EP3158095A1 - Copper-nickel-silicon alloys - Google Patents

Abstract

A copper base alloy having an improved combination of yield strength and electrical conductivity consisting essentially of between about 1.0 and about 6.0 weight percent Ni, up to about 3.0 weight percent Co, between about 0.5 and about 2.0 weight percent Si, between about 0.01 and about 0.5 weight percent Mg, up to about 1.0 weight percent Cr, up to about 1.0 weight percent Sn, and up to about 1.0 weight percent Mn, the balance being copper and impurities, the alloy processed to have a yield strength of at least about 137ksi, and an electrical conductivity of at least about 25% IACS.

Description

COPPER-NICKEL-SILICON ALLOYS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application

Serial No. 61/044,900, filed April 14, 2008, U.S. Provisional Patent Application No. 61/016,441 , filed December 21 , 2007, and U.S. Utility Patent Application No. 12/336,731 , filed December 17, 2008, the entire disclosures of which are incorporated herein, by reference. BACKGROUND

[0002] This invention relates to copper base alloys, and in particular to copper- nickel-silicon base alloys.

[0003] Copper-nickei-silicon base alloys are widely used for the production of high strength, electrically conductive parts such as connectors and lead frames. C7025, developed by Olin Corporation, is an important example of a copper-nickel-silicon base alloy that provides good mechanical {yield strength 95 ksi - 110 ksi) and good electrical properties {35% iACS) . See U.S. Patent Nos. 4,594,221 and 4,728,372, incorporated herein by reference. More recently, C7035, a cobalt modified copper, nickel, silicon alloy, has been developed by Olin Corporation and Wieland Werke, which can provide even better mechanical (yield strength 100 ksi - 130 ksi) and electrical properties (40-55% IACS). See U.S. Patent No. 7,182,823, incorporated herein by reference.

[0004] The properties of copper alloys that can be important include formability, conductivity, strength, ductility, and resistance to stress relaxation. [0005] Formability is typically evaluated by a bend test where copper strips are bent 90° around a mandrel of known radius. A roller bend test employs a roller to form the strip around the mandrel. Alternatively, a v-block test uses the mandrel to push the strip into an open die, forcing it to conform to the radius of the mandrel. For both tests the minimum bend radius (mbr) as a function of strip thickness (t) is then reported as mbr/t. The minimum bend radius is the smallest radius mandrel around which a strip can be bent without cracks visible at a magnification of 10x to 2Ox. Generally mbr/t is reported for both good way bends, defined as the bend axis is normal to the rolling direction, and for bad way bends, defined as the bend axis is parallel to the rolling direction. An mbr/t of up to 4 t for both good way bends and bad way bends is deemed to constitute good formability. More preferred is an mbr/t of up to 2.

[0006] Electrical conductivity is typically measured as a percentage of IACS.

IACS refers to International Annealed Copper Standard that assigns "pure" copper a conductivity value of 100% IACS at 20° C Throughout this disclosure, all electrical and mechanical testing is performed at room temperature, nominally 20° C, unless otherwise specified. The qualifying expression "about" indicates that exactitude is not required and should be interpreted as +/-10% of a recited value.

[0007] Strength is usually measured as yield strength. A high strength copper alloy has a yield strength in excess of 95 ksi (655.1 MPa) and preferably in excess of 110 ksi (758.5 MPa). As the gauge of the copper alloy formed into components decreases and as miniaturization of these components continues, a combination of strength and conductivity for a given temper will be more important than either strength or conductivity viewed alone.

[0008] Ductility can be measured by elongation. One measure of elongation is

A10 elongation, which is the permanent extension of the gauge length after fracture, expressed as a percentage of the originai gauge length L₀ where L₀ is taken equal to 10 mm.

[0009] Acceptable resistance to stress relaxation is viewed as at least 70% of an imparted stress remaining after a test sample is exposed to a temperature of 150° C for 3000 hours and at least 90% of an imparted stress remaining after a test sample is exposed to a temperature of 105° C for 1000 hours.

[0010] Stress relaxation resistance was measured via the ring method [Fox A.:

Research and Standards 4 (1964) 480] wherein a strip of 50mm length is clamped onto the outer radius of a steel ring initiating stress at the outer surface of the strip. With exposure to elevated temperatures elastic stresses change into plastic deformation. This process depends upon time, temperature and initial stress defined by the radius of the steel ring. Experiments were performed between 50°C/96h and 210°C/384h. After each annealing the remaining flexion of the strip is measured and the corresponding stress reduction calculated according to [Graves G.B.: Wire Industry 46 (1979) 421]. Using the Larson-Miller-Parameter P an extrapolation from the performed short time experiments at higher temperatures to long time experiments at lower temperatures can be done [Boegei A.: Metail 48 (1994) 872].

[0011] Stress relaxation may also be measured by a lift-off method as described in ASTM (American Society for Testing and Materials) Standard E328-86. This test measures the reduction in stress in a copper alloy sample held at fixed strain for times up to 3000 hours. The technique consists of constraining the free end of a cantilever beam to a fixed deflection and measuring the load exerted by the beam on the constraint as a function of time at temperature. This is accomplished by securing the cantilever beam test sample in a specially designed test rack. The standard test condition is to load the cantilever beam to 80% of the room temperature 0.2% offset yield strength. If the calculated deflection exceeds about 0.2 inch, the initial stress is reduced until the deflection is less than 0.2 inch and the load is recalculated. The test procedure is to load the cantilever beam to the calculated load value, adjust a threaded screw in the test rack to maintain the deflection, and locking the threaded screw in place with a nut. The toad required to lift the cantilever beam from the threaded screw is the initial load. The test rack is placed in a furnace set to a desired test temperature. The test rack is periodically removed, allowed to cool to room temperature, and the load required to lift the cantilever beam from the threaded screw is measured. The percent stress remaining at the selected log times is calculated and the data are plotted on semi-log graph paper with stress remaining on the ordinate (vertical) and log time on the abscissa (horizontal). A straight line is fitted through the data using a linear regression technique. Interpolation and extrapolation are used to produce stress remaining values at 1 , 1000, 3000, and 100,000 hours.

[0012] The resistance to stress relaxation is orientation sensitive and may be reported in the longitudinal (L) direction where 0° testing is conducted with the long dimension of the test sample in the direction of strip rolling and the deflection of the test sample is parallel to the strip rolling direction. The resistance to stress relaxation may be reported in the transverse (T) direction where 90° testing is conducted with the long dimension of the test sample perpendicular to the strip rolling direction and the deflection of the test sample is perpendicular to the strip rolling direction.

[0013] Table 1 shows the mechanical and electrical properties of some of the commerciaily available copper alloys of which the inventors are aware:

[0014] As good as these alloys are, and as widespread their use, there remain applications where alloys with higher strength and in particular higher strength without sacrificing other desirable properties such as conductivity, resistance to stress relaxation, and/or formability. While beryllium coppers can provide high strength, because of their beryllium content, they are not suitable for many applications. Among beryllium-free copper alloys, high strength (e.g., yield strength above about 130 ksi) is usually accompanied by significant diminishment of other desirable properties, in particular formabiiity. SUMMARY

[0015] One aspect of the present invention is an age-hardening copper-nickel- silicon base alloy that can be processed to make a commercially useful strip product for use in electrical connectors and interconnections for the automotive and multimedia industries, in particular, and for any other applications requiring high yield strength and moderately high electrical conductivity in a strip, plate, wire or casting. Another aspect of the present invention is a processing method to make a commercially useful strip product for use in electrical connectors and interconnections for the automotive and multimedia industries and any other applications requiring high yield strength and moderately high electrical conductivity.

[0016] In accordance with one preferred embodiment of this invention, a copper-nickel-silicon base alloy having an improved combination of yield strength and electrical conductivity is provided that consists essentially of between about 1.0 and about 6.0 weight percent Ni, up to about 3.0 weight percent Co, between about 0.5 and about 2.0 weight percent Si₁ between about 0.01 and about 0.5 weight percent Mg, up to about 1.0 weight percent Cr, up to about 1.0 weight percent Sn₁ and up to about 1.0 weight percent Mn, the balance being copper and impurities. This alloy is processed to have a yield strength of at least about 137 ksi, and an electrical conductivity of at least about 32% IACS.

[0017] In accordance with another preferred embodiment of this invention, a copper base alloy having an improved combination of yield strength and electrical conductivity is provided that consists essentially of: between about 3.0 and about 5.0 weight percent Ni; up to about 2.0 weight percent Co; between about 0.7 and about 1.5 weight percent Si; between about 0.03 and about 0.25 weight percent Mg; up to about 0.6 weight percent Cr; up to about 1.0 weight percent Sn, and up to about 1.0 weight percent Mn, the balance being copper and impurities. This alloy is processed to have a yieid strength of at least about 137 ksi, and an electrical conductivity of at least about 32% IACS.

[0018] In accordance with another preferred embodiment of this invention, a copper-nickel-silicon base alloy having an improved combination of yield strength and electrical conductivity is provided that consists essentially of: between about 3.5 and about 3.9 weight percent Ni; between about 0.8 and about 1.0 weight percent Co; between about 1.0 and about 1.2 weight percent Si; between about 0.05 and about 0.15 weight percent Mg; up to about 0.1 weight percent Cr; up to about 1.0 weight percent Sn, and up to about 1.0 weight percent Mn, the balance being copper and impurities. This alioy is processed to have a yield strength of at least about 137 ksi, and an electrical conductivity of at least about 32% IACS.

[0019] The alloys are preferably processed to have a yield strength of at least about 137 ksi, and an electrical conductivity of at least about 38% IACS, more preferably to have a yield strength of at least about 143 ksi, and an electrical conductivity of at least about 37% IACS, and most preferably to have a yield strength of at least about 157 ksi, and an electrical conductivity of at least about 32% !ACS.

[0020] The ratio of (Ni+Co)/(Si-Cr/5) is preferably between about 3 and about 7, and more preferably between about 3.5 and about 5.0. The Ratio of Ni/Co is preferably between about 3 and about 5.

[0021] The alloys and processing methods of the various embodiments provide copper base alloys having an improved combination of yield strength and electrical conductivity, and preferably stress relaxation resistance as well. In particular the alloys have higher strength and greater resistance to stress relaxation than previously achieved with Cu- Ni-Si alloys, while maintaining reasonable levels of conductivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Fig. 1 is a flow chart of the treatment of the alloys in Example 1 ;

[0023] Fig. 2 is a flow chart of the treatment of the alloys in Example 2;

[0024] Fig. 3 is a flow chart of the treatment of the alloys in Example 3;

[0025] Fig. 4 is a graph of the yield strength versus conductivity for the alloys of

Example 3;

[0026] Fig. 5 is a graph of yield strength versus bend formability (MBR/t) for the alloys of Example 3;

[0027] Fig. 6 is a flow chart of the treatment of the alloys of Example 4; [0028] Fig. 7 is a graph of yield strength versus conductivity for the alloys of

Table 5 processed by a SA-CR-age-CR-age process of Example 4;

[0029] Fig. 8 is a graph of yield strength versus bend formability (MBR/t) for the alloys of Table 5 processed by SA-CR-age-CR-age process of Example 4;

[0030] Fig. 9 is flow chart of the treatment of the alloys in Example 5;

[0031] Fig. 10 is a graph of yield strength vs Ni/Co ratio for alloys without chromium having similar alloying ievels of Example 5;

[0032] Fig. 11 is flow chart of the treatment of the alioys in Example 6;

[0033] Fig. 12 is a flow chart of the treatment of the alloys in Example 7;

[0034] Fig. 13 is a graph showing the effect of stoichiometric ratio on yield strength in copper-nickel-chromium-silicon alloys from Example 7;

[0035] Fig. 14 is a graph showing the effect of stoichiometric ratio on yield strength in copper-nickel-cobalt-silicon alioys from Example 7;

[0036] Fig. 15 is a graph showing the effect of effect of stoichiometric ratio on yield strength in copper-nickel-chromium-cobalt-silicon alloys from Example 7;

[0037] Fig. 16 is a graph showing the effect of stoichiometric ratio on eiectrical conductivity in copper-nickel-chromium-silicon alloys from Example 7;

[0038] Fig. 17 is a graph showing the effect of stoichiometric ratio on electrical conductivity in copper-nickel-cobalt-silicon alloys from Example 7;

[0039] Fig. 18 is a graph showing the effect of stoichiometric ratio on electrical conductivity in copper-nickel-chromium-cobalt-silicon alloys from Example 7; [0040] Fig. 19 is a flow chart of the treatment of the alloys in Example 8;

[0041] Fig. 20 is a graph showing the effect of stoichiometric ratio on %!ACS in

Example 8 alloys processed by the SA-CR-age-CR-age approach with 475°C/300°C ages.

[0042] Fig. 21 is a graph showing the effect of stoichiometric ratio on yield strength in Example 8 alloys processed by the SA-CR-age-CR-age approach with 475°C/300°C ages;

[0043] Fig. 22 is a flow chart of the treatment of the alloys in Example 9

[0044] Fig. 23 is a schematic diagram of tapered edge hot rolling specimen;

[0045] Fig. 24 is a photograph of hot rolled K224 (without Cr), showing large edge cracks;

[0046] Fig. 25 is a photograph of hot rolled K225 (0.11 Cr), showing no edge cracks;

[0047] Fig. 26A is photograph of the results from tool wear testing of non-Cr alloy RN033407; and

[0048] Fig. 26B is a photograph of the Result from tool wear test of Cr- containing alloy RN834062;

[0049] Fig. 27 is a flow chart of the treatment of the alloys in Example 10;

[0050] Fig. 28 is a graph showing the effect of stoichiometric ratio on %IACS in

Example 8 and Example 10 (low Cr and Mn) alloys processed by the SA-CR-age-CR-age approach with 475°C/300°C ages; and [0051] Fig. 29 is a graph showing the effect of stoichiometric ratio on yield strength in Example 8 and Example 10 (low Cr and Mn) alloys processed by the SA-CR-age- CR-age approach with 475°C/300°C ages;

[0052] Fig. 30 is a flow chart of the treatment of the alloys in Example 11 ; and

[0053] Fig. 31 is a fiow chart of the treatment of the alloys in Example 12;

[0054] Fig. 32 is a flow chart of the treatment of the alloys in Example 13;

[0055] Fig. 33 is a flow chart of the treatment of the alloys in Example 14;

[0056] Fig. 34 is a flow chart of the treatment of the alloys in Example 15;

[0057] Fig. 35 is a flow chart of the treatment of the alloys in Example 16;

[0058] Fig. 36 is a graph of 90° V-block - MBFi/t BW versus yield strength for alloys and processes of Examples 13, 14, 15, and 16; and

[0059] Fig. 37 is a graph of %IACS versus yield strength for alloys and processes of Examples 13, 14, 15, and 16. DETAILED DESCRIPTION

[0060] There is a need in the marketplace for copper strip alloys with higher strength and electrical conductivity, along with good stress relaxation resistance. This combination of properties is particularly important for parts that are formed into various electrical interconnections for use in multimedia electrical connector and terminal applications. Commercially available copper alloys, such as C510 (phosphor bronze), C7025, C7035, C17410 and C17460 are being used in these applications for their generally favorable combinations of strength and conductivity. However, while these alloys have adequate strength for most current carrying applications, the continuing trend for miniaturization of components demands copper ailoys that offer high strength in combination with reasonably good electrical conductivity and reasonably good stress relaxation resistance along with reasonable cost. It is also desirable to minimize or eliminate potentially toxic alloying elements such as beryllium.

[0061] Alloys that are used for multimedia interconnects require high strength to avoid damage during connector insertion and to maintain good contact force while in service. For these applications, good but not especially high electrical conductivity is all that is required, since the conductivity merely needs to be enough to carry a signal current, and need not be the high levels needed to avoid excessive I²R heating in higher power applications. For these applications, there are even more stringent requirements for mechanical stability at room and slightly elevated service temperatures, as characterized by good stress relaxation resistance at about 100⁰C, for example.

[0062] The alloy compositions of the preferred embodiments of this invention, and the scheme used to process to the finish tempers surprisingly provide highly desirable combination of properties for meeting the needs of both automotive and multimedia applications, namely very high strength along with moderately high conductivity, in particular, the ailoys of the preferred embodiments of the present invention are capable of being processed to strip products with combinations of yield strength / electrical conductivity of at least about 137 ksi with a conductivity of at least about 38% IACS, more preferably a yield strength of at least about 143 ksi, with a conductivity of at least about 37% IACS, and most preferably a yield strength of about 157 ksi, with a conductivity of at least about 32% IACS.

[0063] The alloys of the preferred embodiment of the present invention, have an improved combination of yield strength and electrical conductivity, good stress relaxation resistance, along with modest levels of bendability, consist essentially of from about 1.0 to about 6.0 weight percent nickel, from about 0.5 to about 2.0 weight percent silicon, from 0.0 to about 3.0 weight percent cobalt, from about 0.01 to about 0.5 weight percent magnesium, from 0.0 to about 1.0 weight percent chromium, and from 0.0 to about 1.0 weight percent of each of tin and manganese, the balance of the alioy being copper and impurities. More preferably, the alloy consists essentially of from about 3.0 to about 5.0 weight percent nickel, from about 0.7 and about 1.5 weight percent silicon, from 0.0 to about 2.0 weight percent cobalt, from about 0.03 to about 0.25 weight percent magnesium, from about 0.0 to about 0.6% weight percent chromium, and from 0.0 to 1.0 weight percent of each of tin and manganese, the balance being copper and impurities. Where an optimum level of yield strength and electrical conductivity is needed, e.g. a combination of 140 ksi YS / 30% IACS, the most preferred alloy ranges are from about 3.5 to about 3.9 weight percent nickel; from about 1.0 to about 1.2 weight percent silicon; from about 0.8 to about 1.0 weight percent cobalt, from about 0.05 to about 0.15 weight percent magnesium, from 0 to about 0.1 weight percent chromium, and from 0.0 to about 1.0 weight percent of each of tin and manganese, the balance being copper and impurities. Generally, excessive coarse second phases are present when alloying elements are substantially beyond the indicated upper limits. [0064] The electrical conductivity and yield strength of the alloy are highest when the (Ni+Co)/(Si-Cr/5) ratio is controlled between about 3 and about 7, and more preferably between about 3.5 and about 5. The ratio of Ni/Co is optima! for yield strength and conductivity when controlled between about 3 and about 5.

[0065] Magnesium generally increases stress relaxation resistance and softening resistance in the finished products; it also increases softening resistance during in- process aging annealing heat treatments. When present at low levels, Sn generally provides solid solution strengthening and also increases softening resistance during in-process aging annealing heat treatments, without excessively harming conductivity. Low levels of Mn generally improve bend formability, although with a loss of conductivity.

[0066] The preferred embodiment of the process of the present invention comprises melting and casting; hot rolling (preferably from 750° to 1050⁰C), optional milling to remove oxide, and an optional homogenizatϊon or intermediate bell anneal, cold rolling to a convenient gauge for solutionizing, solution annealing treatment (preferably at 800° - 1050⁰C for 10 seconds to one hour) followed by a quench or rapid cool to ambient temperature to obtain an electrical conductivity of less than about 20% IACS (11.6 MS/m) and an equiaxed grain size of about 5 - 20 μm; a 0 to 75% cold rolling reduction in thickness; an age hardening anneal (preferably at 300 - 600⁰C from 10 minutes to 10 hours); and optionally a further cold rolling 10 to 75% reduction in thickness to finish gauge; and second age hardening anneal (preferably at 250 to 500⁰C for 10 minutes to 10 hours). The resulting alloy can also be processed to finish gauge without using an in-process solutionizing heat treatment by using cycles of lower temperature bel! annealing treatments with intervening cold work. In addition, one or more optional recrystallization anneal{s) may be added to the process during the reduction from hot roiled gauge to the thickness appropriate for solutionizing.

[0067] The preferred scheme to result in alloy with a yield strength of at least about 140 ksi, and a conductivity of at least about 30% IACS conductivity involves solutionizing at about 900° to 1000⁰C, cold rolling by about 25%, aging at about 450° - 500⁰C for 3 - 9 hours, cold rolling by about 20 - 25% to finish gauge, and aging 300° - 350⁰C for 3 - 9 hours.

[0068] While this disclosure is particularly drawn to a process for the manufacture of copper alloy strip, the alloys of the invention and the processes of the invention are equally amenable to the manufacture of other copper alloy products, such as foil, wire, bar and tube. !n addition, processes other than conventional casting, such as strip casting, powder metallurgy and spray casting are also within the scope of the invention.

[0069] The alloys and methods of the preferred embodiments will be better understood from the following illustrative examples:

Example 1 - Increasing Alloy Levels Increases Strength; Cobalt Substitution Improves Both Strength and Conductivity

[0070] A series of ten pound laboratory ingots with the compositions listed in

Table 2 were melted in a silica crucible and Durvilte cast into steel molds, which after gating were approximately 4" X4" X 1.75". Fig. 1 is a flow chart of the process of this Example 1. After soaking two hours at 900⁰C they were hot rolled in three passes to 1.1" (1.6" / 1.35" / 1.1"), reheated at 900⁰C for 10 minutes, and further hot rolled in three passes to 0.50" (0.9" / 0.7" / 0.5"), followed by a water quench, followed by a homogenization or over-aging anneal at 590° for 6 hours. After trimming and milling to remove the surface oxide, the alloys were cold rolled to 0.012" and solution heat treated in a fiuidized bed furnace for the time and temperature listed in Table 2. Time and temperature were selected to achieve approximately constant grain size. The alloys were then subjected to an aging anneal of 400° to 500⁰C for 3 hours, designed to increase strength and conductivity. The alloys were then coid rolled 25% to 0.009" and aged at 300° to 400⁰C for 4 hours. Properties measured after the second age anneal are presented in Table 3. The data indicate that yield strength increases with increasing alloying levels in the ternary alloys J994 through J999, from 127 to 141 ksi yield strength when Si levels range from 0.8 to 1.3%, respectively. Comparing J994, K001 and K002 to examine the effect of Co on alloys near 0.8% Si, the substitution of Co for Ni increases both yield strength and conductivity. Considering a Co substitution for Ni in alloys with ~1.2%Si, K003 shows a decrease in yield strength and an increase in conductivity, while K004 shows an increase in yield strength and decrease in conductivity when compared to J998.

[0071] Having a Ni/Co ratio of about 3 (K002 and K004) leads to a higher strength than a Nt/Co ratio of 1 (K001 and K003), particularly at the higher Si level. Mn alloys K011 and K012 show evidence that Mn substitution for Ni improves the strength/bend properties, but at a significant loss of conductivity. Sn appears to provide solid solution strengthening, when comparing J994 to K036 and K037.

Example 2 - Cobalt Improves Strength

[0072] Selected alloys of Example 1 were solution heat treated in a fluiclizeci bed furnace for the time and temperature listed in Table 2. Fig. 2 is a flow chart of the process of this Example 2. Subsequently the alloys were cold rolled 25 % to 0.009" then subjected to an aging anneal of 400° to 500⁰C for 3 hours. After an additional cold reduction of 22% to 0.007", samples were aged annealed at temperatures of 300° to 400⁰C for 3 hours. Properties from representative conditions are listed in Table 4. Bend properties in many cases are somewhat better at similar strengths than the process in Example 1. Co (K003 and K004) and Sn (K037) additions provide the highest strength increase of the alloys in this example.

Example 3 - Cobalt and Chromium Levels and (Ni+Co)/(Si-Cr/5) Ratio

[0073] A series of ten pound laboratory ingots with the compositions listed in

Table 5 were melted in a silica crucible and Durville cast into steel molds, which after gating were approximately 4" X 4"X 1.75". Figure 3 is a flow chart of the process of this Example 3. After soaking two hours at 900⁰C they were hot roiled in three passes to 1.1" (1.6" / 1.35" / 1.1"), reheated at 900⁰C for 10 minutes, and further hot rolled in three passes to 0.50" (0.9" / 0.7" / 0.5"), followed by a water quench. The quenched plates were then soaked at 590° C for 6 hours, trimmed and then milled to remove surface oxides developed during hot rolling. The alloys were then cold rolled to 0.012" and solution heat treated in a fluidized bed furnace for 60 seconds at the temperatures listed in Table 5. The temperature was selected to maintain a fairly constant grain size. Alloys were then subjected to an aging anneal of 400° to 500⁰C for 3 hours, designed to increase strength and conductivity. The alloys were then cold rolled 25% to 0.009" and aged at 300° to 400⁰C for 4 hours. Properties measured after the second age anneal are presented in Table 6. From this data set, it can be observed that additions to a base Alloy of Cu-Ni-Si of Co (K068), Cr (K072), or both Co and Cr (K070) achieve the best combinations of strength, conductivity and bend formability. It is also noted that relatively high Si levels of 1.2% and above were present in the samples with the highest strength. While there was some evidence of strengthening from Sn, this was accompanied by poor bend formability. in Table 5, it can be seen that the ratio (Ni+Co)/{Si-Cr/5) is very close to 4 for most of the alloys, particularly K068, K070 and K072. Also, the Ni/Co ratio was close to 3 for K068 and K070. Yield strength is plotted against conductivity in Figure 4, and against bend formability in Figure 5. The values for K068, K070 and K072 are identified to show their unusually good combination of properties.

Example 4 - Cobalt and Chromium for Strength and Formability

[0074] The alloys of Example 3 were solution heat treated in a fluidized bed furnace for 60 seconds at the temperature listed in Table 5. Figure 6 is a flow chart of the process of this Example 4. Subsequently the alloys were cold rolled 25 % to 0.009" then subjected to an aging anneal of 400° to 500⁰C for 3 hours. After an additional cold reduction of 22% to 0.007", samples were aged annealed at temperatures of 300° to 400⁰C for 3 hours. Properties from representative conditions are listed in Table 7. Similar to Example 3, of particular note are alloys K068, K070 and K072, which show that alloys containing Co, Cr or a combination of both achieve the highest strength levels. The bend formability data indicates that K068 and K070 which both contain Co have the best formability at higher strength. Yield strength is plotted against conductivity in Figure 7, and against bend formability in Figure 8. The values for alloys K068, K070 and K072 are noted.

Example 5 - NickekCobalt Ratio

[0075] A series of ten pound laboratory ingots with the compositions listed in

Table 8 were melted in a silica crucible and Durville cast into steel molds, which after gating were approximately 4" X 4" X 1.75". Figure 9 is a flow chart of the process of this Example 5. This group of alloys was based on K068, K070 and K072 from Table 5, wherein overall alloying level and Ni/Co ratio were varied while keeping the stoichiometric ratio ((Ni+Co)/(Si- Cr/5)) close to 4.2. After soaking two hours at 900⁰C they were hot roiled in three passes to 1.1" (1.6" / 1.35" / 1.1"), reheated at 900⁰C for 10 minutes, and further hot rolled in three passes to 0.50" (0.9" / 0.7" / 0.5"), followed by a water quench. The quenched plates were then soaked at 590° C for 6 hours, trimmed and then milled to remove surface oxides developed during hot rolling. The ailoys were then cold rolled to 0.012" and solution heat treated in a fluidized bed furnace for 60 seconds at the temperature listed in Table 8. The temperature was selected to maintain a fairly constant grain size. Alloys were then subjected to an aging anneal of 450° to 500⁰C for 3 hours, designed to increase strength and conductivity. The alloys were then cold rolled 25% to 0.009" and aged at 300 to 400⁰C for 4 hours. Properties measured after the second age anneal for the process with a 475°C first age and 300⁰C second age are presented in Table 9. For the Co-only set of compositions {K077 to K085), yield strength values tend to increase with higher alloying content. For example, K078, with a Ni+Co+Cr+Si value of 6.24, had a yield strength of 155 ksi while K084 with a Ni+Co+Cr+Si value of 5.22 had a 139 ksi yield strength. A Ni/Co ratio of 3 to 4 provides better strength than a ratio of 5, when one compares K077 (Ni/Co ratio of 3.62) and K078 {Ni/Co ratio of 3.83) to K079 (Ni/Co ratio of 5.04), as well as comparing K080 (Ni/Co ratio of 3.32) and K081 (Ni/Co ratio of 3.93) to K082 (Ni/Co ratio of 4.89). The plots of yield strength vs Ni/Co ratio in Figure 10 illustrate this, with the exception of K085, which has a higher Si level than K083 and K084. The Co-and-Cr-containing alloys, K086 to K094, were not as sensitive to overall alloying levels and Ni/Co ratio as the Co-only alloys. The Cr-only alloys (K095 to K097) also had comparable properties to the other alloy types.

[0076] The alloys of Table 8 were solution heat treated in a fluidized bed furnace 60 seconds at the temperature listed in Table 8. Subsequently the alloys were cold rolled 25 % to 0.009" then subjected to an aging annea! of 450 to 500⁰C for 3 hours. After an additional cold reduction of 22% to 0.007", samples were aged annealed at temperatures of 300 to 400⁰C for 3 hours. Properties from samples given first and second ages at 450⁰C and 300⁰C, respectively, are listed in Table 10. The Co-only alloys displayed a sensitivity to overall alloying levels with this scheme which was not found in alloys containing Cr. The only Co-only alloys at 150 ksi yield strength and above were K077 and K078, while all Cr- containing alloys reached or came close to that strength level. Strength-bend properties for this process are fairly similar to those in Table 9.

Example 6 - Nickel:Cobalt Ratio

[0077] Laboratory ingots with the compositions listed in Table 11 were melted in a graphite crucible and Tamman cast into steel molds, which after gating were 4.33" X 2.17"X1.02". Figure 11 is a flow chart of the process of this Example 6. For a target Si- content of 1% and Cr-content of 0.5% one alloy is Co-containing and the other is Co-free, the Ni-content is adjusted in order to keep a stoichiometric ratio ((Ni+Co)/{Si-Cr/5)) of close to 4.2. After soaking two hours at 900⁰C they were hot rolled to 0.472", thereby reheated after each pass at 900⁰C for 10 minutes. After the last pass the bar was water quenched. After trimming and milling to 0.394" in order to remove the surface oxide, the alloys were co!d rolled to 0.0106" and solution heat treated in a fluidized bed furnace for the time and temperature listed in Table 11. Time and temperature were selected to achieve grain sizes below 20μm. The alloys were then subjected to an aging anneal of 450 to 500⁰C for 3 hours, designed to increase strength and conductivity. The alloys were then cold rolled 25 % to 0.0079" and aged at 300 or 400⁰C for 3 hours. Properties measured after the second age anneal are presented in Table 12. The formabiiity was measured via V-block. The data indicates that both alloys are capable of achieving a yield strength of 135 ksi, yet the Co-containing variant BS shows a better softening resistance that can be seen with increasing the age annealing temperature. The slightly better bad way bendability of variant BS is presumably due to the slightly lower grain size after solution annealing.

Example 7 - (Ni+Co)/(Si-Cr/5) Ratio

[0078] A group of alloys was cast and processed using once more the basic compositions of K068 (Co only), K070 (Co and Cr) and K072 (Cr only) from Table 5 as a base, but in this case with a gradual drop in Si levels, thus increasing the (Ni+Co)/(Si-Cr/5) stoichiometric ratio above the 3.6 to 4.2 range of previous alloys. Ni and Co levels were designed to be constant for each of the three alloy types. A series of ten pound laboratory ingots with the compositions listed in Table 11 were melted in a silica crucible and Durville cast into steel molds, which after gating were approximately 4" X 4" X 1.75". K143 to K146 are variants of K072, K160 to K163 variants of K070, and K164 to K167 are variants of K068. Figure 12 is a flow chart of the process of this Example 7. After soaking two hours at 900⁰C they were hot rolled in three passes to 1.1" (1.6" / 1.35" / 1.1"), reheated at 900⁰C for 10 minutes, and further hot rolled in three passes to 0.50" (0.9" / 0.7" / 0.5"), followed by a water quench. The quenched plates were then soaked at 590° C for 6 hours, trimmed and then milled to remove surface oxides developed during hot rolling. The alloys were then cold rolled to 0.012" and solution heat treated in a fiuidized bed furnace for 60 seconds at the temperatures listed in Table 13. The temperature was selected to maintain a fairly constant grain size. The alloys were then coid rolled 25% to 0.009" and aged 450, 475 and 500⁰C for 3 hours. Properties after each aging temperature for alloys of the current example, as well as K068, K070, K072, K078, K087 and K089 are listed in Table 14. For each alloy type, yield strength decreases as the stoichiometric ratio increases above about 4.5, and falls below 120 ksi at a ratio of around 5.5. This is shown in Figures 13 to 15 for the Cr alloys (plus K072 data), the Co-alloys (plus K068 and K078 data), and the Co-Cr alloys (plus K070, K087 and K089 data), respectively. In the Co and Cr alloys, conductivity decreases as the stoichiometric ratio increases above about 4.5, while for the alloys with both Co and Cr there is not a clear relationship between stoichiometry and conductivity. This is shown graphically in Figures 16 through 18. Based on this data it is evident that the best yield strength- conductivity properties are produced when the stoichiometric ratio is kept between 3.5 and 5.0.

Example 8 - (Ni+Co)/(Si-Cr/5) Ratio

[0079] A series of ten pound laboratory ingots with the compositions listed in

Table 15 were melted in a silica crucible and Durviile cast into steel molds, which after gating were approximately 4" X 4" X 1.75". Figure 19 is a flow chart of the process of this Example 8. After soaking two hours at 900⁰C they were hot rolled in three passes to 1.1" (1.6" / 1.35" / 1.1"), reheated at 900⁰C for 10 minutes, and further hot rolled in three passes to 0.50" (0.9" / 0.7" / 0.5"), followed by a water quench. The quenched plates were then soaked at 590° C for 6 hours, trimmed and then milled to remove surface oxides developed during hot rolling. The alloys were then cold rolled to 0.012" and solution heat treated in a fluidized bed furnace for 60 seconds at 95O⁰C. Grain size ranged from 6 to 12 μm. Alloys were then subjected to an aging anneal of 450 or 475°C for 3 hours, designed to increase strength and conductivity. The alloys were then cold rolled 25 % to 0.009" and aged at 300⁰C for 4 hours. Properties measured after the second age anneal are presented in Table 16.

[0080] Table 17 has properties measured after samples were solution heat treated in a fluidized bed furnace for 60 seconds at 95O⁰C₁ cold rolled 25% to 0.009", given an aging anneal at 475°C for 3 hours, cold rolled 22% to 0.007", and given a final anneal of 300⁰C for 3 hours. The results show the viability of a range of compositions with Si from 1.0 to 1.2%, with a Nt/Co ratio of 4, and a stoichiometric ratio (((Ni+Co)/(Si-Cr/5))) of 3.5 to 5.0. This is shown graphically in Figures 20 and 21 , which plot conductivity and yield strength data from Table 17 versus the stoichiometric ratio. These plots show yield strengths of 140 ksi or higher combined with conductivities of 25 %IACS or higher are obtained for this process when the ratio is between 3.0 and 5.0. Cr was not found to influence properties significantly in the alloys of this example.

[0081] Stress relaxation tests were run on samples of K188 and K205 which were cold rolled to 0.012" from milled hot rolled plate, solution annealed at 950⁰C for 60 seconds, cold roiled 25% to 0.009", and age annealed at 475⁰C for 3 hours. The stress relaxation tests were run at 150⁰C for 3000 hours on samples of longitudinal and transverse orientation. Results in Table 18 show that both alloys had excellent stress relaxation resistance, over 85% stress remaining after 1000 hours at 150⁰C, regardless of Cr content or sample orientation.

Example 9 - Effect of Cr

[0082] A series of ten pound laboratory ingots with the compositions listed in

Table 19 were melted in a silica crucible and Durville cast into steel molds, which after gating were approximately 4" X 4" X 1.75". Figure 22 is a flow chart of the process of this Example 9. The ingots were then machined to have tapered edges, as illustrated schematically in Figure 23, to create a higher state of tensile stress at the edges. This condition is more prone to edge cracking than the standard flat edges, and thus more sensitive to alloying additions, in this case Cr. The alloys were soaked for two hours at 900⁰C, and rolled in two passes to 1.12" (1.4" / 1.12") then water quenched. After examination for cracks, the bars were reheated at 900⁰C for two hours, and rolled in three passes to 0.50" (0.9" / 0.7" / 0.5"), followed by a water quench. It was found that without Cr, K224 developed large cracks during the first few passes of hot rolling, which enlarged during the remaining passes. None of the Cr-containing alloys developed large cracks during hot roiling. A few of the alloys showed small cracks after initial passes believed to be due to casting defects, but these did not enlarge during subsequent passes. The Cr effect was the same independent of Cr ievel, from 0.11% to 0.55%. Examples of edge conditions of K224 and K225 after hot rolling are shown in Figures 24 and 25. The addition of even a small amount of Cr would reduce cracking in plant production, thus improving yield after hot roliing and coil milling. Data from plant-cast bars (i.e., bars cast as pilot product dc castings), whose compositions are listed in Table 20, show the beneficial effect of Cr on preventing hot rolling cracks and therefore improving yield. Table 21 lists the normalized casting plant yield (CPY) of six Cr-containing and four non-Cr bars, where the normalized CPY is obtained as follows: First the individualized CPY is calculated as the ratio of coil milled weight to cast bar weight. Second the bar with the highest CPY, in this case RN 03341O₁ is assigned a normalized CPY of 100%. Third the normalized CPY of all other bars is calculated by dividing the CPY of each bar by the CPY of RN033410. The normalized CPY of bars without Cr is 48-82% compares to 82-100% for the Cr-containing bars

[0083] Limiting the Cr level wouid be desirable due to the abrasiveness of Cr- silicides, which is demonstrated in Figure 26. Figure 26A shows wear on a tool steel ball which was slid for 3000 linear inches (1500 inches on each side of the strip) under a 100 gm load over the strip surface with lard oil as a lubricant of a non-Cr sample (RN033407) that was plant solution annealed at 975°C, cold rolled 25% then aged a 450⁰C and sulfuric acid cleaned, while Figure 26B has a similar condition using a sample of a Cr-containing alloy (RN834062). The polished appearance of the ball shown in Fig. 26 shows that the Cr- containing alloy caused much more wear, leading to a significantly larger volume of material being removed from the ball. This is seen in Fig. 26 as a much larger wear scar for the Cr- containing alioy. The larger wear scar suggests that during stamping of a sheet of the alloy into parts, a high amount of tool wear would occur.

[0084] A single casting run produced three bars with the composition shown in

Table 21a. Casting plant yield of the bars, which was normalized similarly to the data of Table 21 where RN033410 is considered 100%, is given in Table 21 b. The CPY of the !ow-Cr bars compares favorably with the Cr-containing bars of Table 21. This is believed to be due to Cr reducing cracking during hot rolling even at these low levels. RN037969 has a normalized CPY% above 100 due to the fact that the yield of this bar was higher than RN033410 in the earlier example.

Example 10 - Effect of Cr₁ Mn

[0085] A series of ten pound laboratory ingots with the compositions listed in

Table 22 were melted in a silica crucible and Durville cast into steel molds, which after gating were approximately 4" X 4" X 1.75". Figure 27 is a flow chart of the process of this Example 10. Alloy K259 contains a smaller level of Cr than those alloys in Example 9, to investigate the lower limits of the beneficial effect of Cr on hot rolling. Alloys K251 , K254 and K260 contain low levels of Mn, to determine if Mn affects hot roϋability in the alloy of this invention. The ingots were then machined to have tapered edges, as illustrated schematically in Fig. 23, to create a higher state of tensile stress at the edges. The alloys were soaked for two hours at 900⁰C, and rolled in two passes to 1.12" (1.4" / 1.12") then water quenched. After examination for cracks, the bars were reheated at 900⁰C for two hours, and rolled in three passes to 0.50" (0.9" / 0.7" / 0.5"), followed by a water quench. K259, with 0.058% Cr, hot rolled without edge crack formation. The Mn-containing alloys, along with K261 (with neither Cr nor Mn) developed large edge cracks. Thus a Cr addition near 0.05%, with a preferred range of 0.025 to 0.1% Cr, appears to be appropriate to balance hot reliability and formation of abrasive particles that would lead to tool wear.

[0086] The quenched bars were then soaked at 590^s C for 6 hours, trimmed and then milled to remove surface oxides developed during hot rolling. The alloys were then cold rolled to 0.012" and solution heat treated in a fiuidized bed furnace for 60 seconds at 950⁰C. Alloys were then subjected to an aging anneal of 475°C for 3 hours, designed to increase strength and conductivity. The alloys were then cold rolled 25 % to 0,009" and aged at 300⁰C for 3 hours. Alternatively, after solution heat treatment the alloys were cold rolled 25% to 0.009", given an aging anneal at 475⁰C for 3 hours, cold roiled 22% to 0.007", and given a final anneal of 300⁰C for 3 hours. Properties after the final age for both process paths are listed in Table 23. For both processes, the exceptionally good property combination of 150 ksi yield strength and at least 31 % IACS are achieved, with low levels of Cr, Mn or neither. Conductivity and yield strength are plotted in Figures 28 and 29 against the stoichiometric ratio ((Ni+Co)/(Si-Cr/5)) along with data from example 8 to demonstrate the unusually good properties reached when the ratio is kept between 3.0 and 5.0.

Ratio = (Ni+Co)/(Si-Cr/5)

Example 11 - Effect of Processing

[0087] Sections of plant cast bar RN032037, whose composition is in Table 20, were processed from plant hot rolled and coil milied plate 0.600" thick. Samples were further processed by a variety of processing paths shown in Fig. 30. Process A involved cold rolling to 0.012" and solution heat treating in a fluidized bed furnace for 60 seconds at 950⁰C₁ age annealing at 500⁰C for 3 hours, cold rolling 25% to 0.009", and giving a second anneal at 350⁰C for 4 hours. In process B_F the metal was rolled to 0.050" and given an intermediate bell anneal ("IMBA") of 575⁰C for 8 hours. Then the samples were subject to cold rolling to 0.012" and solution heat treating in a fluidized bed furnace for 60 seconds at 95O⁰C, age annealing at 500⁰C for 3 hours, cold roliing 25% to 0.009", and giving a second anneal at 350⁰C for 4 hours. In process C, The alloy was rolled to 0.024" and solution heat treated in a fluidized bed furnace for 60 seconds at 95O⁰C₁ followed by cold rolling to 0.012" and a second solution heat treatment in a fluidized bed furnace for 60 seconds at 95O⁰C. Subsequently, the process involved age annealing at 500⁰C for 3 hours, cold rolling 25% to 0.009", and giving a second anneal at 35O⁰C for 4 hours. In process D, cold roliing to 0.012" was followed by solution heat treatment in a fluidized bed furnace for 60 seconds at 950⁰C the alloy was cold rolled 25% to 0.009", given an aging anneal at 475⁰C for 3 hours, cold rolled 22% to 0.007", and given a final anneal of 300⁰C for 3 hours. In process E, the metal was rolled to 0.050" and given an intermediate bell anneal of 575°C for 8 hours. Then the samples were rolled to 0.024" and solution heat treated in a fluidized bed furnace for 60 seconds at 950⁰C, followed by cold rolling to 0.012" and a second solution heat treatment in a fluidized bed furnace for 60 seconds at 950⁰C. Subsequently, the process involved age annealing at 500⁰C for 3 hours, cold rolling 25% to 0.009", and giving a second anneal at 350⁰C for 4 hours.

Example 12 Effect of Processing

[0088] Sections of plant cast bar RN032037, whose composition is in Table 20, were processed from plant hot rolled and coil milled plate 0.600" thick. Process variables were systematically varied to explore a matrix containing ranges of processing conditions. Figure 31 is a flow chart of the process of this Example 12. After cold rolling to 0.012", samples were solution annealed in a fluidized bed furnace at temperatures of 925, 950, 975 and 1000⁰C for 60 seconds. Coupons were then given age anneals at temperatures of 450, 475, 500 and 525°C for three hours. Samples were then cold rolled to final thickness at varying reductions of 15, 25 and 35%. Finally, samples were given a second age anneal for four hours at 300, 325, 350 and 375⁰C. Table 25 contains properties of samples with different solution anneal temperatures while the rest of the process was held constant. As solution temperature is increased, yield strength increases, while conductivity decreases. Additionally, bend formabiltty worsens at the higher solution annealing temperatures, due to the large grain size developed during the 975 and 1000⁰C anneals. Thus a solution annealed grain size below 20μm is preferred.

[0089] When the temperature of the first age is varied while the other processing variables are held constant, it is found that the highest strength levels are due to the intermediate aging temperatures, as shown for the 475 and 500⁰C ages in Table 26. Also, the conductivity increased with increasing aging temperature. Thus the first age temperature can be manipulated to provide various desirable combinations of strength and conductivity.

[0090] When the roll reduction between the first and second ages was varied, yield strength was found to increase with increasing reduction, in this case up to 35%, while conductivity was unaffected. A larger increase in strength was found when going from 15 to 25% reduction than when going from 25 to 35%. Bend formability was found to worsen with higher reductions. The roll reduction can be manipulated to affect the strength-formability characteristics of the material produced. Use of roll reduction above 35% may be useful to produce peak strength, albeit with poorer formability.

[0091 ] Table 28 shows that the second age anneal temperature does not have a large effect on properties when the other processing variables are held constant. Conductivity was found to increase as the temperature of the second age increased, but to a small degree. Thus a wide operating range is acceptable for this step of the process.

^*not measured [0092] Samples from the Cr-free plant-cast bar RN033407 {composition in

Table 20) were rolled in the laboratory from the coil milled condition at 0.460" down to 0.012". Subsequently samples were solution heat treated in a fluidized bed furnace for 60 seconds at 900⁰C. Coupons were then rolled 25% to 0.009" and age annealed at 425, 450 and 475°C for times of 4 and 8 hours at each temperature. Subsequently samples were cold rolled 22% to 0.007" and given a final anneal of 300⁰C for three hours. The best combination of strength and conductivity resulted from the 45O⁰C for 8 hour age, with the properties from that condition and others listed in Table 28a. Comparing the 450°C/8 hr data to the properties in Table 25, it is clear that further reducing the solution annealing temperature to 900⁰C lowers the yield strength and increases conductivity to produce the unique combination of 140 ksi and 39 %IACS. In addition, the processing including a 900⁰C solution annealing temperature produced improved bend formability when compared to processing involving higher solution anneal temperatures.

Example 13 - Effect of Si and Mg

[0093] Laboratory ingots with the compositions listed in Table 29 were melted in a graphite crucible and Tamman cast into steel molds, which after gating were 4.33"X2.17"X1.02". All alloys were targeted to have a Cr-content of 0.5%. The Si-content was varied between 1.0% and 1.5%. For the high-Si 1.5% variants the Ni/Co ratio was varied between 4.98 and 11.37 with a fixed stoichiometric ratio ((Ni+Co)/(Si-Cr/5)) around 4. The influence of Mg was tested by alloy BW with the same alloy composition as BV but with additionally 0.1% Mg.

[0094] Figure 32 is a flow chart of the process of this Example 13. After soaking two hours at 900⁰C they were hot rolled to 0.472", thereby reheated after each pass at 900⁰C for 10 minutes. After the last pass the bar was water quenched. After trimming and milling to 0.394" in order to remove the surface oxide, the alloys were cold rolled to 0.012" and solution heat treated in a fluidized bed furnace for the time and temperature listed in Table 29. Time and temperature were selected to achieve grain sizes below 20μm.

[0095] Subsequently the alloys were cold rolled 25 % to 0.009" then subjected to an aging anneal of 450 and 475⁰C for 3 hours. Properties of samples are listed in Table 30. The formability was measured via V-block. With increasing Si-content the yield strength is increasing from 121 ksi for the 1.05% Si alioy to 135ksi for the 1.51% Si alloy. For the 1.16% Si variants Mg results in a benefit to yield strength of 5-7ksi. Lowering the Ni/Co ratio from 11.37 to 4.98 enhances yield strength for the high Si (1.5%) alloys. Stress relaxation was tested by the ring method with a target initial stress of 0.8 times yield strength. Table 31 shows the stress relaxation data for variants BV, BW and BX. Comparing BV and BW, due to Mg addition the stress relaxation resistance increases from 66.3% to 86.6% for the 150°C/1000h condition and from 48.5% to 72.3% for the 200°C/1000h condition. The stress relaxation resistance of the higher Si-containing BX amounts to 82.3% for the 150°C/1000h condition and 68.7% for the 200°C/1000h condition.

Table 29 Alloys of Examples 13 and 15, wt%

^*) Ratio = (Ni+Co)/(Si-Cr/5)

Table 30 Properties fro SA-Cr-AA Process of Example 13

Table 31 Stree Relaxation of Process SA - CR 25% - AA 450°C/3h of Example 13

Example 14 - Effect of Si and Mg

[0096] Figure 33 is a flow chart of the process of this Example 14. Specimens of Example 13 were subsequently cold rolled to 0.007" with a cold reduction of 22%. Thereafter the samples were aged annealed at temperatures of 300 ⁰C to 400⁰C for 3 hours. Properties from samples given second ages at 300⁰C are listed in Table 32. The formabitity was measured via V-block.

[0097] The highest yield strength was achieved with a first aging temperature of

450⁰C. With increasing Si-content the yield strength is increasing from 131 ksi for the Si 1.05% alloy to 147ksi for the Sh .51% alloy. For the Si 1.16% variants Mg results in a benefit to yield strength of 7-10ksi. Lowering the Ni/Co ratio from 11.37 to 4.98 enhances yield strength for the high Si 1.5% alloys by 3ksi. Stress relaxation was tested by the ring method with a target initial stress of 0.8 times yield strength. Table 33 shows the stress relaxation data for BV, BW and BX for the process SA - CR - 1.AA 450⁰C - CR - 2.AA 300⁰C.

[0098] Comparing BV and BW, due to Mg addition the stress relaxation resistance increases from 72.6% to 85.6% for the 150°C/1000h condition and from 55.8% to 69.3% for the 200°C/1000h condition. The stress relaxation resistance of the higher Si- containing BX amounts to 81.1% for the 15O⁰CAIOOOh condition and 66.1% for the 200°C/1000h condition. Table 32 Properties from SA-C R- 1 AA-C R-2 AA Process of Example 14

Table 33 Stress Relaxation Process SA-CR-1AA450°C-CR-2AA300°C of Example 14

Example 15: Effect of Si and Mg

[0099] Laboratory ingots with the compositions listed in Table 34 were melted in a graphite crucible and Tamman cast into steel molds, which after gating were 4.33"X2.17"X1.02". The alloys were Cr-free and with a stoichiometric ratio ((Ni+Co)/(Si-Cr/5)) around 4.2. The Ni/Co ratio was about 4.5. Two alloys have a targeted Si-content of 1.1 %, but varying Mg-content and one alloy has an Si-content of 1.4% and additionally Mg. Figure 34 is a flow chart of the process of this Example 15. After soaking two hours at 900⁰C they were hot rolled to 0.472", thereby reheated after each pass at 900⁰C for 10 minutes. After the last pass the bar was water quenched. After trimming and milling to 0.394" in order to remove the surface oxide, the alloys were cold rolled to 0.012" and solution heat treated in a fluidized bed furnace for the time and temperature listed in Table 34. Time and temperature were selected to achieve grain sizes below 20μm.

[00100] Subsequently the alloys were cold rolled 25 % to 0.009" then subjected to an aging anneal of 450 and 475°C for 3 hours. Properties of samples are listed in Table 35. The yield strength, formability measured with V-block and conductivity of the Cr-free FL and FM are similar to the Cr-containing BV and BW from Example 13, with comparable Si- content of 1.1%, Ni/Co ratio and stoichiometric ratio. As in Example 13, an addition of 0.1%Mg results in a benefit to yield strength of 7-8ksi.

[00101] With increasing Si-content from 1.17% to 1.39% the yieid strength is increasing from 126.6 to 130.5 ksi at the same solution annealing temperature. For variant FN, increasing the solution annealing temperature from 950⁰C to 1000⁰C results in an increase of yield strength of 10ksi.

[00102] Stress relaxation was tested by the ring method with a target initial stress of 0.8 times yield strength. Table 36 shows the stress relaxation data for the processes with a solution annealing temperature of 950⁰C. Compared to the Cr-containing 1.16% Si samples of Example 13, BV and BW, the stress relaxation of FL and FM is slightly lower. Similar to Example 13, a Mg addition of 0.1% results in a stress relaxation increase from 64.6% to 82.7% for the 150°C/1000h condition and from 44.3% to 69.2% for the 200°C/1000h condition. The stress relaxation resistance of the Mg-containing, Si1.39% variant FN amounts to 84.1 % for the 150°C/100Oh condition and 65.9% for the 200°C/1000h condition.

^• Rat o = + o - r Table 35 Properties from SA-CR-AA Process of Example 15

Table 36 Stress Relaxation of Process SA 95O⁰C - CR 25% - AA 450°C/3h of Example 15

Exampie 16: Effect of Si and Mg

[00103] Figure 35 is a flow chart of the process of this Example 16. Specimens of Example 15 were subsequently cold roiled to 0.007" with a cold reduction of 22%. Thereafter the samples were aged annealed at temperatures of 300⁰C to 35O⁰C for 3 hours. Properties from samples given second ages at 300⁰C are listed in Table 37. The formability was measured via V-block. The highest yield strength was achieved with a first aging temperature of 450⁰C. [00104] FM shows a higher yield strength of 11 ksi in comparison to FL₁ that is partly ascribed to the Mg-content and partly ascribed to the slightly higher Si-content. The yield strength, bendability and conductivity of the Cr-free FL and FM are similar to the Cr- containing BV and BW from example 15, with comparable Si-content, Ni/Co ratio and stoichiometric ratio.

[00105] Increasing Si-content from 1.17% to 1.39% leads to the same yield strength of about 144ksi for a solution annealing temperature of 95O⁰C. For variant FN, increasing the solution annealing temperature from 950⁰C to 1000⁰C results in an increase of yield strength from 143 to 158 ksi.

[00106] Stress relaxation was tested by the ring method with a target initial stress of 0.8 times yield strength. Table 38 shows the stress relaxation data for FL and FM for the process SA 95O⁰C - CR - 1.AA 450⁰C - CR - 2.AA 300⁰C. Compared to the Cr-containing 1.16% Si samples of example 15, BV and BW, the stress relaxation of FL and FM is lower by 2-3%. Similar to example 15, a Mg addition of 0.1% results in a stress relaxation increase from 70.0% to 82.0% for the 150°C/1000h condition and from 52.3% to 66.9% for the 200°C/1000h condition. The stress relaxation resistance of the Mg-containing, Sh .39% variant FN amounts to 85.0% for the 150°C/1000h condition and 66.4% for the 200°C/1000h condition. Table 37 Properties from SA-C R- 1 AA-C R-2 A A Process of Example 16

Table 38 Stress Reiaxation of Process SA 95O⁰C-CR-IAA 450°C-CR-2AA 300⁰C of

Example 16

[00107] Figure 36 shows the relation between 90°-minBR/t BW and yield strength for the alloys and processes of Examples 13, 14, 15, and 16. Both processes SA - CR - AA and SA - CR - AA - CR - AA form two groups with a certain formability - yield strength relation. The solid lines are just a guide to the eye and mark increasing Min BR/t and increasing yield strength with higher Si-content and/or Mg-addition. There is almost no difference in yield strength and formability - yield strength relationship between the Cr- containing and Cr-free variants. [00108] Figure 37 shows the relation between %IACS and yield strength for the alloys and processes of Examples 13, 14, 15, and 16. The Cr-free and the Cr-containing aϋoys show the same capability in achieving a conductivity of 30%iACS together with high yield strength. The SA - CR - AA - CR - AA process achieves higher yield strength than the SA - CR - AA process, but at the same conductivity.

Claims

What is claimed is:

1. A copper base alloy having an improved combination of yield strength and electrical conductivity consisting essentially of: between about 1.0 and about 6.0 weight percent Ni; up to about 3.0 weight percent Co; between about 0.5 and about 2.0 weight percent Si; between about 0.01 and about 0.5 weight percent Mg; up to about 1.0 weight percent Cr; up to about 1.0 weight percent Sn, and up to about 1.0 weight percent Mn, the balance being copper and impurities, the alloy processed to have a yield strength of at least about 137ksi, and an electrical conductivity of at least about 25% IACS.

2. The alloy according to claim 1 wherein the alloy has a conductivity of at least about 30% IACS.

3. The alloy according to claim 1 wherein the ailoy is processed to have a yield strength of at least about 137 ksi, and an electrical conductivity of at ieast about 38% IACS.

4. The alloy according to claim 1 wherein the alloy is processed to have a yield strength of at ieast about 143 ksi , and an electrical conductivity of at least about 37% IACS.

5. The alioy according to claim 1 wherein the alloy is processed to have a yield strength of at least about 157 ksi, and an electrical conductivity of at least about 32% IACS.

6. A copper base alloy having an improved combination of yield strength and formability consisting essentially of: between about 1.0 and about 6.0 weight percent Ni; up to about 3.0 weight percent Co; between about 0.5 and about 2.0 weight percent Si; between about 0.01 and about 0.5 weight percent Mg; up to about 1.0 weight percent Cr; up to about 1.0 weight percent Sn, and up to about 1.0 weight percent Mn, the balance being copper and impurities, the alloy processed to have a yieid strength of at least about 137ksi, and an mbr/t of less than 41 for both good way bends and bad way bends.

7. The copper base alloy according to claim 6 wherein the alloy has an mbr/t of less than about 21 for both good way bends and bad way bends.

8. The copper base alloy according to claim 6 wherein the alloy has an electrical conductivity of at least about 25% IACS.

9. The copper base alioy according to claim 8 wherein the alloy has an electrical conductivity of at least about 30% IACS.

10. A copper base alloy having an improved combination of yield strength, electrical conductivity, and formability, consisting essentially of: between about 1.0 and about 6.0 weight percent Ni; up to about 3.0 weight percent Co; between about 0.5 and about 2.0 weight percent Si; between about 0.01 and about 0.5 weight percent Mg; up to about 1.0 weight percent Cr; up to about 1.0 weight percent Sn, and up to about 1.0 weight percent Mn, the balance being copper and impurities, the ratio of (Ni+Co)/(Si-Cr/5) being between about 3 and about 7.

11. The alloy according to claim 10 wherein the alloy is processed to have an mbr/t of less than about 41 for both good way bends and bad way bends.

12. The alloy according to claim 10 wherein the alloy is processed to have an mbr/t of less than about 2 1 for both good way bends and bad way bends.

13. The alloy according to claim 10 wherein the alloy is processed to have a yield strength of at least about 137ksi, and an electrical conductivity of at least about 38% IACS.

14. The alloy according to claim 10 wherein the alloy is processed to have a yield strength of at least about 143 ksi , and an electrical conductivity of at least about 37% IACS.

15. The alloy according to ciaim 10 wherein the alloy is processed to have a yield strength of at least about 157 ksi, and an electrical conductivity of at least about 32% IACS.

16. The cooper base aiioy according to claim 1 wherein the alloy is in the form of foil, wire, bar or tube.

17. A copper base alloy having an improved combination of yield strength, electrical conductivity, and formability, consisting essentially of: between about 3.0 and about 5.0 weight percent Ni; up to about 2.0 weight percent Co; between about 0.7 and about 1.5 weight percent Si; between about 0.03 and about 0.25 weight percent Mg; up to about 0.6 weight percent Cr; up to about 1.0 weight percent Sn, and up to about 1.0 weight percent Mn, the balance being copper and impurities, the ratio of (Ni+Co)/(Si-Cr/5) being between about 3 and about 7.

18. A copper base alloy having an improved combination of yield strength, electrical conductivity, and formability, consisting essentially of: between about 3.0 and about 5.0 weight percent Ni; up to about 2.0 weight percent Co; between about 0.7 and about 1.5 weight percent Si; between about 0.03 and about 0.25 weight percent Mg; up to about 0.6 weight percent Cr; up to about 1.0 weight percent Sn, and up to about 1.0 weight percent Mn, the balance being copper and impurities, the alloy processed to have a yield strength of at least about 137ksi, and an electrical conductivity of at least about 25% IACS.

19. The alloy according to claim 18 wherein the alloy is processed to have a yield strength of at least about 137 ksi, and an electrical conductivity of at least about 38% IACS.

20. The alioy according to claim 18 wherein the alloy is processed to have a yield strength of at least about 143 ksi , and an electrical conductivity of at least about 37% IACS.

21. The alloy according to claim 18 wherein the alloy is processed to have a yield strength of at least about 157 ksi, and an electrical conductivity of at least about 32% IACS.

22. A copper base alloy having an improved combination of yield strength, electrical conductivity, stress relaxation resistance, consisting essentially of: between about 3.5 and about 3.9 weight percent Ni; between about 0.8 and about 1.0 weight percent Co; between about 1.0 and about 1.2 weight percent Si; between about 0.05 and about 0.15 weight percent Mg; up to about 0.1 weight percent Cr; up to about 1.0 weight percent Sn, and up to about 1.0 weight percent Mn, the balance being copper and impurities, the alloy processed to have a yield strength of at least about 140ksi, and an electrical conductivity of at least about 30% IACS.

23. The alloy according to claim 22 wherein the ratio of (Ni+Co)/(Si-Cr/5) is between about 3.5 and about 5.0.

24. The alloy according to claim 23 wherein the ration of Ni/Co is between about 3 and about 5.

25. The ailoy according to claim 22 wherein the ration of Ni/Co is between about 3 and about 5.

26. A process for making a copper base alloy including nickel, silicon, cobalt and chromium, comprising: melting and casting the alloy; hot rolling from about 750° to about 1050⁰C; cold rolling to a convenient gauge for solutionizing; solution annealing the alloy at between about 800° and about 1050⁰C for from about 10 seconds to about one hour; and subsequently quenching or rapidly cooling the alloy to ambient temperature to obtain an electrical conductivity of less than about 20% IACS (11.6 MS/m) and an equiaxed grain size of about 5 - 20 μm; cold rolling the alloy for a 0 to about 75% reduction in thickness; subjecting the alloy to an hardening anneal at about 300° to about 600⁰C for about 10 minutes to about 10 hours; subsequently cold rolling the alloy for an about 10 to about 75% reduction in thickness to finish gauge; subjecting the alloy to a second age hardening anneal at 250 to about 500⁰C for about 10 minutes to about 10 hours to achieve.

27. The process according to claim 26 further comprising an intermediate recrystallization anneal after the hot roiling.

28. The process according to claim 26 wherein the alloy consists essentially of between about 1.0 and about 6.0 weight percent Ni; up to about 3.0 weight percent Co; between about 0.5 and about 2.0 weight percent Si; between about 0.01 and about 0.5 weight percent Mg; up to about 1.0 weight percent Cr; up to about 1.0 weight percent Sn₁ and up to about 1.0 weight percent Mn, the balance being copper and impurities.

29. The process according to claim 28 wherein the alloy consists essentially of: between about 3.0 and about 5.0 weight percent Ni; up to about 2.0 weight percent Co; between about 0.7 and about 1.5 weight percent Si; between about 0.03 and about 0.25 weight percent Mg; up to about 0.6 weight percent Cr; up to about 1.0 weight percent Sn, and up to about 1.0 weight percent Mn₁ the balance being copper and unavoidable impurities.

30. The process according to claim 29 wherein the ratio of {Ni+Co)/(Si-Cr/5) being between about 3 and about 7.

31. The process according to claim 29 wherein the alloy comprises between about 3.5 and about 3.9 weight percent Ni; between about 0.8 and about 1.0 weight percent Co; between about 1.0 and about 1.2 weight percent Si; between about 0.05 and about 0.15 weight percent Mg; up to about 0.1 weight percent Cr; up to about 1.0 weight percent Sn, and up to about 1.0 weight percent Mn, the balance being copper and impurities.