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2XXX ALUMINUM LITHIUM ALLOYS

20210404038 · 2021-12-30

    Inventors

    Cpc classification

    International classification

    Abstract

    New 2xxx aluminum alloys having are disclosed. The new 2xxx aluminum alloys generally include 2.5-3.9 wt. % Cu, 0.82-1.20 wt. % Li, 0.5-2.0 wt. % Zn, 0.10-0.60 wt. % Mn, 0.05-0.35 wt. % Mg, from 0.05 to 0.50 wt. % of at least one grain structure control element, wherein the at least one grain structure control element is selected from the group consisting of Zr, Sc, Cr, V, Hf, other rare earth elements, and combinations thereof, up to 0.22 wt. % Ag, up to 0.15 wt. % Fe, up to 0.12 wt. % Si, and up to 0.15 wt. % Ti, the balance being aluminum, incidental elements and impurities. The new 2xxx aluminum alloys may realize an improved combination of two or more of strength, fracture toughness, elongation, and corrosion resistance.

    Claims

    1. A 2xxx aluminum alloy comprising: 3.1-3.8 wt. % Cu; 0.82-1.20 wt. % Li; 0.5-1.4 wt. % Zn; 0.10-0.60 wt. % Mn; 0.05-0.35 wt. % Mg; from 0.05 to 0.50 wt. % of at least one grain structure control element, wherein the at least one grain structure control element is selected from the group consisting of Zr, Sc, Cr, V, Hf, other rare earth elements, and combinations thereof, up to 0.05 wt. % Ag; up to 0.15 wt. % Fe; up to 0.12 wt. % Si; and up to 0.15 wt. % Ti; the balance being aluminum, incidental elements and impurities.

    2. The 2xxx aluminum alloy of claim 1, wherein the 2xxx aluminum alloy includes not greater than 0.01 wt. % Ag.

    3. The 2xxx aluminum alloy of claim 1, wherein the 2xxx aluminum alloy includes at least 0.7 wt. % Zn.

    4. The 2xxx aluminum alloy of claim 1, wherein the 2xxx aluminum alloy includes at least 0.10 wt. % Mg.

    5. The 2xxx aluminum alloy of claim 1, wherein (wt. % Cu)/(wt. % Zn) is not greater than 4.10.

    6. The 2xxx aluminum alloy of claim 1, wherein the 2xxx aluminum alloy is in the form of a wrought product having a thickness of at least 101.6 mm; and wherein the wrought product realizes at least one of: (i) a tensile yield strength (ST) of at least 440 MPa in the T8 temper; (ii) a plane-strain (K.sub.IC) fracture toughness (S-L) of at least 20 MPa-sqrt-m in the T8 temper; (iii) an elongation (ST) of at least 1.5% in the T8 temper; or (iv) wherein the wrought product is stress corrosion cracking resistant in the T8 temper.

    7. A 2xxx aluminum alloy comprising: 2.5-3.4 wt. % Cu; 0.82-1.20 wt. % Li; 1.1-2.0 wt. % Zn; 0.10-0.60 wt. % Mn; 0.05-0.35 wt. % Mg; from 0.05 to 0.50 wt. % of at least one grain structure control element, wherein the at least one grain structure control element is selected from the group consisting of Zr, Sc, Cr, V, Hf, other rare earth elements, and combinations thereof, up to 0.05 wt. % Ag; up to 0.15 wt. % Fe; up to 0.12 wt. % Si; and up to 0.15 wt. % Ti; the balance being aluminum, incidental elements and impurities.

    8. The 2xxx aluminum alloy of claim 7, wherein the 2xxx aluminum alloy includes not greater than 0.01 wt. % Ag.

    9. The 2xxx aluminum alloy of claim 7, wherein the 2xxx aluminum alloy includes at least 1.3 wt. % Zn.

    10. The 2xxx aluminum alloy of claim 7, wherein the 2xxx aluminum alloy includes not greater than 3.2 wt. % Cu.

    11. The 2xxx aluminum alloy of claim 7, wherein the 2xxx aluminum alloy includes at least 0.10 wt. % Mg.

    12. The 2xxx aluminum alloy of claim 7, wherein (wt. % Cu)/(wt. % Zn) is not greater than 3.5.

    13. The 2xxx aluminum alloy of claim 7, wherein the 2xxx aluminum alloy is in the form of a wrought product having a thickness of at least 101.6 mm; and wherein the wrought product realizes at least one of: (i) a tensile yield strength (ST) of at least 440 MPa in the T8 temper; (ii) a plane-strain (K.sub.IC) fracture toughness (S-L) of at least 20 MPa-sqrt-m in the T8 temper; (iii) an elongation (ST) of at least 1.5% in the T8 temper; or (iv) wherein the wrought product is stress corrosion cracking resistant in the T8 temper.

    Description

    BRIEF DESCRIPTION OF THE DRAWINGS

    [0063] FIGS. 1-2 are graphs illustrating the performance of various aluminum alloy products of Example 1.

    [0064] FIG. 3 is a graph illustrating the performance of various aluminum alloys products of Example 2.

    DETAILED DESCRIPTION

    Example 1—Plate Testing

    [0065] Various Al—Li alloys were cast as ingot and homogenized. The composition of each ingot is shown in Table 3a, below. Alloys A and B are invention alloys. Alloy C and the 2070 alloy are non-invention alloys. The 2070 alloy is described in, for instance, commonly-owned U.S. Patent Application Publication No. 2012/0225271.

    TABLE-US-00005 TABLE 3a COMPOSITION OF ALLOYS Alloy Si Fe Cu Mn Mg Zn Li Zr Ti A-1 0.02 0.03 3.57 0.29 0.24 0.94 0.92 0.10 0.02 A-2 0.05 0.03 3.46 0.32 0.27 1.00 0.94 0.10 0.02 B 0.04 0.04 2.96 0.32 0.21 1.42 0.98 0.09 0.02 C 0.05 0.04 3.70 0.33 0.38 0.84 0.97 0.10 0.02 2070 0.02 0.03 3.48 0.30 0.22 0.36 1.13 0.10 0.02

    [0066] The balance of each alloy was aluminum, incidental elements and impurities, with no one impurity exceeding 0.05 wt. %, and with the total amount of impurities not exceeding 0.15 wt. %. After homogenization, the alloys were hot rolled to final gauge, solution heat treated, quenched and stretched about 6%. Approximate final gauges are provided in Table 3b, below.

    TABLE-US-00006 TABLE 3b ALLOYS AND FINAL GAUGE Final Gauge Final Gauge Alloy (mm) (in.) A-1(i) 100 3.94 A-1(ii) 150 5.91 A-2(i) 100 3.94 A-2(ii) 150 5.91 B(i) 100 3.94 B(ii) 150 5.91 C(i) 100 3.94 C(ii) 150 5.91 2070(i) 100 3.94 2070(ii) 120 4.72

    [0067] Various two-step artificial aging practices are completed on the alloys, the first step being completed at 290° F. (143.3° C.) for various times, as provided in Table 4, below, the second step being 12 hours at 225° F. (107.2° C.). Various mechanical properties of the aged aluminum alloy plates are measured in accordance with ASTM E8 and B557. Fracture toughness properties of some samples were also measured and in accordance with ASTM E399. As shown by the below data and corresponding FIG. 1-2, the invention alloys realized an improved combination of properties in the short transverse direction.

    TABLE-US-00007 TABLE 4 Mechanical Properties (Short Transverse Direction) 1.sup.st Step Age Time TYS(ST) UTS(ST) Elong. K.sub.IC (S-L) Alloy (hrs) (MPa) (MPa) (ST)(%) (MPa-sqrt-m) A-1(i) 25 461.3 526.0 3.2 21.6 A-1(i) 30 466.1 531.9 3.7 23.1 A-1(i) 50 482.6 543.3 3.1 20.9 A-2(i) 25 466.0 529.0 4.7 21.2 A-2(i) 30 484.0 543.0 3.8 19.1 B(i) 40 446.1 509.5 3.7 25.9 B(i) 60 451.3 511.6 4.1 24.7 C(i) 25 473.3 538.5 2.8 19.7 C(i) 45 497.5 555.0 2.1 19.2 2070(i) 30 467.8 535.0 3.3 20.5 2070(i) 50 489.5 548.8 2.4 15.8 A-1(ii) 30 460.2 515.7 3.1 20.5 A-1(ii) 50 475.4 521.2 2.0 20.4 A-2(ii) 25 442.0 496.0 3.6 24.7 A-2(ii) 25 443.8 495.0 3.0 22.5 A-2(ii) 30 451.5 504.0 3.0 22.9 B(ii) 40 440.2 484.0 2.8 22.1 B(ii) 60 443.0 489.5 2.5 23.5 C(ii) 25 465.1 517.5 2.7 19.0 C(ii) 45 486.1 534.0 2.2 18.7 2070(ii) 30 461.3 527.4 3.4 18.2* (120 mm) 2070(ii) 50 482.6 538.1 2.7 16.5* (120 mm) *= K.sub.Q value

    [0068] At 100 mm, the new alloys generally realize improved fracture toughness at equivalent strength. For instance, invention alloy A-1 realizes about 3 MPa-sqrt-m higher strength over the 2070 alloy at about equivalent strength (at 30 hours of aging). Invention alloy A-2 also is improved over the 2070 alloy, and the A-2 alloy would be expected to achieve results similar to that of the Alloy A-1 if the silicon content of the A-2 alloy were reduced to 0.02 wt. %. Invention alloy B realizes very high fracture toughness at reduced strength levels, but would be expected to achieve results at least as good as A-1, if aged to equivalent strength. The improved properties are even more pronounced at 150 mm, where all of the invention alloys realized much better fracture toughness at equivalent strength. Notably, the invention alloys include less magnesium than non-invention alloy C. The invention alloys also have a Cu:Zn ratio (weight) of not greater than 4.25:1, whereas the non-invention alloys realize higher Cu:Zn ratios. The invention alloys also have more zinc than alloy C and non-invention alloy 2070.

    [0069] The stress corrosion cracking (SCC) resistance properties of many of the alloys were tested in the ST direction and in accordance with ASTM G44/G47. All of the invention alloys at all aging conditions realized, or were expected to realize, no failures at net stresses of 310 MPa and 379 MPa over a period of 30 days of testing (some alloys are still in test). Conversely, alloy C realized multiple failures at net stresses of 310 MPa and 379 MPa within the 30 day period and under the same testing conditions. This may be due to the fact that alloy C includes high magnesium, which may make alloy C prone to stress corrosion cracking. Alloy C could be aged further to improve corrosion, but its already poor fracture toughness would decrease. Conversely, invention alloys A and B achieve a good combination of four properties: strength, elongation, fracture toughness and stress corrosion cracking resistance.

    Example 2—Additional Plate Testing

    [0070] Three additional Al—Li alloys (all invention) were cast as ingot and homogenized, the compositions of which are shown in Table 5, below.

    TABLE-US-00008 TABLE 5 Compositions of Example 2 Alloys Alloy Si Fe Cu Mn Mg Zn Ag Li Zr Ti 1 0.04 0.04 3.46 0.27 0.26 0.98 — 0.96 0.10 0.03 2 0.07 0.07 3.63 0.27 0.26 0.97 — 0.96 0.09 0.02 3 0.06 0.04 3.50 0.26 0.22 0.96 — 0.97 0.09 0.02
    The balance of each alloy was aluminum, incidental elements and impurities, with no one impurity exceeding 0.05 wt. %, and with the total amount of impurities not exceeding 0.15 wt. %. After homogenization, the alloys were hot rolled to final gauge, solution heat treated, quenched and then stretched about 6%. The alloys were then artificially aged at various times and temperatures. The aging conditions are shown in Table 6.

    TABLE-US-00009 TABLE 6 Aging Conditions for Example 2 Alloys Condition First Step Second Step A 20 hours at 290° F. 12 hours at 225° F. B 30 hours at 290° F. C 40 hours at 290° F.
    The alloys were cooled to room temperature between aging steps.

    [0071] The through-thickness mechanical properties of the alloys were then tested, the results of which are shown in Table 7, below.

    TABLE-US-00010 TABLE 8 SCC test results (days in test) Final Gauge Aging Sample Sample Sample Alloy (mm) Condition 1 2 3 1 59.8 A T T T B T T T 2 60.8 A T T T B T T T 3 107.4 A T T T B T T T T = still had not failed after 20 days in test.

    [0072] As shown in FIG. 3, Alloys 1-2, having a thickness of about 60 mm, realize an excellent combination of strength and fracture toughness. Alloy 3 realizes a similar strength-toughness trend as the 100 mm alloys of Example 1.

    [0073] The stress corrosion cracking (SCC) resistance properties of many of the alloys were also tested in the ST direction as per Example 1 at a net stress of 310 MPa. The results are provided in Table 8, below.

    TABLE-US-00011 TABLE 7 Mechanical Properties of Example 2 Alloys Final ST ST ST S-L Gauge Aging TYS UTS Elong. K.sub.IC Alloy (mm) Condition (MPa) (MPa) (%) (MPa√m) 1 59.8 A 455 535 7.8 27.3 B 464 542 7.3 23.9 C 473 548 8.5 22.7 2 60.8 A 454 523 7.8 22.7 B 464 532 7.0 21.8 C 468 538 5.3 21.3 3 107.4 A 443 510 6.0 22.7 B 460 524 5.8 22.0 C 463 523 5.0 22.3

    [0074] 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.