Abstract:
A family of alloys based upon aluminum-copper-magnesium-silver alloys to which lithium has been added, within specified ranges, exhibits superior ambient- and elevated-temperature strength, superior ductility at ambient and elevated temperatures, extrudability, forgeability, weldability, and an unexpected natural aging response.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. Pat. Application Ser. No. 07/083,333, filed Aug. 10, 1987, now abandoned. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to lithium-containing alloys of aluminum which are characterized by a unique combination of mechanical and physical characteristics. Specifically, the aluminum-copper-magnesium-silver-lithium alloys of this invention possess exceptionally high strength, ductility, low density, excellent weldability, and an exceptional natural aging response. 
     BACKGROUND OF THE INVENTION 
     Aluminum and its alloys have long been known to have desirable properties such as low cost, relatively low density, corrosion resistance, and the ability to be fabricated relatively easily into a wide variety of shapes and configurations for various applications. Aluminum, as a base metal for alloying purposes, is generally approximately 99 per cent pure, with iron and silicon comprising the major impurities. 
     A number of aluminum alloys have been found having good weldability, and characteristics such as medium to high strength. Several of these aluminum alloy compositions are based upon aluminum-copper systems, wherein significant strengthening is induced by the precipitation of CuAl 2 . In recent work, Polmear has disclosed an aluminum-copper-magnesium-silver alloy composition designed for elevated temperature service that has high room temperature strength. No weldability data for the alloy have been reported. Polmear reported that the presence of small amounts of magnesium and silver create a previously unreported novel precipitate (i.e. omega phase) which additionally strengthens the alloy; such precipitates being coherent platelets of very minimal thickness, and high stability at slightly elevated temperatures. The strengthening in such alloys appears to be a function of the presence of both magnesium and silver. See &#34;Development of an Experimental Wrought aluminum Alloy for Use at Elevated Temperatures,&#34; Polmear, ALUMINUM ALLOYS: THEIR PHYSICAL AND MECHANICAL PROPERTIES E. A. Starke, Jr. and T. H. Sanders, Jr., editors, Volume I of Conference Proceedings of International Conference, University of Virginia, Charlottesville, VA 15-°June 1986, pages 661-674, Chameleon Press, London. 
     Lithium additions to aluminum alloys are known to produce a variety of low density, age-hardenable alloys, such as alloys of aluminum-magnesium-lithium, and aluminum-copper-lithium. Such alloys have seen limited use, due to difficulty in melting and casting and relatively low ductility and toughness in wrought products. Among conventional commercially available aluminum-lithium alloys, the only generally accepted weldable aluminum-lithium alloy is the Soviet alloy 01420, as disclosed in British patent 1,172,736, of Fridlyander et al., comprising Al-5Mg-2Li. This alloy is reported to have medium to high strength, low density, and a modulus of elasticity higher than standard aluminum alloys. In U.S. Pat. No. 2,381,219, of I. M. LeBaron, assigned to Alcoa, aluminum base alloys containing Cu and Li are disclosed. These alloys are &#34;Mg-free&#34;, i.e. the alloys have less than 0.01 percent Mg which is present as an impurity. In addition, the alloys disclosed by LeBaron require the presence of at least one element selected from Cd, Hg, Ag, Sn, In, and Zn. The surprising increase in strength observed in the Al-Li alloys of the present invention, containing both Ag and Mg, is not observed in LeBaron. 
     U.S. Pat. No. 2,915,391 to Criner, assigned to Alcoa, discloses Al-Cu-Mn base alloys containing Cu, Li, Mg, and Cd. Criner teaches that Mn is essential for developing high strength at elevated temperatures and that Cd, in combination with Mg and Li, is essential for strengthening the Al-Cu-Mn system. Criner does not achieve properties comparable to those of the present invention, i.e. ultra high strength, strong natural aging response, high ductility at several technologically useful strength levels, weldability, etc. 
     A paper appearing in the Journal of Japan Institute of Light Metals lists Al-Li-Mg base alloys to which one of the elements Ag, Cu, or Zn has been added (see &#34;Aging Phenomena of Al-Li-Mg Alloy Affected by Additional Elements,&#34; Hayashi et al, Journal of Japan Institute of Light Metals, Vol. 32, No. 7, July 1982). While the reference does disclose the addition of Ag to an alloy consisting of Al, Li, and Mg, no disclosure is made of the addition of silver to a copper containing alloy. Further, the reference does not teach the addition of grain refining elements as required in the alloys of the present invention. Since the purpose of the paper is to study the effect of specific alloying additions on the aging behavior of ternary Al-Li-Mg alloys, the authors specifically desired to limit additions to the individual elements Ag, Cu, and Zn listed without combining such additional elements or adding further grain refining elements. 
     U.S. Pat. No. 3,306,717 to Lindstrand et al relates to filler metal for welding Al-Zn-Mg base alloys. The filler metal comprises Al with 2-8 weight percent Mg, 0.1-10 weight percent Ag, and up to 8 weight percent Si. In addition, the filler metal may contain up to 1.0 weight percent each of Mn and Cr, up to 0.5 weight percent each of Cu, Ti and V, and up to 0.1 weight percent each of Li, Zr and B. The only example given by Lindstrand et al lists a filler metal composition of Al - 5 Mg-0.9 Ag. The reference does not relate to the production of the Al-Cu-Mg-Ag-Li base alloys which are the subject of the present invention. Rather, the reference is directed to the production of Al-Mg-Ag containing alloys that are suitable for use only as welding filler metal. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide relatively low density, high strength aluminum alloys. 
     It is another object of the present invention to provide lightweight aluminum alloys having high strength and good weldability. 
     By the addition of lithium to alloys similar to those suggested by Polmear, we have achieved surprisingly high strength, a degree of ductility unexpected in lithium-containing aluminum alloys, god weldability, and a natural aging response superior to any previously reported for an aluminum alloy. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1: Isochronal aging curves for Al-Cu-Mg-Ag-Li Alloy 049. 
     FIG. 2: Isochronal aging curves for Al-Cu-Mg-Ag-Li Alloy 051. 
     FIG. 3: Isochronal aging curves for Al-Mg-Ag-Li Alloy 050. 
     FIG. 4: Isothermal aging at 160° C. for Alloy 049. 
     FIG. 5: Isothermal aging at 160° C. for Alloy 050. 
     FIG. 6: Natural aging response of Alloy 049 extrusion with and without 3% stretch. 
     FIG. 7: Natural aging response of Alloy 051 extrusion with and without 3% stretch. 
     FIG. 8: Natural aging response of Alloy 050 extrusion with and without 3% stretch. 
     FIG. 9: Room Temperature tensile properties of Alloy 049 for various aging times at 160° C. 
     FIG. 10: Compressive yield strength of Alloy 051 for various deformation temperatures. 
     FIG. 11: Tensile yield strength vs. temperature for alloy 049. 
     FIG. 12: Ultimate tensile strength vs. temperature for alloy 049. 
     FIG. 13: Ultimate tensile strength vs. weight percent lithium of Al-Cu based alloys in the SUA temper. 
     FIG. 14: Yield strength vs. weight percent lithium of Al-Cu based alloys in the SUA temper. 
     FIG. 15: Natural aged strength of three percent stretched Al-Cu based alloys as a function of lithium content. 
     FIG. 16: Natural aged strength of unstretched Al-Cu based alloys as a function of lithium content. 
     FIG. 17: Natural aging response of unstretched 049 Alloy after quenching from 504° C. into various media. 
     FIG. 18: Strength vs. elongation for alloy 049. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The primary elements of the alloys of the present invention are aluminum, copper, magnesium, silver and lithium, with grain refining additive elements such as zirconium. Although emphasis herein shall be placed upon use of zirconium for grain refinement, conventional grain refiners such as chromium, manganese, titanium, boron, vanadium, hafnium, titanium diboride, and mixtures thereof, may be used. 
     In general, the alloys of this invention comprise from about 2.0 percent to about 9.8 percent by weight for the total of copper plus magnesium, preferably from about 2.5 to about 8.5 percent, and more preferably from about 3.1 to about 7.5 percent. Silver may generally comprise from about 0.01 to about 2.0 percent by weight of the alloy, preferably 0.05 to 1.2 percent, and more preferably 0.10 to 1.0 percent. The highest strengths are achieved with Ag concentrations of between about 0.3 and 0.5 percent. Lithium may comprise from about 0.05 to 4.1 percent by weight of the alloy, preferably 0.20 to 3.1 percent, and most preferably 0.50 to 2.7 percent. Below about 0.05 percent Li, significant reductions in density are not realized while above about 4.1 percent the solubility limit of Li is passed. Similarly, the total amount of grain refiner present may comprise from about 0.05 to 1.0  percent by weight of the alloy, preferably 0.05 to 0.6 percent, and most preferably 0.05 to 0.5 percent. 
     The alloys may be broadly characterized as either aluminum-copper based, or aluminum-magnesium based, with compositions varying as set forth in Table I. In those alloys classified as aluminum-copper based, the copper may comprise from about 2.0 to about 6.8 percent by weight, preferably from about 3.0 to about 6.5  percent, more preferably from about 4.0 to about 6.5 percent, and most preferably from about 4.8 to 5.2 percent. Below about 2.0 percent Cu, strengths decrease to an unacceptable degree. Above 6.8 percent Cu, density increases while corrosion resistance and fracture toughness decrease. In such alloys, the magnesium may comprise from about 0.01 to about 3.0 weight percent, preferably 0.05 to 2.0 percent, more preferably 0.10 to 1.0 percent, and most preferably 0.3 to 0.5 percent. The highest strengths are achieved in alloys containing 0.3 to 0.5 percent Mg, with gradual decreases in tensile properties below and above this range. Tensile properties are highly dependent upon Li content in the Al-Cu based alloys. The highest 
     strengths are attained with Li levels of 1.1-1.5 percent with decreases below about 1.0 percent and above 1.4 percent. 
     In those alloys classified as aluminum-magnesium based, the magnesium may comprise from about 2.0 to about 9.8 percent by weight, preferably from 2.5 to 7.0 percent, and most preferably from about 3.0 to 5.5 percent. In such alloys, the copper may comprise from 0 to 1.5 percent by weight, preferably from 0.01 to 1.0 percent, and most preferably from 0.10 to 1.0 percent. 
     The alloys are stronger by far than conventional alloys of the closest known compositions, and stronger than would be predicted based on the scientific literature. Furthermore, they have greater specific properties than conventional weldable Al alloys. They also have a surprisingly strong natural aging response, which is extremely useful for welding. Their weldability, defined as the resistance to hot cracking that can occur during welding, is excellent. This is surprising, in view of the disappointing weldability of recently commercialized Al-Li alloys. 
     Three alloy melts having the compositions as set forth hereinafter in Table II were prepared. Each alloy was cast, homogenized, extruded, solutionized, quenched, and stretched, using the parameters set forth in Table III. 
     
                       TABLE I______________________________________COMPOSITIONAL RANGES                     More     Most    Broad  Preferred Preferred                              Preferred______________________________________Al--Cu BasedCu         2.0-6.8  3.0-6.5   4.0-6.5                                4.8-5.2Mg         0.01-3.0 0.05-2.0  0.10-1.0                                0.3-0.5Ag         0.01-2.0 0.05-1.2  0.10-1.0                                0.3-0.5Li         0.05-4.1 0.20-3.1  0.50-2.7                                1.0-1.4Grain Refiners      0.05-1.0 0.05-0.6  0.05-0.5                                0.08-0.2Al         Balance  Balance   Balance                                BalanceAl--Mg BasedCu         0-1.5    0.01-1.0  0.10-1.0                                0.10-1.0Mg         2.0-9.8  2.5-7.0   3.0-5.5                                3.0-5.5Ag         0.01-2.0 0.05-1.2  0.10-1.0                                0.3-0.5Li         0.05-4.1 0.20-3.1  0.50-2.7                                0.50-2.7Grain Refiners      0.05-1.0 0.05-0.6  0.05-0.5                                0.05-0.5Al         Balance  Balance   Balance                                Balance______________________________________ 
    
     
                                           TABLE II__________________________________________________________________________COMPOSITIONS (Weight Percent)                   H        DensityHeat #   Cu Mg Ag Li Zr (ppm)                       Al   g/cm.sup.3                                (lb/in.sup.3)__________________________________________________________________________049 Planned    6.30       0.40          0.40             1.40                0.14                   --  Balance                            2.73                                (0.098)    Actual    6.20       0.37          0.39             1.21                0.17                   0.201                       Balance050 Planned    0  5.00          0.40             2.00                0.14                   --  Balance                            2.52                                (0.091)    Actual    -- 4.90          0.39             1.91                0.15                   0.541                       Balance051 Planned    6.30       0.40          0.40             1.70                0.14                   --  Balance                            2.72                                (0.098)    Actual    6.51       0.40          0.38             1.45                0.16                   0.622                       Balance__________________________________________________________________________ 
    
     
                                           TABLE III__________________________________________________________________________PROCESSING PARAMETERSPour      Homogenization                Extrusion Ram*Heat   Temperature     Temp. Time Temp.                    Speed                         SHT                            Stretch#  (°C.)     (°C.)           (h)  (°C.)                    (in/min)                         (°C.)                            %__________________________________________________________________________049   740    450 (16 h) + 510 (8 h)                370 0.10 504                            3.6050   740    450 (16 h) + 510 (8 h)                375 0.10 465                            3.0051   740    450 (16 h) + 510 (8 h)                373 0.12 504                            3.0__________________________________________________________________________ *for 6inch diameter billets in a 6.375 inch chamber extruding into 0.375 × 4.0 inch flat plate 
    
     AGING RESPONSE 
     Isochronal aging curves were developed for the three alloys to identify advantageous aging temperatures, i.e., those which would produce high hardness in a practical period of time (FIGS. 1-3). Then, artificial aging curves were developed at selected temperatures and natural aging studies were performed with different amounts of stretch (see FIGS. 4 through 8). The copper-containing alloys, e.g., alloy 049, display a rapid and extremely strong aging response at 160° C. (FIG. 4), a temperature where Al-Cu alloys normally respond sluggishly, although a decrease in hardness is noted during the early stages of aging (i.e., &#34;reversion&#34;). 
     The Al-Cu-Mg-Ag-Li alloys show a natural aging response that is extraordinary, and particularly significant in terms of utility (FIGS. 6, 7). The response is so rapid for alloy 049 that within ten hours after quenching, hardness increases from 48 to 72 R B , both with a 3% cold stretch prior to aging, and also without prior cold work. This is extremely important because al.1 existing pilot-commercial Al-Li alloys have insufficient strength to replace existing high technology alloys unless they are cold worked prior to aging. This is especially problematical for forging alloys, where it is most often not practical to induce cold work prior to aging. It is significant that the natural aging response without cold work is ultimately greater than that with cold work, an extremely beneficial attribute for forging. This natural aging response is observed for both heats 049 and 051. Alloy 050 displayed a slight natural aging response with no stretch, and a more rapid response with stretch (FIG. 8). 
     In contrast, known 2xxx alloys have a very slight, insignificant natural aging response without prior cold work. Ultimate tensile strengths such as were obtained with the subject alloys were totally unanticipated on the basis of 2xxx alloys. 
     TENSILE PROPERTIES 
     The alloys were tested in tension in various aging conditions in both the longitudinal (L) and long transverse (LT) directions. In Table IV, one can see that the properties are clearly exceptional and substantially stronger than any conventional weldable aluminum alloy, and also stronger than Soviet alloy 01420, the only commercial Al-Li alloy designed to be weldable. 
     The highest strengths reported are generally in the &#34;slightly underaged&#34; (SUA) temper, where toughness is expected to be higher than in the peak-aged temper. One can look at the artificial aging curves (FIGS. 4 and 5) to assess the degree of underaging in the 160° C. (24h) temper reported. 
     The new alloys also demonstrate unexpectedly good properties in the naturally aged condition (Table V). In fact, Al-Cu-Mg-Ag-Li alloy 049 is stronger in the naturally aged condition than any conventional weldable aluminum alloy is in its peak strength condition. This has important implications for welding, where a strong natural aging response provides the potential to restore strength in weldments. Moreover, it is extremely significant that this exceptional natural aging response exists without prior cold work. Consequently, a useful vehicle exists to increase the strength of weldments and forgings in which inducing cold work is often not practical. Even better naturally aged properties were obtained in subsequently prepared alloys, as described hereinafter (Table XIV). Alloy 050, an Al-Mg-Ag-Li alloy, in the stretched and naturally aged condition (T3 temper) is essentially as strong as alloy 01420 in the artificially aged condition. The alloys of the present invention also have superb specific properties, with the specific strength of 049 almost twice that of 2219 T81 (Table VI). 
     With artificial aging, the experimental alloys 049 and 051 are actually as strong as, or stronger than,, any ingot metallurgy aluminum base alloy, both weldable and non-weldable, as can be seen by comparison of Tables V and VII, and FIG. 9. 
     In contrast, the Ag-containing, Mg-free, Al-Li alloy developed by LeBaron did not show the surprising strength increases contained in the present invention. In fact, the presence of Ag decreased strength slightly (see Table VIII). 
     The present Al-Cu-Mg-Ag-Li alloys (049 and 051) show a significant strength increase with respect to the experimental Al-Cu-Mg-Ag-Mn-Zr-Ti-Fe-Si alloy developed by Polmear. As may be seen, improvements of 34 percent and 23 percent were observed for yield strength and ultimate tensile strength, respectively, for alloy 049 when compared to the Polmear alloy (Table VIII). 
     
                                           TABLE IV__________________________________________________________________________TENSILE PROPERTIES OF EXPERIMENTAL ANDCONVENTIONAL WELDABLE ALLOYS     Aging     Temp         (time)             E.sub.Measured                   YS   UTS  El   DensityID #    Orientation     °C.         (h) (× 10.sup.3 ksi)                   (ksi)                        (ksi)                             %    (lb/in.sup.3)__________________________________________________________________________Novel Weldable Alloys (SUA)049 L     160 (24)             11.3  100.4                        103.3                             5.1  0.098    LT    160 (24)             11.3  94.1 97.8 1.9051 L     160 (24)             11.5  89.8 94.9 5.2  0.098    LT    160 (24)             11.3  90.2 92.8 1.3050 L     160 (14)             11.1  53.5 72.5 7.7  0.091    LT    160 (14)             11.1  52.5 76.2 14.1Conventional Weldable Alloys2219    L             10.6**                   44.0**                        61.0**                             6.0**                                  0.102T815083    L             10.3***                   31.0***                        44.0***                             12.0***                                  0.096***H3217039    L             10.4***                   50.0***                        60.0***                             14.0***                                  0.099***T6101420    L             11.1* 42.2*                        61.7*                             16.9*                                  0.0908*__________________________________________________________________________ *Typical actual data from 50lb heats. **Minima for plate. The minima for extrusion are 42.0 ksi YS, 58.0 ksi UTS. ***Handbood Minima 
    
     
                       TABLE V______________________________________TENSILE PROPERTIES OF ALLOYS      Aging Condition            Temp.   (time) YS    UTS   ElAlloy #  Orientation            °C.                    (h)    (ksi) (ksi) (%)______________________________________Novel Alloys in Various Tempers049    L         NA*     (1000 h)                           55.6**                                 74.0**                                       16.5  LT        NA*     (3000 h)                           52.0**                                 71.5**                                       21.7  L         160     (14 h) 94.6  98.2  5.2  L         160     (24 h) 100.4 103.2 5.1050    L         NA*     (1000 h)                           44.9**                                 59.4**                                       11.0  LT        NA*     (3000 h)                           38.6**                                 59.4**                                       16.9  L         160     (14 h) 53.5  72.5  7.7  L         160     (14 h) 52.5  76.2  14.1Handbook Property Minima (for extrusions)2219             T81            42.0  58.0  6.0______________________________________ *NA = naturally aged with aging time following **Cold stretched three precent prior to natural aging. 
    
     
                       TABLE VI______________________________________SPECIFIC PROPERTIES OF EXPERIMENTAL ALLOYS(Slightly Underaged Temper)         UTS/ρ E/ρAlloy #       (× 10.sup.3 in)                   (× 10.sup.6 in)______________________________________Novel Al--Li Weldable Alloys049           1053      115050           798       122051           967       117Handbook Property Minima2219 T81      592       103______________________________________ 
    
     
                       TABLE VII______________________________________Highest Strength Non-WeldableAluminum I/M Alloys (Extrusions, Typical Values)                                E     Den-               YS     UTS  El   (× 10.sup.3                                      sityAlloy  System       (ksi)  (ksi)                           %    ksi)  (lb/in.sup.3)______________________________________7001 T6  Al--Zn--Mg   91     98   9    10.3  0.1037178 T6  Al--Zn--Mg   78     88   11   10.3  0.1028091   Al--Li--Cu--Mg               88.5   91.4 4    11.7  0.0917T651______________________________________ 
    
     
                       TABLE VIII______________________________________TENSILE PROPERTIES OF VARIOUS ALLOYS                  YS      UTS     ElAlloy                  (ksi)   (ksi)   %______________________________________LeBaron                75.9    82.1    7.8Al--4.5 Cu--0.7 Mn--0.25 Si--0.15 Fe--1.0 Li--0.15 CdLeBaron                74.5    80.6    7.5Al--4.5 Cu--0.8 Mn--0.25 Si--0.15 Fe--1.0 Li--0.15 Cd--0.15 AgPolmear experimental alloy                  75.0    84.1    7.5Al--6.7 Cu--0.46 Mg--0.50 Ag--0.48 Mn--0.18 Zr--0.07 Si--0.1 Fe--0.06 Ti049                    100.4   103.3   5.1Al--6.2 Cu--0.37 Mg--0.39 Ag--1.21 Li--0.17 Zr______________________________________ 
    
     Weldability 
     Fusion Weldability 
     Tungsten Inert Gas 
     Alloy 049 was manually TIG (tungsten inert gas) welded with both conventional 2319 filler and parent metal filler. Alloy 050 was manually TIG welded with both conventional 5356 filler and parent metal filler. V-notch butt weldments with a fair amount of constraint were made. TIG (tungsten inert gas) welding. The V-notch weldment does not produce weldments of particularly high joint efficiency (i.e. strength weldment/strength parent alloy). However, constrained V-notch butt weldments are instructive for demonstrating weldability when welding parameters are not known for a new material. In addition, automatic TIG square butt weldments were made on alloys 049, 050, and 051 using conventional fillers. 
     Whereas weldability is defined as the resistance to hot cracking, none of the weldments displayed any hot cracking susceptibility despite the constraint imposed. Furthermore, the welding parameters used (Table IX), which were selected based on analogy to conventional alloys, led to good metal flow during welding and caused the welders to claim that the alloys welded as easily as conventional alloys 2219 and 5083. 
     The alloys had low hydrogen content (Table II), yet weldments did display gas-formed pores at the weld bead-parent alloy interface. The porosity is believed to have resulted from improper handling during welding. This porosity caused the weldments to fail in tension at that interface. Nevertheless, the strengths of several weldments are quite good (see Table X) and suggest that very good weld strengths are possible. Corrective care to weldment pretreatment was exercised in subsequent welding tests, and no significant porosity was detected by radiographic techniques. In fact, TIG weldments of an 049-type alloy (059, described hereinafter) using parent metal filler, passed the very stringent quality control production test for porosity which is used on the Titan missile. 
     Electron Beam Welding 
     Autogenous electron beam (EB) weldments were performed on an alloy similar to alloy 049, alloy 061 described hereinafter. A square butt weld was fabricated along the longitudinal axes of two 100mm wide plates of alloy 061. The welding was performed at 140 kv potential and 80 mA current at a travel speed of 500 mm/min. in a single pass. 
     The alloy proved to be readily weldable by this technique, and the two 18mm thick plates were easily joined in the full penetration pass. 
     The weldments were radiographed and showed negligible porosity, and long transverse tensile properties were determined. The tensile strengths were exceptionally high, and are from material in the as-welded condition with only 12 days natural aging (see Table XI). Although the apparent elongation over the 4 inch length is 0.3 percent, the deformation was localized to the narrow (about 5mm) weld zone, so the true strain-to-failure ratio in this localized region is much higher. This is supported by the much higher 9% reduction in area. 
     Friction Weldability 
     Several specimens of 049-type alloy 061 were stretched to 0.5 inch diameter, 2 inch cylindrical rods, and were friction welded using parameters in Table XII. Although a detailed study was not undertaken to develop optimized friction welding parameters, good strengths were obtained (Table XII). For example, the tensile strength of joints were as high as 57.9 ksi with no post-welding heat treatment, demonstrating that this alloy is amenable to friction welding. 
     
                                           TABLE IX__________________________________________________________________________Welding Parameters Used forNovel Alloys__________________________________________________________________________MANUAL TIG PROCEDURE    Filler    Voltage         Current              # of                  Time per pass                            LengthAlloy    Material    (volts)         (amps)              Passes                  second(s) (inches)__________________________________________________________________________049 2319 18-24         190-250              4   155, 120, 121, 148                            (10                               in.)049 Parent    20-24         150-205              4   71, 61, 41, 53                            (5 in.)050 5356 18-24         150-210              4   161, 138, 112, 115                            (10                               in.)050 Parent    19-22         160-210              4   63, 52, 46, 48                            (5 in.)__________________________________________________________________________ 3/16 in. diameter, 2% thoriated tungsten electrode Coverages: 100% He at 8 cu ft/h or 100% Ar at 25 cu ft/h. 75° V-Notch Preheat base metal to 170° F. Gas Cup size: 3/8 in. 
    
     
         AUTOMATIC TIG PROCEDURE  Weld     Voltage                Current                     Travel Speed                            Wire Speed  Pass     (Volts)                (Amps)                     (in/min)                            (in/min)__________________________________________________________________________  Seal Pass           11.2 190  12.0   --  Penetration Pass           11.4 245  9.8    --  Filler Pass           11.7 195-200                     9.8    46-55__________________________________________________________________________ DC curfrent straight polarity 049 and 051 used 2319 filler wire 050 used 5356 filler wire, square butt welds Coverages: 100% He at 8 cu ft/h. or 100% ar at 25 cu ft/h. 
    
     
                                           TABLE X__________________________________________________________________________Tensile Properties from TIG WeldmentsParent  Post-Welding    Weld                       YS UTS                             El*                                Type of TIGAlloy    Filler   Temper          Bead                       (ksi)                          (ksi)                             (%)                                Welding__________________________________________________________________________049 2319   NA (500 h)      On  31.6                          38.9                             3.0                                Manual049 2319   NA (500 h)      Flush                       28.8                          39.0                             3.0                                Manual049 2319   NA (500 h)      Flush                       31.8                          47.5                             5.7                                Auto049 2319   SHT (504° C./WQ/NA (770 h)                   Flush                       42.8                          61.0                             9.5                                Auto049 2319   SHT (504° C./WQ/160° C. (24 h)                   Flush                       56.8                          58.6                             0.4                                Auto049 2319   SHT (504° C./WQ/NA (770 h)                   Flush                       33.0                          51.3                             6.0                                Manual049 049 NA (500 h)      On  38.4                          44.0                             0.5                                Manual049 049 NA (500 h)      Flush                       38.5                          40.6                             0.5                                Manual050 5356   NA (500 h)      On  22.3                          40.6                             6.5                                Manual050 5356   NA (500 h)      Flush                       22.5                          43.2                             14 Manual050 5356   NA (500 h)      Flush                       24.6                          48.0                             13 Auto050 050 NA (500 h)      On  27.1                          42.8                             6  Manual050 050 NA (500 h)      Flush                       22.5                          51.0                             17 Flush__________________________________________________________________________ All alloys were in the SUA temper before welding *Elongation is from a 1inch gage length. 
    
     
                       TABLE XI______________________________________Long Transverse Electron Beam Weldment Propertiesof Alloy 061         Appar-         Apparent                                ReductionTemper Before Welding         ent     UTS    Elongation                                in AreaWelding       YS      ksi    %       %______________________________________SUA           60.5    62.4   0.3     9SUA           60.4    63.0   0.3     9______________________________________ As welded, NA (12 days). 
    
     
                       TABLE XII______________________________________Friction Welding of Alloy 061 in SUA TemperRotational   Friction Forging  Condition   TensileSpeed   Force    Force    After       Strength(rpm)   (lbs)    (lbs)    Welding     (ksi)______________________________________3000    1200     2400     NA (4 h)    43.83000    2000     3000     NA (4 h)    44.53000    4000     5000     NA (24 h)   40.53000    4000     5000     NA (192 h)  57.93000    4000     5000     AW-160° C. (20 h)                                 59.6______________________________________ *Water quenched 15 s after friction welding. 
    
     ELEVATED TEMPERATURE DATA 
     Elevated temperature properties were determined using hot compression tests on alloy 051 and conventional weldable alloy 2219, the leading conventional alloy for 120° C. service. (Table XIII, FIG. 10). 
     The compression tests were conducted at a strain rate of 8×10 -3  s -1  after holding at temperature for 30 minutes. The novel alloy showed exceptional warm temperature strength, well above that of 2219 (see FIG. 10), throughout the entire temperature range investigated, which is considered to be beyond the useable temperature range of 2219. In fact, alloy 051 has considerably higher yield strength at 200° C. than 2219 has at room temperature, and very nearly the same yield strength at 250° C. that 2219 has at room temperature. 
     Several tensile tests were performed at elevated temperatures (Tables XIII, FIGS. 11 and 12) and strength values were found to be exceptional. Both tensile and yield strengths are superior to alloy 2014. 
     
                       TABLE XIII______________________________________Elevated Temperature Data for Novel Alloys and 2219______________________________________Elevated Temperature Compression Data of NovelAlloy and 2219                 Deformation                 Temperature                            YS*Alloy    Orientation  (°C.)                            (ksi)______________________________________051      L            24         94.3                 100        92.0                 150        84.8                 200        74.1                 250        52.12219-T87 L            24         56.0                 150        49.4                 250        31.3______________________________________Elevated Temperature Tensile Data for Alloy 049   Deformation   Temperature YS     UTS   El   ETemper  °C.  ksi    ksi   (%)  (× 10.sup.6______________________________________                                 psi)SUA     93          95.3   99.0  8.1  12.1SUA     93          94.4   94.8  6.11 11.5NA      93          55.9   70.6  NA   11.5SUA     150         86.7   90.1  6.2  11.2SUA     150         86.1   89.2  7.2  11.4NA      150         79.6   83.4  10.5 10.8______________________________________ *0.2 percent off set yield strength. 
    
     ADDITIONAL ALLOYS 
     Having obtained the exceptional properties demonstrated for alloys 049-051, ten additional 50-lb. heats were fabricated in accordance with the compositions set forth in Table XIV. Several tests were near-duplicates of 049 and 050, to demonstrate reproducibility, and others were attempts to improve specific properties. For example, Al-Cu based alloys similar to 049 were fabricated with higher Li levels to decrease density and increase modulus. Other Al-Cu based alloys were made with lower Cu content to decrease density and to determine whether hot cracking susceptibility increases at the Cu level investigated, as predicted by data from Al-Cu binary alloys. Meister and Martin, &#34;Welding of Aluminum and Aluminum Alloys,&#34; Defense Metals Information Center, Battelle Memorial Institute, Columbus, Ohio, 1967.) Additionally, two Al-Cu based Alloys similar to 049 were fabricated with lower Cu levels of 3.0 to 4.5 weight percent. The compositions and tensile properties of extrusions of these alloys in the T8 temper are given in Table XIVa. 
     Two Al-Mg based alloys similar to 050 were prepared, one of the same nominal composition (062), and one fabricated with 0.2 percent Cu to assess the effect of Cu on strength. The alloys were cast and homogenized using parameters similar to those in Table II. Extrusion and processing parameters are in Table XIV, and comparative tensile properties are shown in Tables XV. 
     The near duplicate tests of alloy 049 (i.e. alloys 059, 060, 061) reproduced the unexpectedly high properties of alloy 049 superbly (see Table XVI). The increased addition of Li to Al-Cu based alloy (064, 065, 066, 067) did indeed decrease density (Table XIV) but had an unexpected effect on strength. Both tensile and yield strength decreased, in the slightly underaged condition, with increasing Li content in the range studied (see FIGS. 13, 14). The same trend was observed for the naturally aged data both with and without cold stretch (see FIGS. 15, 16). This strength decrease is the opposite effect for virtually all practical Al-Cu-Li alloy compositions. In fact, very recent Japanese work (Yo Kojima et al., &#34;Effect of Lithium Addition on the Elevated Temperature Properties of 2219 Alloy,&#34; Journal of Japan Institute of Light Metals, Vol. 36, No. 11, Nov. 1986, pp. 737-743.) related to Li-modified 2219 alloys (A1-6 wt % Cu) shows a directly related increase in yield strength with increasing Li content from 0 to 2 weight percent (see Table XVII). 
     The natural aging tensile data for alloys similar to type 049 alloys are higher than any reported in the literature for aluminum alloys. In fact, the tensile strengths without cold work, 84.2 to 86.1 ksi, are significantly higher than the properties of 2219 in the fully artificially aged condition. (See Table XVIII.) 
     Despite the fact that strength decreases with Li content from about 1.2 percent to about 1.9 weight percent, the strengths at the higher lithium level alloys are still competitive with other high strength alloys as well as conventional alloys. Thus, there are several technologically useful families of alloys within the scope of the present invention; for example, an ultra high-strength alloy (049) with a four percent decrease in density with respect to 2219, and a high strength alloy (065) with a six percent or higher density decrease. 
     Attempts to decrease density by lowering the copper content were successful in that strength did not change with a decrease in copper content from 6.3 to 5.4 weight percent at both the 1.4 weight percent and 1.7 weight percent lithium levels. 
     
                                           TABLE XIV__________________________________________________________________________EXTRUSIONS OF ADDITIONAL COMPOSITIONS                     Ext.                         Ext. Ram                              ExtrusionAlloy     Planned Compositions (wt. %)                     Temp                         Speed                              Dimension                                    DensityID #      Cu Mg Ag Li Zr  (°C.)                         (in/min)                              (in)  g/cm.sup.3                                        (lb/in.sup.3)__________________________________________________________________________058 Planned     6.30        0.40           0.40              1.40                 0.15                     358 0.10 2 DIA rod                                    2.71                                        (0.098)    Measured     5.79        0.38           0.40              1.34                 0.17059 Planned     6.30        0.40           0.40              1.40                 0.15                     364 0.12 4 × 3/8                                    2.72                                        (0.098)    Measured     6.21        0.40           0.43              1.39                 0.16060 Planned     6.30        0.40           0.40              1.40                 0.15                     355 0.20 4 × 3/8                                    2.72                                        (0.098)    Measured     6.18        0.40           0.42              1.32                 0.155061 Planned     6.30        0.40           0.40              1.40                 0.15                     364 0.12 2 × 3/4                                    2.72                                        (0.098)    Measured     6.33        0.41           0.42              1.34                 0.16062 Planned     0.00        5.00           0.40              2.00                 0.15                     349 0.12 2 × 3/4                                    2.53                                        (0.091)    Measured     -- 5.40           0.42              2.10                 0.135063 Planned     0.20        5.00           0.40              2.00                 0.15                     327 0.08 4 × 3/4                                    2.50                                        (0.090)    Measured     0.22        5.25           0.41              2.02                 0.14064 Planned     6.30        0.40           0.40              1.70                 0.15                     356 0.12 4 × 3/8                                    2.69                                        (0.097    Measured     6.30        0.41           0.41              1.62                 0.155065 Planned     6.30        0.40           0.40              2.00                 0.15                     344 0.12 4 × 3/8                                    2.68                                        (0.097)    Measured     6.31        0.46           0.41              1.86                 0.145066 Planned     5.40        0.40           0.40              1.40                 0.15                     328 0.12 4 × 3/8                                    2.70                                        (0.098)    Measured     5.56        0.46           0.41              1.38                 0.165067 Planned     5.40        0.40           0.40              1.70                 0.15                     334 0.12 4 × 3/8                                    2.67                                        (0.096)    Measured     5.55        0.44           0.40              1.66                 0.16__________________________________________________________________________ 
    
     
                       TABLE XIVa______________________________________Composition and Tensile Properties of Additional AlloysAlloy                                  YS    UTS  ElID #  Cu    Mg     Ag  Li  Zr   Temper (ksi) (ksi)                                             (%)______________________________________068   5.0   0.4    0.4 1.3 0.14 T8     100.5 103.5                                             8.8069   4.5   0.4    0.4 1.3 0.14 T8     100.8 103.3                                             8.5______________________________________ 
    
     
                       TABLE XV______________________________________Tensile Properties of Al--Mg Based Alloys                       YS     UTS  ElAlloy Temper      Orientation                       (ksi)  (ksi)                                   (%)______________________________________050   SUA         L         53.5   72.5 7.7 SUA         LT        52.5   76.2 14.1 T3*         L         44.9   59.4 11.9062   SUA         L         55.3   75.2 9.2 T3*         L         45.5   61.8 15.1063   SUA         L         57.9   75.5 6.7 SUA         LT        51.9   73.3 9.2 T3*         L         46.1   60.0 12.401420 SUA         L         42.2   61.7 16.6 SUA         LT        38.2   61.7 16.9______________________________________ *T3 = stretched 3%, natural aged 1200 h. 
    
     
                       TABLE XVI______________________________________Slightly Underaged Tensile Propertiesof Near Duplicate Heats of Alloy 049     AgingAlloy           Temp     (time)                          YS     UTS   ElID #  Orientation           °C.                    (h)   (ksi)  (ksi) %______________________________________049   L         160      (24)  100.4  103.3 5.1 LT        160      (24)  94.1   97.8  1.9059   L         160      (20)  99.8   102.4 5 LT        160      (20)  95.8   99.4  3060   L         160      (24)  98.7   101.5 5.4 LT        160      (24)  94.1   99.0  3.0061   L         160      (24)  101.4  104.0 4.7______________________________________ 
    
     
                       TABLE XVII______________________________________Room Temperature Yield Strength of Li-modified 2219Increases with Increasing Li ContentAlloy           YS (ksi)______________________________________2219            46.92219 + 1% Li    67.52219 + 2% Li    81.0Al + 2% Li      24.2______________________________________ 
    
     
                       TABLE XVIII______________________________________Natural Aging Response of Al--Cu Based Alloys(NA 1200 h)            YS      UTS   ElAlloy   Stretch  (ksi)   (ksi) %______________________________________060     3%       57.5    74.9  14.4   0%       62.2    86.1  17.6061     3%       59.0    77.0  17.4   0%       64.5    85.2  14.4066     3%       59.0    77.1  14.6   0%       62.9    84.2  13.22219 T81   yes      42.0    58.0  6     Handbook                                Minimum for                                Extrusions            51.0    66.0  10    Typical______________________________________ 
    
     Forgeability 
     A casting of alloy 058 was extruded to 2 inch diameter rod at 358° C. Sections of this rod were used as forging stock material to assess the forgability of Al-Cu based alloys. Ten 4-inch long sections were cut from the rod, and were forged using a closed die for the arm torque shaft used on a fighter aircraft. The alloy exhibited excellent forgability in this complex forging in that all ten forgings showed complete die filling and no tendency toward cracking over a range of forging temperatures from 275°to 410° C. A forging was subsequently solution heat treated at 504° C. for 90 minutes, and water quenched at 20° C. After 24 hours of natural aging, the forgings had a hardness of 77 R B , similar to that of the extruded bar. Furthermore, after aging at 160° C. for 20 hours the hardness readings on the forgings ranged from 98 to 104 R B  (ultimate tensile strength in ksi and hardness in R B  roughly correspond one to one). This experiment demonstrates the exceptional potential of this alloy to achieve high strength in forgings without the benefit of cold work to stimulate precipitation during artificial aging. Other Al-Li alloys fail to meet strength goals in complex forgings because many forgings are not amenable to cold working, and these other alloys need cold work to reach high strength. 
     Quench Sensitivity 
     Quench sensitivity refers to the inability of a material to attain its maximum strength characteristics from precipitation processes when its cooling rate after solution heat treatment is decreased during quenching, i.e., effected by various liquid media or from heat transfer limitations through the bulk of the quenched piece. It is advantageous to have a material with low quench sensitivity where cooling rates are not critical. Quench &#34;insensitivity&#34; is valuable for weldments where it may not be feasible to re-heat-treat the alloy or where the weld bead and heat affected zones cool relatively slowly after welding. 
     As a preliminary assessment of quench sensitivity in the Al-Cu based alloy, a hardness profile was measured across a quenched two inch diameter rod (four foot length of extrusion 058). After solution heat treatment at 910° F. for 1.5 hour, 20° C. water quenching, the material was natural aged for 1400 hours, and Rockwell B measurements were taken in increments of 1/8 inch from the perifery toward the center of the extrusion as shown in Table XIX. The maximum deviation in hardness is less than 4 R B  indicating low quench sensitivity. Similar hardness profiles across the 2 in.×3/4 in. extrusion 061 showed less than 2 R B  points deviation through the thickness. 
     As a further evaluation of quench sensitivity, sections of alloy 049 were quenched in either water at room temperature, ice water (0° C.), or boiling water (100° C.) after solution heat treatment at 504° C. FIG. 17 shows the natural aging response of the alloy resulting after quenching from these three different quenching rates. A strong natural aging response is noted for all three quench rates. At the longest recorded aging times, no more than six Rockwell Points separate the slowest (boiling water) and fastest (ice water) quenching rates while there is little difference between standard room temperature water quench and boiling water quench. Thus, Al-Cu-Mg-Ag-Li alloys appear to be sufficiently quench insensitive to have potential for restoring strength in weldments and forgings. 
     This result also indicates that the exceptional strength of Al-Cu based alloys in the naturally aged condition, e.g. 62.2 ksi YS and 86.1 ksi UTS for alloy 061, could be increased further by quenching into ice water. Indeed, the natural aging curves in FIG. 17 indicate that tensile strengths greater than 85 ksi can be obtained after an ice water quench, in about 1000 hours. This is technologically significant because quenching at 0° C. is a practical plant operation. Given the unexpectedly high properties of the alloys of the present invention, it was decided to make additions of silver or silver plus magnesium to recently commercialized aluminum-lithium alloys 2090, 8090, and 8091. The compositions of these alloys are in Table XX. Additions were made of 0.4 weight percent silver to 8090 and 8091, and 0.4 weight percent silver plus 0.4 weight percent magnesium to 2090. These alloys were successfully cast and found to have improved properties. 
     
                       TABLE XIX______________________________________Hardness Profiles Across a Two Inch Diameter Rodof Extrusion 058Distance From       Hardness (R.sub.B)Surface     Reading(in.)       1            2      3______________________________________1/8         78.5         79     792/8         81.0         80.5   80.53/8         81.0         81.0   81.04/8         80.5         81.0   80.55/8         79.5         80.5   80.56/8         79.0         79.0   79.07/8         77.5         78.5   79.01           77.5______________________________________ 
    
     
                       TABLE XX______________________________________Modified Compositions of Commercial AlloysAlloy     Cu     Mg      Li   Ag   Zr    Al______________________________________2090 Modified     2.7    0.4     2.2  0.4  0.14  Balance8090 Modified     1.3    0.7     2.5  0.4  0.14  Balance8091 Modified     1.9    0.9     2.6  0.4  0.14  Balance______________________________________ 
    
     The alloys of the present invention also possess excellent cryogenic properties. Tests performed at cryogenic temperatures reveal improvements in tensile and yield strengths. For example, Alloy 049 in the T8 temper at -196° C. (-320° F.) displays tensile properties of 105.8 ksi YS, 108.6 ksi UTS and 3.6 percent elongation. Alloy 066 in the TB temper displays tensile properties of 101.2 ksi YS, 105.2 ksi UTS and 4.0 percent elongation at -68° C. (-80° F.), and tensile properties of 118.9 ksi YS, 124.7 ksi UTS and 3.2 percent elongation at -196° C. (-320° F.). Alloy 068 in the T8 temper at -196° C. (-320° F.) displays tensile properties of 113.6 ksi YS, 121.8 ksi UTS and 7.8 percent elongation. In the T6 temper, Alloy 68 at -196°  C. (-320° F.) possesses tensile properties of 114.4 ksi YS, 119.0 ksi UTS and 2.5 percent elongation. The excellent cryogenic properties attained with the alloys of the present invention give important implications for space applications where cryogenic alloys are often necessary for fuel and oxidized tankage. 
     This invention thus provides a family of alloy compositions which, when suitably processed, provides exceptional strength--far greater than existing ingot metallurgy alloys of similar aluminum-based materials. The reasons for this ultra-high strength are not completely understood. Extensive transmission electron microscopy and selected area diffraction experiments failed to detect an omega phase in alloy 049, as might be expected from Polmear&#39;s work. It was observed that the T 1  phase (Al 2  CuLi) is exceptionally refined in alloy 049, which may help to explain the ultra-high strength. The alloys have lower density than similar alloys as a result of the addition of lithium. The alloys show surprisingly good ductility (in the naturally aged and underaged conditions), which is unexpected for an alloy containing lithium. Furthermore, the alloys have surprising and unexpectedly high strength in the naturally-aged condition, which makes them extremely promising for weldable and forging applications. The alloys have better combinations of strength and ductility than recently commercialized Al-Li alloys such as 2090, 2091, and 8090 (see FIG. 18). Welding trails indicate that the alloys of the present invention are extremely weldable using both conventional and parent metal fillers. 
     It is to be understood that the above description of the present invention is susceptible to various modifications, changes, and adaptations by those skilled in the art, and that the same are to be considered to be within the spirit and scope of the invention as set forth by the claims which follow.