Method for manufacturing copper alloy wire and copper alloy wire

Abstract: High strength, high conductivity copper alloy wire and a cable therefrom and method for manufacturing same, wherein the copper alloy contains chromium from 0.15-1.30%, zirconium from 0.01-0.15% and the balance essentially copper. The alloy wire is heat treated, cold worked to an intermediate gage, heat treated, cold worked to final gage, and finally heat treated.

Description: BACKGROUND OF THE INVENTION The present invention relates to a high strength, high conductivity copper alloy wire or cable and a method for manufacturing same, wherein the copper alloy wire consists essentially of from 0.15-1.30% chromium, from 0.01-0.15% zirconium, balance essentially copper. Copper alloys are the natural choice for conductor wire alloys due to their high electrical conductivity. In fact, commercially pure copper is the most widely used conductor. High performance conductor alloys are required where the properties of copper are not sufficient for a particular application. Thus, in addition to electrical conductivity these alloys must often meet a combination of often conflicting properties. These properties may include strength, ductility, softening resistance and flex life. Indeed, ASTM B624 describes the requirements for a high strength, high conductivity copper alloy wire for electrical applications. These specifications require the alloy to have a minimum tensile strength of 413.7 Mpa (60 ksi), a minimum electrical conductivity of 85% IACS with an elongation of 7-9%. U.S. military specifications for high strength copper alloy cables require a minimum elongation of 6% and a minimum tensile strength of 413.7 Mpa (60 ksi). Alloying elements may be added to copper to impart strength beyond what can be achieved by cold work. However, if such elements dissolve in the matrix they rapidly reduce the electrical conductivity of the alloy. U.S. Patents 4,727,002 and 4,594,116 show high strength, high conductivity copper alloy wire including specific alloying additions. EP 569 036 A2 discloses a wire for electrical railways and method for producing the same. The wire consists of 0.1 to 1.0 % Cr, 0.01 to 0.3 % Zr and 10 ppm or less O, and if required, further contains at least one element selected from the group consisting of 0.1 to 0.1 % Si and 0.01 to 0.05 % Mg, with the balance being Cu and inevitable integrities. This application concerns a wire for electric railways and therefore requires creep resistance, resistance to sliding wear and the ability to be pressure welded and processing steps are intended to optimise these requirements. Typical sizes for the wire are several mm in diameter. There are no requirements for elongation and the electrical conductivity obtained in this process is 80 % IACS or less. This document does not disclosed a solution for manufacturing high strength high conductivity conductors. It is, therefore, desirable to develop a high strength, high conductivity copper alloy wire and a cable therefrom at a reasonable cost and in a commercially viable procedure. Further objectives of the present invention will appear hereinafter. SUMMARY OF THE INVENTION It has now been found that the foregoing objectives can be readily obtained in accordance with the present invention as claimed. The present invention provides a method for manufacturing high strength, high conductivity copper alloy wire and a cable therefrom. The method comprises: providing a copper alloy wire having a gage of 6.35 mm (0.25 inch) or less and consisting essentially of chromium from 0.15-1.30%, zirconium from 0.01-0.15%, balance essentially copper; first heat treating said wire for at least one-third of a minute at a temperature of 871-982°C (1600-1800°F) after which a controlled cooling is generally employed, e.g., quench or slow interrupted cooling; followed by first cold working, preferably drawing, said alloy to an intermediate gage of 0.762-3.175 mm (0.030-0.125 inch); followed by second heat treating said alloy for 15 minutes to 10 hours at 316-538°C (600-1000°F); followed by a second or final cold working, preferably drawing, said alloy to final gage of 0.254 mm (0.010 inch) or less; and finally heat treating said alloy for 15 minutes to 10 hours at 316-538°C (600-1000°F). If desired, additional steps may be employed, as after the second heat treating step but before the final cold working step, one can cold work, preferably draw, to a gage of greater than 0.2068 mm (0.03 inch), followed by heat treating, as for example, for less than one minute. The high strength, high conductivity copper alloy wire of the present invention comprises: a copper alloy consisting essentially of chromium from 0.15-1.30%, zirconium from 0.01-0.15%, balance essentially copper; said wire having a gage of 0.254 mm (0.010 inch) or less; wherein a major portion of the chromium, and zirconium are present as precipitated, sub-micron sized particles in a copper matrix; and wherein said wire has a tensile strength of at least 379.2 MPa (55 ksi), an electrical conductivity of at least 85% IACS, and a minimum elongation of 6%. Desirably, the copper alloy wire of the present invention has a tensile strength of at least 413.7 Mpa (60 ksi), an electrical conductivity of at least 90% IACS, and a minimum elongation of 7%, and optimally a minimum elongation of at least 9%. It is particularly desirable to provide a multi-stranded copper alloy cable of the copper alloy wire of the present invention, with from 2-400 strands of from 0.0254-0.2032 mm (0.001-0.008 inch) wire, preferably from 0.0508-0.17780 mm (0.002-0.007 inch) wire. Each of the fine wires in the cable is preferably coated for corrosion resistance, as preferably silver or nickel plated. The multi-stranded conductor cable of the present invention is highly advantageous, for example, it has good conductivity, strength, elongation and fatigue life. It has good high temperature stability to allow a variety of coatings to be applied for particular applications. Further features of the present invention will appear hereinbelow. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be more readily understood from a consideration of the accompanying drawings, wherein: Figure 1 is a graph of elongation versus strength of an alloy of the present invention processed in accordance with the present invention and the same alloy processed differently; and Figure 2 is a graph of elongation versus strength of an alloy of the present invention processed in accordance with the present invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS In accordance with the present invention, the copper alloy wire contains chromium from 0.15-1.30%, zirconium from 0.01-0.15%, and the balance essentially copper. In particular, the following are desirable: (1) chromium - 0.05-0.50%, zirconium - 0.05-0.15%, copper - essentially balance; (2) chromium - 0.50-1.30%, zirconium - 0.01-0.05%, copper - essentially balance. In addition, the copper alloy wire of the present invention may contain small amounts of additional alloying ingredients for particular purposes, as for example silicon, magnesium and/or tin, generally up to 0.1% each and as low as 0.001% each. Throughout the present specification, all percentages are by weight. In addition, a major portion of the chromium and zirconium are present as precipitated, sub-micron sized particles in a copper matrix. The precipitates in the matrix in the present invention strengthen the alloy without a great sacrifice to electrical conductivity due to the processing of the present invention. Thus, the present invention takes advantage of the alloying elements, the form thereof in the matrix and the synergistic effect that the combination of these two elements provides. The distribution of the particles is substantially uniform throughout the copper matrix and has a significant effect on elongation of the copper alloy wire of the present invention, especially in smaller wire diameters. Traditionally, age hardenable copper alloy wire is processed by solution treating in the single phase region and quench to produce a super saturated solid solution, cold work (preferably draw), and age. In a copper alloy wire where both high strength and high electrical conductivity are required, the final aging step is expected to concurrently increase both the strength and electrical conductivity of the alloy. However, disadvantageously, as aging proceeds the electrical conductivity continues to increase while strength, following an initial increase, reaches a maximum and then decreases with continued aging. Thus, the maximum in strength and electrical conductivity do not coincide. In accordance with the present invention, the aforesaid copper alloy wire obtains an excellent combination of strength, electrical conductivity and elongation in accordance with the processing of the present invention. In accordance with the present invention, the copper alloy wire is subjected to a first heat treatment step for at least one-third of a minute at a temperature of 871-982°C (1600-1800°F), generally for one-half of a minute to 2 hours, to solutionize the alloy, i.e., to attempt to get a portion of the alloying additions, and desirably the major portion, into solution. This first annealing step could be a strand or batch anneal and is generally conducted on the wire at a gage of 2.032-6.35 mm (0.08-0.25 inch). Desirably, the wire is quenched after the heat treatment. The alloy wire is then cold worked, generally drawn, in a first cold working step to an intermediate gage of 0.762-3.175 mm (0.030-0.125 inch), and preferably to a gage of 1.016-2.032 mm (0.040-0.080 inch). The alloy wire is then given a second heat treatment for 15 minutes to 10 hours at 316-538°C (600-1000°F), preferably for 30 minutes to 4 hours, to precipitate the chromium and zirconium. The electrical conductivity of the alloy following this step is generally a minimum of 85% IACS and preferably a minimum of 90% IACS. The alloy wire is then given a second cold working step, generally drawn, preferably to final gage of 0.254 mm (0.010 inch) or less, especially when used as strands in a cable. If desired, other cycles can be interposed in the above process, as for example after the second heat treatment step but before the final cold working step, one can desirably cold work, generally draw, to a gage of greater than 0.2068 mm (0.03 inch), followed by heat treating for one-third of a minute to 10 hours at temperatures of between 316 & 760°C (600 & 1400°F). After the second cold working step, the alloy is finally heat treated for 15 minutes to 10 hours at 316-538°C (600-1000°F). The second heat treatment step ages the alloy wire to provide the desired electrical conductivity. This may require overaging beyond the peak tensile strength. The final heat treatment step obtains the desired combination of tensile strength and elongation, and also restores the electrical conductivity lost in the second cold working step. The alloys of the present invention advantageously can be drawn to fine and ultrafine gage sizes appropriate for stranded conductor applications and are particularly advantageous when used in multi-stranded conductor cable applications, plated or unplated. Regardless of whether the alloy wire has been aged or in solution treated condition, these alloys can be drawn to greater than 99% reduction in area. As shown in ASTM B624, elongation of fine wire is generally less than larger gage wire. The alloys of the present invention show good elongation even at small gages. The present invention and improvements resulting therefrom will be more readily apparent from a consideration of the following exemplifcative examples. EXAMPLE 1 This example utilized a copper alloy wire having the following composition: chromium - 0.30%, zirconium - 0.09%, silicon - 0.028%, copper - essentially balance. The starting material was copper alloy wire having a gage of 2.5908 mm (0.102 inch) and conductivity of 77% IACS, processed by solution treatment at 0.4318 mm (0.170 inch), then drawn to 2.5908 mm (0.102 inch). The alloy was processed under various conditions as shown in Table I, below, with properties also shown below. Sample Condition Diameter mm (Inch) Tensile Strength Mpa (ksi) Elongation % in 2.54 mm (10 inches) Elec. Cond. % IACS (1) As drawn 1.016 (0.045) 503.3 (73.0) -- -- (2) Cond.(1) + heat treat 2 hrs-399°C (750°F) 1.016 (0.045) 444.7 (64.5) 3.6 82.5 (3) As drawn 0.508 (0.020) 560.5 (81.3) 1.8 -- (4) Cond.(3) + heat treat 2 hrs-399°C (750°F) 0.508 (0.020) 488.1 (70.8) 4.0 83.8 (5) Cond.(3) + heat treat 2 hrs-454°C (850°F) 0.508 (0.020) 422 (61.2) 7.2 92.9 (6) Cond.(3) + heat treat 2 hrs-510°C (950°F) 0.508 (0.020) 360.6 (52.3) 10.6 95.1 (7) Cond.(2) + drawn 0.508 (0.020) 602.6 (87.4) 2.2 -- (8) Cond.(7) + heat treat 2 hrs-399°C (750°F) 0.508 (0.020) 508.8 (73.8) 5.1 89.3 (9) Cond.(7) + heat treat 2 hrs-454°C (850°F) 0.508 (0.020) 437.1 (63.4) 8.6 93.7 (10) Cond.(7) + heat treat 2 hrs-510°C (950°F) 0.508 (0.020) 372.3 (54.0) 12.2 95.0 The alloy aged at the intermediate gage at 1.143 mm (0.045 inch), followed by drawing and aging, i.e., samples 8-10, attains higher electrical conductivity and tensile strength than the alloy aged at finish size only, i.e., samples 4-6. As shown in Figure 1, the wire processed according to the present invention, Process A, at the same strength, also has a higher elongation than the conventionally processed wire of Process B. The conventionally processed alloy wire of Process B was solution treated, cold drawn and aged. EXAMPLE 2 This example utilized a copper alloy wire having the following composition: chromium - 0.92%, zirconium - 0.014%, copper - essentially balance. The starting material was copper alloy wire having a gage of 2.5908 mm (0.102 inch) and 87% IACS, having been solution treated, drawn to 2.5908 mm (0.102 inch), and aged. The alloy was processed under various conditions as shown in Table II, below, with properties also shown below. Sample Condition Diameter mm (Inch) Tensile Strength Mpa (ksi) Elongation % in 2.54 mm (10 inches) Elec. Cond. % IACS (11) As drawn 1.27 (0.050) 617.7 (89.6) -- 82.1 (12) Cond.(11) + heat treat 2 hrs-454°C (850°F) 1.27 (0.050) 471.6 (68.4) 8.8 90.5 (13) As drawn 0.635 (0.025) 654.3 (94.9) 2.5 78.4 (14) Cond.(13) + heat treat 2 hrs-343°C (650°F) 0.635 (0.025) 555.7 (80.6) 4.5 84.4 (15) Cond.(13) + heat treat 2 hrs-399°C (750°F) 0.635 (0.025) 486.8 (70.6) 6.3 89.6 (16) Cond.(13) + heat treat 2 hrs-454°C (850°F) 0.635 (0.025) 422 (61.2) 10.6 92.7 (17) Cond.(13) + heat treat 2 hrs-510°C (950°F) 0.635 (0.025) 361.3 (52.4) 16.9 95.1 (18) Cond.(12) + drawn 0.635 (0.025) 616.4 (89.4) 1.7 88.1 (19) Cond.(18) + heat treat 2 hrs-343°C (650°F) 0.635 (0.025) 549.5 (79.7) 3.4 91.1 (20) Cond.(18) + heat treat 2 hrs-399°C (750°F) 0.635 (0.025) 489.5 (71.0) 6.1 93.0 (21) Cond.(18) + heat treat 2 hrs-454°C (850°F) 0.635 (0.025) 417.8 (60.6) 10.1 94.2 (22) Cond.(18) + heat treat 2 hrs-510°C (950°F) 0.635 (0.025) 353.7 (51.3) 18.1 95.1 The results indicate that the wire aged at 1.27 mm (0.050 inch) diameter followed by drawing and aging at finish achieves higher electrical conductivity. Figure 2 illustrates elongation versus strength. The wire of the present invention processed according to the present invention shows an excellent combination of strength, conductivity and elongation. EXAMPLE 3 This example utilized a copper alloy wire having the following composition: chromium - 0.92%, zirconium - 0.016%, copper - essentially balance. The wire was drawn and aged at 2.5908 mm (0.102 inch) diameter. The wire was then drawn to 0.508 to 0.254 mm (0.020 to 0.010 inch) diameter. The wire could easily be drawn to 0.254 mm (0.010 inch) diameter without any problems. Tensile properties and electrical conductivity of the aged wire are listed in Table III, below. In all cases, the aged wire showed an electrical conductivity of greater than 90% IACS, with an excellent combination of tensile strength and elongation. Sample Diameter mm (Inch) Temperature °C (°F) Time hr. Tensile Strength Mpa (ksi) Elongation % in 2.54 mm (10 inches) Elec. Cond. % IACS (23) 0.508 (0.020) 454 (850) 1 497.8 (72.7) 5 93.6 (24) 0.4572 (0.018) 454 (850) 1 500.6 (72.6) 6 94.6 (25) 0.3556 (0.014) 454 (850) 1 497.8 (72.7) 6 94.4 (26) 0.3556 (0.014) 454 (850) 1 496.4 (72.0) 6 94.9 (27) 0.3302 (0.013) 454 (850) 1 491.6 (71.3) 6 94.2 (28) 0.2794 (0.011) 454 (850) 1 495.7 (71.9) 6 94.0 (29) 0.254 (0.010) 454 (850) 1 488.8 (70.9) 6 94.5 (30) 0.508 (0.020) 482 (900) 1 428.9 (62.2) 9 94.6 (31) 0.4572 (0.018) 482 (900) 1 420.6 (61.0) 10 95.8 (32) 0.3556 (0.014) 482 (900) 1 419.9 (60.9) 11 95.6 (33) 0.3556 (0.014) 482 (900) 1 426.8 (61.9) 11 96.0 (34) 0.3302 (0.013) 482 (900) 1 427.8 (61.6) 11 96.3 (35) 0.2794 (0.011) 482 (900) 1 427.5 (62.0) 11 95.9 (36) 0.254 (0.010) 482 (900) 1 415.8 (60.3) 11 95.3 EXAMPLE 4 The alloy of Example 3, copper - 0.92% chromium - 0.016% zirconium, was initially solution treated, drawn to 2.5908 mm (0.102 inch) diameter and aged. The wire was then drawn to 1.016 mm (0.040 inch) diameter and heat treated at 732°C (1350°F) for 1/3 minute. This heat treatment softens the alloy without greatly influencing the electrical conductivity. This wire was then silver plated, drawn to 0.127 mm (0.005 inch) diameter and stranded to a 24 AWG or 19/36 construction. The stranded conductor was finally heat treated at 382°C (720°F) for 3 hours. The properties of the stranded conductor are as follows: Tensile strength, Mpa (ksi) - 409.5 (59.4) Elongation, % in 254 mm (10 inches) - 15.6 Electrical Conductivity, % IACS - 87

Claims: Method for manufacturing high strength, high conductivity copper alloy wire, which comprises: providing a copper alloy wire having a gage of 6.35 mm (0.25 inch) or less and consisting of chromium from 0.15-1.30%, zirconium from 0.01-0.15%, balance copper; first solution heat treating said wire for at least one minute at a temperature of 871-982°C (1600-1800°F); first cold working said alloy to an intermediate gage of 0.762-3.175 mm (0.030-0.125 inch); second heat treating said alloy for 15 minutes to 10 hours at 316-538°C (600-1000°F); finally cold working said alloy to final gage of 0.254 mm (0.010 inch) or less; and finally heat treating said alloy for 15 minutes to 10 hours at 316-538°C (600-1000°F) and wherein a major portion of the chromium and zirconium present as precipitated, sub-micron sized particles substantially uniformly distributed in a copper matrix, wherein the resultant wire has a tensile strength of at least 379.2 MPa (55 ksi), an electrical conductivity of at least 85 % IACS, and a minimum elongation of 6 % in 254 mm (10 inches). Method according to claim 1, wherein after the second heat treating step but before the final cold working step, the alloy wire is cold worked to a gage of greater than 0.2068 mm (0.03 inch), followed by heat treating for at least less than one minute to 10 hours at temperatures of between 316 & 760 °C (600 & 1400 °F). Method according to claim 1, including a cooling step after the first heat treating step. Method according to claim 1, wherein said cold working steps are drawing steps. Method according to claim 4, wherein the first heat treating step is from one minute to 2 hours at a gage of from of 2.032-6.35 mm (0.08-0.25 inch). Method according to claim 4, wherein said first cold working step is to an intermediate gage of 1.016-6.32 mm (0.040-0.080 inch). Method according to claim 4, wherein said second heat treating step is for 30 minutes to 4 hours. Method according to claim 3, wherein the alloy wire is quenched after the first heat treating step. Method according to claim 4, wherein said alloy wire additionally contains at least one of silicon, magnesium and tin in an amount of up to 0.1% each. Method according to claim 4, wherein the resultant wire has a tensile strength of at least 413.7 Mpa (60 ksi), an electrical conductivity of at least 90% IACS, and a minimum elongation of 7%. A copper alloy wire having high strength and high conductivity, which comprises: a solution heat treated, cold worked and aged copper alloy consisting of chromium from 0.15-1.30%, zirconium from 0.01-0.15%, balance copper; said wire having a gage of 0.254 mm (0.010 inch) or less; wherein a major portion of the chromium and zirconium are present as precipitated, sub-micron sized particles in a copper matrix; wherein said particles are substantially uniformly precipitated in a copper matrix and wherein said wire has a tensile strength of at least 379.2 MPa (55 ksi), an electrical conductivity of at least 85% IACS, and a minimum elongation of 6 % in 254 mm (10 inches). A copper alloy wire according to claim 11, wherein said wire is heat treated, cold worked to an intermediate gage, heat treated, cold worked to final gage, and finally heat treated. A copper alloy wire according to claim 11, wherein said wire has a tensile strength of at least 448.2 Mpa (65 ksi), an electrical conductivity of at least 90% IACS, and a minimum elongation of 7%. A copper alloy wire according to claim 11, wherein said alloy additionally contains at least one of silicon, magnesium and tin in an amount of up to 0.1% each. A copper alloy wire according to claim 11, wherein said copper alloy contains chromium from 0.15-0.50%, zirconium from 0.05-0.15%, and the balance copper. A copper alloy wire according to claim 11, wherein said copper alloy contains chromium from 0.50-1.30%, zirconium from 0.01-0.05%, and the balance copper. A multi-stranded copper alloy cable having high strength and high conductivity, which comprises: 2 to 400 strands of a copper alloy wire consisting essentially of chromium from 0.15-1.30%, zirconium from 0.01-0.15%, balance copper; each of said wires having a gage of 0.0254-0.2032 mm (0.001-0.008 inch); wherein a major portion of the chromium and zirconium are present as precipitated, sub-micron sized particles in a copper matrix wherein said particles are substantially uniformly precipitated in a copper matrix and wherein said cable has a tensile strength of at least 379.2 MPa (55 ksi), an electrical conductivity of at least 85% IACS, and a minimum elongation of 6% in 254 mm (10 inches). A copper alloy cable according to claim 17, wherein each of said strands is heat treated, cold worked to an intermediate gage, heat treated, cold worked to final gage, and finally heat treated. A copper alloy cable according to claim 17, wherein said cable has a tensile strength of at least 413.7 Mpa (60 ksi), an electrical conductivity of at least 90% IACS, and a minimum elongation of 7%. A copper alloy cable according to claim 17, wherein said strands additionally contain at least one of silicon, magnesium and tin in an amount of up to 0.1 % each. A copper alloy cable according to claim 17, wherein said strands contain chromium from 0.15-0.50%, zirconium from 0.05-0.15%, and the balance essentially copper. A copper alloy cable according to claim 17, wherein said strands contain chromium from 0.50-1.30%, zirconium from 0.01-0.05%, and the balance essentially copper.

Inventors: FISK ERIC, SALEH JOSEPH, FISK, ERIC, SALEH, JOSEPH
Applicants: FISK ALLOY WIRE INC, FISK ALLOY WIRE, INC.
Application year: 1998
Main classification: C22C9
IPC codes: C22F1, H01B1, C22C9