Low Cost, Substantially Zr-Free Aluminum-Lithium Alloy for Thin Sheet Product with High Formability

A low cost, substantially Zr-free, low density 2xxx aluminum-lithium alloy is disclosed. The aluminum-lithium alloy can be produced to high formability sheet products capable of being formed into wrought products with a thickness of 0.01″ to 0.249″. Aluminum-lithium alloys of the invention comprise from 3.2 to 4.1 wt. % Cu, 1.0 to 1.8 wt. % Li, 0.8 to 1.2 wt. % Mg, 0.10 to 0.50 wt. % Zn, 0.10 to 1.0 wt. % Mn, up to 0.12 wt. % Si, up to 0.15 wt. % Fe, up to 0.15 wt. % Ti, up to 0.15 wt. % incidental elements, with the total of these incidental elements not exceeding 0.35 wt. %, and the balance being aluminum. Ag should not be intentionally added and should not be more than 0.1 wt. % as a non-intentionally added element. Zr should not be intentionally added and should not be more than 0.05 wt. % as a non-intentionally added element. Mg is at least equal to or higher than 2*Zn in weight percent in the invented alloy. Methods for manufacturing wrought products including aluminum-lithium alloys of the present invention are also provided.

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Description
BACKGROUND OF THE INVENTION 1. Field of the Invention

This present invention generally relates to Aluminum-Copper-Lithium-Magnesium based alloy products.

2. Description of Related Art

In order to aggressively reduce aircraft weight for better fliel efficiency, low density aluminum-lithium alloys are being aggressively pursued by airframe and aluminum material manufacturers. The forming process is very crucial for making the complex parts, especially for aircraft applications requiring aluminum sheet. While formability is important, airframe manufacturers also desire lower density, higher strength, better corrosion resistance, and higher fracture toughness to achieve weight reduction, lower aircraft maintenance, and operational cost.

It is an extreme metallurgical and technical challenge to produce aluminum-lithium (Al—Li) products in thin sheets, where high performance is also required in terms of material strength, formability, fracture toughness, fatigue resistance, and corrosion resistance.

One of the metallurgical goals is to achieve the desired microstructure and texture to provide the desired properties. This is especially difficult to control for thin sheet, Al—Li products. The microstructure and texture are strongly affected by chemical composition of the alloy and most of the manufacturing steps, i.e. homogenization, hot and cold rolling, annealing, solution heat treatment, and stretching.

Al—Li sheet, especially thin sheet, is much more difficult to manufacture than conventional 2xxx and 7xxx alloys. This is the result of thin Al—Li sheets being more sensitive to rolling cracking, surface oxidation, and distortion. Due to these limitations, there is a small processing window that can be used to optimize the desired microstructure and texture.

Therefore, this is a significant challenge to design an aluminum-lithium sheet alloy which achieves the desired combination of properties (strength, formability, and cost with good damage tolerance and corrosion resistance). These fabrication technical challenges severely restrict the production of high strength thin sheet Al—Li products.

As a consequence, there is only one Al—Li alloy, i.e. AA2090, registered for rolling sheet products with a thickness less than 0.063″, and only one additional alloy, i.e. AA2198, registered for rolling sheet products with a thickness less than 0.125″, and only two additional alloys, i.e. AA2195 and AA2199, registered for rolling sheet/plate products with a thickness less than 0.5″, based on “Registration Record Series—Tempers for Aluminum and Aluminum Alloys Production” published in 2011 and “Addendum to 2011 Tan Sheets of Registration Record Series Tempers for Aluminum and Aluminum Alloys Production” published in 2017 by The Aluminum Association.

These metallurgical and technical challenges for rolling thin sheet products are also reflected in the patents and patent applications. In fact, a significant amount of patents or patent applications are mostly related to plate products (>0.5″), but only a few apply to sheet products.

From a formability perspective, the desired metallurgical structure would have fine recrystallized grains. This is a critical feature in obtaining the desired formability. The grain structure can be affected by both chemistry and processing parameters. From a chemistry perspective, it is well known that Zr is widely added as a grain structure control element in most Al—Li and 7xxx alloy series. In “International Alloy Designation and. Chemical Composition Limits for Wrought Aluminum and Wrought Aluminum Alloys” published up to January 2017, there are 29 active Al—Li alloys registered in the Aluminum Association. All 29 alloys contain Zr. Meanwhile, there are numerous Zr containing Al—Li patent and patent applications.

Although it is believed that Zr is added as dispersoid element to prevent recrystallization for most conventional aluminum alloys, it is not clear or not fully understood for Al—Li alloys with much more complicated alloying elements. One study claims that Zr is added in Al—Li alloys to form the coherent Al3Zr phase, which is effective in preventing recrystallization but results in a strong “pan cake” shape deformation grain structure with pronounced crystallographic texture. However, another study claims that Zr is not effective for anti-recrystallization due to the addition of other elements such as Mn in AA2198 type Al—Li alloys. Another study concludes that there is a very complicated interaction between Zr and other dispersoid elements in Al—Li alloys and the authors believe that Zr has very low potency to prevent the recrystallization since Zr has very low solute supersaturation near dendrite boundaries where the recrystallization is most likely to initiate.

Beside the complicated impact of Zr on recrystallization, the impact of Zr addition on strength is further complicated since it can potentially affect the strengthening phases associated with Li. Studies indicate that Al3Zr can take in up to 1.3 at % Li, resulting in potentially lower strengths.

To summarize, there is no clear or obvious teaching from the prior art on the effect of Zr in aluminum-lithium thin products regarding the recrystallization, or crystallographic texture, or strength.

The cost of Al—Li alloy products is also challenging. Silver (Ag) is added to many new generation Al—Li alloys in order to improve the final product properties, adding significant alloy costs. Among the four registered Al—Li alloys sheet products mentioned previously, two of them (AA2198 and AA2195) contain Ag. In addition, Ag is very popular for Al—Li alloys as demonstrated by a significant amount of Al—Li alloy patents and patent applications. Thus it is a significant challenge to provide a low cost Al—Li sheet via eliminating Ag additions while simultaneously maintaining the product performance that Ag provides as demonstrated by these prior art examples.

An aluminum-lithium alloy for aircraft fuselage sheet or light-gauge plate applications are known based on the registered AA2198 Al—Li sheet alloy. This alloy comprises 0.1 to 0.8 wt. % Ag, so it is not considered a low cost alloy. Furthermore it has a relatively low strength for an Al—Li alloy.

An aluminum-copper-magnesium alloy having ancillary additions of lithium is known based on the registered AA2060 Al—Li alloy. The claimed level for lithium is only from 0.01 to 0.8 wt. %; because of this limited addition of lithium, this is not considered to be really a “low-density” alloy.

An improved aluminum-copper-lithium alloys is known based on the registered AA2055 Al—Li alloy. This alloy comprises 0.3 to 0.7 wt. % Ag, so it is not considered to be a low cost alloy. The alloy is used for high-strength extrusions.

An alloy with a broad chemical composition range, including 0.2 to 0.8 wt. % Ag, is known based on the registered AA2050 Al—Li plate alloy. This is not considered to be a low-cost alloy. AA2050 is designed for Al—Li plate products from 12.7 mm (0.5″) to 127 mm (5′) and includes 0.15 to 0.35 wt. % Ag. In addition, the alloy is suitable for plate in thickness range of 30 mm (1.2″) to 100 mm (3.9″).

Another aluminum alloy is known including 0.05 to 1.2 wt. % Ag, so it is not considered to be a low-cost alloy. The main advantage of this alloy is to have high strength, ductility, excellent weldability, and natural aging response.

In general, the current related prior art teaches that (1) there is a strong need for low density, high formability, low cost, high strength together with good damage tolerance and corrosion properties Al—Li alloys capable of producing thin sheet products; (2) it is an extreme metallurgical and technical challenge to produce such products; (3) expensive Ag additions are made for better metallurgical quality, but this significantly increases the Al—Li product cost. (4) Zr is widely added to Al—Li alloys, but there is no clear understanding of its role.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a low cost, high formability, substantially Zr-free, low density Al—Li alloy suitable for making transportation components, such as aerospace structural components. Aluminum-lithium alloys of the invention comprise from 3.2 to 4.1 wt. % Cu, 1.0 to 1.8 wt. % Li, 0.8 to 1.2 wt. % Mg, 0.10 to 0.50 wt. % Zn, 0.10 to 1.0 wt. % Mn, up to 0.12 wt. % Si, up to 0.15 wt. % Fe, up to 0.15 wt. % Ti, up to 0.15 wt. % incidental elements, with the total of these incidental elements not exceeding 0.35 wt. %, and the balance being aluminum. Ag should not be more than 0.1 wt. % and is preferably not intentionally added. Zr should not be more than 0.05 wt. % and is preferably not intentionally added. Mg is at least equal to or higher than 2*Zn in weight percent in the invented alloy. Methods for manufacturing wrought aluminum-lithium alloys products of the present invention are also provided.

Preferably, the aluminum-lithium alloy of the present invention is a sheet, extrusion or forged wrought product having a thickness of 0.01-0.249 inch, more preferably 0.01-0.125 inch thickness. It has been surprisingly discovered that the aluminum-lithium alloy of the present invention having no Ag, or very low amounts of not intentionally added Ag, no Zr, or very low amounts of not intentionally added Zr, and high Mg content is capable of producing 0.01 to 0.249 inch thickness sheet products with excellent formability, low density, low cost, high strength, and good damage tolerance properties and corrosion resistance. Another aspect of the present invention is a method to manufacture aluminum-lithium alloys of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the present invention will become apparent from the following detailed description of a preferred embodiment thereof, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a graph showing the Forming Limit Diagrams (FLD) of Al—Li T3 temper 0.05″ gage sheets;

FIG. 2 is a graph showing the Forming Limit Diagrams (FLD) of Al—Li T3 temper 0.09″ to 0.1″ gage sheets;

FIG. 3 is a graph showing the comparison of the combination of density and bending performance between Ag free low cost invention alloy and non-invention alloys sheets at 0.05″ thickness;

FIG. 4 is a graph showing the comparison of the combination of density and bending performance between Ag free low cost invention alloy and non-invention alloys sheets at 0.09″ to 0.11″ thickness;

FIG. 5 is a graph showing the LT TYS at different aging times under 330 F aging temperature of 0.05″ sheets;

FIG. 6 is a graph showing the combination of specific tensile yield strength (TYS) and minimum bend ratio at LT direction;

FIG. 7 is a graph showing the combination of specific tensile yield strength (TYS) and minimum bend ratio at L direction;

FIG. 8 is a photo showing the typical surface images after 72 hours and 672 hours MASTMASSIS testing exposure times;

FIG. 9 is a graph showing the da/dN as a function of stress intensity factor of Al—Li sheets in T8 temper;

FIG. 10 is a graph showing the comparison of fatigue crack growth rates between invention alloy sheet and traditional 7075-T6 sheet;

FIG. 11 is a graph showing the effective crack resistance KReff as a function of effective crack extension (Daeff) of Al—Li sheets in T8 temper;

FIG. 12 is a photo showing the grain structures of Al—Li sheet 115565B4;

FIG. 13 is a photo showing the grain structures of Al—Li sheet 115702B3;

FIG. 14 is a photo showing the grain structures of Al—Li sheet 115733B8;

FIG. 15 is a photo showing the grain structures of Al—Li sheet 115713B0;

FIG. 16 is a photo showing the grain structures of Al—Li sheet 638309A5;

FIG. 17 is a photo showing the grain structures of Al—Li sheet 115654B6;

FIG. 18 is a graph showing the ratios of “Soft” to “Hard” texture components for 0.05″ thickness sheets;

FIG. 19 is a graph showing the ratios of “Soft” to “Hard” texture components for about 0.1″ thickness sheets;

FIG. 20 is a graph showing the typical, minimum, preferred minimum, and more preferred minimum ratios of “Soft” to “Hard” texture components as function of gage at Th/4 location; and

FIG. 21 is a graph showing the typical, minimum, preferred minimum, and more preferred minimum ratios of “Soft” to “Hard” texture components as function of gage at Th/2 location.

 DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to aluminum-lithium alloys, specifically aluminum-copper-lithium-magnesium alloys. The aluminum-lithium alloy of the present invention comprises from 3.2 to 4.1 wt. % Cu, 1.0 to 1.8 wt. % Li, 0.8 to 1.2 wt. % Mg, 0.10 to 0.50 wt. % Zn, 0.10 to 1.0 wt. % Mn, up to 0.12 wt. % Si, up to 0.15 wt. % Fe, up to 0.15 wt. % Ti, up to 0.15 wt. % incidental elements, with the total of these incidental elements not exceeding 0.35 wt. %, and the balance being aluminum. Ag should not be intentionally added and should not be more than 0.1 wt. % as an incidental element. The aluminum-lithium alloy of the present invention shall be “substantially Zr-free”, meaning that Zr should not be intentionally added and should not be more than 0.05 wt. % as an incidental element. Mg is at least equal or higher than 2*Zn in weight percent in the invented alloy.

In an alternate embodiment, the aluminum-lithium alloy comprises from 3.4 to 3.9 wt. % Cu, 1.1 to 1.7 wt. % Li, 0.8 to 1.2 wt. % Mg, 0.20 to 0.50 wt. % Zn, 0.20 to 0.6 wt. % Mn, a maximum of 0.12 wt. % Si, a maximum of 0.15 wt. % Fe. Such embodiment of the aluminum-lithium alloy would also have Mg content that is at least equal to or higher than 2*Zn in weight percent. Additionally, the aluminum-lithium alloy may include less than 0.1 wt. % of not intentionally added Ag, preferably less than 0.05 wt. % of not intentionally Ag, and more preferably less than 0.01 wt. % of not intentionally Ag. The aluminum-lithium alloy may include less than 0.05, or 0.04, or 0.03, or 0.02, or even 0.01 wt. % of not intentionally Zr. In a preferred embodiment, no Ag and. Zr are intentionally added to the aluminum-lithium alloy.

The aluminum-lithium alloy of the present invention can be used to produce wrought products, preferably, having a thickness range of 0.01-0.249 inch, more preferably in the thickness range of 0.01-0.125 inch. In addition to low density and low cost, the aluminum-lithium alloys of the present invention are wrought products having excellent formability, high strength, and good damage tolerance and corrosion properties.

Such products are suitable for use in many structural applications, especially for aerospace structural components such as frames, stringers, and fuselages. The aluminum-lithium alloy of the present invention can be used for the fabrication of sheet metal components using several manufacturing processes. Common methods are roll forming, stretch forming, hammer drop forming, stamping, draw forming, and hydroforming. Example components that can be made from these forming methods, include but are not limited to, fiiselage frames, fuselage stringers, contoured fuselage skins, constant cross-section skins, electrical wire harnesses clips, brackets for cable used in control systems, attachment points for interior components to primary structures such as fuselage frames, shear ties for attaching fuselage frames to fuselage skins, shear ties for attaching wing ribs to wing skins, wing ribs, clips to attach wing ribs to wing spars, empennage skins, empennage ribs, nacelle skins, engine leading edge inlet skins, pressure bulkhead skins, pylon skins, bracketry for attaching avionics to structural components, bracketry for attaching passenger oxygen systems, avionics enclosures, shelving for avionics components, etc.

The present application discloses an alloy that is substantially Zr-free without the intentional addition of Zr, which is almost exclusively added in all the 29 active Al—Li alloys that have been registered in Aluminum Association based on “International Alloy Designation and Chemical Composition Limits for Wrought Aluminum and Wrought Aluminum Alloys” published up to January 2017. As discussed in the “Background of the Invention” section, although Zr is widely believed to form Al3Zr dispersoid particles to control the grain structure and also potentially improve strength, the exact impact of Zr in complicated Al—Li alloys thin products is not clear or fully understood. The presently disclosed substantially Zr-free Al—Li alloy innovatively changes the metallurgical approach to obtain a desired grain structure for excellent formability and strength suitable for aerospace applications.

Therefore, in one embodiment, Zr is not intentionally added in the aluminum-lithium alloy of the present invention. Zr may exist in the alloy as a result of a non-intentionally added incidental element. In this case, the Zr should not be more than 0.05 wt. %. The aluminum-lithium alloy may include alternate embodiments having less than 0.05 wt. % Ag, less than 0.04 wt. % Zr, less than 0.03 wt. % Zr, less than 0.02 wt. % Zr or less than 0.01 wt. % Zr.

Copper is added to the aluminum-lithium alloy in the present invention in the range of 3.2 to 4.1 wt. %, mainly to enhance the strength but also to improve the combination of strength, formability and fracture toughness. An excessive amount of Cu can result in unfavorable intermetallic particles which can negatively affect material properties such as ductility, formability, and fracture toughness. In these cases the interaction of Cu with other elements such as Li and Mg also must also be considered. In addition to the alternate upper and lower limits listed above for Zr, the present invention includes alternate embodiments wherein the upper or lower limit for the amount of Cu may be selected from 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, and 4.1 wt. %. In the preferred embodiment, the Cu is from 3.4 to 3.9 wt. % to provide compositions that enhance specific product performance while maintaining relatively high performance in the remaining attributes as compared to the prior art.

Lithium is added to the aluminum-lithium alloy in the present invention in the range of 1.0 to 1.8 wt. %. The primary benefit for adding Li element is to reduce the density and increase the elastic modulus and strength. Combined with other elements such as Cu, Li is critical in improving the strength, damage tolerance and corrosion performance. Too high an amount of Li content, however, can negatively impact fracture toughness, anisotropy of tensile properties, and formability. In addition to the alternate upper and lower limits listed above for Zr and Cu, the present invention includes alternate embodiments wherein the upper or lower limit for the amount of Li may be selected from 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8 wt. %. In one preferred embodiment, Li is in the range of 1.1 to 1.7 wt. %.

Mg is added to the aluminum-lithium alloy in the present invention in the range of 0.8 to 1.2 wt. %. The primary purpose of adding Mg is to enhance the strength with the secondary purpose of slightly reducing the density. However, too high an amount of Mg can reduce Li solubility in the matrix, thus negatively impacting the aging potential for higher strength. In addition to the alternate upper and lower limits listed above for Zr, Cu, and Li, the present invention includes alternate embodiments wherein the upper or lower limit for the amount of Mg may be selected from 0.8, 0.9, 1.0, 1.1, and 1.2 wt. %.

The addition of low levels of Zn in the aluminum-lithium alloy of the present invention aims at improving corrosion resistance. It is believed that Zinc goes into solid solution within the grains and shifts the pitting potential of the matrix to less noble and decreases the electrochemical potential difference between the grain boundary and the matrix, thus improving static and dynamic corrosion Properties. In one embodiment, the addition of Zn is from 0.1 to 0.5 wt %. In addition to the alternate upper and lower limits listed above for Zr, Cu, Li, and Mg, the present invention includes alternate embodiments wherein the upper or lower limit for the amount of Zn may be selected from 0.1, 0.2, 0.3, 0.4, and 0.5 wt. %. In one preferred embodiment, Zn is in the range of 0.2 to 0.5 wt. %.

However, the addition of Zn has to be cautious since the beneficial impact of Zn on corrosion resistance can be strongly influenced by Mg addition. The prior art claims that both too high and too low Mg/Zn have worse corrosion resistance evaluated by exfoliation and SCC testing methods. However, such claims were based on very low Mg levels from 0.05 to 0.6 wt. %. In the present patent application, the Mg level is much higher (0.8 to 1.2 wt. %). In addition, the Mg/Zn ratio can also potentially affect the texture. The texture can also be affected by other alloying elements such as Cu and Li. The present patent application demonstrated that higher than 2.0 of Mg/Zn ratio has excellent corrosion resistance for high Mg levels in the range of 0.8 to 1.2 wt. %. In one embodiment, the Mg/Zn ratio should be higher than 2.0. Due also to the negative impact of Zn on density, this Mg/Zn ratio higher than 2.0 contributes to the low density of the present invention Al—Li alloy.

In one embodiment, Ag is not intentionally added in the aluminum-lithium alloy of the present invention. Ag may exist in the alloy as a result of a non-intentionally addition. In this case, the Ag should not be more than 0.10 wt. %. In addition to the alternate upper and lower limits listed above for Zr, Cu, Li, Mg, and Zn, the present invention includes alternate embodiments wherein the aluminum-lithium alloy may include less than 0.1 wt. % of not intentionally added Ag, less than 0.05 wt. % of not intentionally added Ag, or less than 0.01 wt. % of not intentionally added Ag. The prior art teaches that Ag is necessary to improve the final product properties and is therefore included in many aluminum-lithium alloys as well as many patents and patent applications. However, Ag significantly increases the cost of the alloys. In the preferred embodiment of the aluminum-lithium alloy of the present invention, Ag is not intentionally included in order to reduce the cost. It is surprising to find that the aluminum-lithium alloy of the present invention, without the addition of Ag for providing low cost, can be used to produce high strength, high formability, excellent corrosion resistance, and good damage tolerance performance sheet products suitable for structural applications particularly in aerospace.

Mn is intentionally added to improve the grain structure for better mechanical isotropy and formability. In addition to the alternate upper and lower limits listed above for Zr, Cu, Li, Mg, Zn, and Ag, the present invention includes alternate embodiments wherein the upper or lower limits for the amounts of Mn may be selected from 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0 wt. %. In one preferred embodiment, the addition of Mn is in the range from 0.20 to 0.6 wt. %.

Ti can be added up to 0.15 wt. %. The purpose of adding Ti is mainly for grain refinement in casting. In addition to the alternate upper and lower limits listed above for Zr, Cu, Li, Mg, Zn, Ag, and Mn the present invention includes alternate embodiments wherein the upper limit for the amount of Ti may be selected from 0.01, 0.02, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14 and 0.15 wt. % Ti.

Si and. Fe may be present in the aluminum-lithium alloy of the present invention as impurities but are not intentionally added. When present their content must be ≤0.12 wt. % for Si, and ≤0.15 wt. % for Fe, preferably ≤0.05 wt. % for Si and ≤0.08 wt. % for Fe. In one embodiment, the aluminum-lithium alloy of the present invention includes a maximum content of 0.12 wt. % for Si, and 0.15 wt. % for Fe. In one preferred embodiment, a maximum contents are 0.05 wt. % for Si and 0.08 wt. % for Fe.

The aluminum-lithium alloy of the present invention may also include low levels of “incidental elements” that are not included intentionally. The “incidental elements” means any other elements except those described above (Al, Cu, Li, Mg, Zr, Zn, Mn, Ag, Fe, Si, and Ti).

The low cost, high formability, substantially Zr-free Al—Li alloy of the present invention may be used to produce wrought products. In one embodiment, the aluminum-lithium alloy of the present invention is capable of producing rolled products, preferably, a sheet or coil product in the thickness range of 0.01-0.249 inch, more preferably in the range of 0.01-0.125 inch.

The rolled products may be manufactured using known processes such as casting, homogenization, hot rolling, optionally cold rolling, solution heat treating and quenching, optionally stretching and levelling, and ageing treatments. The ingot may be cast by traditional direct chill (DC) casting method. The ingot may be homogenized at temperatures from 454 to 549° C. (850 to 1020° F.), preferably from 482 to 543° C. (900 to 1010° F.), and more preferably from 496 to 538° C. (925 to 1000° F.). The hot rolling temperature may be from 343 to 499° C. (650 to 930° F.), preferably from 357 to 482° C. (675 to 900° F.), and more preferably from 371 to 466° C. (700 to 870° F.). The optional cold rolling may be needed particularly for the thinnest gauges. The cold work reduction can be from 20% to 95%, preferably from 40% to 90%. The products may be solution heat treated at temperature range of 454 to 543° C. (850 to 1010° F.), preferably 482 to 538° C. (900 to 1000° F.), and more preferably 493 to 532° C. (920 to 990° F.). The wrought products are cold water quenched to room temperature and may be optionally stretched or cold worked up to 15%, preferably from 2 to 8%. The quenched product may be subjected to any aging practices known by those skilled in the art including, but not limited to, one-step aging practices that produce a final desirable temper, such as T8 temper, for better combination of strength, fracture toughness, and corrosion resistance which are highly desirable for aerospace members. The aging temperature can be in the range of 121 to 205° C. (250 to 400° F.) preferably from 135 to 193° C. (275 to 380° F.), and more preferably from 149 to 182° C. (300 to 360° F.) and the aging time can be in the range of 2 to 60 hours, preferably from 10 to 48 hours.

The unique chemistry along with proper processing of the aluminum-lithium alloy of the present patent application result in thin sheet with surprising material characteristics such as ideal crystallographic texture, which strongly affect material performance such as formability. The texture is normally evaluated by X-Ray diffractometer facility and the volume fractions of texture components can be determined. The most common texture components for aluminum alloy sheet include Cube: {001},<100>; R-Cube: {001},<110>; Goss: {011}<100%; Brass: {011}<211>; S: {123}<634>, Copper-{112}<111>. It is also widely believed that Brass and S textures are “hard” textures since they are “hard” to be deformed and. Cube and R-Cube are “soft” textures since they are “easier” to be deformed. The ratio of “soft”/“hard” texture components is critical for formability: the higher this ratio, the better the formability. In one embodiment, the ratio of “soft”/“hard” texture of T3 temper components is higher than “0.75−0.5*gage” and “0.85−5.0*gage” at sheet quarter thickness (th/4) and center thickness (th/2) respectively. In a preferred embodiment, this ratio is higher than “0.83−0.5*gage” and “0.98−5.0*gage” at quarter thickness (th/4) and center thickness (th/2) respectively. In a more preferred embodiment, this ratio is higher than “0.9−0.5*gage” and “1.1−5.0*gage” at quarter thickness (th/4) and center thickness (th/2) respectively. The unit of the gage is inch.

Such distinctive crystallographic texture material characteristic due to unique chemistry gives the ideal combination of strength, density and formability required for aerospace application. In one embodiment, the minimum LT bend ratio is less than “24.30−0.0292*“Specific LT TYS””, and the minimum L bend ratio is less than “13.11−0.0146*“Specific L TYS””. In a preferred embodiment, the minimum LT bend ratio is less than “23.65−0.0292*“Specific LT TYS””, and the minimum L bend ratio is less than “12.88−0.0146*“Specific L TYS””. The Specific LT TYS equals the Long-Transverse Tensile Yield Strength (in ksi) divided by density (in lb/in3). The Specific L TYS equals the Longitudinal Tensile Yield Strength (in ksi) divided by density (in lb/in3). So the unit of specific strength is “ksi/(lb/in3)”.

Many aerospace parts, such as frames, need to be formed to the designed geometry for final applications. Therefore, the formability is also a critical consideration along with static and dynamic material properties. The formability is normally evaluated by simple bending test method and/or more sophisticated Forming Limit Diagram (FLD) method. The formability of T3 temper sheet is primarily focused for the aluminum-lithium alloy of the present invention. For high strength 7xxx and 2xxx alloy sheet, the O temper is commonly provided from aluminum producers (aluminum mill) to airframe manufacturers. The O temper sheet is processed in different ways such as forming, solutionizing, cold water quenching, and aging. The T3 temper sheet provided has a significant cost advantage since it eliminates the process of solutionizing and cold water quenching process steps at the airframer.

The following examples illustrate various aspects of the invention and are not intended to limit the scope of the invention.

Example 1: Lab Scale Ingot Based Product Study

In order to explore the role of Zr in Al—Li alloy on thin product performance, especially strength property, three pairs of Zr and substantially Zr-free containing book-mold ingots with the approximate dimension of 1.25″×6″×12″ were cast and processed into 0.05″ sheet products. Table 1 gives the chemical compositions of these 6 book mold ingots. The first pair (#1 vs. #2) has relatively high Cu and no Ag, #1 being substantially Zr-free and #2 containing Zr. The second pair (#3 vs. #4) has low Cu and no Ag, #3 being substantially Zr-free and #4 containing Zr. The third pair (#5 vs. #6) has relatively high Li and Mg, and has Ag added, #5 being substantially Zr-freeand #6 containing Zr.

TABLE 1 Chemical compositions of samples Sample Alloy Compositions, wt. % ID Zr Si Fe Cu Li Mg Ag Zr Zn Mn 1 No Zr 0.061 0.090 4.09 1.07 0.84 0.000 0.001 0.371 0.344 2 Zr 0.051 0.092 4.05 1.02 0.83 0.000 0.055 0.382 0.343 3 No Zr 0.046 0.089 3.53 1.08 0.84 0.000 0.001 0.358 0.349 4 Zr 0.047 0.090 3.52 1.03 0.82 0.000 0.065 0.369 0.354 5 No Zr 0.052 0.090 3.88 1.31 1.07 0.287 0.001 0.003 0.358 6 Zr 0.052 0.091 3.88 1.28 1.06 0.280 0.065 0.003 0.357

Book mold ingots were surface scalped, homogenized, hot rolled, cold rolled, solution heat treated, quenched, stretched, and aged to final T8 temper 0.05″ thickness sheets.

The ingots were homogenized at temperatures from 496 to 538° C. (925 to 1000° F.). The hot rolling temperatures were in the range of 399 to 466° C. (750 to 870° F.). The ingots were hot rolled at multiple passes into 0.06 to 0.20″ thickness sheets. Although the cold rolling is optional, all the example book mold sheets were further cold rolled to 0.05″ thickness. The cold rolled sheets were solution heat treated at a temperature range from 493 to 532° C. (920 to 990° F.). The sheets were cold water quenched to room temperature. Although the stretching or cold working is optional, all the example sheets were stretched at 2 to 6%. The stretched sheets were aged to T8 temper in the temperature range of 166° C. (330° F.) for 24 hours. Tensile properties were evaluated for T8 temper sheets.

Table 2 gives the sheet tensile properties in the T8 (aged) temper. The 0.2% offset yield strength (TYS) and ultimate tensile strength (UTS) along rolling direction (L) were measured under ASTM B557 specification. Based on the first pair (#1 and #2), the substantially Zr-free alloy #1 has 4.3 ksi higher strength than Zr containing alloy #2. Although not as significant as pair 1 (#1 and #2), the low Cu level second pair (#3 and #4) shows that the substantially Zr-free alloy (#3) has 1.1 ksi higher strength than #2. For third pair (#5 and #6), the substantially Zr-free alloy Zr #5 and. Zr containing alloy #6 have very similar strength, indicating that the benefit of Zr on strength (seen on first and second pair) only exists in the absence of Ag. This result also shows that the effect of Zr on strength is not obvious and could be very complicated for Al—Li alloys: by comparing third pair (#5 and #6), with addition of Ag, and first pair (#1 and #2), without addition of Ag, it is surprising to observe that No Ag first pair has similar strength as Ag containing third pair.

TABLE 2 Density and tensile properties of lab scale sheet products T8 Temper Sheet Tensile Properties Sample Density, Specific LTYS, ID Zr lbs/in{circumflex over ( )}3 L UTS, ksi L TYS, ksi ksi/(lb/in{circumflex over ( )}3) 1 No Zr 0.0974 81.25 78.95 811 2 Zr 0.0975 77.50 74.70 766 3 No Zr 0.0970 73.15 70.55 728 4 Zr 0.0971 71.70 69.45 715 5 No Zr 0.0964 78.10 76.05 789 6 Zr 0.0966 78.35 75.70 784

Example 2: Full Industrial Scale Examples

Based on “Example 1” lab scale investigation on the role of Zr on the strength property was investigated. Six industrial scale 406 mm (16″) thick ingots of Al—Li alloys were cast by DC (Direct Chill) casting process and produced to 0.05″ to 0.11″ thickness sheets. The substantially Zr-free alloys with the non-intentionally added Zr levels in the industrial scale example ingots reflect the normal industrial practice. Table 3 gives the chemical compositions of these industrial scale ingots. Three lots (115565B4, 115733B8 and 115654B6) were inventive alloys. The other three alloys are not inventive alloys due to different Zr, Ag and Cu contents. The Lot 638309A5 is AA2198 alloy, which was used as a baseline alloy of Al—Li sheet product. All the invention alloys have much lower densities due to low Cu, high Li, high Mg, no Ag, and low Zr.

TABLE 3 Chemical Compositions and Densities of Full Industrial Scale Examples Invention Gage, Chemical Compositions, wt. % Density, Alloy? Lot # in Si Fe Cu Mn Li Mg Ag Zn Ti Zr lbs/(in{circumflex over ( )}3) Yes 115565B4 0.108 0.024 0.039 3.695 0.368 1.497 1.007 0.000 0.348 0.018 0.039 0.0958 115733B8 0.050 0.025 0.043 3.690 0.328 1.293 0.982 0.000 0.365 0.017 0.038 0.0964 115654B6 0.025 0.033 0.037 3.565 0.335 1.425 0.980 0.000 0.353 0.022 0.046 0.0960 No 115702B3 0.085 0.029 0.049 4.110 0.348 1.064 0.974 0.000 0.359 0.025 0.076 0.0974 115713B0 0.050 0.028 0.048 4.165 0.354 1.068 1.000 0.000 0.365 0.024 0.078 0.0974 638309A5 0.050 0.030 0.050 3.180 0.350 0.910 0.540 0.270 0.020 0.020 0.100 0.0974

The ingots were homogenized at temperatures from 496 to 538° C. (925 to 1000° F.). The hot rolling temperatures were from 371 to 466° C. (700 to 870° F.). The ingots were hot rolled at multiple passes into 0.06 to 0.20″ thickness. Although the cold rolling is optional, all sheets were further cold rolled to 0.108″, 0.085″, 0.05″, and 0.025″ thickness. The cold rolled sheets were solution heat treated at a temperature range from 493 to 532° C. (920 to 990° F.). The sheets were cold water quenched to room temperature. Although the stretching or cold working is optional, all example sheets were stretched by 2 to 7%. The stretched sheets without artificial aging were used for T3 temper tensile and formability evaluations. The stretched sheets were further aged to T8 temper for strength, fracture, and fatigue performance evaluation. The aging temperature was from 166° C. (330° F.) to 171° C. (340° F.) for 14 to 32 hours.

The most critical performance for T3 temper sheet or coil is formability since the T3 temper sheet or coil will be formed first into the parts with different profiles and then artificially aged to the T8 temper for service application. The formability was evaluated by both standard uniaxial bend and. Forming Limit Diagram (FLD) tests.

FIGS. 1 and 2 show the Forming Limit Diagrams (FLD), at respectively 0.05″ and about 0.1″ thickness of Invention and Non-Invention sheets. The FLD was evaluated based on ASTM E2218-02 (Reapproved 2008) specification. A Forming Limit Curve (FLC) was generated by the points identified by necking on the samples.

As shown in FIG. 1, with the same 0.05″ gage, the invention alloy sheet 115733B8 has better formability (higher critical major strain) than non-invention alloy sheet 115713B0 for all forming conditions. This observation is true for higher gage range (0.09″ to 0.1″), the invention alloy sheet 115565B4 has better formability (higher critical major strain) than non-invention alloy sheet 115702B0 although the advantage is stronger at some conditions than other conditions.

The T3 temper sheet bending performance was also evaluated based on ASTM 290-09. One end of the sheet specimen along with the bend support die was held together in a vise. A force was applied on the other end of the sheet to bend against the radius of a support die to 180°. After bending, the surface of the specimen was examined to determine if there were cracks. The bend ratio R/t, i.e. support die radius (R) to sheet thickness (t), is normally used to evaluate bending performance. The lower the bend ratio indicates the better the bending performance.

Table 4 gives the bending performance of Ag free low cost alloy sheets in T3 temper. In general, the invention alloy sheets have better bending formability. This observation is the same as those on previous FLD evaluation results. The L direction normally has a lower bend ratio without surface cracking. The lower ratio represents better bending performance. For the similar gage and same testing orientation, the invention alloy sheets have better bending performance than non-invention alloy sheets. In addition, the inventive alloys have better bending performance than the widely used 2024 T3 sheets, where the minimum bending ratio required by the industry specification AMS 4037 is 2.5t.

TABLE 4 Bending performance of Ag free low cost alloy sheets in T3 temper Invention Bending Surface Cracking Conditions Minimum Gage, in Alloy? Lots Direction 1.0*t 1.6*t 2.5*t Bend Ratio, *t 0.025 Yes 115654B6 L Crack No Crack No Crack N/A 1.6 LT Crack Crack No Crack 2.5 0.8*t 1.25*t 1.6*t 1.88*t 2*t 0.05 Yes 115733B8 L Crack Crack No Crack No Crack No Crack 1.6 LT Crack Crack Crack No Crack No Crack 1.88 No 115713B0 L Crack Crack Crack No Crack No Crack 1.88 LT Crack Crack Crack Crack No Crack 2 1.21*t 1.4*t 1.75*t 1.87*t 0.09-0.10 Yes 115565B4 L N/A Crack No Crack No Crack No Crack 1.4 LT Crack Crack No Crack No Crack 1.75 No 115702B3 1.12*t 1.19*t 1.54*t 1.79*t 2.23*t L Crack Crack Crack No Crack No Crack 1.79 LT Crack Crack Crack Crack No Crack 2.23

Density is another critical factor for aerospace application. The invention alloys advantages become more apparent when both density and formability are considered together. FIGS. 3 and 4 give the comparison of the combination of density and bending performance between Ag free low cost invention alloy and non-invention alloys sheets. The invention alloy sheets have both lower density and lower minimum bend ratio compared with non-invention alloy sheets.

The tensile properties of T3 temper sheets along rolling direction (L), long transverse direction (LT) and 45 degree off the rolling direction (L45) are given in Table 5. The invention alloy sheets have higher strength than existing T3 temper 2198 alloy sheet and also 2024-T3 minimum per AMS4037. The difference of strength in different tensile orientations, L, LT and L45, (i.e. the in-plane anisotropy) is also very low for the invention alloy.

TABLE 5 The tensile properties of T3 temper sheets Invention Direc- Dupli- UTS, TYS, El, Alloy? Lot Ga, in tion cate ksi ksi % Yes 115654B6 0.025 L 1 61.3 42.4 20 2 61.6 42.2 19 L45 1 60.4 40.1 19 2 59.6 39.9 20 LT 1 60.6 41 16 2 60.6 40.7 19 115733B8 0.05 L 1 64.4 49.5 19 2 63.8 49.2 17 L45 1 62.2 45.7 17 2 62.3 45.6 16 LT 1 62.8 45.1 17 2 63 46.4 17 115565B4 0.108 L 1 63.8 47.6 22 2 64.2 47.8 19 L45 1 62.3 44.9 21 2 62.4 44.5 24 LT 1 63.8 44.8 21 2 63.6 45 23 No 115713B0 0.05 L 1 68.1 52.3 19 2 67.8 52.1 20 L45 1 66.1 47.4 19 2 66.5 47.4 17 LT 1 68 50.3 17 2 68.2 49.1 16 115702B3 0.085 L 1 68.3 51.6 21 2 67.9 50.8 20 L45 1 65.7 46.6 22 2 66 47.2 23 LT 1 68 49.1 17 2 68.4 48.8 20 638309A5 0.05 L 1 54.7 40.9 16 2 54.8 40.9 17 L45 1 52.5 37 17 2 52.9 37.5 18 LT 1 53.4 37.5 16 2 52.8 37 12

Table 6 and FIG. 5 give the tensile properties in the LT orientation for different aging times at 330° F. The inventive alloy sheets have much higher strength than existing 2198 baseline alloy sheet for all the aging times. Again, the Ag free invention alloy sheets have both lower density and lower minimum bend ratio compared with the non-invention Ag free alloy sheets.

TABLE 6 The LT tensile properties at different aging times under 330 F. aging temperature Aging Invention time, UTS, TYS, EL, Alloy? Lot Ga, in hours ksi ksi % Yes 115565B4 0.107 17.2 75.7 66.9 10.5 21.5 77.2 70.4 9.5 30.8 77.9 72.3 6.8 32.0 76.6 70.4 8.3 115733B8 0.05 17.2 75.1 67.4 9.5 21.5 76.4 69.5 9.3 30.8 77.2 71.2 6.5 32.0 75.8 69.7 7.5 115654B6 0.025 17.2 70.1 62.0 9.8 21.5 71.0 63.5 8.5 30.8 73.8 67.4 7.0 46.3 74.0 68.7 6.5 No 115702B3 0.085 17.2 79.4 71.5 9.5 21.5 80.7 74.3 8.5 30.8 81.5 76.0 8.0 115713B0 0.05 17.2 78.4 70.8 9.8 21.5 79.7 73.0 8.5 30.8 80.4 73.5 7.3 No (2198 Baseline) 638309A5 0.05 24.0 69.6 63.3 9.5 32.0 70.0 64.1 8.0

Based on the aging response results, the specific aging practice (target aging practice), was selected depending on alloy and gage. The comprehensive characterization including strength in-plane anisotropy, corrosion resistance, fracture toughness, and fatigue resistance performance were conducted and disclosed in the present patent application.

Table 7 gives the tensile properties along L, LT, and L45 orientations for the different alloys and gages. The inventive alloy sheets have much higher strength than the baseline 2198 alloy (638309A5). The strengths of invention alloy sheets are slightly lower than those of non-invention alloy sheets 115702B3 and 115713B0. Again, the Ag free invention alloy sheets have both lower density and lower minimum bend ratio compared with non-invention Ag free alloy sheets 115713B0 and 115702B3.

TABLE 7 The tensile properties along L, LT, and L45 orientations for the different alloys and gages Aging Invention Gage, Temperature, Aging Testing Alloy? Lot in F. Hours Direction Repeats UTS, ksi TYS, ksi EL, % Yes 115654B6 0.025 340 25 L 1 75.4 73.2 7.0 2 75.1 73.2 6.0 L45 1 68.9 61.7 5.5 2 67.0 58.1 9.0 LT 1 74.4 68.8 6.0 2 73.6 68.5 7.0 115733B8 0.05 330 32 L 1 77.9 73.1 7.5 2 77.3 72.9 8.5 L45 1 75.6 69.2 8.5 2 75.6 69.3 8.0 LT 1 76.0 69.9 7.5 2 75.6 69.5 7.5 115565B4 0.108 330 32 L 1 77.6 72.1 8.5 2 78.1 72.9 8.5 L45 1 75.8 69.3 9.5 2 76.0 69.3 9.0 LT 1 76.2 70.1 8.5 2 76.9 70.7 8.0 No 115713B0 0.05 330 24 L 1 83.4 81.4 7.5 2 83.0 80.8 7.5 L45 1 81.1 74.5 9.0 2 80.6 74.5 9.0 LT 1 82.3 76.0 7.0 2 83.0 77.7 8.0 115702B3 0.085 330 24 L 1 82.5 77.0 8.0 2 81.9 76.6 7.5 L45 1 79.2 72.7 9.0 2 79.5 73.1 8.5 LT 1 81.2 75.0 8.5 2 81.0 75.0 8.0 No 638309A5 0.05 330 24 L 1 70.4 66.1 9 2 71 67.1 9 L45 1 68.9 61.2 11 2 69.1 61.7 11 LT 1 68.8 62 8.5 2 68.9 61.8 8.5

As discussed earlier, the combination of strength, density, and formability is critical for aerospace application. The distinctiveness of the invention alloy can be demonstrated in the FIGS. 6 and 7 which represent the combination of specific tensile yield strength (TYS) and minimum bend ratio in L and LT directions respectively. The minimum LT bend ratio of present inventive alloy sheets can be less than “24.30−0.0292*“Specific LT TYS””, and the minimum L bend ratio of present alloy sheet can be less than “13.11−0.0146*“Specific L TYS””. Preferably, the minimum LT bend ratio is less than “23.65−0.0292*“Specific LT TYS””, and the minimum L bend ratio is less than “12.88−0.0146*“Specific L TYS””. The specific strength equals the strength divided by density. The unit of specific strength is “ksi/(lb/in3)”.

Corrosion resistance is a key design consideration for airframe manufacturers. The MASTMASSIS test is generally considered to be a good representative accelerated corrosion test method for Al—Li based alloys.

The MASTMASSIS test was based on ASTM G85-11 Annex-2 under dry-bottom conditions. The sample size was 2.0″ L×2.0″ LT at middle of sheet thickness. The temperature of the exposure chamber through the duration of the test was 49±2° C.

The 0.05″ invention alloy sheet 115733B8 was tested at T/2 (center of thickness) thickness location. The testing duration times were 24, 48, 96, 168, 336, 504, and 672 hrs. FIG. 8 is a picture of typical surface images after 72 hours and 672 hours MASTMASSIS testing exposure times. The surfaces are very clean and shiny. No exfoliation is evident for all the exposure times. The excellent corrosion resistance of pitting/EA can be concluded for all exposure times.

The Fatigue Crack Growth Rate (FCGR) was evaluated based on ASTM E647-08 (9.1). FIG. 9 is a graph showing the da/dN as a function of stress intensity factor of all Ag free inventive and non-inventive alloys sheets in T8 temper. The testing condition includes L-T orientation, stress ratio of 0.1 and a frequency of 10 Hz. It is interesting to observe that all sheets have similar fatigue crack growth resistance performance although the invention alloy sheets (115654B6, 115733B8, 115565B4) have lower density and better formability than non-invention alloy sheets (115713B0,115702B3).

The excellent fatigue crack growth resistance of invention alloy can be demonstrated in FIG. 10. The 7075-T6 data is from ASM Handbook. The invention alloy sheets have much slower fatigue crack growth rate (da/dN) than commonly used 7075-T6 sheet.

The fracture toughness was evaluated based on ASTM E561-10e2 and ASTM B646-06a. The commonly used 16″ wide and 40″ long specimen was used for center cracked tension fracture toughness testing. FIG. 11 is a graph showing the effective crack resistance KReff as function of effective crack extension (Daeff) of Al—Li sheets. All Al—Li sheets were tested in the T8 temper and the L-T orientation. The inventive alloy sheets (115654B6 and 115733B8) have similar fracture toughness as non-invention alloy sheets (115713B0 and 115702B3). It should be mentioned that the inventive alloy sheets (115654B6, 115733B8) have lower density and better formability than non-invention alloy sheets (115713B0 and 115702B3).

This Example 2 (Full Industrial Scale Examples) demonstrates that the distinct and unique chemical compositions (no Ag, substantially Zr-free, and combination of Cu, Li, Mg, Mn, and Zn) of present invention alloy can provide superior formability, low density, and excellent strength, corrosion resistance, fracture toughness and fatigue crack growth resistance of Al—Li sheet products.

Such distinctive performances, especially formability, are the resultant responses of the unique microstructure and crystallographic texture, which are disclosed as follows, due to the distinctive chemistry.

FIGS. 12 to 17 gives the grain structures of Al—Li sheets. It is well known that the grain structure is strongly affected by sheet gage. Therefore, the comparison of microstructure is gage dependent. For similar 0.09 to 0.11″ gage sheets, the invention alloy sheet 115565B4 has finer and a more equi-axed grain structure than the non-invention alloy sheet 115702B3. At 0.05″ gage, the present invention alloy sheet 115713B0 has much finer, equi-axed grain structure than the non-invention alloy sheets 115713B0 and 638309A5. For very thin sheet (0.025″) the invention alloy 115654B6, a very fined, equi-axed grain structure was clearly observed. It was well known in the industry that finer and more equi-axed grain structure normally has less forming anisotropy and better formability performance. The ideal grain structures of the invention alloy sheets are attributed mainly to the unique substantially Zr-free chemical composition along with the unique combination of Cu, Li, Mn, and Mg.

The crystallographic texture strongly affects final product properties, especially formability. A Rigaku D/Max X-Ray diffractometer was used to measure the T3 temper sheet textures. The alpha rotation angle was from 15° to 90°, and alpha step angle was 5° by the Schulz back-reflection method using CuKα radiation. Four pole figures: {111}, {200}, {220}, and {311} were generated and then used to calculate the Orientation Distribution Functions (ODF) and the volume fractions of most common texture components in terms of Cube: {001},<100>; R-Cube: {001},<110>; Goss: {011}<100>; Brass: {011}<211>; S: {123}<634>, Copper-{112}<111>. It is widely believed that Brass and S textures are “hard” textures since they are “hard” to be deformed and Cube and R-Cube are “soft” textures since they are “easier” to be deformed.

Table 8 summarizes the main texture components and their volume fractions of T3 temper sheets at T/4 (quarter thickness) and T/2 (middle thickness) locations. It is well established that texture is strongly related to final sheet thickness. The non-invention alloy sheets (115713B8 and 115702B3) have very typical rolling textures—very strong Brass and S textures “hard” components. In contrast, at similar sheet thicknesses, the invention alloy sheets (115565B4 and 115733B8) have very strong Cube and R-Cube “soft” textures. The ratios of “Soft” to “Hard” texture components were given in FIGS. 18 and 19 for two sheet thicknesses. The Soft=Cube %+R-Cube %, and Hard=Brass+S %. Again, the invention alloy sheets have much higher ratios of “Soft” to “Hard” texture components than non-invention alloy sheets. Since the processing practices were the same for the invention and non-invention alloy sheets, such distinctive texture differences can be attributed to the lack of Zr and the combination of other elements such as Cu, Li, Mg, Mn.

The distinctiveness of crystallographic texture in terms of the ratio of “Soft” to “Hard” texture components can be further demonstrated in FIGS. 20 and 21 for Th/4 and Th/2 respectively. The minimum ratios for intention alloy are higher than “0.75−0.5*gage” and “0.85−5.0*gage” at sheet quarter thickness (th/4) and center thickness (th/2) respectively. The preferred ratios are higher than “0.83−0.5*gage” and “0.98−5.0*gage” at th/4 and th/2 respectively for invention alloys. The more preferred ratios are higher than “0.9−0.5*gage” and “1.1−5.0*gage” at th/4 and th/2 respectively for invention alloys. The unit of the gage is inch.

TABLE 8 Texture components and their volume fractions of T3 temper sheets at T/4 (quarter thickness) and T/2 (middle thickness) locations Invention Cube Goss Brass S Copper R-Cube “Soft”/ Sample ID Alloy? Gage, in Location % % % % % % “Hard” 115733B8 Yes 0.05 T/4 6.35 2.30 5.62 7.63 3.53 5.96 0.929 T/2 6.75 2.33 5.28 8.46 4.34 5.82 0.915 115713B8 No 0.05 T/4 5.63 2.36 6.92 9.31 3.80 5.01 0.656 T/2 5.05 2.56 10.36 11.87 3.61 4.49 0.429 115565B4 Yes 0.108 T/4 6.54 2.28 5.48 7.69 3.75 5.31 0.900 T/2 5.18 2.36 7.85 8.30 2.91 4.93 0.626 115702B3 No 0.085 T/4 5.39 2.46 7.94 8.58 3.71 4.55 0.602 T/2 4.09 2.40 13.84 11.64 2.77 3.74 0.307

While specific embodiments of the invention have been disclosed, it will be appreciated by those skilled in the art that various modifications and alterations to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth if the appended claims and any and all equivalents thereof.

Claims

1-33. (canceled)

34. A low cost, high formability, substantially Zr-free, Al—Li alloy comprising: from 3.2 to 4.1 wt. % Cu, from 1.0 to 1.8 wt. % Li, from 0.8 to 1.2 wt. % Mg, from 0.10 to 0.50 wt. % Zn, from 0.1 to 1.0 wt. % Mn, less than 0.1 wt. % Ag, less than 0.05 wt. % Zr, up to 0.15 wt. % Ti, up to 0.12 wt. % Si, up to 0.15 wt. % Fe,

up to 0.15 wt. % each incidental elements, with the total of these incidental elements not exceeding 0.35 wt. %,
with the balance being aluminum, and
wherein Mg content is at least equal to or higher than two times of Zn in weight percent.

35. The aluminum-lithium alloy of claim 34, comprising 3.4 to 3.9 wt. % Cu.

36. The aluminum-lithium alloy of claim 34, comprising 1.1 to 1.7 wt. % Li.

37. The aluminum-lithium alloy of claim 34, comprising 0.20 to 0.50 wt. % Zn.

38. The aluminum-lithium alloy of claim 34, comprising 0.2 to 0.6 wt. % Mn.

39. The aluminum-lithium alloy of claim 34, wherein no Zr is intentionally added to the aluminum alloy.

40. The aluminum-lithium alloy of claim 34, comprising a maximum of 0.05 wt. % Ag.

41. The aluminum-lithium alloy of claim 34, comprising a maximum of 0.01 wt. % Ag.

42. The aluminum-lithium alloy of claim 34, wherein no Ag is intentionally added to the aluminum alloy.

43. The aluminum-lithium alloy of claim 34, comprising a maximum 0.05 wt. % Si.

44. The aluminum-lithium alloy of claim 34, comprising a maximum 0.08 wt. % Fe.

45. The aluminum-lithium alloy of claim 34, wherein said aluminum-lithium alloy has a thickness of 0.01-0.249 inch.

46. The aluminum-lithium alloy of claim 34, wherein said aluminum-lithium alloy has a thickness of 0.01-0.125 inch.

47. A rolled product comprising an aluminum-lithium alloy according to claim 34, having a thickness of 0.01″ to 0.249″, exhibiting in a solution heat-treated, quenched and stretched condition a ratio of “soft” to “hard” texture higher than “0.75−0.5*gage” and “0.9−5.0*gage”at sheet quarter thickness (th/4) and center thickness (th/2) respectively, the unit of gage being inch.

48. A rolled product comprising an aluminum-lithium alloy according to claim 34, having a thickness of 0.01″ to 0.249″, exhibiting in a solution heat-treated, quenched and stretched condition a ratio of “soft” to “hard” texture higher than “0.8−0.5*gage” and “1.0−5.0*gage”at sheet quarter thickness (th/4) and center thickness (th/2) respectively, the unit of gage being inch.

49. The rolled product of claim 48, wherein the aluminum-lithium alloy is in the form of a sheet or a coil having a thickness of 0.01″ to 0.125″.

50. A rolled product comprising an aluminum-lithium alloy according to claim 34, having a thickness of 0.01″ to 0.249″, exhibiting in a solution heat-treated, quenched, stretched and artificially aged condition a minimum LT bend ratio of less than “24.30-0.0292*“Specific LT TYS””, and a minimum L bend ratio of less than “13.11-0.0146*“Specific L TYS””, the unit of specific strength being “ksi/(lb/in3)”.

51. A rolled product comprising an aluminum-lithium alloy according to claim 34, having a thickness of 0.01″ to 0.249″, exhibiting in a solution heat-treated, quenched, stretched and artificially aged condition a minimum LT bend ratio of less than “23.65-0.0292*“Specific LT TYS””, and a minimum L bend ratio of less than “12.88-0.0146*“Specific L TYS””, the unit of specific strength being “ksi/(lb/in3)”.

52. A method of manufacturing a high strength, high formability, low cost aluminum-lithium alloy, the method comprising:

a. casting stock of an ingot of aluminum alloy comprising the aluminum-lithium alloy product according to claim 34 producing a cast stock
b. homogenizing the cast stock producing a homogenized cast stock;
c. hot working the homogenized cast stock by one or more methods selected from the group consisting of rolling, extrusion, and forging forming a worked stock;
d. optionally cold rolling the worked stock;
e. solution heat treating (SHT) the optionally cold rolled, worked stock producing a SHT stock;
f. cold water quenching said SHT stock to produce a cold water quenched SHT stock;
g. optionally stretching the cold water quenched SHT stock; and
h. artificially ageing of the cold water quenched, optionally stretched SHT stock.

53. The method of claim 52, wherein said step of homogenizing includes homogenizing at temperatures from 454 to 549° C. (850 to 1020° F.); wherein said step of hot working includes hot rolling at a temperature of 343 to 499° C. (650 to 930° F.); wherein said step of optionally cold work includes cold reduction at 20% to 95%; wherein said step of solution heat treating includes solution heat treated at temperature range from 454 to 543° C. (850 to 1010° F.); wherein said step of optionally stretching includes stretching up to 15%; and wherein said step of ageing includes 121 to 205° F. (250 to 400° F.) and the aging time can be in the range of 2 to 60 hours.

Patent History
Publication number: 20190169727
Type: Application
Filed: Dec 4, 2017
Publication Date: Jun 6, 2019
Applicant: Kaiser Aluminum Fabricated Products, LLC (Foothills Ranch, CA)
Inventors: Zhengdong Long (Spokane, WA), Philippe Lassince (Albi), Robert A. Matuska (Heath, OH), Florence Andrea Baldwin (Mead, WA), Ravi Rastogi (Liberty Lake, WA), Roy Austin Nash (Spokane, WA), Jason Nicholas Scheuring (Spokane, WA), Gary D. Holmesmith (Medical Lake, WA), Yansheng Liu (Spokane Valley, WA)
Application Number: 15/830,569
Classifications
International Classification: C22F 1/057 (20060101); C22C 21/14 (20060101); C22C 21/16 (20060101); C22C 21/18 (20060101); B22D 7/00 (20060101); C22F 1/00 (20060101); B21B 3/00 (20060101); B21D 25/00 (20060101);