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HEAT TREATABLE ALUMINUM ALLOYS HAVING MAGNESIUM AND ZINC AND METHODS FOR PRODUCING THE SAME

20170145545 ยท 2017-05-25

    Inventors

    Cpc classification

    International classification

    Abstract

    New heat treatable aluminum alloys having magnesium and zinc are disclosed. The new aluminum alloys generally contain 3.0-6.0 wt. % Mg, 2.5-5.0 wt. % Zn, where (wt. % Mg)/(wt. % Zn) is from 0.60 to 2.40.

    Claims

    1. An automotive aluminum alloy sheet product consisting of: 3.75-6.0 wt. % Mg; 2.5-5.0 wt. % Zn; wherein (wt. % Mg)/(wt. % Zn) is from 0.75 to 2.40 up to 1.0 wt. % Cu; up to 0.5 wt. % Si; optionally at least one secondary element selected from the group consisting of Zr, Sc, Cr, Mn, Hf, V, Ti, and rare earth elements, and in the following amounts: up to 0.20 wt. % Zr; up to 0.30 wt. % Sc; up to 0.50 wt. % Cr; up to 1.0 wt. % Mn; up to 0.25 wt. % each of any of Hf, V, and rare earth elements; up to 0.15 wt. % Ti; up to 0.35 wt. Fe; up to 0.01 wt. % Li as an impurity; and the balance being aluminum and other elements, wherein the automotive aluminum alloy sheet product includes not greater than 0.15 wt. % each of these other elements, and wherein the total of these other elements does not exceed 0.35 wt. %.

    2. The automotive aluminum alloy sheet product of claim 1, wherein the automotive aluminum alloy sheet product includes at least 3.75 wt. % Mg.

    3. The automotive aluminum alloy sheet product of claim 1, wherein the automotive aluminum alloy sheet product includes not greater than 5.5 wt. % Mg.

    4. The automotive aluminum alloy sheet product of claim 1, wherein the automotive aluminum alloy sheet product includes not greater than 5.0 wt. % Mg.

    5. The automotive aluminum alloy sheet product of claim 1, wherein the automotive aluminum alloy sheet product includes not greater than 4.5 wt. % Mg.

    6. The automotive aluminum alloy sheet product of claim 1, wherein the automotive aluminum alloy sheet product includes at least 2.75 wt. % Zn.

    7. The automotive aluminum alloy sheet product of claim 1, wherein the automotive aluminum alloy sheet product includes at least 3.0 wt. % Zn.

    8. The automotive aluminum alloy sheet product of claim 1, wherein the automotive aluminum alloy sheet product includes at least 3.25 wt. % Zn.

    9. The automotive aluminum alloy sheet product of claim 1, wherein the automotive aluminum alloy sheet product includes not greater than 4.5 wt. % Zn.

    10. The automotive aluminum alloy sheet product of claim 1, wherein the automotive aluminum alloy sheet product includes not greater than 4.0 wt. % Zn.

    11. The automotive aluminum alloy sheet product of claim 1, wherein (wt. % Mg)/(wt. % Zn) is at least 0.75.

    12. The automotive aluminum alloy sheet product of claim 1, wherein (wt. % Mg)/(wt. % Zn) is at least 0.90.

    13. The automotive aluminum alloy sheet product of claim 1, wherein (wt. % Mg)/(wt. % Zn) is at least 1.00.

    14. The automotive aluminum alloy sheet product of claim 1, wherein (wt. % Mg)/(wt. % Zn) is at least 1.02.

    15. The automotive aluminum alloy sheet product of claim 1, wherein (wt. % Mg)/(wt. % Zn) is not greater than 2.00.

    16. The automotive aluminum alloy sheet product of claim 1, wherein (wt. % Mg)/(wt. % Zn) is not greater than 1.75.

    17. The automotive aluminum alloy sheet product of claim 1, wherein (wt. % Mg)/(wt. % Zn) is not greater than 1.50.

    18. The automotive aluminum alloy sheet product of claim 1, wherein the automotive aluminum alloy sheet product is one of a hood, a fender, a door, a roof, a trunk lid, or a body-in-white product of an automobile.

    19. A method comprising: (a) casting an aluminum alloy into an aluminum alloy body, wherein the aluminum alloy body consists of: 75-6.0 wt. % Mg; 5-5.0 wt. % Zn; wherein (wt. % Mg)/(wt. % Zn) is from 0.75 to 2.40 up to 1.0 wt. % Cu; up to 0.5 wt. % Si; optionally at least one secondary element selected from the group consisting of Zr, Sc, Cr, Mn, Hf, V, Ti, and rare earth elements, and in the following amounts: up to 0.20 wt. % Zr; up to 0.30 wt. % Sc; up to 0.50 wt. % Cr; up to 1.0 wt. % Mn; up to 0.25 wt. % each of any of Hf, V, and rare earth elements; up to 0.15 wt. % Ti; up to 0.35 wt. Fe; up to 0.01 wt. % Li as an impurity; and the balance being aluminum and other elements, wherein the aluminum alloy sheet product includes not greater than 0.15 wt. % each of these other elements, and wherein the total of these other elements does not exceed 0.35 wt. %; (b) processing the aluminum alloy body into one of a W temper and a T temper, wherein the processing step (b) comprises solution heat treating and then quenching the aluminum alloy body.

    20. The method of claim 19, wherein the processing step (b) comprises artificial aging the aluminum alloy body to one of a T6, T7 or a T8 temper, wherein the aluminum alloy body in the T6 or T7 temper realizes a higher strength than the aluminum alloy body in a T4 temper, or wherein the aluminum alloy body in the T8 temper realizes a higher strength than the aluminum alloy body in a T3 temper.

    Description

    BRIEF DESCRIPTION OF THE DRAWINGS

    [0022] FIGS. 1-3 are graphs illustrating results of Example 1.

    [0023] FIG. 4 contains micrographs of alloys of Example 1 showing their corrosion resistance.

    DETAILED DESCRIPTION

    Example 1

    [0024] Six book mold ingots were cast (2.25 (H)3.75 (W)14 (L)) having the compositions shown in Table 1, below.

    TABLE-US-00001 TABLE 1 Composition of Ex. 1 Alloys (in wt. %) Alloy Mg Zn Mg/Zn Cu Mn Note 1 3.88 2.13 1.82 0.48 0.31 Non-invention 2 3.31 3.2 1.03 0.48 0.32 Invention 3 4.34 3.25 1.34 0 0.53 Invention 4 3.87 2.17 1.78 0.25 0.32 Non-invention 5 3.89 2.19 1.78 0.25 0.64 Non-invention 6 3.72 3.56 1.04 0 0.32 Invention
    The alloys all contained not greater than about 0.12 wt. % Fe, not greater than about 0.11 wt. % Si, from about 0.01 to about 0.02 wt. % Ti, and from about 0.10 to 0.11 wt. % Zr. The remainder of the aluminum alloy was aluminum and other elements, where the aluminum alloy included not greater than 0.03 wt. % each of other elements, and with the total of these other elements not exceeding 0.10 wt. %.

    [0025] The ingots were processed to a T6-style temper. Specifically, the ingots were homogenized, hot rolled to 0.5 gauge, solution heat treated and cold water quenched, and then stretched about 1-2% for flatness. The products were then naturally aged at least 96 hours at room temperature and then artificially aged at various temperatures for various times (shown below). After aging, mechanical properties were measured, the results of which are provided in Tables 2-4, below. Strength and elongation properties were measured in accordance with ASTM E8 and B557. Charpy impact energy tests were performed according to ASTM E23-07a.

    TABLE-US-00002 TABLE 2 Properties (L) of Ex. 1 alloys - Aged at 325 F. Aging Time TYS UTS Elong. Alloy (hours) (ksi) (ksi) (%) 2 0 31.6 50.2 32.0 2 36.4 51.6 22.0 4 44.6 58.7 21.0 8 48.3 61.7 21.0 12 53.0 65.5 18.0 3 0 29.4 52.8 32.0 2 41.5 57.0 21.0 4 44.5 58.1 19.0 8 48.2 61.4 19.0 12 52.7 65.8 15.0 4 0 23.7 47.4 36.0 2 23.9 46.5 34.0 4 23.2 44.8 33.0 8 24.4 44.8 30.0 12 26.4 46.7 29.0 6 0 33.2 51.9 29.0 2 49.1 59.8 19.0 4 51.4 61.5 18.0 8 53.5 63.7 17.0 12 56.0 66.9 16.0

    TABLE-US-00003 TABLE 3 Properties (L) of Ex. 1 alloys - Aged at 350 F. Aging Time TYS UTS Elong. Charpy Impact Alloy (hours) (ksi) (ksi) (%) Energy (ft-lbf) 1 0 24.6 40.1 36.0 2 25.6 47.1 30.0 4 27.7 48.8 31.0 8 28.6 48.5 28.0 12 28.6 46.6 24.0 2 0 31.6 50.2 32.0 2 45.8 59.3 19.0 4 50.4 63.6 19.0 157 8 46.4 60.4 18.0 12 46.6 60.9 18.0 3 0 29.4 52.8 32.0 2 41.4 56.4 18.0 4 44.9 60.3 17.0 156 8 43.6 58.8 17.0 12 46.5 61.8 16.0 4 0 23.7 47.4 36.0 2 24.2 45.5 28.0 4 26.4 46.5 28.5 8 30.0 50.5 21.0 12 27.5 45.5 27.0 5 0 23.7 47.0 36.0 2 24.7 47.2 26.0 4 26.2 46.5 24.0 8 28.6 48.8 24.0 12 26.1 43.8 22.0 6 0 33.2 51.9 29.0 2 51.7 62.5 18.0 4 50.4 62.3 17.0 154 8 51.6 64.2 16.0 12 48.6 62.0 16.0

    TABLE-US-00004 TABLE 4 Properties (L) of Ex. 1 alloys - Aged at 375 F. Aging Time TYS UTS Elong. Alloy (hours) (ksi) (ksi) (%) 1 0 24.6 40.1 36.0 1 26.0 47.4 35.0 2 26.3 45.7 32.0 4 28.1 47.0 27.0 8 29.2 47.7 26.0 2 0 31.6 50.2 32.0 1 42.0 57.0 20.0 2 50.0 63.9 19.0 4 40.6 56.2 18.0 8 43.0 57.8 18.0 3 0 29.4 52.8 32.0 1 43.9 58.7 17.0 2 45.2 60.6 17.0 4 41.4 57.5 18.0 8 41.7 57.9 19.0 4 0 23.7 47.4 36.0 1 27.6 46.9 26.0 2 30.3 51.1 22.0 4 28.8 48.0 22.0 8 27.5 46.2 27.0 5 0 24.7 47.0 36.0 1 25.9 48.2 30.0 2 28.3 49.5 26.0 4 27.4 46.4 20.0 8 28.6 47.9 21.0 6 0 33.2 51.9 29.0 1 46.0 58.0 18.0 2 44.6 58.4 18.0 4 46.4 60.6 17.0 8 45.5 60.6 17.0

    [0026] As shown above, and in FIGS. 1-3, the invention alloys having at least 3.0 wt. % Zn achieve higher strengths than the non-invention alloys having 2.19 wt. % Zn or less. The invention alloy also realize high charpy impact resistance, all realizing about 154-157 ft-lbf. By comparison, conventional alloy 6061 realized a charpy impact resistance of about 85 ft-lbf under similar processing conditions.

    [0027] The invention alloys also realized good intergranular corrosion resistance. Alloys 3, 4 and 6 were tested for intergranular corrosion in accordance with ASTM G110. Conventional alloy 6061 was also tested for comparison purposes. As shown in FIG. 4 and in Table 5, below, the invention alloys realized improved intergranular corrosion resistance as compared to conventional alloy 6061.

    TABLE-US-00005 TABLE 5 Corrosion Properties of Alloys - Peak Strength Condition (385 F. for 2 hours) G110 - Depth of Attack - 24 hours (in.) Alloy T/10 (ave.) T10 (max.) Surface (ave.) Surface (max.) 1 0.00886 0.00948 0.00499 0.00847 2 0.00811 0.01060 0.00685 0.00929 3 0.00062 0.00091 0.00200 0.00287 4 0.00063 0.00084 0.00291 0.00494 5 0.00064 0.00071 0.00522 0.00935 6 0.00078 0.00100 0.00729 0.02348 6061 0.01044 0.01385 0.00822 0.01141

    Example 2

    [0028] Alloy 6 of Example 1 was also processed with high cold work after solution heat treatment. Specifically, Alloy 6 was hot rolled to an intermediate gauge of 1.0 inch, solution heat treated, cold water quenched, and then cold rolled 50% (i.e., reduced in thickness by 50%) to a final gauge of 0.5 inch, thereby inducing 50% cold work. Alloy 6 was then artificially aged at 350 F. for 0.5 hour and 2 hours. Before and after aging, mechanical properties were measured, the results of which are provided in Table 6, below. Strength and elongation properties were measured in accordance with ASTM E8 and B557.

    TABLE-US-00006 TABLE 6 Properties (L) of Ex. 2, Alloy 6 - Aged at 350 F. Aging Time TYS UTS Elong. (hours) (ksi) (ksi) (%) 0 58.5 68.6 13.0 0.5 58.9 67.2 16.0 2 56.0 64.7 16.0

    [0029] As shown above, the 0.5 inch plate realizes high strength and with good elongation, achieving about a peak tensile yield strength of about 59 ksi, with an elongation of about 16% and with only 30 minutes of aging. By comparison, conventional alloy 5083 at similar thickness generally realizes a tensile yield strength (LT) of about 36 ksi at similar elongation and similar corrosion resistance.

    [0030] 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.