Patent Application
20250066883
Aluminum alloys are useful in a variety of applications. However, improving one property of an aluminum alloy without degrading another property is elusive. For example, it is difficult to increase the strength of a wrought aluminum alloy without affecting other properties such as fracture toughness or corrosion resistance. 7xxx (Al—Zn—Mg based) are prone to corrosion. See, e.g., Bonn, W. Gruhl, “The stress corrosion behaviour of high strength AlZnMg alloys,” Paper held at the International Meeting of Associazione Italiana di Metallurgie, “Aluminum Alloys in Aircraft Industries,” Turin, October 1976.
One U.S. Patent describing AA7050 alloys is U.S. Pat. No. 7,135,077. This patent describes alloys having a “lightly recrystallized microstructure” and “a high as-cast grain size,” which “could lead to a specific microstructure of the transformed and heat treated product that has a beneficial effect on the toughness, with no reduction in strength or other properties.”
Broadly, the present patent application relates to new 7xxx aluminum alloy products having an improved combination of properties, such as an improved combination of strength, ductility, and fracture toughness. The improved combination of properties may be due to, for instance, the new 7xxx aluminum alloy having a tailored microstructure. For instance, a new 7xxx aluminum alloy may include from 10-40% recrystallized grains. In one embodiment, at least some recrystallized grains are located on a periphery of unrecrystallized grains. In one embodiment, the recrystallized grains are achieved at least partially due to (i) the use of not greater than 0.11 wt. % Zr (or other anti-recrystallization agents) in the 7xxx aluminum alloy product, (ii) particle stimulated nucleation, or (iii) both. The improved combination of properties may be due to, at least in part, the new 7xxx aluminum alloy products having an appropriate grain size, such as an average grain size (d-bar) of at least 300 micrometers, wherein the average grain size is an area-weighted average circular equivalent diameter grain size. In one embodiment, the new 7xxx aluminum alloy products include a tailored amount of recrystallized areas relative to the average grain size of the new 7xxx aluminum alloy products. In one embodiment, a new 7xxx aluminum alloy product realizes an ID:d-bar ratio of from 0.5 and 2.0, wherein the ID:d-bar ratio is a ratio of (A) the average intercept distance (ID) to (B) the average grain size (d-bar) of the 7xxx aluminum alloy product. For purpose of calculating this ratio, the average intercept distance (ID) is the average distance between recrystallized areas of the 7xxx aluminum alloy product. Methods of determining average grain size (d-bar) and intercept distance, among other microstructural features, are described in the Microstructure Assessment Procedure, described below.
i. Compositions
The new 7xxx aluminum alloy products may be any 7xxx aluminum alloy suited for improvement by having the tailored microstructures described herein. Generally, the new 7xxx aluminum alloys will include from 5-10 wt. % Zn, 1-3 wt. % Mg and 1-3 wt. % Cu, among other things. In one embodiment, a new 7xxx aluminum alloy includes other minor alloying additions, such as manganese (e.g., 0.05-0.60 wt. % Mn).
In one embodiment, a new 7xxx aluminum alloy product may contain a low amount of recrystallization inhibitors, such as a low amount of zirconium, to facilitate partial recrystallization of the new 7xxx aluminum alloy product. In one embodiment, a new 7xxx aluminum alloy product may include not greater than 0.11 wt. % Zr, such as from 0.01 to 0.11 wt. % Zr. In one embodiment, a new 7xxx aluminum alloy product includes not greater than 0.10 wt. % Zr. In another embodiment, a new 7xxx aluminum alloy product includes not greater than 0.09 wt. % Zr. In yet another embodiment, a new 7xxx aluminum alloy product includes not greater than 0.08 wt. % Zr. In another embodiment, a new 7xxx aluminum alloy product includes not greater than 0.07 wt. % Zr.
In one embodiment, a new 7xxx aluminum alloy product includes at least 0.03 wt. % Zr. In another embodiment, a new 7xxx aluminum alloy product includes at least 0.04 wt. % Zr. In yet another embodiment, a new 7xxx aluminum alloy product includes at least 0.05 wt. % Zr. In another embodiment, a new 7xxx aluminum alloy product includes at least 0.06 wt. % Zr. In yet another embodiment, a new 7xxx aluminum alloy product includes at least 0.07 wt. % Zr.
As noted above, the new 7xxx aluminum alloys may include 0.05-0.60 wt. % Mn. In one embodiment, a 7xxx aluminum alloy includes at least 0.08 wt. %. Mn. In another embodiment, a new 7xxx aluminum alloy includes at least 0.10 wt. % Mn. In yet another embodiment, a new 7xxx aluminum alloy includes at least 0.12 wt. % Mn. In another embodiment, a new 7xxx aluminum alloy includes at least 0.15 wt. % Mn. In yet another embodiment, a new 7xxx aluminum alloy includes at least 0.18 wt. % Mn. In another embodiment, a new 7xxx aluminum alloy includes at least 0.20 wt. % Mn. In yet another embodiment, a new 7xxx aluminum alloy includes at least 0.22 wt. % Mn. In another embodiment, a new 7xxx aluminum alloy includes at least 0.25 wt. % Mn.
In one embodiment, a 7xxx aluminum alloy includes not greater than 0.55 wt. % Mn. In another embodiment, a 7xxx aluminum alloy includes not greater than 0.50 wt. % Mn. In yet another embodiment, a 7xxx aluminum alloy includes not greater than 0.45 wt. % Mn. In another embodiment, a 7xxx aluminum alloy includes not greater than 0.40 wt. % Mn. In yet another embodiment, a 7xxx aluminum alloy includes not greater than 0.35 wt. % Mn. In another embodiment, a 7xxx aluminum alloy includes not greater than 0.30 wt. % Mn. In yet another embodiment, a 7xxx aluminum alloy includes not greater than 0.28 wt. % Mn.
In some embodiments, a new 7xxx aluminum alloy is Mn-free containing less than 0.05 wt. % Mn.
The new 7xxx aluminum alloys may include up to 0.20 wt. % Cr. In one approach, a 7xxx aluminum alloy includes from 0.05 to 0.20 wt. % Cr. In another approach, a 7xxx aluminum alloy includes not greater than 0.15 wt. % Cr. In one embodiment, a 7xxx aluminum alloy includes not greater than 0.10 wt. % Cr. In another embodiment, a 7xxx aluminum alloy includes not greater than 0.08 wt. % Cr. In yet another embodiment, a 7xxx aluminum alloy includes not greater than 0.05 wt. % Cr. In another embodiment, a 7xxx aluminum alloy includes not greater than 0.04 wt. % Cr. In yet another embodiment, a 7xxx aluminum alloy includes not greater than 0.03 wt. % Cr. In another embodiment, a 7xxx aluminum alloy includes not greater than 0.02 wt. % Cr. In yet another embodiment, a 7xxx aluminum alloy includes not greater than 0.01 wt. % Cr. In another embodiment, a 7xxx aluminum alloy includes not greater than 0.005 wt. % Cr.
The new 7xxx aluminum alloys may include up to 0.20 wt. % V. In one approach, a 7xxx aluminum alloy includes from 0.05 to 0.20 wt. % V. In another approach, a 7xxx aluminum alloy includes not greater than 0.15 wt. % V. In one embodiment, a 7xxx aluminum alloy includes not greater than 0.10 wt. % V. In another embodiment, a 7xxx aluminum alloy includes not greater than 0.08 wt. % V. In yet another embodiment, a 7xxx aluminum alloy includes not greater than 0.05 wt. % V. In another embodiment, a 7xxx aluminum alloy includes not greater than 0.04 wt. % V. In yet another embodiment, a 7xxx aluminum alloy includes not greater than 0.03 wt. % V. In another embodiment, a 7xxx aluminum alloy includes not greater than 0.02 wt. % V. In yet another embodiment, a 7xxx aluminum alloy includes not greater than 0.01 wt. % V. In another embodiment, a 7xxx aluminum alloy includes not greater than 0.005 wt. % V.
The new 7xxx aluminum alloys may include up to 0.20 wt. % Fe. In one embodiment, a 7xxx aluminum alloy includes at least 0.01 wt. % Fe. In another embodiment, a 7xxx aluminum alloy includes at least 0.03 wt. % Fe. In yet another embodiment, a 7xxx aluminum alloy includes at least 0.05 wt. % Fe. In another embodiment, a 7xxx aluminum alloy includes at least 0.07 wt. % Fe. In yet another embodiment, a 7xxx aluminum alloy includes at least 0.09 wt. % Fc.
In one embodiment, a 7xxx aluminum alloy includes not greater than 0.18 wt. % Fc. In another embodiment, a 7xxx aluminum alloy includes not greater than 0.16 wt. % Fe. In yet another embodiment, a 7xxx aluminum alloy includes not greater than 0.14 wt. % Fe. In another embodiment, a 7xxx aluminum alloy includes not greater than 0.12 wt. % Fe. In some embodiments, iron is restricted to fairly low levels, which may facilitate improved bend properties. In one embodiment, a 7xxx aluminum alloy includes not greater than 0.10 wt. % Fe. In another embodiment, a 7xxx aluminum alloy includes not greater than 0.08 wt. % Fe. In yet another embodiment, a 7xxx aluminum alloy includes not greater than 0.06 wt. % Fe. In another embodiment, a 7xxx aluminum alloy includes not greater than 0.05 wt. % Fe. In yet another embodiment, a 7xxx aluminum alloy includes not greater than 0.04 wt. % Fc.
The new 7xxx aluminum alloys may include up to 0.15 wt. % Si. In one embodiment, a 7xxx aluminum alloy includes at least 0.01 wt. % Si. In another embodiment, a 7xxx aluminum alloy includes at least 0.03 wt. % Si. In yet another embodiment, a 7xxx aluminum alloy includes at least 0.05 wt. % Si.
In one embodiment, a 7xxx aluminum alloy includes not greater than 0.12 wt. % Si. In another embodiment, a 7xxx aluminum alloy includes not greater than 0.10 wt. % Si. In yet another embodiment, a 7xxx aluminum alloy includes not greater than 0.08 wt. % Si. In some embodiments, silicon is restricted to fairly low levels, which may facilitate improved bend properties. In one embodiment, a 7xxx aluminum alloy includes not greater than 0.07 wt. % Si.
In another embodiment, a 7xxx aluminum alloy includes not greater than 0.06 wt. % Si. In yet another embodiment, a 7xxx aluminum alloy includes not greater than 0.05 wt. % Si. In another embodiment, a 7xxx aluminum alloy includes not greater than 0.04 wt. % Si. In yet another embodiment, a 7xxx aluminum alloy includes not greater than 0.03 wt. % Si.
The new 7xxx aluminum alloys may include up to 0.15 wt. % Ti. In one embodiment, a 7xxx aluminum alloy includes at least 0.005 wt. % Ti. In another embodiment, a 7xxx aluminum alloy includes at least 0.01 wt. % Ti. In yet another embodiment, a 7xxx aluminum alloy includes at least 0.015 wt. % Ti. In another embodiment, a 7xxx aluminum alloy includes at least 0.020 wt. 9% Ti. In yet another embodiment, a 7xxx aluminum alloy includes at least 0.025 wt. % Ti
In one embodiment, a 7xxx aluminum alloy includes not greater than 0.12 wt. % Ti. In another embodiment, a 7xxx aluminum alloy includes not greater than 0.10 wt. % Ti. In yet another embodiment, a 7xxx aluminum alloy includes not greater than 0.08 wt. % Ti. In yet another embodiment, a 7xxx aluminum alloy includes not greater than 0.05 wt. % Ti.
The new 7xxx aluminum alloys generally include the stated alloying ingredients, the balance being aluminum, optional incidental elements, and impurities. As used herein, “incidental elements” means those elements or materials, other than the above listed elements, that may optionally be added to the alloy to assist in the production of the alloy. Examples of incidental elements include casting aids, such as deoxidizers. Optional incidental elements may be included in the alloy in a cumulative amount of up to 1.0 wt. %. As one non-limiting example, one or more incidental elements may be added to the alloy during casting to reduce or restrict (and in some instances eliminate) ingot cracking due to, for example, oxide fold, pit and oxide patches. These types of incidental elements are generally referred to herein as deoxidizers. Examples of some deoxidizers include Ca, Sr, and Be. When calcium (Ca) is included in the alloy, it is generally present in an amount of up to about 0.05 wt. %, or up to about 0.03 wt. %. In some embodiments, Ca is included in the alloy in an amount of about 0.001-0.03 wt % or about 0.05 wt. %, such as 0.001-0.008 wt. % (or 10 to 80 ppm). Strontium (Sr) may be included in the alloy as a substitute for Ca (in whole or in part), and thus may be included in the alloy in the same or similar amounts as Ca. Traditionally, beryllium (Be) additions have helped to reduce the tendency of ingot cracking, though for environmental, health and safety reasons, some embodiments of the alloy are substantially Be-free. When Be is included in the alloy, it is generally present in an amount of up to about 20 ppm. Incidental elements may be present in minor amounts, or may be present in significant amounts, and may add desirable or other characteristics on their own without departing from the alloy described herein, so long as the alloy retains the desirable characteristics described herein. It is to be understood, however, that the scope of this disclosure should not/cannot be avoided through the mere addition of an element or elements in quantities that would not otherwise impact on the combinations of properties desired and attained herein.
The new 7xxx aluminum alloys may contain low amounts of impurities. In one embodiment, a new 7xxx aluminum alloy includes not greater than 0.15 wt. %, in total, of the impurities, and wherein the aluminum alloy includes not greater than 0.05 wt. % of each of the impurities. In another embodiment, a new 7xxx aluminum alloy includes not greater than 0.10 wt. %, in total, of the impurities, and wherein the aluminum alloy includes not greater than 0.03 wt. % of each of the impurities.
In one embodiment, the new 7xxx aluminum alloy product has a composition consistent with AA7050, wherein the AA7050 consistent alloy may include from 0 to 0.11 wt. % Zr. That is, the new 7xxx aluminum alloy product has a composition consistent with conventional AA7050, but includes from 0 to 0.11 wt. % Zr, as opposed to the amount normally specified for AA7050. AA7150 may also be used and appropriately modified to have from 0 to 0.11 wt. % Zr.
In another embodiment, a new 7xxx aluminum alloy product has a composition consistent with AA7x40, wherein the AA7x40 consistent alloy may include from 0 to 0.11 wt. % Zr. That is, the new 7xxx aluminum alloy product has a composition consistent with conventional AA7x40 alloys, but includes from 0 to 0.11 wt. % Zr, as opposed to the amount normally specified for AA7x40 alloys. As used herein, AA7x40 alloys include 7040 and 7140 as well as other alloys that may be registered to the 7x40 designation.
In another embodiment, a new 7xxx aluminum alloy product has a composition consistent with AA7x85, wherein the AA7x85 consistent alloy may include from 0 to 0.11 wt. % Zr. That is, the new 7xxx aluminum alloy product has a composition consistent with conventional AA7x85 alloys, but includes from 0 to 0.11 wt. % Zr, as opposed to the amount normally specified for AA7x85 alloys. As used herein, AA7x85 alloys include 7085 and 7185 as well as other alloys that may be registered to the 7x85 designation.
In another embodiment, a new 7xxx aluminum alloy product has a composition consistent with AA7x65, wherein the AA7x65 consistent alloy may include from 0 to 0.11 wt. % Zr. That is, the new 7xxx aluminum alloy product has a composition consistent with conventional AA7x65 alloys, but includes from 0 to 0.11 wt. % Zr, as opposed to the amount normally specified for AA7x65 alloys. As used herein, AA7x65 alloys include 7065 as well as other alloys that may be registered to the 7x65 designation.
In another embodiment, a new 7xxx aluminum alloy product has a composition consistent with AA7x99, wherein the AA7x99 consistent alloy may include from 0 to 0.11 wt. % Zr. That is, the new 7xxx aluminum alloy product has a composition consistent with conventional AA7x99 alloys, but includes from 0 to 0.11 wt. % Zr, as opposed to the amount normally specified for AA7x99 alloys. As used herein, AA7x99 alloys include 7099 and 7199 as well as other alloys that may be registered to the 7x99 designation.
In one embodiment, a new 7xxx aluminum alloy has a composition as per commonly-owned U.S. Patent Application Publication No. 2017/0088920, i.e., a new 7xxx aluminum alloy includes 6.0-10.0 wt. % Zn, 1.3-2.3 wt. % Mg, and 1.2-2.6 wt. % Cu, up to 0.50 wt. % Mn, up to 0.15 wt. % Zr, up to 0.15 wt. % Ti, up to 0.15 wt. % Si, and up to 0.15 wt. % Fe, the balance being aluminum and other elements, wherein the wrought 7xxx aluminum alloy product includes not greater than 0.05 wt. % of any one of the other elements, and wherein the wrought 7xxx aluminum alloy product includes not greater than 0.15 wt. % in total of the other elements. The disclosures of U.S. Patent Application Publication No. 2017/0088920 as it relates to compositions of 7xxx aluminum alloys are incorporated herein by reference.
In one embodiment, a new 7xxx aluminum alloy has a composition as per commonly-owned U.S. Patent Application Publication No. 2020/0115780, i.e., a new 7xxx aluminum alloy includes from 0.15 to 0.50 wt. % Mn in combination with 5.5-7.5 wt. % Zn, 0.95-2.20 wt. % Mg, and 1.50-2.40 wt. % Cu, the balance being aluminum, normal grain structure control materials, grain refiners, and impurities, such as one or more of Zr, Cr, Sc, and Hf as grain structure control materials (e.g., from 0.05-0.25 wt. % each of one or more of Zr, Cr, Sc, and Hf), limiting the total amounts of these elements such that large primary particles do not form in the alloy, up to 0.15 wt. % Ti as a grain refiner, optionally with some of the titanium in the form of TiB2 and/or TiC, up to 0.20 wt. % Fe and up to 0.15 wt. % Si as impurities. The disclosures of U.S. Patent Application Publication No. 2020/0115780 as it relates to compositions of 7xxx aluminum alloys are incorporated herein by reference.
In another embodiment, a new 7xxx aluminum alloy has a composition as per commonly-owned U.S. Patent Application Publication No. 2021/0340656, i.e., a new 7xxx aluminum alloy includes from 0.05 to 1.0 wt. % Ag, from 5.5 to 9.0 wt. % Zn, from 1.2 to 2.6 wt. % Cu, from 1.3 to 2.5 wt. % Mg, up to 0.60 wt. % Mn, up to 1.0 wt. % of at least one grain structure control material, wherein the at least one grain structure control material is selected from the group consisting of Zr, Cr, V, Hf, other rare earth elements, and combinations thereof, up to 0.15 wt. % Ti, up to 0.20 wt. % Fe, up to 0.15 wt. % Si, not greater than 0.08 wt. % Sc, and not greater than 0.05 wt. % Li, the balance being aluminum, optional incidental elements and impurities. The disclosures of U.S. Patent Application Publication No. 2021/0340656 as it relates to compositions of 7xxx aluminum alloys are incorporated herein by reference.
In another embodiment, a new 7xxx aluminum alloy has a composition as per commonly-owned U.S. Patent Application Publication No. 2022/0106672, i.e., a new 7xxx aluminum alloy includes 5.5-6.5 wt. % Zn, 1.7-2.3 wt. % Cu, 1.3-1.7 wt. % Mg the balance being aluminum, normal grain structure control materials, grain refiners, and impurities, such as one or more of Zr, Cr, Sc, and Hf as grain structure control materials (e.g., from 0.05-0.25 wt. % each of one or more of Zr, Cr, Sc, and Hf), limiting the total amounts of these elements such that large primary particles do not form in the alloy, less than 0.15 wt. % Mn, up to 0.15 wt. % Ti as a grain refiner, optionally with some of the titanium in the form of TiB2 and/or TiC, and up to 0.20 wt. % Fe and up to 0.15 wt. % Si as impurities. The disclosures of U.S. Patent Application Publication No. 2022/0106672 as it relates to compositions of 7xxx aluminum alloys are incorporated herein by reference.
The new 7xxx aluminum alloys are generally substantially free of lithium, i.e., lithium is included only as an impurity, and generally at less than 0.04 wt. % Li, or less than 0.01 wt. % Li. The new 7xxx aluminum alloys are generally substantially free of silver, i.e., silver is included only as an impurity, and generally at less than 0.04 wt. % Ag, or less than 0.01 wt. % Ag. The new 7xxx aluminum alloys are generally substantially free of lead, i.e., lead is included only as an impurity, and generally at less than 0.04 wt. % Pb, or less than 0.01 wt. % Pb. The new 7xxx aluminum alloys are generally substantially free of cadmium, i.e., cadmium is included only as an impurity, and generally at less than 0.04 wt. % Cd, or less than 0.01 wt. % Cd. The new 7xxx aluminum alloys are generally substantially free of thallium, i.e., thallium is included only as an impurity, and generally at less than 0.04 wt. % Tl, or less than 0.01 wt. % Tl. The new 7xxx aluminum alloys are generally substantially free of scandium, i.e., scandium is included only as an impurity, and generally at less than 0.04 wt. % Sc, or less than 0.01 wt. % Sc. The new 7xxx aluminum alloys are generally substantially free of nickel, i.e., nickel is included only as an impurity, and generally at less than 0.04 wt. % Ni, or less than 0.01 wt. % Ni.
ii. Methods of Production
The new 7xxx aluminum alloys may be produced by casting (e.g., direct chill casting or continuously casting) into an ingot or strip followed by appropriate processing to achieve a variety of tempers, such as one of a T temper, a W temper, an O temper, or an F temper as per ANSI H35.1 (2009). In one embodiment, a new aluminum alloy is processed to a “T temper” (thermally treated), such as into any of a T1, T2, T3, T4, T5, T6, T7, T8, T9 or T10 temper as per ANSI H35.1 (2009). Of these, T6 and T7 tempers may be particularly relevant.
For instance, the new alloy may be prepared into wrought form, and in the appropriate temper, by direct chill (DC) casting the aluminum alloy into ingot form. After conventional scalping, lathing or peeling (if needed) and homogenization, which homogenization may be completed before or after scalping, the ingots may be further processed by hot working the product. The product may then be optionally cold worked and/or optionally annealed. After any cold work and any anneal (which may occur multiple times and in any order), the product may then be solution heat treated, quenched, such as in a gas (e.g. air), or a liquid (e.g., water) or both and to an appropriate temperature (e.g., quenched to ambient temperature), and then naturally and/or artificially aged.
In one approach, a new 7xxx product aluminum alloy product is processed to one of a F, W or T temper, wherein the processing comprises hot rolling the 7xxx aluminum alloy product to one of an intermediate gauge and a final gauge. In one embodiment, the hot rolling comprises (a) first rolling in a first direction and (b) second rolling in a second direction. In one embodiment, the first direction is one of the longitudinal and the transverse direction and the second direction is offset by from 45° to 90° from the first direction. It has been surprisingly found that hot rolling in at least two directions may facilitate one or more of the improved properties described herein.
The new 7xxx aluminum alloy products may have any suitable final gauge thickness. In one embodiment, a new 7xxx aluminum alloy is in the form of a thick wrought product. Thick wrought aluminum alloy products are those wrought products having a cross-sectional thickness of at least 50.8 mm (2 inches). The improved properties described herein may be achieved with thick wrought products having a thickness of up to 305 mm (12 inches). The wrought products may be rolled products, forged products or extruded products. In one embodiment, a new 7xxx aluminum alloy product has a thickness of at least 76.2 mm (3 inches). In another embodiment, a new 7xxx aluminum alloy product has a thickness of at least 101.6 mm (4 inches). In yet another embodiment, a new 7xxx aluminum alloy product has a thickness of at least 127 mm (5 inches). In another embodiment, a new 7xxx aluminum alloy product has a thickness of at least 152.4 mm (6 inches). In yet another embodiment, a new 7xxx aluminum alloy product has a thickness of at least 177.8 mm (7 inches). In another embodiment, a new 7xxx aluminum alloy product has a thickness of at least 203.2 mm (8 inches). In yet another embodiment, a new 7xxx aluminum alloy product has a thickness of at least 228.6 mm (9 inches). In one embodiment, a new 7xxx aluminum alloy product has a thickness of from 177.8 to 254 mm (7 to 10 inches).
iii. Microstructure
As noted above, the new 7xxx aluminum alloy products may realize a unique microstructure, which may at least partially give rise to the unique properties described herein. For instance, the 7xxx aluminum alloys may be partially recrystallized having from 10-40 vol. % recrystallized grains, as determined using the Recrystallization Determination Procedure, described below. As used herein, a fully unrecrystallized product contains less than 10% recrystallized grains, as determined using the Recrystallization Determination Procedure, described below. A partially recrystallized product contains from 10-90% recrystallized grains. A fully recrystallized product contains more than 90% recrystallized grains. Partially recrystallized products having from 10-40 vol. % recrystallized grains are within the preferred amount of recrystallization, but any partially recrystallized 7xxx aluminum alloy product may be within the scope of the present disclosure if it achieves the properties described herein.
In one approach, a new 7xxx aluminum alloy product is a partially recrystallized product having 10-40 vol. % recrystallized grains. In one embodiment, a partially recrystallized 7xxx aluminum alloy product comprises at least 12.5 vol. % recrystallized grains. In another embodiment, a partially recrystallized 7xxx aluminum alloy product comprises at least 15 vol. % recrystallized grains. In yet another embodiment, a partially recrystallized 7xxx aluminum alloy product comprises at least 17.5 vol. % recrystallized grains. In another embodiment, a partially recrystallized 7xxx aluminum alloy product comprises at least 20 vol. % recrystallized grains. In one embodiment, a partially recrystallized 7xxx aluminum alloy product comprises not greater than 37.5 vol. % recrystallized grains. In another embodiment, a partially recrystallized 7xxx aluminum alloy product comprises not greater than 35 vol. % recrystallized grains. In yet another embodiment, a partially recrystallized 7xxx aluminum alloy product comprises not greater than 32.5 vol. % recrystallized grains. In another embodiment, a partially recrystallized 7xxx aluminum alloy product comprises not greater than 30 vol. % recrystallized grains.
As noted above, in one embodiment, a partially recrystallized product may be produced by (i) the use of not greater than 0.11 wt. % Zr (or other anti-recrystallization agents) in the 7xxx aluminum alloy product, (ii) particle stimulated nucleation, or (iii) both. As it relates to particle simulated nucleation (PSN), a new 7xxx aluminum alloy may include a sufficient amount of second phase particles to promote PSN. Recrystallization via PSN may occur if suitable conditions and an amount of second phase particles exist during plastic deformation of a 7xxx aluminum alloy as it is processed into a suitable wrought product form.
In some embodiments, at least some recrystallized grains are located on a periphery of unrecrystallized grains. For instance, one or more recrystallized grains may partially or wholly surround at least some unrecrystallized grains. In one embodiment, at least some recrystallized grains only partially surround at least some unrecrystallized grains.
As noted above, a new 7xxx aluminum alloy product may realize an average grain size (d-bin) of at least 300 micrometers, wherein the average grain size is an area-weighted average circular equivalent diameter grain size. Grain size is to be determined in accordance with the Microstructure Assessment Procedure, described below. In one embodiment, a new 7xxx aluminum alloy product may realize an average grain size (d-bin) of at least 350 micrometers. In another embodiment, a new 7xxx aluminum alloy product may realize an average grain size (d-bin) of at least 400 micrometers. In yet another embodiment, a new 7xxx aluminum alloy product may realize an average grain size (d-bin) of at least 450 micrometers. In another embodiment, a new 7xxx aluminum alloy product may realize an average grain size (d-bin) of at least 500 micrometers.
As noted above, a new 7xxx aluminum alloy product may include a tailored amount of recrystallized areas relative to the average grain size of the new 7xxx aluminum alloy products. In one embodiment, a new 7xxx aluminum alloy product realizes an ID:d-bar ratio of from 0.5 and 2.0, wherein the ID:d-bar ratio is a ratio of (A) the average intercept distance (ID) to (B) the average grain size (d-bar) of the 7xxx aluminum alloy product. For purpose of calculating this ratio, the average intercept distance (ID) is the average distance between recrystallized areas of the 7xxx aluminum alloy product and is to be determined in accordance with the Microstructure Assessment Procedure, described below. In one embodiment, a new 7xxx aluminum alloy product realizes an ID:d-bar ratio of at least 0.6. In another embodiment, a new 7xxx aluminum alloy product realizes an ID:d-bar ratio of at least 0.7. In yet another embodiment, a new 7xxx aluminum alloy product realizes an ID:d-bar ratio of at least 0.8. In another embodiment, a new 7xxx aluminum alloy product realizes an ID:d-bar ratio of at least 0.9. In yet another embodiment, a new 7xxx aluminum alloy product realizes an ID:d-bar ratio of at least 1.0.
In one embodiment, a new 7xxx aluminum alloy product realizes an ID:d-bar ratio of not greater than 1.9. In another embodiment, a new 7xxx aluminum alloy product realizes an ID:d-bar ratio of not greater than 1.8. In yet another embodiment, a new 7xxx aluminum alloy product realizes an ID:d-bar ratio of not greater than 1.7. In another embodiment, a new 7xxx aluminum alloy product realizes an ID:d-bar ratio of not greater than 1.6. In yet another embodiment, a new 7xxx aluminum alloy product realizes an ID:d-bar ratio of not greater than 1.5. In another embodiment, a new 7xxx aluminum alloy product realizes an ID:d-bar ratio of not greater than 1.4. In yet another embodiment, a new 7xxx aluminum alloy product realizes an ID:d-bar ratio of not greater than 1.35. In another embodiment, a new 7xxx aluminum alloy product realizes an ID:d-bar ratio of not greater than 1.3. In yet another embodiment, a new 7xxx aluminum alloy product realizes an ID:d-bar ratio of not greater than 1.25.
iv. Properties
As noted above, the new 7xxx aluminum alloy products described herein may realize an improved combination of properties, such as an improved combination of two or more of strength, ductility, and fracture toughness.
In one embodiment, a new 7xxx aluminum alloy product realizes improved properties over a compositionally equivalent aluminum alloy at equivalent longitudinal strength, wherein the compositionally equivalent alloy is fully unrecrystallized.
In one approach, the improved properties are selected from the group consisting of LT elongation, ST elongation, T-L KIC fracture toughness, S-L KIC fracture toughness, and combinations thereof. The improvements may be realized in any wrought product form, but may be especially applicable to thick plate products having the microstructural features described herein.
In one embodiment, the improved properties are at least LT elongation properties, wherein a new 7xxx aluminum alloy product realizes at least 1% higher LT elongation as compared to the compositionally equivalent aluminum alloy. In another embodiment, a new 7xxx aluminum alloy product realizes at least 2% higher LT elongation as compared to the compositionally equivalent aluminum alloy. In yet another embodiment, a new 7xxx aluminum alloy product realizes at least 3% higher LT elongation as compared to the compositionally equivalent aluminum alloy. In another embodiment, a new 7xxx aluminum alloy product realizes at least 4% higher LT elongation as compared to the compositionally equivalent aluminum alloy. In yet another embodiment, a new 7xxx aluminum alloy product realizes at least 5% higher LT elongation as compared to the compositionally equivalent aluminum alloy. In another embodiment, a new 7xxx aluminum alloy product realizes at least 6% higher LT elongation as compared to the compositionally equivalent aluminum alloy. In yet another embodiment, a new 7xxx aluminum alloy product realizes at least 7% higher LT elongation as compared to the compositionally equivalent aluminum alloy. In another embodiment, a new 7xxx aluminum alloy product realizes at least 8% higher LT elongation as compared to the compositionally equivalent aluminum alloy. In yet another embodiment, a new 7xxx aluminum alloy product realizes at least 9% higher LT elongation as compared to the compositionally equivalent aluminum alloy. In another embodiment, a new 7xxx aluminum alloy product realizes at least 10% higher LT elongation as compared to the compositionally equivalent aluminum alloy. In yet another embodiment, a new 7xxx aluminum alloy product realizes at least 15% higher LT elongation as compared to the compositionally equivalent aluminum alloy. In another embodiment, a new 7xxx aluminum alloy product realizes at least 20% higher LT elongation as compared to the compositionally equivalent aluminum alloy. In yet another embodiment, a new 7xxx aluminum alloy product realizes at least 25% higher LT elongation as compared to the compositionally equivalent aluminum alloy. In another embodiment, a new 7xxx aluminum alloy product realizes at least 30% higher LT elongation as compared to the compositionally equivalent aluminum alloy. In yet another embodiment, a new 7xxx aluminum alloy product realizes at least 35% higher LT elongation as compared to the compositionally equivalent aluminum alloy. In another embodiment, a new 7xxx aluminum alloy product realizes at least 40% higher LT elongation as compared to the compositionally equivalent aluminum alloy.
In one embodiment, the improved properties are at least T-L fracture toughness properties, wherein a new 7xxx aluminum alloy product realizes at least 1% higher T-L KIC properties as compared to the compositionally equivalent aluminum alloy. In another embodiment, a new 7xxx aluminum alloy product realizes at least 2% higher T-L KIC properties as compared to the compositionally equivalent aluminum alloy. In yet another embodiment, a new 7xxx aluminum alloy product realizes at least 3% higher T-L KIC properties as compared to the compositionally equivalent aluminum alloy. In another embodiment, a new 7xxx aluminum alloy product realizes at least 4% higher T-L KIC properties as compared to the compositionally equivalent aluminum alloy. In another embodiment, a new 7xxx aluminum alloy product realizes at least 5% higher T-L KIC properties as compared to the compositionally equivalent aluminum alloy.
In one embodiment, the improved properties are at least ST elongation properties, wherein a new 7xxx aluminum alloy product realizes at least 1% higher ST elongation as compared to the compositionally equivalent aluminum alloy. In another embodiment, a new 7xxx aluminum alloy product realizes at least 2% higher ST elongation as compared to the compositionally equivalent aluminum alloy. In yet another embodiment, a new 7xxx aluminum alloy product realizes at least 3% higher ST elongation as compared to the compositionally equivalent aluminum alloy. In another embodiment, a new 7xxx aluminum alloy product realizes at least 4% higher ST elongation as compared to the compositionally equivalent aluminum alloy. In yet another embodiment, a new 7xxx aluminum alloy product realizes at least 5% higher ST elongation as compared to the compositionally equivalent aluminum alloy. In another embodiment, a new 7xxx aluminum alloy product realizes at least 6% higher ST elongation as compared to the compositionally equivalent aluminum alloy. In yet another embodiment, a new 7xxx aluminum alloy product realizes at least 7% higher ST elongation as compared to the compositionally equivalent aluminum alloy. In another embodiment, a new 7xxx aluminum alloy product realizes at least 8% higher ST elongation as compared to the compositionally equivalent aluminum alloy. In yet another embodiment, a new 7xxx aluminum alloy product realizes at least 9% higher ST elongation as compared to the compositionally equivalent aluminum alloy. In another embodiment, a new 7xxx aluminum alloy product realizes at least 10% higher ST elongation as compared to the compositionally equivalent aluminum alloy. In yet another embodiment, a new 7xxx aluminum alloy product realizes at least 15% higher ST elongation as compared to the compositionally equivalent aluminum alloy. In another embodiment, a new 7xxx aluminum alloy product realizes at least 20% higher ST elongation as compared to the compositionally equivalent aluminum alloy.
In one embodiment, the improved properties are at least S-L fracture toughness properties, wherein a new 7xxx aluminum alloy product realizes at least 1% higher S-L KIC properties as compared to the compositionally equivalent aluminum alloy. In another embodiment, a new 7xxx aluminum alloy product realizes at least 2% higher S-L KIC properties as compared to the compositionally equivalent aluminum alloy. In yet another embodiment, a new 7xxx aluminum alloy product realizes at least 3% higher S-L KIC properties as compared to the compositionally equivalent aluminum alloy. In another embodiment, a new 7xxx aluminum alloy product realizes at least 4% higher S-L KIC properties as compared to the compositionally equivalent aluminum alloy. In another embodiment, a new 7xxx aluminum alloy product realizes at least 5% higher S-L KIC properties as compared to the compositionally equivalent aluminum alloy.
In one embodiment, a new 7xxx aluminum alloy product realizes at least two of higher LT elongation, higher ST elongation, higher T-L KIC, and higher S-L KIC as compared to a compositionally equivalent aluminum alloy at equivalent longitudinal strength. In another embodiment, a new 7xxx aluminum alloy product realizes at least three of higher LT elongation, higher ST elongation, higher T-L KIC, and higher S-L KIC as compared to a compositionally equivalent aluminum alloy at equivalent longitudinal strength. In yet another embodiment, a new 7xxx aluminum alloy product realizes all of higher LT elongation, higher ST elongation, higher T-L KIC, and higher S-L KIC as compared to a compositionally equivalent aluminum alloy at equivalent longitudinal strength. These improvements may be realized in any wrought product form, but may be especially applicable to thick plate products having the microstructural features described herein.
In one approach, the new 7xxx aluminum alloy product has a composition consistent with AA7050, wherein the AA7050 consistent alloy may include from 0 to 0.11 wt. % Zr and the compositionally equivalent aluminum alloy is a standard AA7050 alloy having 0.11-0.13 wt. % Zr. In one embodiment, the AA7050 consistent alloy realizes at least one of higher LT elongation, higher ST elongation, higher T-L KIC, and higher S-L KIC as compared to the standard AA7050 alloy at equivalent longitudinal strength. In another embodiment, the AA7050 consistent alloy realizes at least two of higher LT elongation, higher ST elongation, higher T-L KIC, and higher S-L KIC as compared to the standard AA7050 alloy at equivalent longitudinal strength. In yet another embodiment, the AA7050 consistent alloy realizes at least three of higher LT elongation, higher ST elongation, higher T-L KIC, and higher S-L KIC as compared to the standard AA7050 alloy at equivalent longitudinal strength. In another embodiment, the AA7050 consistent alloy realizes all of higher LT elongation, higher ST elongation, higher T-L KIC, and higher S-L KIC as compared to the standard AA7050 alloy at equivalent longitudinal strength. These improvements may be realized in any wrought product form suited to AA7050, but may be especially applicable to thick plate AA7050 products having the microstructural features described herein.
The new aluminum alloys described herein may be used in a variety of product applications, such as in aerospace applications. For instance, the new alloys may be used as ribs, spars, frames (thick and thin), side of body fittings/attachments, bulky fittings/lugs, bulkheads, monolithic/built-up cargo floor structures, and landing gear/pylon/engine support structures for airplanes/aerospace vehicles. The new alloys may also be used as armor products, such as in armored vehicles and the like.
vi. Definitions
“Wrought aluminum alloy product” means an aluminum alloy product that is hot worked after casting, and includes rolled products (sheet or plate), forged products, and extruded products.
“Hot working” such as by hot rolling means working the aluminum alloy product at elevated temperature, and generally at least 121.1° C. (250° F.). Strain-hardening is restricted/avoided during hot working, which generally differentiates hot working from cold working.
“Cold working” such as by cold rolling means working the aluminum alloy product at temperatures that are not considered hot working temperatures, generally below about 121.1° C. (250° F.) (e.g., at ambient).
Temper definitions are per ANSI H35.1 (2009), entitled “American National Standard Alloy and Temper Designation Systems for Aluminum,” published by The Aluminum Association.
Strength and elongation are measured in accordance with ASTM E8/E8M-21 and B557-15. Fracture toughness is measured in accordance with ASTM E399-20a and B645-21.
vii. Microstructure Assessment Procedure
The following procedures and definitions apply to measuring microstructure features (e.g., percent recrystallization, grain size, grain intercepts) for products made in accordance with present patent application.
The term “grain” has the meaning defined in ASTM E2627-13 (2019) § 3.1.6, i.e. “a group of similarly oriented neighboring points on the scan grid. The group is surrounded by a perimeter where misorientation across that perimeter exceeds a specified tolerance value.”
“Grain size” is calculated by the following equation:
“Average Intercept Distance” means the average distance between recrystallized grains (sometimes called “first grains” herein) as determined by ASTM E112-13 (2021) § 17.6 and E1382-97 (2015) § 13.7.5. Here, the measured chord lengths are not the distances between grain boundaries, but rather the distances between recrystallized areas. Furthermore, the “parallel straight test lines” were not applied randomly, but aligned with the rolling or longitudinal direction (L) to determine the distribution along that specific axis. Average Intercept Distance (ID) was measured using commercial image analysis software MIPAR, version 3.3.4.
“Percent recrystallized” and the like means the volume percent of a wrought aluminum alloy product having recrystallized grains. The amount of recrystallized grains is determined by EBSD (electron backscatter diffraction) analysis of a suitable area of the wrought aluminum alloy product, as per the Recrystallization Determination Procedure, below. Generally the measured area should be homogenous and representative of the bulk volume being analyzed. As described in ASTM standards (E112, E930, E1181), accuracy will increase with the number of grains measured. Per ASTM E2627-13 (2019) § 12.4 the area measured should contain at least 500 grains.
a. Recrystallization Determination Procedure
“Recrystallized grains” means those grains of a crystalline microstructure that meet the “first grain criteria”, defined below, and as measured using the electron backscatter diffraction (EBSD) sampling procedure, described below.
The EBSD analysis is to be completed at defined volumes of the plate, notably the T/4 (defined as 25% distance from the plate surfaces) on the L-ST plane, using the EBSD sample procedure, below. The size of the sample to be analyzed will generally vary by gauge; for thinner plates, the ST dimension may need to be limited to avoid microstructural heterogeneities. Prior to measurement, the EBSD samples are prepared by standard metallographic sample preparation methods. For example, the EBSD samples are metallographically prepared and then polished (e.g., using 0.05 micron colloidal silica). The samples are then etched by immersing in a solution of 0.5% hydrofluoric acid HF solution for 5 seconds, and then rinsed and dried.
The “EBSD sample procedure” is as follows:
“First grain volume” (FGV) means the volume fraction of first type grains of the crystalline material.
“Percent Recrystallized” (ReX %) is determined via the formula: FGV*100%.
viii. Miscellaneous
These and other aspects, advantages, and novel features of this new technology are set forth in part in the description that follows and will become apparent to those skilled in the art upon examination of the following description and figures, or may be learned by practicing one or more embodiments of the technology provided for by the present disclosure.
Among those benefits and improvements that have been disclosed, other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying figures. Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely illustrative of the invention that may be embodied in various forms. In addition, each of the examples given in connection with the various embodiments of the invention is intended to be illustrative, and not restrictive.
Throughout the specification and claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise. The phrases “in one embodiment” and “in some embodiments” as used herein do not necessarily refer to the same embodiment(s), though they may. Furthermore, the phrases “in another embodiment” and “in some other embodiments” as used herein do not necessarily refer to a different embodiment, although they may. Thus, various embodiments of the invention may be readily combined, without departing from the scope or spirit of the invention.
In addition, as used herein, the term “or” is an inclusive “or” operator, and is equivalent to the term “and/or,” unless the context clearly dictates otherwise. The term “based on” is not exclusive and allows for being based on additional factors not described, unless the context clearly dictates otherwise. In addition, throughout the specification, the meaning of “a,” “an,” and “the” include plural references, unless the context clearly dictates otherwise. The meaning of “in” includes “in” and “on”, unless the context clearly dictates otherwise.
While a number of embodiments of the present invention have been described, it is understood that these embodiments are illustrative only, and not restrictive, and that many modifications may become apparent to those of ordinary skill in the art. Further still, unless the context clearly requires otherwise, the various steps may be carried out in any desired order, and any applicable steps may be added and/or eliminated.
Several different AA7050 materials were produced, the compositions of which are shown below.
AA7050 Alloys 1-3 and 7-8 with 0.08 wt. % Zr are invention alloys. AA7050 alloys 4-6 and 9-11 with 0.11 wt. % Zr are non-invention alloys.
To produce the materials, ingots were conventionally scalped/peeled, homogenized, and then rolled to a final gauge of either 220 mm (8.7 inches) or 170 mm (6.7 inches). These plates were then solution heat treated, then cold water quenched, then stretched, then naturally aged for a minimum of 72 hours and then artificially aged to a T7451 temper. The mechanical properties of the materials are shown in Tables 2a-2c, below. Microscopy data is shown in Table 4, below. Percent recrystallization, grain size, and intercept distances were determined in accordance with the Microstructure Assessment Procedure, included herein.
Tables 3a-3c, below, compare the average invention versus average non-invention properties for the alloys at the two gauges.
As shown, the invention alloys generally realize similar or slightly worse performance in the L direction. This is more than compensated by the improvement in elongation and fracture toughness in the LT and ST directions and at generally similar strength.
As the microscopy data shows, the invention alloys are partially recrystallized and realize much smaller distances between recrystallized areas as compared to the non-invention alloys. The grain size is also much smaller. The ratio of the Average Intercept Distance to Average Grain Size is significantly different, as well.
Although the unexpected improvements shown above are relative to a partially recrystallized AA7050 product, it is anticipated that such unexpected improvements could be realized in other 7xxx aluminum alloy products, including those described herein.
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.
This application is a continuation of International Patent Application No. PCT/US2023/022409, entitled “New 7XXX Aluminum Alloy Products,” filed May 16, 2023, which claims the benefit of U.S. Provisional Patent Application No. 63/343,074 entitled “New 7XXX Aluminum Alloy Products,” filed May 17, 2022. Each of the above-identified patent applications are hereby incorporated by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63343074 | May 2022 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/US2023/022409 | May 2023 | WO |
| Child | 18940036 | US |
