Abstract:
The yield strength of UNS C17460 BeCu alloy can be significantly enhanced without compromising electrical conductivity or bend formability by age hardening the alloy during manufacture using two separate heat treatment steps and cold rolling the alloy for enhancing age hardening response between these two heat treatment steps rather than before age hardening begins as in current technology.

Description:
[0001]     Chip sockets for personal computers are composed of numerous tiny preformed current-carrying springs mounted in close proximity to one another. These sockets are typically made by forming the individual springs from metal strip, then assembling the springs into a large grid array in a non-conducting base plate.  
         [0002]     In order to function properly, such springs should be made from a metal which exhibits a particular combination of properties, specifically (1) high yield strength, (2) an electrical conductivity of at least 45% IACS and (3) bend formability of no more than about 2 R/t to about 3 R/t in the transverse and longitudinal directions. Bend formability is the ability of a metal sample to bend without cracking and is normally described in terms of the minimum radius R to which a metal sample of thickness t can bent 90 degrees without cracking. A transverse bend (traditionally termed a “Bad Way” bend in the connector industry) has its bend axis parallel to the rolling direction of the strip. A longitudinal bend (traditionally termed a “Good Way” bend) has its bend axis perpendicular to the rolling direction of the strip. Bend formability is another measure of alloy ductility. These combined chip socket performance requirements are sufficiently severe that existing commercial current-carrying spring alloys, whether the “high strength” copper-beryllium alloys such as C17200; or the “high conductivity” copper-beryllium alloys such as C17460, C17410, C17510 or C17500; or various non-beryllium-containing copper alloys, are inadequate in one or more individual properties and are hence marginal, if not unsuited, for present and next generation large grid array chip socket applications.  
         [0003]     Miniaturization is a constant objective in the design evolution of electronic components. In the context of chip socket manufacture, this translates into increasingly denser spacing and/or larger area grid arrays of individual small springs. This, in turn, requires that the metal forming these springs be even stronger, without sacrificing electrical conductivity or bendability, to accommodate variable spring deflections from lack of co-planarity over the large array area and/or misalignments when mating components are inserted into the large array. If the material is incapable of such accommodation, some portion of the springs in a grid array will become permanently deformed and cease to function, resulting in loss or interruption of signal transmission. Unfortunately, the maximum 0.2% yield strength that can be obtained in the “high conductivity” copper-beryllium alloys used today, when manufactured to exhibit the desired electrical conductivity of at least 45% IACS and bend formability of 1.5 to 5 R/t, is 125 ksi.  
         [0004]     Accordingly, it is desirable to provide a new copper-beryllium alloy which can be made to exhibit an even greater 0.2% yield strength, for example as high as 130 ksi or more or even 140 ksi or more, while at the same time still exhibiting the necessary electrical conductivities and bend formabilities indicated above, i.e., an electrical conductivity of at least 45% IACS, with bend formability in both the transverse and longitudinal directions of no more than about 3 R/t.  
         [0005]     Another field of electronic interconnects relates to insulation displacement connectors (IDC&#39;s) which comprise relatively flat spring blades with a knife-edged slot to cut through the insulation of an inserted wire. Evolving designs of IDC&#39;s have also created a need for higher strength materials with conductivity in excess of the existing commercial “high strength” copper-beryllium alloys such as C17200. Desirable properties for such new IDC applications include 0.2% yield strength of at least about 130 ksi to about 140 ksi, with electrical conductivity of at least about 45% IACS. Because these IDC&#39;s are essentially flat, excellent bendability is not a significant performance requirement. Hence, “Good Way” bendability of no more than about 5 R/t and “Bad Way” bend formability of no more than about 9 R/t are adequate for the task.  
       SUMMARY OF THE INVENTION  
       [0006]     In accordance with the present invention, it has been discovered that alloys UNS C17410 and C17460 can be made to exhibit these improved yield strengths, without sacrificing electrical conductivity or bendability, by age hardening the alloys with two separate heat treatment steps, with cold working being carried out between these heat treatments rather than before heat treatment begins as in current technology.  
         [0007]     Thus, the present invention provides a new copper-beryllium alloy comprising about 0.15 to 0.5 wt. % Be, about 0.35 to 1.40 wt. % Ni and/or Co, up to about 0.5 wt. % Zr, with the balance being copper and incidental impurities, wherein the alloy exhibits an electrical conductivity of at least about 45% IACS, a bend formability of less than about 3 R/t in the “Good Way” or longitudinal direction and less than about 9 R/t in the “Bad Way” or transverse direction, and a 0.2% yield strength of at least about 130 ksi.  
         [0008]     In addition, the present invention provides a new process for manufacturing a copper-beryllium alloy having an improved combination of electrical conductivity, bend formability and yield strength, the alloy mass containing 0.15 to 0.5 wt. % Be, about 0.35 to 1.40 wt. % Ni and/or Co and up to about 0.5 wt. % Zr, with the balance being copper and incidental impurities, the process comprising age hardening the alloy by heat treating the alloy in a first age hardening heat treatment step carried out directly after final solution annealing, cold rolling the mass before age hardening is completed, and finalizing age hardening by subjecting the mass to at least a second age hardening heat treatment. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The present invention may be more readily understood by reference to the following drawings wherein:  
         [0010]      FIG. 1  is a schematic representation illustrating the combination of properties exhibited by the alloys of the present invention in relation to the properties of prior art alloys;  
         [0011]      FIG. 2  is a schematic representation illustrating the thermal and mechanical processing profile experienced by a BeCu alloy which is manufactured into strip by conventional technology,  FIG. 2  also illustrating the effect on properties of the different processing steps in this manufacturing method; and  
         [0012]      FIG. 3  is a schematic representation similar to  FIG. 2  illustrating the thermal and mechanical processing profile and effect on properties of the manufacturing method of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0000]     Improved Combination of Properties  
         [0013]     As indicated above, the present invention provides alloy strip products having a unique combination of properties unavailable in conventional technology. This is illustrated in  FIG. 1 , which is a schematic representation of the alloys of the present invention in relation to alloys of the prior art in terms of electrical conductivity, bendability and yield strength. As shown in this figure, prior art alloys having electrical conductivities of 45% IACS or higher and good bend formability, when made by conventional technology, exhibit 0.2% yield strengths less than 125 ksi. Other prior art alloys, such as C17200, can be made to exhibit good bend formability and 0.2% yield strengths greater than 125 ksi. Such alloys, however, exhibit poor electrical conductivities, i.e., values of 25% IACS or less. The inventive alloys, however, because of the way they are made, exhibit all three excellent properties, i.e. electrical conductivities of at least 45% IACS, bend formabilities of 1 to 8 R/t in both the longitudinal and transverse directions, and 0.2% yield strengths of at least about 130 ksi, preferably at least about 140 ksi.  
         [0000]     Alloy Strip and Wire  
         [0014]     The present invention is directed to making copper-beryllium alloy strip and wire. By “strip” and “wire” is meant metal products which are produced by subjecting an ingot to a series of hot and cold working steps, usually with one or more intermediate solution anneals, to reduce the thickness of the metal mass by a factor of at least about 200 between ingot and finished product. Strip products are typically rectangular in configuration and are worked by hot and cold rolling steps. Wire products are normally circular in cross-section and are worked, at least in later stages of reduction, by drawing through a die one or more times. Wire products of the invention will normally have thicknesses (diameters) of no more than about 0.5 inch, more typically no more than about 0.38 inch, with thicknesses on the order of about 0.25 to 0.001 inch being more typical. Strip products of the invention will normally have thicknesses of and no more than about 0.02 inch. Thickness of about 0.01 inch or less, and especially about 0.003 to about 0.008 inch, are more typical, with 0.002 inch or even less anticipated in future chip socket designs.  
         [0000]     Alloy Chemistry  
         [0015]     The present invention is applicable to BeCu alloys comprising 
        about 0.15 to 0.5 wt. % Be,     about 0.35 to 1.40 wt. % Ni and/or Co, with the proviso that 
            if the alloy contains no Co, the Ni content is at least 1.0 wt %,     if the alloy contains no Ni, the Co content is no more than 0.60 wt %, and     if the alloy contains both Ni and Co, their combined total not exceed 1.4 wt % and the Co content not exceed 0.35 wt %,    
            up to 0.5 (and preferably 0.05 to 0.5 wt. %) Zr,     with the balance being copper and incidental impurities.        
 
         [0023]     Preferred alloys are C17460, which contains about 0.15 to 0.5 wt. % Be, about 1.0 to 1.40 wt. % Ni, up to 0.5 wt. % Zr and the balance Cu plus incidental impurities, as well as C17410, which contains about 0.15 to 0.5 wt. % Be, about 0.35 to 0.60 wt. % Co and the balance Cu plus incidental impurities.  
         [0024]     These alloys may contain additional ingredients, provided that the properties of the alloys are not adversely affected to any significant degree. Examples of such additional ingredients are Fe, Al, Si, Sn, Zn, Cr, V, Mo, Mn, W, Ag, Au, Ta, Nb, Ti, Hf, P, Mg, Ca, Se, Te, S and Pb. The total amount of such additional ingredients should not exceed 0.5 wt. %.  
         [0000]     Manufacturing Method  
         [0025]      FIG. 2  illustrates conventional technology for manufacturing strip products from C17410, C17460, C17510 and other “high conductivity” copper-beryllium alloys such as C17500, etc. As shown in this figure, a melt of the alloy is cast into an ingot, allowed to cool to low temperature, typically room temperature, and then reheated to a temperature above its solvus temperature where it is hot rolled for thickness reduction. Cooling to a low temperature can be omitted if desired. After hot rolling, the ingot is cooled to a low temperature, then cold rolled to further reduce its thickness. One or more optional intermediate anneals may be imparted to soften the cold worked alloy and enable greater total cold reduction. Such cold reduction is carried out to reach a desired ready-to-finish thickness at which the strip is given a final solution anneal at a temperature above its solvus temperature, followed by rapid quenching. Pickling or other surface treating can be used to clean and smooth the strip surfaces.  
         [0026]     Once the cold rolusolution anneal regime is complete, the alloy is age hardened to increase its strength. Like most precipitation hardenable alloys, copper-beryllium alloys also exhibit enhanced response to age hardening if they are cold worked first. Therefore, as illustrated in  FIG. 2 , the alloy after the final solution anneal at the ready-to-finish thickness is conventionally subjected to a final cold rolling step, typically in the amount of about 10% to as much as about 90% in thickness reduction to achieve the final product thickness and to prepare the metal for the subsequent age hardening heat treatment step. Thereafter, the alloy is heated to an age hardening temperature below the solvus temperature where it is held long enough for the alloy to develop a significant increase in yield strength. See, U.S. Pat. No. 6,387,195, the disclosure of which is incorporated herein by reference, for a further discussion of age hardening.  
         [0027]      FIG. 2  also illustrates the effect of the various metallurgical treatments described above on the properties of the alloy. In particular,  FIG. 2  shows that this age hardening procedure, including the final cold rolling step, increases the 0.2% yield strength of the alloy essentially to its maximum attainable value, which in the case of alloys C17410, C17460 and C17510 is about 120 to 125 ksi. In addition,  FIG. 2  also shows that, although age hardening reduces ductility (elongation), the final product is still quite ductile. This is particularly desirable in alloy strip to be used for forming chip socket springs, since bendability and ductility are closely related properties.  
         [0028]     In accordance with the present invention, a modified procedure is used to age harden the alloy. This is illustrated in  FIG. 3 , which shows that after final solution anneal the alloy is directly subjected to age hardening heat treatment rather than being cold rolled first. In this context, “directly” means that there is no intermediate cold rolling step. The desired intermediate strength after the first age hardening treatment is preferably the “peak”, or essentially maximum, strength attainable in the solution annealed and directly age hardened state; or may range into the slightly “overaged” heat treatment regime. “Peak” aging attends thermal treatment in a narrow range of aging temperature and soak time at this temperature, resulting in highest achievable strength and a particular level of electrical conductivity. “Underaging” refers to thermal treatment at temperatures less than and/or at times shorter than “peak” aging conditions for a given solution annealed alloy, and results in lower strength with lower conductivity. “Overaging” refers to aging at higher temperatures and/or longer times than “peak” aging conditions and generates lower strength with higher conductivity. Then, after the first age hardening has produced the desired intermediate strength, the alloy is cold rolled in an amount of 10 to 70%, preferably, 15 to 60%, more preferably 25 to 40%, in terms of thickness reduction to further enhance its age hardening response. Thereafter, the alloy is again heated under age hardening conditions to complete the age hardening process and produce the final product alloy.  
         [0029]     In accordance with the present invention, it has been found that this modified procedure results in a still further increase in yield strength of the product alloys over and above that obtainable with current technology, without sacrificing ductility (elongation). This is also illustrated in  FIG. 3  which shows that, while the ductility of the product alloy is essentially the same as that of the alloy of  FIG. 2 , the 0.2% yield strength of the product alloy has been increased to as much as 130 ksi or more in two embodiments of the invention (Embodiment II and III) and to as much as 140 ksi or more in another embodiment of the invention (Embodiment I).  
         [0030]     The particular conditions used for the modified age hardening procedure of the present invention are essentially the same as those used in the conventional process and can easily be determined by routine experimentation. In this connection, it is well known that age hardening of strip products can be carried out in batch operation, in which a coil or other bulk arrangement of the strip is heat heated in an age hardening furnace for a suitable period of time, typically about 3 to about 20 hours. Alternatively, the strip can be age hardened continuously by passing a continuous length of the strip through an age hardening furnace, from a pay-off coil on the input side of the furnace to a take-up coil on the output side of the furnace, for a much shorter period of time, normally no more than 10 minutes, more typically no more than 5 minutes.  
         [0031]     Age hardening in batch operation occurs as a practical matter in a fairly narrow temperature range roughly midway between the solvus temperature and room temperature. See, U.S. Pat. No. 6,387,195, mentioned above. For the alloys of the present invention, this temperature range is generally about 500° F. to 1000° F., more typically 500° F. to 900° F. Age hardening in continuous operation normally occurs at higher temperatures, which for the inventive alloys is generally at 750° F. to 1200° F., more typically 750° F. to 1000° F.  
         [0032]     As indicated above, the first age hardening is preferably carried out to achieve the “peak” or a slightly “overaged” strength level of which the solution annealed and directly age hardened alloy is capable. The thermal treatment conditions producing this first age hardened strength level in the inventive alloy are most conducive to bulk age hardening conditions. Strength superior to the maximum strength attainable from conventionally processed “high conductivity” copper-beryllium alloys is then achieved by cold working the material after the first age hardening, resulting is an increase in strength from work hardening, with attendant loss of ductility. This cold working is then followed by a second thermal treatment. One aim of the second thermal treatment is to at least stress relieve the first age hardened and cold worked strip in order to restore ductility to provide satisfactory bendability, yet retain much or all of the first age hardened plus work hardened strength. A continuous-type second thermal treatment step is particularly suited to this objective, although batch-type thermal cycles can also be selected to achieve a similar end. Preferably, the second thermal treatment step is carried out to superimpose a further aging response atop the first age hardened plus cold worked strength level, resulting in very high final strength, coupled with quite useful ductility and bendability. Batch-type second thermal treatment conditions are well-suited to this task, but appropriate continuous-type thermal treatment cycles can also be selected for this purpose.  
       Preferred Embodiments  
       [0033]     In accordance with a first preferred embodiment of the invention (Embodiment I), alloy strip having a 0.2% yield strength of at least about 140 ksi, an electrical conductivity of at least about 45% IACS and a bend formability of about 3 R/t or less, preferably about 2.5 R/t or less, in both longitudinal and transverse directions can be produced. This can be accomplished by carrying out 
        final solution anneal at about 25 to 50° F. higher than the normal solution anneal temperatures, i.e., at temperatures of about 1700 to 1750° F., more preferably about 1725° F. (with anneal times concomitantly shorter so as to achieve a small to moderate average [Is average correct?] grain size, e.g., on the order of 0.015 mm-0.030 mm, preferably 0.015 mm-0.025 mm),     the first age hardening heat treatment step at about 700 to 800° F., more preferably about 750° F., for at least about 3 and preferably at least about 5 hours, preferably to achieve approximate peak or slight overaging,     cold working by an amount of about 15 to 30%, more preferably about 20 to 25%, in thickness reduction, and     the second age hardening step in bulk at about 450° F. to 700° F., more typically about 500 to 600° F., for at least about 3 hours and preferably at least about 5 hours.        
 
         [0038]     In accordance with a second preferred embodiment of the invention (Embodiment II), alloy strip having a 0.2% yield strength of at least about 130 ksi, an electrical conductivity of at least about 45% IACS and a bend formability of 3 R/t or less, preferably about 2.5 R/t or less, in both longitudinal and transverse directions can be produced. This is accomplished by carrying out 
        final solution anneal at normal solution anneal temperatures, i.e. about 1650 to 1725° F., more preferably about 1675 to 1700° F. (with anneal times chosen to achieve a small to moderate average grain size, e.g., on the order of 0.015 mm-0.030 mm, preferably 0.015 mm-0.025 mm),     the first age hardening heat treatment step at about 850 to 950° F., more preferably about 900° F., for at least about 5 hours, preferably to achieve slight overaging,     cold working by an amount of about 15 to 50%, more preferably about 20 to 40% in thickness reduction, and     the second age hardening step in continuous fashion at about 725° F. to 825° F., more typically about 750 to 800° F. for no more than about 5 minutes, preferably no more than about 3 minutes.        
 
         [0043]     In accordance with a third preferred embodiment of the invention (Embodiment III), alloy strip having a 0.2% yield strength of at least about 130 ksi, an electrical conductivity of at least about 45% IACS and a bend formability in the transverse direction of about 2 to 2.5 R/t and a bend formability in the longitudinal direction of about S to 8 R/t can be produced. This is accomplished by carrying out 
        final solution anneal at normal solution anneal temperatures, i.e. about 1650 to 1725° F., more preferably about 1675 to 1700° F. (with anneal times chosen to achieve a small to moderate average grain size, e.g., on the order of 0.015 mm-0.030 mm, preferably 0.015 mm-0.025 mm),     the first age hardening heat treatment step at about 725 to 825° F., more preferably about 750 to 800° F., preferably for at least about 3 hours and preferably at least about 5 hours, preferably to achieve approximate peak aging,     cold working by an amount of about 45 to 65%, more preferably about 50 to 60% in thickness reduction, and     the second age hardening step 
            in bulk at about 550° F. to 800° F. for at least about 3 hours and preferably at least about 5 hours, or     in continuous fashion at about 750° F. to 900° F., for no more than 5 minutes, preferably no more than 3 minutes.    
               
 
       WORKING EXAMPLES  
       [0050]     In order to further describe the present invention, a series of 26 alloy strips were made in accordance with the present invention. Alloys of slightly different chemical compositions, but all meeting the specifications of UNS C17460, were used to form the strip products made in accordance with the present invention. In addition, Comparative Examples A and B represent an alloy outside the composition range of the alloys of the present invention, i.e., commercial C17510, subjected to processing consistent with Embodiment II of the present invention. Furthermore, Comparative Examples C to F show manufacturers&#39; published properties for commercial “high conductivity” copper-beryllium alloys of the prior art. See, “Guide to Copper Beryllium”, Brush Wellman Inc., 2002. Comparative Example F also used an alloy conforming to C17460. Comparative Examples C and D employed alloys conforming to UNS C17510. Comparative Example E employed an alloy conforming to UNS C17410. The compositions of each of these alloys is set forth in the following Table 1:  
                                     TABLE 1                           Alloy Composition, wt. %                    Ni                       [unless noted       Alloy   Be   otherwise]   Zr   Cu*               A   0.32   1.23   0.13   Balance       B   0.33   1.28   0.07   Balance       C   0.32   1.24   0.08   Balance       D   0.37   1.54   0.02   Balance       UNS C17460   0.15-0.50   1.00-1.40   0.5 max   Balance       UNS C17410   0.15-0.50   [0.35-0.60 Co]   Not specified   Balance       UNS C17510   0.2-0.6   1.4-2.2   Not specified   Balance                 *Includes incidental impurities             
 
         [0051]     The finish thicknesses of alloy strip products produced in these examples was as follows  
                                                       Example 1    0.004 inch           Examples 2-19   0.00787 inch           Examples 20-26   0.00394 inch           Comp. Ex A-B   0.00394 inch           Comp. Ex. C-F   Thickness not specified               (commercial strip)                      
 
         [0052]     The strip products made in accordance with the present invention were age hardened using a two-step heating process in which the first heating step began directly after final solution anneal, i.e., without cold rolling first. After the first heating step, these strip products were cold rolled by amounts ranging from 20 to 60% in thickness reduction and then subjected to a second age hardening heating step. In Examples 1 to 11 and 22 to 26 the second age hardening step was carried out in batch operation by placing the alloy in bulk in an aging furnace for 5 hours. In Examples 12 to 19 the second stage age hardening step was carried out by a simulated continuous process in which the strip was placed in a molten salt bath for 2 minutes. In Examples 20 and 21 as well as Comparative Examples A and B, second stage age hardening was carried out by passing a continuous length of the strip, from one end to the other, through a 45 foot long aging furnace at a speed which resulted in a dwell time of about 2.25 minutes. In Comparative Examples C to E the alloys were commercially mill hardened in a conventional manner by solution annealing, then cold rolling by an amount of 10 to about 90% in terms of thickness reduction prior to age hardening, and finally heat treated at proprietary batch-type age hardening conditions in the “peak” aging regime for each alloy.  
         [0053]     The conditions used in the various metallurgical treatment steps applied in each example are set forth in the following Table 2, while the results obtained are set forth in the following Table 3:  
                                             TABLE 2                           Metallurgical Processing Conditions                    Ready-                               to-Finish       1 st     Cold   2 nd                 Anneal   Embod-   Aging   Work   Aging       No.   Alloy   (F)   iment   Step   (%)   Step                1   A   1700   III   800 F/5 hr   50   650 F/5 hr        2   B   1675   III   750 F/5 hr   60   700 F/5 hr        3   B   1675   III   800 F/5 hr   60   650 F/5 hr        4   B   1675   III   750 F/5 hr   50   650 F/5 hr        5   B   1675   III   800 F/5 hr   50   550 F/5 hr        6   B   1675   III   750 F/5 hr   50   800 F/5 hr        7   B   1700   III   750 F/5 hr   60   700 F/5 hr        8   B   1700   III   800 F/5 hr   60   650 F/5 hr        9   B   1700   III   800 F/5 hr   60   800 F/5 hr       10   B   1700   III   750 F/5 hr   50   700 F/5 hr       11   B   1700   III   800 F/5 hr   50   800 F/5 hr       12   B   1675   III   800 F/5 hr   60   800 F/2 min       13   B   1675   III   800 F/5 hr   60   900 F/2 min       14   B   1700   III   800 F/5 hr   60   900 F/2 min       15   B   1675   III   800 F/5 hr   50   750 F/2 min       16   B   1675   III   800 F/5 hr   50   900 F/2 min       17   B   1700   III   800 F/5 hr   50   900 F/2 min       18   B   1675   II   900 F/5 hr   20   800 F/2 min       19   B   1700   II   900 F/5 hr   20   800 F/2 min       20   B   1700   II   900 F/5 hr   40   750 F/2.25 min       21   B   1700   II   900 F/5 hr   25   750 F/2.25 min       22   C   1725   I   750 F/5 hr   25   500 F/5 hr       23   C   1725   I   750 F/5 hr   25   550 F/5 hr       24   C   1725   I   750 F/5 hr   25   600 F/5 hr       25   C   1725   I   750 F/5 hr   25   700 F/5 hr       26   C   1725   I   750 F/5 hr   25   800 F/5 hr       A   D   1700   II   900 F/5 hr   25   750 F/2.25 min       B   D   1700   II   900 F/5 hr   40   750 F/2.25 min       C   C17510   Yes   Prior art   No   Yes   Final “peak”                               age       D   C17410   Yes   Prior art   No   Yes   Final “peak”                               age       E   C17460   Yes   Prior art   No   Yes   Final “peak”                               age                  
 
         [0054]    
       
         
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                   
               
               
                 Alloy Properties 
               
             
          
           
               
                   
                   
                   
                   
                   
                 Longitudinal 
                 Transverse 
               
               
                   
                   
                 Ultimate 
                   
                   
                 (Good Way) 
                 (Bad Way) 
               
               
                   
                 0.2% Yield 
                 Tensile 
                   
                 Electrical 
                 Bend 
                 Bend 
               
               
                   
                 Strength 
                 Strength 
                 Elongation 
                 Conductivity 
                 Formability 
                 Formability 
               
               
                 No. 
                 (ksi) 
                 (ksi) 
                 (%) 
                 (% IACS) 
                 (R/t) 
                 (R/t) 
               
               
                   
               
             
          
           
               
                  1 
                 140.9 
                 147.9 
                 2.0 
                 52.0 
                 1.5 
                 7.5 
               
               
                  2 
                 144.2 
                 148.8 
                 1.4 
                 48.3 
                 2.5 
                 8 
               
               
                  3 
                 145.6 
                 150.5 
                 1.2 
                 47.0 
                 2.5 
                 8 
               
               
                  4 
                 141.6 
                 147.3 
                 1.6 
                 45.7 
                 2.3 
                 &gt;7.5 
               
               
                  5 
                 142.5 
                 147.3 
                 1.2 
                 45.9 
                 2.3 
                 &lt;7.5 
               
               
                  6 
                 132.5 
                 135.7 
                 2.2 
                 51.1 
                 2 
                 5 
               
               
                  7 
                 144.3 
                 150.1 
                 1.3 
                 45.6 
                 2.5 
                 8 
               
               
                  8 
                 146.5 
                 151.9 
                 1.9 
                 46.4 
                 2.5 
                 8 
               
               
                  9 
                 130.5 
                 134.8 
                 1.0 
                 52.3 
                 1.8 
                 &gt;6.3 
               
               
                 10 
                 144.7 
                 150.8 
                 1.3 
                 46.3 
                 2.3 
                 8 
               
               
                 11 
                 133.1 
                 138.3 
                 1.9 
                 51.9 
                 2.1 
                 &lt;6.3 
               
               
                 12 
                 139.7 
                 144.6 
                 1.9 
                 45.4 
                 1.5 
                 8 
               
               
                 13 
                 130.4 
                 135.8 
                 2.8 
                 45.5 
                 1.5 
                 6 
               
               
                 14 
                 133.0 
                 138.6 
                 2.3 
                 45.2 
                 1.5 
                 6 
               
               
                 15 
                 138.6 
                 142.9 
                 1.7 
                 45.7 
                 1.5 
                 6 
               
               
                 16 
                 130.7 
                 135.9 
                 3.0 
                 47.1 
                 1.5 
                 5.3 
               
               
                 17 
                 132.8 
                 138.3 
                 2.6 
                 46.5 
                 1.5 
                 5.3 
               
               
                 18 
                 129.9 
                 133.0 
                 3.8 
                 49.9 
                 2.2 
                 2 
               
               
                 19 
                 131.0 
                 131.5 
                 5.0 
                 49.2 
                 1.9 
                 2 
               
               
                 20 
                 129.7 
                 130.2 
                 2.0 
                 No data 
                 No data 
                 No data 
               
               
                 21 
                 128.0 
                 132.0 
                 2.0 
                 No data 
                 0.5 
                 0.5 
               
               
                 22 
                 149.0 
                 155.7 
                 3.0 
                 47.9 
                 1 
                 1.5 
               
               
                 23 
                 147.7 
                 154.6 
                 1.0 
                 48.6 
                 2 
                 3 
               
               
                 24 
                 142.8 
                 150.6 
                 1.0 
                 47.3 
                 3 
                 2 
               
               
                 25 
                 134.4 
                 141.0 
                 1.5 
                 46.8 
                 1.5 
                 1.5 
               
               
                 26 
                 131.8 
                 137.5 
                 2.0 
                 46.8 
                 1.5 
                 2 
               
               
                 A 
                 124.8 
                 128.6 
                 2.0 
                 No data 
                 0.25 
                 0.25 
               
               
                 B 
                 127.2 
                 132.3 
                 2.0 
                 No data 
                 No data 
                 No data 
               
               
                 C 
                  95-120 
                 110-135 
                 8-20 
                 48-60 
                 2.0 
                 2.0 
               
               
                 C17510 HT 
               
               
                 D 
                 100-120 
                 110-130 
                 7-17 
                 45-60 
                 1.2 
                 5.0 
               
               
                 C17410 HT 
               
               
                 E 
                 105-125 
                 120-140 
                 10 min 
                 50 min 
                 1.5 
                 1.5 
               
               
                 C17460 HT 
               
               
                   
               
             
          
         
       
     
         [0055]     The foregoing data show that the present invention can reliably and consistently produce alloys inhibiting electrical conductivities of at least 45% IACS, bend formabilities of 1 to 2.5 R/t in the longitudinal direction and no more than about 8 R/t in the transverse direction, and a 0.2% yield lengths of about 130 ksi or more. In addition, the foregoing data further show that preferred embodiments of the present invention can produce such alloys which exhibit bend formabilities of about 3 R/t or less in both the longitudinal and transverse directions as well as 0.2% yield strengths of as high as 140 ksi and even higher. Finally, these data further show that alloys outside the scope of the present invention, whether because of being made by conventional technology (Comparative Examples C to E), or because of having a different chemical composition (Comparative Examples A and B), do not exhibit these properties.  
         [0056]     Although only a few embodiments of the present invention have been described above, it should be appreciated that many modifications can be made without departing from the spirit and scope of the invention. For example, although  FIGS. 2 and 3  suggest that the different metallurgical treatments illustrated therein are carried out immediately after one another, significant time delays can be accommodated between successive steps without affecting the invention in any significant way. For example, hot rolling can be delayed indefinitely after casting, if desired. Similarly, the various cold rolling and solution anneal and steps shown in these figures can also be delayed for any length of time relative to preceding steps. Furthermore, although the above description indicates that age hardening is done with only two heat treatment steps, three, four or more heat treatment steps could be used, so long as the first heat treatment step is carried out directly after final solution anneal, as indicated above. All such modifications are intended to be included within the scope of the present invention, which is to be limited only by the following claims: