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NEW 6XXX ALUMINUM ALLOYS, AND METHODS OF MAKING THE SAME

20170198376 ยท 2017-07-13

    Inventors

    Cpc classification

    International classification

    Abstract

    New 6xxx aluminum alloys having an improved combination of properties are disclosed. Generally, the new 6xxx aluminum alloys contain 1.00-1.45 wt. % Si, 0.32-0.51 wt. % Mg, wherein a ratio of wt. % Si to wt. % Mg is in the range of from 2.0:1 (Si:Mg) to 4.5:1 (Si:Mg), 0.12-0.44 wt. % Cu, 0.08-0.19 wt. % Fe, 0.02-0.30 wt. % Mn, 0.01-0.06 wt. % Cr, 0.01-0.14 wt. % Ti, and 0.25 wt. % Zn, the balance being aluminum and impurities, wherein the aluminum alloy includes 0.05 wt. % of any one impurity, and wherein the aluminum alloy includes 0.15 in total of all impurities.

    Claims

    1. An aluminum alloy consisting essentially of: 1.00-1.45 wt. % Si; 0.32-0.51 wt. % Mg; wherein a ratio of wt. % Si to wt. % Mg is in the range of from 2.0:1 (Si:Mg) to 4.5:1 (Si:Mg); 0.12-0.44 wt. % Cu; 0.08-0.30 wt. % Fe; 0.02-0.09 wt. % Mn; 0.01-0.06 wt. % Cr; 0.01-0.14 wt. % Ti; 0.25 wt. % Zn; the balance being aluminum and impurities, wherein the aluminum alloy includes0.05 wt. % of any one impurity, and wherein the aluminum alloy includes0.15 in total of all impurities.

    2. The aluminum alloy of claim 1, having from 1.03 wt. % to 1.40 wt. % Si.

    3. The aluminum alloy of claim 1, having from 1.09 wt. % to 1.30 wt. % Si.

    4. The aluminum alloy of claim 1, having from 0.32 wt. % to 0.51 wt. % Mg.

    5. The aluminum alloy of claim 1, having from 0.35 wt. % to 0.47 wt. % Mg.

    6. The aluminum alloy of claim 1, wherein the ratio of wt. % Si to wt. % Mg is in the range of from 2.10:1 to 4.25 (Si:Mg).

    7. The aluminum alloy of claim 1, wherein the ratio of wt. % Si to wt. % Mg is in the range of from 2.40:1 to 3.60 (Si:Mg).

    8. The aluminum alloy of claim 1, having from 0.12 wt. % to 0.25 wt. % Cu.

    9. The aluminum alloy of claim 1, having from 0.15 wt. % to 0.20 wt. % Cu.

    10. The aluminum alloy of claim 1, having from 0.27 wt. % to 0.40 wt. % Cu.

    11. The aluminum alloy of claim 1, having from 0.06 to 0.14 wt. % Ti.

    12. The aluminum alloy of claim 1, having from 0.08 to 0.12 wt. % Ti.

    13. The aluminum alloy of claim 1, having not greater than 0.03 wt. % Zn.

    14. A method comprising: (a) continuously casting the 6xxx aluminum alloy of claim 1 into a 6xxx aluminum alloy strip (6AAS) having a casting thickness; (b) rolling the 6AAS to a target thickness, wherein the rolling comprises rolling the 6AAS in-line to the target thickness via at least two rolling stands, wherein the rolling comprises reducing the casting thickness by from 15% to 80% via the at least two rolling stands to achieve the target thickness; (ii) wherein the casting thickness of the 6AAS is reduced by from 1% to 50% by a first rolling stand, thereby producing an intermediate thickness; (iii) wherein the intermediate thickness of the 6AAS is reduced by from 1% to 70% by at least a second rolling stand; and (c) after the rolling step (b), solution heat-treating the 6AAS in-line or offline; (d) after the solution heat-treating the 6AAS in step (c), quenching the 6AAS.

    15. The method of claim 14, wherein the first rolling stand is a hot rolling stand.

    16. The method of claim 14, wherein the first rolling stand and a second rolling stand are hot rolling stands.

    17. The method of claim 14, wherein the rolling step (b) is free of any annealing treatment.

    18. The method of claim 14, wherein the 6AAS enters the first stand at a temperature of 700-1000 F.

    19. The method of claim 14, wherein the 6AAS enters a second stand at a temperature of 400-800 F.

    20. The method of claim 14, comprising: after the quenching, shipping the 6AAS as a coiled product, wherein the coiled product is in a T4 or a T43 temper; preparing formed products from the coiled product; and paint baking the formed products.

    Description

    BRIEF DESCRIPTION OF THE DRAWINGS

    [0049] FIG. 1 is a flow chart illustrating one embodiment of processing steps of the present invention.

    [0050] FIG. 2 is an additional embodiment of the apparatus used in carrying out the method of the present invention. This line is equipped with four rolling mills to reach a finer finished gauge.

    DETAILED DESCRIPTION

    Examples

    [0051] The following examples are intended to illustrate the invention and should not be construed as limiting the invention in any way.

    Example 1

    [0052] Two 6xxx aluminum alloys were continuously cast, and then rolled to an intermediate gauge in-line over two rolling stands. These 6xxx aluminum alloys were then cold rolled (off-line) to final gauge, then solution heat treated, then quenched, and then naturally aged for several days. Various mechanical properties of these alloys were then measured. The compositions, various processing conditions, and various properties of these alloys are shown in Tables 1-4, below.

    TABLE-US-00002 TABLE 1 Compositions of Continuously Cast 6xxx Aluminum Alloys (in wt. %) Material Si Fe Cu Mn Mg Cr Zn Ti Alloy CC1 1.14 0.16 0.15 0.05 0.38 0.02 0.01 0.09 Alloy CC2 1.13 0.17 0.34 0.05 0.38 0.02 0.01 0.08

    [0053] The balance of the alloys was aluminum and unavoidable impurities.

    TABLE-US-00003 TABLE 2 Processing Parameters for Continuously Cast 6xxx Aluminum Alloys Offline 1.sup.st Stand 2.sup.nd Stand Cold Cast Final Reduction Reduction Rolling Lot Gauge Gauge (%) (HR) (%) (HR) Reduction Material No. (in.) (in.) (inline) (inline) (%) (CR) Alloy CC1 531 0.140 0.0453 25 42 26 Alloy CC1 471 0.140 0.0591 25 24 26 Alloy CC2 541 0.140 0.0453 25 42 26 Alloy CC2 511 0.140 0.0591 25 24 26

    [0054] Upon 30 days of natural aging, various samples of the two 6xxx aluminum alloys were then artificially aged, with some samples being pre-strained (PS) by stretching prior to the artificial aging. Various mechanical properties and the intergranular corrosion resistance of these alloys were then measured, the results of which are shown in Tables 5-6, below.

    TABLE-US-00004 TABLE 6 IG Corrosion Resistance Properties for Example 1 Alloys Final Pre- Depth of Lot Gauge strain Art. Attack Mat. No. (in.) (PS) Aging (microns) Alloy 531 0.0453 0% 45 min @ 182 CC1 383 F. Alloy 471 0.0591 0% 45 min @ 192 CC1 383 F. Alloy 541 0.0453 0% 45 min @ 230 CC2 383 F. Alloy 511 0.0591 0% 45 min @ 225 CC2 383 F.

    [0055] As shown, alloys CC1-CC2 realize an improved combination of strength, formability, and corrosion resistance.

    Example 2

    [0056] Five additional 6xxx aluminum alloys were prepared as per Example 1. The compositions, various processing conditions, and various properties of these alloys are shown in Tables 7-10, below.

    TABLE-US-00005 TABLE 7 Compositions of Example 2 Alloys (in wt. %) Material Si Fe Cu Mn Mg Cr Zn Ti Alloy CC3 1.14 0.16 0.15 0.05 0.39 0.018 0.01 0.026 Alloy CC4 1.13 0.17 0.34 0.05 0.38 0.019 0.01 0.080

    [0057] The balance of the alloys was aluminum and unavoidable impurities.

    TABLE-US-00006 TABLE 8 Processing Parameters for Example 2 Alloys Offline 1.sup.st Stand 2.sup.nd Stand Cold Cast Final Reduction Reduction Rolling Lot Gauge Gauge (%) (HR) (%) (HR) Reduction Material No. (in.) (in.) (inline) (inline) (%) (CR) Alloy CC3 491 0.135 0.0591 24 23 26 Alloy CC4 571 0.14 0.0669 25 14 26

    TABLE-US-00007 TABLE 9 Mechanical Properties for Example 2 Alloys Final Natural U. T. Lot Gauge Age Meas. TYS UTS Elong. Elong. Material No. (in.) (days) Direction (MPa) (MPa) (%) (%) Alloy CC3 491 0.0591 30 L 142 248 24.9 29.9 Alloy CC3 491 0.0591 30 LT 139 247 24.8 30.6 Alloy CC3 491 0.0591 30 45 139 247 25.0 31.1 Alloy CC4 571 0.0669 30 L 152 263 25.3 30.1 Alloy CC4 571 0.0669 30 LT 149 263 24.5 30.5 Alloy CC4 571 0.0669 30 45 148 261 25.4 30.5

    TABLE-US-00008 TABLE 10 Additional Mechanical Properties for Example 2 Alloys Final Natural Lot Gauge Age Meas. R Material No. (in.) (days) Direction Value Delta R Alloy CC3 491 0.0591 30 L 0.78 0.01 Alloy CC3 491 0.0591 30 LT 0.76 Alloy CC3 491 0.0591 30 45 0.76 Alloy CC4 571 0.0669 30 L 0.75 0.03 Alloy CC4 571 0.0669 30 LT 0.77 Alloy CC4 571 0.0669 30 45 0.79

    [0058] Upon 30 days of natural aging, various samples of the five 6xxx aluminum alloys were then artificially aged, with some samples being pre-strained (PS) by stretching prior to the artificial aging. Various mechanical properties and the intergranular corrosion resistance of these alloys were then measured, the results of which are shown in Tables 11-12, below.

    TABLE-US-00009 TABLE 12 IG Corrosion Resistance Properties for Example 2 Alloys Final Pre- Depth of Lot Gauge strain Art. Attack Mat. No. (in.) (PS) Aging (microns) Alloy 491 0.0591 0% 45 min @ 227 CC3 383 F. Alloy 571 0.0669 0% 45 min @ 230 CC4 383 F.

    [0059] As shown, alloy CC3-CC4 realize an improved combination of strength, formability, and corrosion resistance. Measurement Standards

    [0060] The yield strength, tensile strength, and elongation measurements were all conducted in accordance with ASTM E8 and B557.

    [0061] FLD.sub.o (Engr %) was measured in accordance with ISO 12004-2:2008 standard, wherein the ISO standard is modified such that fractures more than 15% of the punch diameter away from the apex of the dome are counted as valid.

    [0062] As used herein, R value is the plastic strain ratio or the ratio of the true width strain to the true thickness strain as defined in the equation r value=w/t. The R value is measured using an extensometer to gather width strain data during a tensile test while measuring longitudinal strain with an extensometer. The true plastic length and width strains are then calculated, and the thickness strain is determined from a constant volume assumption. The R value is then calculated as the slope of the true plastic width strain vs true plastic thickness strain plot obtained from the tensile test. Delta R is calculated based on the following equation (1):


    Delta R=Absolute Value [(r.sub.pL+r_LT22*r_45)/2](1)

    where r_L is the R value in the longitudinal direction of the aluminum alloy product, where r_LT is the R value in the long-transverse direction of the aluminum alloy product, and where r_45 is the R value in the 45 direction of the aluminum alloy product.

    [0063] The intergranular corrosion resistance measurements were all conducted in accordance with ISO standard 11846(1995) (Method B) (the maximum value of two samples with five sites per sample is reported in the above examples).

    [0064] Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appending claims.