Patent Application
20090183803
This invention relates to copper base alloys, and in particular to copper-nickel-silicon base alloys.
Copper-nickel-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. Pat. 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. Pat. No. 7,182,823, incorporated herein by reference.
The properties of copper alloys that can be important include formability, conductivity, strength, ductility, and resistance to stress relaxation.
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 10× to 20×. 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.
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.
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.
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 original gauge length L0 where L0 is taken equal to 10 mm.
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.
Stress relaxation resistance was measured via the ring method [Fox A.: Research and Standards 4 (1964) 480] wherein a strip of 50 mm 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./96 h and 210° C./384 h. 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 [Boegel A.: Metall 48 (1994) 872].
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 load 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.
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.
Table 1 shows the mechanical and electrical properties of some of the commercially available copper alloys of which the inventors are aware:
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 formability.
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.
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 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. 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.
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 yield strength of at least about 137 ksi, and an electrical conductivity of at least about 32% IACS.
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 alloy is processed to have a yield strength of at least about 137 ksi, and an electrical conductivity of at least about 32% IACS.
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% IACS.
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.
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.
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 alloys 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.
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 100° C., for example.
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 alloys 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.
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 alloy 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.
The electrical conductivity and yield strength of the alloy are highest when the (Ni+Co)/(Si−Cr/S) 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 optimal for yield strength and conductivity when controlled between about 3 and about 5.
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.
The preferred embodiment of the process of the present invention comprises melting and casting; hot rolling (preferably from 750° to 1050° C.), optional milling to remove oxide, and an optional homogenization or intermediate bell anneal, cold rolling to a convenient gauge for solutionizing, solution annealing treatment (preferably at 800°-1050° C. 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 300-600° C. 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 500° C. 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 bell 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 rolled gauge to the thickness appropriate for solutionizing.
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 1000° C., cold rolling by about 25%, aging at about 450°-500° C. for 3-9 hours, cold rolling by about 20-25% to finish gauge, and aging 300°-350° C. for 3-9 hours.
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. In addition, processes other than conventional casting, such as strip casting, powder metallurgy and spray casting are also within the scope of the invention.
The alloys and methods of the preferred embodiments will be better understood from the following illustrative examples:
A series of ten pound laboratory ingots with the compositions listed in Table 2 were melted in a silica crucible and Durville cast into steel molds, which after gating were approximately 4″×4″×1.75″.
Having a Ni/Co ratio of about 3 (K002 and K004) leads to a higher strength than a Ni/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.
Selected alloys of Example 1 were solution heat treated in a fluidized bed furnace for the time and temperature listed in Table 2.
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″×4″×1.75″.
The alloys of Example 3 were solution heat treated in a fluidized bed furnace for 60 seconds at the temperature listed in Table 5.
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″×4″×1.75″.
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 anneal of 450 to 500° C. for 3 hours. After an additional cold reduction of 22% to 0.007″ samples were aged annealed at temperatures of 300 to 400° C. for 3 hours. Properties from samples given first and second ages at 450° C. and 300° C., 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.
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″×2.17″×1.02″.
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″×4″×1.75″. K143 to K146 are variants of K072, K160 to K163 variants of K070, and K164 to K167 are variants of K068.
A series of ten pound laboratory ingots with the compositions listed in Table 15 were melted in a silica crucible and Durville cast into steel molds, which after gating were approximately 4″×4″×1.75″.
Table 17 has properties measured after samples were solution heat treated in a fluidized bed furnace for 60 seconds at 950° C., 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 300° C. for 3 hours. The results show the viability of a range of compositions with Si from 1.0 to 1.2%, with a Ni/Co ratio of 4, and a stoichiometric ratio (((Ni+Co)/(Si−Cr/5))) of 3.5 to 5.0. This is shown graphically in
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 950° C. for 60 seconds, cold rolled 25% to 0.009″, and age annealed at 475° C. for 3 hours. The stress relaxation tests were run at 150° C. 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 150° C., regardless of Cr content or sample orientation.
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″×4″×1.75″.
Limiting the Cr level would be desirable due to the abrasiveness of Cr-silicides, which is demonstrated in
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 21b. The CPY of the low-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.
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″×4″×1.75″.
The quenched bars 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 950° C. 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 300° C. for 3 hours. Alternatively, after solution heat treatment the alloys were 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 300° C. 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
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. Samples were further processed by a variety of processing paths shown in
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.
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 500° C. 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.
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.
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.
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 900° C. 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 300° C. for three hours. The best combination of strength and conductivity resulted from the 450° C. 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 900° C. lowers the yield strength and increases conductivity to produce the unique combination of 140 ksi and 39% IACS. In addition, the processing including a 900° C. solution annealing temperature produced improved bend formability when compared to processing involving higher solution anneal temperatures.
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″×2.17″×1.02″. 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.
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 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 alloy to 135 ksi for the 1.51% Si alloy. For the 1.16% Si variants Mg results in a benefit to yield strength of 5-7 ksi. 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./1000 h condition and from 48.5% to 72.3% for the 200° C./1000 h condition. The stress relaxation resistance of the higher Si-containing BX amounts to 82.3% for the 150° C./1000 h condition and 68.7% for the 200° C./1000 h condition.
The highest yield strength was achieved with a first aging temperature of 450° C. With increasing Si-content the yield strength is increasing from 131 ksi for the Si 1.05% alloy to 147 ksi for the Si 1.51% alloy. For the Si 1.16% variants Mg results in a benefit to yield strength of 7-10 ksi. Lowering the Ni/Co ratio from 11.37 to 4.98 enhances yield strength for the high Si 1.5% alloys by 3 ksi. 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 450° C.-CR -2.AA 300° C.
Comparing BV and BW, due to Mg addition the stress relaxation resistance increases from 72.6% to 85.6% for the 150° C./1000 h condition and from 55.8% to 69.3% for the 200° C./1000 h condition. The stress relaxation resistance of the higher Si-containing BX amounts to 81.1% for the 150° C./1000 h condition and 66.1% for the 200° C./1000 h condition.
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″×2.17″×1.02″. 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.
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 7-8 ksi.
With increasing Si-content from 1.17% to 1.39% the yield 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 950° C. to 1000° C. results in an increase of yield strength of 10 ksi.
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 950° C. 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./1000 h condition and from 44.3% to 69.2% for the 200° C./1000 h condition. The stress relaxation resistance of the Mg-containing, Si 1.39% variant FN amounts to 84.1% for the 150° C./1000 h condition and 65.9% for the 200° C./1000 h condition.
FM shows a higher yield strength of 11 ksi in comparison to FL, 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.
Increasing Si-content from 1.17% to 1.39% leads to the same yield strength of about 144 ksi for a solution annealing temperature of 950° C. For variant FN, increasing the solution annealing temperature from 950° C. to 1000° C. results in an increase of yield strength from 143 to 158 ksi.
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 950° C.-CR-1.AA 450° C.-CR -2.AA 300° C. 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./1000 h condition and from 52.3% to 66.9% for the 200° C./1000 h condition. The stress relaxation resistance of the Mg-containing, Si 1.39% variant FN amounts to 85.0% for the 150° C./1000 h condition and 66.4% for the 200° C./1000 h condition.
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/044,900, filed Apr. 14, 2008, and U.S. Provisional Patent Application No. 61/016,441, filed Dec. 21, 2007, the entire disclosures of which are incorporated herein, by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61044900 | Apr 2008 | US | |
| 61016441 | Dec 2007 | US |
