and Ag

(18) Eight aluminum alloys of varying composition are bookmold cast, with final dimensions of 1.375411. The composition of each of the alloys is provided in Table 1, below. All values are in weight percent.

(19) TABLE-US-00001 TABLE 1 Composition of Example 1 Alloys Alloy Cu Mg Zn Li 1 4.66 0.39 0.04 0.74 2 3.95 0.46 0.74 3 3.54 0.57 0.77 4 4.11 0.46 0.94 5 3.96 0.47 0.72 6 4.45 0.43 0.86 0.81 7 3.63 0.57 0.85 0.78 8 3.95 0.66 0.86 0.81
All of these alloys also contain about 0.3-0.4 wt. % Mn, about 0.5 wt. % Ag, about 0.01-0.03 wt. % Ti, about 0.11-0.14 wt. % Zr, 0-0.11 wt. % V, less than about 0.04 wt. % Si, and less than about 0.06 wt. % Fe, the balance being aluminum and impurities (e.g., 0.05 wt. % of any other element, and 0.15 wt. % total of all other elements).

(20) After casting, the alloys are homogenized, reheated, hot rolled to 0.2 gauge, solution heat treated, and quenched. Each sheet is then cut in half, with one piece of each sheet remaining in the as-quenched condition, while the other half of each sheet is stretched (about 3%). All sheets are then artificially aged, after which the as-quenched sheets are in the T6 temper, and the stretched sheets are in the T8 temper. For all sheets and in both tempers, longitudinal blanks are produced. After at least 4 days of natural aging, the blanks are artificially aged at 310 F. for about 16, 24, 40, 64, and 96 hours. Tensile testing for each alloy in the T6 and T8 condition is conducted in accordance with ASTM B557. Aging curves for each alloy in the T6 and T8 condition are illustrated in FIGS. 2-9. The difference between the strength in the T8 and T6 tempers is representative of the strength differential across a product.

(21) The T8 temper is a product that is solution heat-treated, cold worked, and then artificially aged, and applies to products that are cold worked to improve strength, or in which the effect of cold work in flattening or straightening is recognized in mechanical property limits. For the purposes of the T8-type alloys tested in this Example 1, the T8 temper was a product that included about 3% cold work in the form of stretch. However, it will be appreciated by those skilled in the art that many variations of the T8 temper exist, and that the present application applies to all such variations of the T8 temper.

(22) The T6 temper is a product that is solution heat-treated and then artificially aged, and applies to products that are not cold worked after solution heat-treatment, or in which the effect of cold work in flattening or straightening may not be recognized in mechanical property limits. For the purposes of the T6-type alloys tested in this application, the T6 temper was a product that was not cold worked. However, it will be appreciated by those skilled in the art that many variations of the T6 temper exist, and that the present application applies to all such variations of the T6 temper.

(23) As illustrated in FIGS. 7 and 10, alloy 6 achieves a small difference (8 ksi) in longitudinal tensile yield strength (TYS0.2% offset) in not greater than about 40 hours of aging. After 40 hours of aging, the difference in strength between the T8 and T6 tempers for alloy 6 is only about 2.7 ksi, which is much lower than the other alloys, as provided in Table 2, below. This may be due to the Cu/Mg ratio in combination with the amount of Zn in the alloy.

(24) TABLE-US-00002 TABLE 2 Properties of Example 1 Alloys Alloy Cu:Mg TYS (40 hrs) TYS (64 hrs) Other 1 11.9 10.35 4.15 No Zn 2 8.6 8 4.25 No Zn 3 6.2 12.75 10.6 No Zn + Low Cu 4 8.9 8.8 7.65 No Zn 5 8.4 8.2 3.4 No Zn 6 10.3 2.7 2.2 7 6.4 9.65 4.6 8 6 16 9.8

(25) Alloy 6 has a Cu/Mg ratio of about 10.3 and includes about 0.8 wt. % Zn. Alloys 7, which has about the same amount of Li and Zn as alloy 6, but has a Cu/Mg ratio of about 6.4, does not achieve a small strength differential in not greater than about 40 hours of aging, but does achieve a small strength differential in not greater than about 64 hours of aging (4.6 ksi). Alloy 8, which has about the same amount of Li and Zn as alloy 6 and has a Cu/Mg ratio of about 6, does not achieve a small strength differential even with 96 hours of aging. These results indicate that a Cu:Mg ratio of at least about 6.1, and preferably of at least about 6.5, in combination with increased Zn and/or Cu levels, may result in the production of wrought products having a low longitudinal TYS differential and in not greater than about 64 hours of artificial aging.

Example 2Additional Bookmold Testing of 2xxx Alloys Having Li, Zn and Ag

(26) Twenty-one aluminum alloys of varying composition are cast as bookmolds. The composition of each of the alloys is provided in Table 3, below. All values are in weight percent.

(27) TABLE-US-00003 TABLE 3 Composition of Example 2 Alloys Alloy Cu Mg Cu/Mg Cu + Mg Other A 2.03 0.67 3.03 2.7 B 2.21 0.37 5.97 2.58 C 2.35 0.23 10.22 2.58 D 2.42 0.14 17.29 2.56 E 3.04 0.76 4 3.8 F 3.29 0.54 6.09 3.83 G 3.54 0.33 10.73 3.87 H 3.61 0.21 17.19 3.82 I 3.94 0.64 6.16 4.58 J 4.28 0.41 10.44 4.69 K 4.23 0.25 16.92 4.48 L 3.51 0.33 10.64 3.84 No Zn M 3.53 0.34 10.38 3.87 0.31% Zn N 3.37 0.54 6.24 3.91 0.31% Zn O 3.67 0.21 17.48 3.88 0.31% Zn P 3.56 0.34 10.47 3.9 0.13% V Q 2.40 0.38 6.32 2.78 1.1% Li R 2.48 0.14 17.71 2.62 1.06% Li S 2.52 0.14 18 2.66 1.43% Li T 3.55 0.33 10.76 3.88 No Ag U 4.56 0.49 9.31 5.05 0.13% V
Unless otherwise indicated, all of these alloys also contained about 0.2-0.3 wt. % Mn, about 0.5 wt. % Ag, about 0.8 wt. % Li, about 0.8 wt. % Zn, about 0.01-0.03 wt. % Ti, about 0.11-0.14 wt. % Zr, less than about 0.04 wt. % Si, and less than about 0.06 wt. % Fe, the balance being aluminum and impurities (e.g., 0.05 wt. % of any other element, and 0.15 wt. % total of all other element). Alloy U is similar to Alloy 6 of Example 1. After casting, all alloys were processed similar to Example 1 to test the strength difference between the T6 and T8 tempers. Those results are illustrated in FIGS. 11-36.

(28) As illustrated in FIGS. 17, 19, 20, 31, and 33, alloys G, I, J and U achieve a small difference (8 ksi) in longitudinal tensile yield strength (TYS) in not greater than about 40 hours of aging, achieving a difference in strength between the T8 and T6 tempers of only about 1.7 ksi, 5.25, 0 ksi, and 1.9 ksi, respectively. All of these alloys have a Cu/Mg ratio of from about 6.1 to about 11. All of these alloys also contain at least about 3.0 wt. % Cu, at least about 0.3 wt. % Mg, about 0.8 wt. % Li, about 0.5 wt. % Ag, about 0.3 wt. % Mn, and about 0.8 wt. % Zn. These alloys also enjoy a relatively high overall strength, alloys I, J and U both having a TYS of at least about 80 ksi, and alloy G having a TYS of about 72 ksi.

(29) Alloys that do not have a Cu/Mg ratio of at least about 6.1 may not achieve a small strength differential. This is illustrated by Alloys A, B, E, F, and Q, particularly Alloy F, as well as FIGS. 11-12, 15-16, 27 and 32. Alloy F contains similar amounts of alloying ingredients as Alloy G, except it contains about 0.54 wt. % Mg, giving it a Cu/Mg ratio of about 6.1. Alloy F does not achieve a small strength differential in not greater than about 40 hours of aging, but does achieve a small strength differential in not greater than about 64 hours of aging, having a strength differential of about 6.9 ksi.

(30) Alloys that have a Cu/Mg ratio of more than about 15 may not achieve a small strength differential and/or may not have high strength. This is illustrated by Alloys D, H, K, O, R, and S, particularly Alloys H and K, as well as FIGS. 14, 18, 21, 25, 28, 29 and 32. Alloy H contains similar amounts of alloying ingredients as alloy G, except it contains about 0.21 wt. % Mg, giving it a Cu/Mg ratio of about 17.2. Alloy H does not achieve a small strength differential between the T8 and T6 tempers in not greater than about 40 hours of artificial aging, having about a 10 ksi strength differential. Alloy H does achieve a small strength differential (about 5.4 ksi) in not greater than about 64 hours of aging, but has a lower strength than similar alloys that have a Cu/Mg ratio of not greater than about 15. Alloy K contains similar amounts of alloying ingredients as Alloy J, except it contains about 0.25 wt. % Mg, giving it a Cu/Mg ratio of about 16.9. Alloy K does not achieve a small strength differential between the T8 and T6 tempers in not greater than about 40 or 64 hours of artificial aging, having about a 12 ksi and 8.5 strength differential, respectively.

(31) As shown, Alloy H does achieve a small strength differential (about 5.4 ksi) in not greater than about 64 hours of aging. Thus, in some embodiments, alloys similar to Alloy H may be beneficial in some circumstances, despite their potentially lower overall strength. Thus, in some embodiments, alloys having a Cu/Mg ratio as high as about 16 or 17 may be useful.

(32) Alloys that do not contain sufficient amounts of Cu and/or Mg may not achieve good strength properties. This is illustrated by Alloys A-D, and F, particularly Alloys C and F, as well as FIGS. 11-14, 16 and 32. Alloy C, which has a Cu/Mg ratio of about 10.22, but only contains about 2.35 wt. % Cu and 0.23 wt. % Mg, has low strength (less than about 57 ksi). Alloy C also does not achieve a small strength differential between the T8 and T6 tempers in not greater than about 40 or 64 hours of artificial aging, having about a 14 ksi and about a 11 ksi strength differential, respectively. Alloy F has a similar Cu/Mg ratio as Alloy I, but contains less Cu and Mg. Alloy F takes longer to achieve a small strength differential and with lower strength relative to Alloy I.

(33) Alloys that do not contain a sufficient amount of Zn may not achieve good strength properties. This is illustrated by Alloys L-O, particularly Alloys L and M, as well as FIGS. 22-25 and 34. Alloys L and M have similar alloying ingredients as Alloy G, but Alloy L has no Zn and Alloy M has 0.31 wt. % Zn. Alloy L does not does not achieve a small strength differential between the T8 and T6 tempers in not greater than about 40 hours of artificial aging, having about an 8.65 ksi strength differential, but does realize a small strength differential in not greater than about 64 hours of aging, achieving about a 7 ksi strength differential. However, alloy L has lower strength than similar alloys containing Zn. Alloy M, containing about 0.3 wt. % Zn, achieves a small strength differential (about 0.65 ksi) in not greater than about 64 hours of aging, and achieves about an 8.45 ksi strength differential in not greater than about 40 hours of aging. This data indicates that smaller amounts of Zn (e.g., as low as about 0.1 wt. %) may be used to achieve a small strength differential if longer aging periods are to be used. However, the new alloys should generally include at least 0.50 wt. % Zn to consistently achieve good strength differential properties, as shown in other examples, below.

(34) Alloys that do not contain a sufficient amount of Ag may not achieve good strength properties. This is illustrated by Alloy T and FIGS. 30 and 35. Alloy T contains alloying ingredients similar to Alloy G, but has no Ag. Alloy T does not achieve a small strength differential between the T8 and T6 tempers in not greater than about 40 or 64 hours of artificial aging, having about a 15 ksi and about a 13.55 ksi strength differential, respectively.

(35) Based on the foregoing, FIGS. 36a-36c are prepared. As illustrated in FIG. 36a, copper levels of from about 2.75 to about 5 wt. % and magnesium levels of about 0.2 to about 0.8 wt. % are expected to produce wrought aluminum alloy products (e.g., forged stepped-extruded, or stretch-formed) that realize a small strength differential (e.g., 8 ksi) across such products, and with a typical longitudinal yield strength of at least about 60 ksi, so long as the copper-to-magnesium ratio is in the range of from about 6.1 to about 17. This small strength differential is usually realized in not greater than about 64 hours of artificial aging, and may be realized in not greater than about 40 hours of artificial aging, or less. FIGS. 36b and 36c provide preferred and more preferred Cu:Mg ratios and minimum strength levels, respectively. Such wrought products should include Li, Ag, Zn, and may optionally include Mn, as described above. Cu, Mg, Ag, Mn, and/or Zn, as well as the optional incidental elements, may be added to the alloy in an amount up to their solubility limit, so long as the strength differential properties described herein, or other desired properties, are not detrimentally affected. The amount of impurities should be restricted, as provided above.

Example 3Additional Bookmold Testing of 2xxx Alloys Having Li, Zn and Ag

(36) Additional bookmold testing is completed. Thirteen aluminum alloys of varying composition are cast as bookmolds. The composition of each of the alloys is provided in Table 4, below. All values are in weight percent.

(37) TABLE-US-00004 TABLE 4 Composition of Example 3 Alloys Alloy Cu Mg Cu + Mg Cu/Mg Other I 3.89 0.30 4.19 12.97 II 3.85 0.36 4.21 10.69 0.41 wt. % Ag III 3.89 0.36 4.25 10.81 0.31 wt. % Ag IV 3.89 0.35 4.24 11.11 0.12 wt. % Ag V 3.84 0.35 4.29 10.97 0.50 wt. % Li VI 3.89 0.35 4.34 11.11 0.88 wt. % Li VII 3.94 0.36 4.30 10.94 1.10 wt. % Li VIII 3.95 0.36 4.31 10.97 1.20 wt. % Li IX 3.94 0.36 4.30 10.94 1.00 wt. % Zn X 3.85 0.36 4.21 10.69 0.60 wt. % Zn XI 3.93 0.36 4.29 10.92 0.39 wt. % Zn XII 4.05 0.36 4.41 11.25 0.4 wt. % Ag 1.03 wt. % Zn XIII 3.91 0.35 4.26 11.17 0.29 wt. % Ag 1.01 wt. % Zn

(38) Unless otherwise indicated, all of these alloys also contained about 0.2-0.3 wt. % Mn, about 0.5 wt. % Ag, about 0.8 wt. % Li, about 0.8 wt. % Zn, about 0.01-0.03 wt. % Ti, about 0.11-0.14 wt. % Zr, less than about 0.04 wt. % Si, and less than about 0.06 wt. % Fe, the balance being aluminum and impurities (e.g., 0.05 wt. % of any other element, and 0.15 wt. % total of all other element). After casting, all alloys were processed similar to Example 1 to test the strength difference between the T6 and T8 tempers, except, unlike Example 1, the T8 products were produced with both 3% and 6% cold work for each alloy. The mechanical properties are tested, and results are illustrated in FIGS. 37-55.

(39) As shown in FIGS. 37-40, and 50-51, the new alloys should include at least about 0.30 wt. % Ag to facilitate good strength differential properties. Alloys I-II with 0.50 wt. % and 0.41 wt. % Ag are able to achieve a small (good) strength differential. Alloy IV with 0.12 wt. % Ag is not able to achieve a small strength differential. Alloy III with 0.31 wt. % Ag achieves a low strength differential after 64 hours of aging relative to the 3% CW product, but not relative to the 6% CW product. As shown in FIGS. 48-49, it may be difficult to achieve good strength differential properties for alloys having low Ag, even with increased Zn. These results indicate that the alloys should include at least about 0.30 wt. % Ag, and, in some cases, at least about 0.35 wt. % Ag, or more, to achieve good strength differential properties. For example, a range targeted around 0.5 wt. % Ag may be useful (e.g., 0.40 to 0.60 wt. % Ag).

(40) As shown in FIGS. 37, 41-44, and 52-53, the new alloys should include no more than 1.10 wt. % Li to facilitate low strength differential properties. Alloys I and V-VII all contain less than 1.10 wt. % Li, and achieve low strength differential properties. Alloy VIII contains 1.20 wt. % Li, but does not achieve low strength differential properties, and, in fact, achieves remarkably poor strength differential properties. Alloy V contains 0.54% Li, and achieves low strength differential properties. These results indicate that the alloys may include Li in the range of from about 0.10 wt. % to 1.10 wt. % Li, preferably in the range of from about 0.5 to about 1.0 wt. % Li, or a narrower range targeted around 0.80 wt. % Li to achieve good properties.

(41) As shown in FIGS. 37, 45-47 and 54-55, the new alloys should include at least 0.4 wt. % Zn, and preferably at least 0.50 wt. % Zn to facilitate low strength differential properties. Alloy XI having 0.39 wt. % Zn achieves low strength differential properties, but not nearly as good as Alloys I, IX, and X, which have 0.6 wt. %, 0.8 wt. % and 1.0 wt. % Zn. These results indicate that, when alloys require shorter aging times and/or lower strength differentials, Zn in the range of 0.5 to 1.0 wt. % should be used, or a narrower range targeted around 0.80 wt. % Zn.

Example 4Additional Bookmold Testing of 2xxx Alloys Having Li and Ag

(42) Additional bookmold testing is completed. Three aluminum alloys of varying composition are cast as bookmolds. The composition of each of the alloys is provided in Table 5, below. All values are in weight percent.

(43) TABLE-US-00005 TABLE 5 Composition of Example 4 Alloys Alloy Cu Mg Cu + Mg Cu/Mg Other AA 3.83 0.34 4.17 11.26 1.09 wt. % Li 0.49 wt. % Ag 0.51 wt. % Zn BB 3.81 0.34 4.15 11.21 1.06 wt. % Li 0.25 wt. % Ag 0.52 wt. % Zn CC 3.98 0.35 4.33 11.37 1.09 wt. % Li 0.12 wt. % Ag 0.52 wt. % Zn

(44) Unless otherwise indicated, all of these alloys also contained about 0.2-0.3 wt. % Mn, about 0.01-0.03 wt. % Ti, about 0.11-0.14 wt. % Zr, less than about 0.04 wt. % Si, and less than about 0.06 wt. % Fe, the balance being aluminum and impurities (e.g., 0.05 wt. % of any other element, and 0.15 wt. % total of all other element). After casting, all alloys were processed similar to Example 1 to test the strength difference between the T6 and T8 tempers, except, unlike Example 1, the T8 products were produced with 1.5% cold work for each alloy, and by a two-step artificial aging practice, with the second step occurring at 320 F.

(45) The mechanical properties are tested, and results are illustrated in FIG. 56. The data at 0 hours of aging is in the as quenched and stretched condition. The remaining data is all related to the second step of artificial aging at 320 F. The results for Alloy AA indicates that higher amounts of Zn may be required when the alloy include lithium near the upper limit of 1.10 wt. % Li. Even though Alloy AA was aged at a higher temperature than the previous examples, it took the alloy a longer equivalent period to reach an 8 ksi strength differential. Alloy BB and CC show that Ag should be maintained above 0.3 wt. %, and preferably above 0.35 or 0.4 wt. %, to achieve good strength differential properties.

Example 5Testing of Die Forgings

(46) Two ingots are cast, having the composition listed in Table 6, below. The ingots are homogenized. The ingots are then sawed into smaller billets. These billets are subjected to a series of die forging operations, including upsetting the as-cast billet, preforming and the final finish operation. All of the hot forming operations are carried out between 700-900 F. The forged parts are then solution heat treated and quenched. Half of these forged parts are then artificially aged, resulting in T6 temper pieces. The remaining forged pieces cold worked 6% by compression, and then artificial aged, resulting in T852 temper pieces.

(47) TABLE-US-00006 TABLE 6 Composition of Example 5 Alloys Alloy Cu Mg Cu + Mg Cu/Mg DF-1 3.51 0.33 3.84 10.64 DF-2 4.09 0.38 4.47 10.76

(48) All of these alloys also contained about 0.3 wt. % Mn, about 0.5 wt. % Ag, about 0.8 wt. % Li, about 0.8 wt. % Zn, about 0.03 wt. % Ti, about 0.12 wt. % Zr, less than about 0.04 wt. % Si, and less than about 0.06 wt. % Fe, the balance being aluminum and impurities (e.g., 0.05 wt. % of any other element, and 0.15 wt. % total of all other element).

(49) The mechanical properties are tested in the T6 and T8 tempers, the T8 temper having about 6% cold work, the results of which are illustrated in FIGS. 57 and 60. The forgings achieve low strength differential properties. Alloy DF-1 achieves a strength differential of less than 3 ksi in only 40 hours of aging. Alloy DF-2 achieves a strength differential of less than 2 ksi in only 40 hours of aging, with the T6 and T8 products achieving substantially equivalent strength sometime between 40 and 64 hours of aging. The results indicate that forgings having larger amounts of cold work differential could be produced and with low or negligible strength differential.

(50) The toughness properties of the alloys are also tested, the results of which are provided in Table 7, below.

(51) TABLE-US-00007 TABLE 7 Strength-Toughness Properties of Example 5 Alloys Strength Toughness Alloy/Temper Aging L TYS (ksi) L-T K.sub.IC (ksiin.) DF-1 (T6) 40 hrs @ 310 F. 77.5 21.4 64 hrs @ 310 F. 80.5 21.3 DF-1 (T8) 40 hrs @ 310 F. 82.6 23.2 64 hrs @ 310 F. 82.8 22.2 DF-2 (T6) 40 hrs @ 310 F. 75.1 26.7 64 hrs @ 310 F. 78.6 21.4 DF-2 (T8) 40 hrs @ 310 F. 78.2 34.4 64 hrs @ 310 F. 76.8 28.3

(52) This data shows that a good combination of strength-toughness can be achieved in wrought aluminum alloy products, and with a low strength differential across such products.

(53) While various embodiments of the present disclosure have been described in detail, it is apparent that modifications and adaptations of those embodiments will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present disclosure.