WO2025137269A1

WO2025137269A1 - Method for strengthening a copper alloy

Info

Publication number: WO2025137269A1
Application number: PCT/US2024/061019
Authority: WO
Inventors: Carole L. Trybus; John C. Kuli; Fritz Grensing
Original assignee: Materion Corp
Current assignee: Materion Corp
Priority date: 2023-12-19
Filing date: 2024-12-19
Publication date: 2025-06-26
Anticipated expiration: 2026-06-19

Abstract

Methods are described for producing copper alloys using a heat treatment to form precipitates along dislocations created by a mechanical deformation. The process may produce copper alloys that are strengthened and having high conductivity.

Description

METHOD FOR STRENGTHENING A COPPER ALLOY

PRIORITY CLAIM

[0001] The present application claims priority to U.S. Provisional Application No. 63/612,319, filed on December 19, 2023, the entire contents and disclosure of which is hereby incorporated by reference.

TECHNICAL FIELD

[0001] The present disclosure relates to a method for strengthening a copper alloy. In particular, the copper alloy comprises chromium. The process involves mechanically deforming the copper casting to form dislocations in the absence of heat and a partial aging to form precipitates. In one embodiment, the precipitates are distributed along the dislocations. Also disclosed are methods of manufacturing such copper alloys, electrical and other components employing copper alloys, and components and articles made from such copper alloys.

BACKGROUND

[0002] Heat treatable copper alloys can be produced using existing processes to provide high electrical conductivity. However, these heat treatable copper alloys often are not chosen for use in commercial electronic devices, components, and parts. This is because, in part, even after full age hardening they do not exhibit a sufficiently high strength-to-weight ratio to supplant other choices such as aluminum or copper alloys, especially in high electrical current applications.

[0003] IP2016156057A discloses a copper alloy sheet containing, by mass, Cr: 0.15-0.60 mass%, Si: 0.01-0.20 mass%, Ti: 0.01 -0.30 mass%, and Zr: 0.01-0.20 mass%, either one or two of them, with the remainder being Cu and inevitable impurities. When the stress relaxation rate after heating at 200°C for 100 hours is denoted as R100, and the stress relaxation rate after heating at 200°C for 1000 hours is denoted as R1000, the increment in the stress relaxation rate (R1000 - R100) is 7% or less, and R1000 is 25% or less. This copper alloy sheet is produced after solution treatment following hot rolling, followed by cold rolling and aging treatment, and the cold rolling includes solid solution treatment in the middle of the process for an electric and electronic component copper alloy sheet. [0004] WO2015182776 describes a copper alloy sheet having a composition containing 1.0 to 6.0 mass% Ni, and 0.2 to 2.0 mass% Si, further containing a total of 0 to 3.000 mass% of at least one type of element selected from the group comprising B, Mg, P, Cr, Mn, Fe, Co, Zn, Zr, Ag and Sn, with the remainder comprising copper and unavoidable impurities, wherein: the strain hardening exponent, HRD, in the rolling direction, RD, is 0.010 to 0.150; and the ratio, URD/UTD, between U D and the strain hardening component, niD, in the transverse direction, TD, is 0.500 to 1.500. On the surface parallel to the rolled surface of the copper alloy sheet at a depth D, the average value, Sa, of the area ratio, S(D), of crystal grains in which the angle of deviation from cube orientation {001 }<100> is within 15° is 5.0 to 30.0%.

[0005] US Pat. No. 6,749,699 describes a copper alloy that consists essentially of, by weight, from 0.15% to 0.7% of Cr, from 0.005% to 0.3% of silver, from 0.01% to 0.15% of titanium, from 0.01% to 0.10% of Si, up to 0.2% of Fe, up to 0.5% of Sn, and the balance Cu and inevitable impurities has a yield strength in excess of 80 ksi, and electrical conductivity in excess of 80% IACS. This copper alloy is free of zirconium.

[0006] It would be desirable to provide high electrical conductivity copper alloys with improved thermo-mechanical properties, as well as processes to maximize the strength-to-weight ratio, formability, current carrying capacity, and/or thermal conductivity. Accordingly, there still remains a need for a method for strengthening copper alloys.

SUMMARY

[0007] As electronics become more compact, design engineers are challenged to create smaller parts that can handle higher power, high temperature environments. The present disclosure relates to copper alloys and a method for strengthening the copper alloy that are suited for handling higher power, higher temperature environments. In one embodiment, there is provided a strengthened copper alloy having a combination of high 0.2% offset yield strength and high electrical conductivity.

[0008] In one aspect there is provided a method for strengthening a copper alloy, the method comprising the steps of: melt casting to form a copper casting containing copper and at least one element selected from the group consisting of chromium , silicon, silver, titanium, and zirconium; mechanically deforming the copper casting to form dislocations in the absence of heat; solution annealing the deformed copper alloy to a temperature of greater than 900°C; cold working the solution annealed copper alloy with a reduction of 30% or more; heating the cold- worked copper alloy to a temperature from 300°C to 500°C for a period not to exceed 1 hour to form precipitates that are at least distributed along the dislocations, wherein the precipitates comprise at least one element selected from the group consisting of chromium, silicon, silver, titanium, and zirconium; cold working the heated copper alloy with a reduction of 30% or more; and heat aging the cold-worked copper alloy at a temperature of up to 500°C for a period not to exceed 12 hours to form a strengthened copper alloy. The present disclosure relates to copper alloys that have a 0.2% offset yield strength of 550 MPa or more and an electrical conductivity of 80% International Annealed Copper Standard (IACS) or more. Also disclosed herein are processes that can be applied to the copper alloys to increase their 0.2% offset yield strength and/or their ultimate tensile strength.

[0009] The copper alloys may have a % total elongation to break of at least 7%. The copper alloys may have a formability ratio of 0.0/0.0, or of better than 1.0/1.0. Combinations of any two or more of these properties are also contemplated.

[0010] Disclosed in various embodiments are copper alloys that comprise: from 0 to 1% by weight of chromium; from 0.02% by weight to 0.1% by weight of silicon; from 0.1% by weight to 0.2% by weight of silver; from 0.015% by weight to 0.05% by weight of titanium; and from 0.02% by weight to 0.06% by weight of zirconium, and the balance being copper, preferably from 97.5% by weight to 99.995% by weight of copper, i.e. balance copper.

[0011] In one aspect there is provided a method for strengthening a copper alloy, the method comprising the steps of: melt casting to form a copper casting containing copper, from 0.5 to 1% by weight of chromium and at least one element selected from the group consisting of silicon, silver, titanium, and zirconium; mechanically deforming the copper casting to form dislocations in the absence of heat; solution annealing the deformed copper alloy to a temperature of greater than 900°C; cold working the solution annealed copper alloy with a reduction of 30% or more; heating the cold-worked copper alloy to a temperature from 300°C to 500°C for a period not to exceed 1 hour to form precipitates that are at least distributed along the dislocations, wherein the precipitates comprise at least one element selected from the group consisting of chromium, silicon, silver, titanium, and zirconium; cold working the heated copper alloy with a reduction of 30% or more; and heat aging the cold-worked copper alloy at a temperature of up to 500°C for a period not to exceed 12 hours to form a strengthened copper alloy. [0012] The present disclosure relates to copper alloys that have a 0.2% offset yield strength of 550 MPa or more and an electrical conductivity of 80% International Annealed Copper Standard (IACS) or more. Also disclosed herein are processes that can be applied to the copper alloys to increase their 0.2% offset yield strength and/or their ultimate tensile strength.

[0013] The copper alloys may have a % total elongation to break of at least 7%. The copper alloys may have a formability ratio of 0.0/0.0, or of better than 1.0/1.0. Combinations of any two or more of these properties are also contemplated.

[0014] Disclosed in various embodiments are copper alloys that comprise: from 0.65 to 1% by weight of chromium; from 0.02% by weight to 0.1% by weight of silicon; from 0.1% by weight to 0.2% by weight of silver; from 0.015% by weight to 0.05% by weight of titanium; and from 0.02% by weight to 0.06% by weight of zirconium, and the balance being copper, preferably from 97.5% by weight to 99.995% by weight of copper, i.e. balance copper.

[0015] In some embodiments, the copper alloy has a 0.2% offset yield strength of 550 MPa or more and an electrical conductivity of 80% IACS or more. In other embodiments, the copper alloy has a 0.2% offset yield strength of from 550 MPa to 850 MPa; an electrical conductivity of from 80% to 90% IACS; an ultimate tensile strength of 550 MPa or more; and a % total elongation to break of at least 8%.

[0016] In one embodiment, the copper alloy contains impurities such as less than or equal to 0.02% by weight any one of cobalt, iron, nickel, beryllium, phosphorous, tin, boron, magnesium, manganese, or zinc, preferably any one of cobalt, iron, or nickel. In particular embodiments, the copper alloy does not contain beryllium, phosphorous, tin, boron, magnesium, manganese, or zinc.

[0017] In one aspect there is provided a copper alloy comprising from 0 to 1% by weight of chromium, preferably 0.5 to 1% by weight of chromium, from 0.02% by weight to 0.1% by weight of silicon, from 0.1% by weight to 0.2% by weight of silver, from 0.015% by weight to 0.05% by weight of titanium, from 0.02% by weight to 0.06% by weight of zirconium, and the balance being copper, for example from 97.5% by weight to 99.995% by weight, wherein the copper alloy is produced by the method comprising: melt casting to form a copper casting; mechanically deforming the copper casting to form dislocations in the absence of heat; solution annealing the deformed copper alloy to a temperature of greater than 900°C; cold working the solution annealed copper alloy with a reduction of 30% or more; heating the cold-worked copper alloy to a temperature from 300°C to 500°C for a period not to exceed 1 hour to form precipitates that are at least distributed along the dislocations, wherein the precipitates comprise at least one element selected from the group consisting of chromium, silicon, silver, titanium, and zirconium; cold working the heated copper alloy with a reduction of 30% or more; and heat aging the cold-worked copper alloy at a temperature of up to 500°C for a period not to exceed 12 hours to form a strengthened copper alloy.

[0018] Also disclosed herein are articles formed from the copper alloys disclosed above and further herein. The article may be used for automotive parts or electronic devices may comprise lead frames, connectors, terminal materials, relays, switches, or sockets, etc.

[0019] These and other non-limiting characteristics are more particularly described below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The following is a brief description of the drawings, which are presented for the purposes of illustrating the exemplary embodiments disclosed herein and not for the purposes of limiting the same.

[0021] FIG. 1 is a flow-chart illustrating a process for strengthening a copper alloy, in accordance with one embodiment of the present disclosure.

DETAILED DESCRIPTION

[0022] The present invention may be understood more readily by reference to the following detailed description of desired embodiments and the examples included therein. Elements, apparatus and methods described herein, however, are not limited to the specific embodiments presented in the detailed description and examples. It should be recognized that these embodiments are merely illustrative of the principles of the present invention. Numerous modifications and adaptations will be readily apparent to those of skill in the art without departing from the spirit and scope of the invention.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict, the present document, including definitions, will control. Preferred methods and materials are described below, although methods and materials similar or equivalent to those described herein can be used in practice or testing of the present disclosure. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. The materials, methods, and examples disclosed herein are illustrative only and not intended to be limiting.

[0024] The singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.

[0025] As used in the specification and in the claims, the term “comprising” may include the embodiments “consisting of’ and “consisting essentially of.” The terms “comprise(s)”, “include(s)”, “having”, “has”, “can”, “contain(s)”, and variants thereof, as used herein, are intended to be open-ended transitional phrases that require the presence of the named ingredients/steps and permit the presence of other ingredients/steps. However, such description should be construed as also describing compositions or methods as “consisting of’ and “consisting essentially of’ the enumerated ingredients/steps, which allows the presence of only the named ingredients/steps, along with any impurities that might result therefrom, and excludes other ingredients/steps.

[0026] All ranges disclosed herein are inclusive of the recited endpoint and independently combinable (for example, the range of “from 550 MPa to 850 MPa” is inclusive of the endpoints, 550 MPa and 850 MPa, and all the intermediate values). The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value; they are sufficiently imprecise to include values approximating these ranges and/or values. The numerical values disclosed herein should be understood to include numerical values, which are the same when reduced to the same number of significant figures and numerical values that differ from the stated value by less than the experimental error of conventional measurement technique of the type described in the present application to determine the value. For the recitation of numeric ranges herein, each intervening number there between with the same degree of precision is explicitly contemplated.

[0027] As used herein, approximating language may be applied to modify any quantitative representation that may vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about” and “substantially”, may not be limited to the precise value specified, in some cases. The modifier “about” should also be considered as disclosing the range defined by the absolute values of the two endpoints. For example, the expression “from about 2 to about 4” also discloses the range “from 2 to 4”. The term “about” may refer to plus or minus 10% of the indicated number. For example, “about 10%” may indicate a range of 9% to 11%, and “about 1” may mean from 0.9-1.1.

[0028] Disclosed herein are copper alloys that containing copper and at least one element selected from the group consisting of chromium, silicon, silver, titanium, and zirconium. IN one embodiment, there is disclosed herein are copper alloys that containing copper, from 0.5 to 1% by weight of chromium, or more preferably from 0.65 to 1% by weight of chromium, and at least one element selected from the group consisting of silicon, silver, titanium, and zirconium. In one embodiment, the copper alloy may be a Cu-Cr alloy that comprises titanium. In one embodiment, the copper alloy may be a Cu-Cr-Si-Ag-Ti-Zr alloy. The disclosed alloys are prepared using a method to strengthen without substantial loss of electrical conductivity. In particular the method comprises mechanically deforming the copper casting to form dislocations and heating the deformed copper alloy to form precipitates. In one embodiment, the precipitates further increase the strength induced by subsequent cold working and solution annealing steps. With suitable formation of precipitates, the disclosed copper alloys exhibit both high 0.2% offset yield strength and high electrical conductivity.

[0029] In accordance with another aspect of the present disclosure, methods of strengthening copper alloys are disclosed that take advantage of forming precipitates. This may be achieved by a partial aging step. More specifically, the methods disclosed involve forming dislocations in the copper alloy and then causing precipitates to create a more strengthened copper alloy. The copper alloy may be fully aged to strengthen the copper alloy at a very high density.

[0030] In one embodiment, copper alloy containing copper, from 0.5 to 1% by weight of chromium and at least one element selected from the group consisting of silicon, silver, titanium, and zirconium. In one embodiment, the copper alloys may contain chromium, silicon, silver, titanium, zirconium, and copper. The chromium is present in the copper alloys in an amount from 0.5% by weight to 1% by weight, e.g., from 0.55% by weight to 1% by weight, from 0.6% by weight to 1% by weight, from 0.62% by weight to 1% by weight, from 0.65% by weight to 1% by weight, from 0.65% by weight to 0.95% by weight or from 0.65% by weight to 0.85% by weight. A high amount of chromium is preferred to form the precipitates in the partial aging step. The silicon may be present in the copper alloys in an amount from 0.02% by weight to 0.1% by weight, e.g., from 0.03% by weight to 0.08% by weight, or from 0.04% by weight to 0.065% by weight. The silver may be present in the copper alloys in an amount from 0.1% by weight to 0.2% by weight, e.g., from 0.11% by weight to 0.15% by weight or from 0.11% by weight to 0.14% by weight. In one embodiment, the copper alloy contains a minimum of 150 ppm or more of titanium, e.g., 250 ppm or more or 300 ppm or more. Accordingly, the titanium may be present in the copper alloys in an amount from 0.015% by weight to 0.05% by weight, e.g., from 0.02% by weight to 0.04% by weight or from 0.025% by weight to 0.035% by weight or from 0.027% by weight to 0.032% by weight. The zirconium may be present in the copper alloys in an amount of up to 0.06% by weight, including from 0.02% by weight to 0.06% by weight, e.g. from 0.02% by weight to 0.04% by weight or from 0.025% by weight to 0.04% by weight. [0031] In one embodiment, the balance of the copper alloy may be copper, excluding impurities. Accordingly, the copper may be present in an amount of 97.5% by weight to 99.995% by weight, e.g., from 98.0% by weight to 99.99% by weight, 98.0% by weight to 99.5% by weight , or 98.0% by weight to 99.0% by weight. In most embodiments, the copper in the copper alloy may be at least 98.0% by weight or more, e.g., at least 98.4% by weight or more, or least 98.5% by weight or more. Any combination of these copper amounts with the each alloying element is contemplated.

[0032] The copper alloys may also have some impurities, but desirably do not. Examples of such impurities may include cobalt, iron, nickel, and sulfur. Some of these elements are sometimes added during processing for specific purposes. In the manufacturing processes of the present disclosure, these elements are ideally not used. For purposes of this disclosure, the individual amounts of less than or equal to 0.03% by weight of any of these elements should be considered to be unavoidable impurities, i.e. their presence is not intended or desired, and the total amount of such unavoidable impurities is usually insignificant. The amount of the unavoidable impurities, including cobalt, iron, nickel, and sulfur may be less than or equal to 0.02% by weight, e.g., less than or equal to 0.01% by weight, or more preferably less than or equal to 0.005% by weight. Some embodiments may have impurities including iron and cobalt, but desirably do not such impurities. Some embodiments can contain up to 0.05% by weight of iron and/or cobalt.. However, preferred embodiments meet the performance and property characteristics, as disclosed herein, in the absence of these impurities. In one embodiment, the amount of iron is controlled to be less than 0.01% by weight to prevent against performance and processing issues.

[0033] Preferably the copper alloy does not comprise other metals than copper, chromium, silicon, silver, titanium, and zirconium. In one embodiment, the copper alloy preferably does not contain beryllium, phosphorous, tin, boron, magnesium, manganese, or zinc.

[0034] In specific embodiments, the copper alloy may comprise: from 0.5% by weight to 1% by weight chromium; from 0.02% by weight to 0.1% by weight silicon; from 0.1% by weight to 0.2% by weight silver; from 0.015% by weight to 0.05% by weight titanium; 0.02% by weight to 0.06% by weight zirconium; and from 98.6% by weight to 99.3% by weight of copper.

[0035] In specific embodiments, the copper alloy may comprise: from 0.65% by weight to 1% by weight chromium; from 0.03% by weight to 0.08% by weight silicon; 0.11% by weight to 0.15% by weight silver; from 0.02% by weight to 0.04% by weight titanium; from 0.02% by weight to 0.04% by weight zirconium; and from 98.7% by weight to 99.1 % by weight of copper. [0036] In specific embodiments, the copper alloy may comprise: from 0.7% by weight to 1% by weight chromium; from 0.03% by weight to 0.08% by weight silicon; 0.11% by weight to 0.15% by weight silver; from 0.02% by weight to 0.04% by weight titanium; from 0.02% by weight to 0.04% by weight zirconium; and from 98.7% by weight to 99.1 % by weight of copper.

[0037] In specific embodiments, the copper alloy may comprise: 0.66% by weight chromium; 0.04% by weight silicon; 0.11% by weight silver; 0.02% by weight titanium; 0.03% by weight zirconium; and 99.14% by weight of copper, with the amounts of impurities being controlled to be less than or equal to 0.01% by weight of nickel and less than or equal to 0.03% by weight of iron.

[0038] In specific embodiments, the copper alloy may comprise: from 0.82% to 0.85% by weight chromium; 0.07% by weight silicon; 0.13% by weight silver; from 0.036% to 0.049% by weight titanium; 0.033% to 0.036% by weight zirconium; and from 98.5% by weight to 99.0% by weight of copper, with the amounts of impurities being controlled to be less than or equal to 0.01% by weight of nickel and less than or equal to 0.01% by weight of iron.

[0039] In specific embodiments, the copper alloy may comprise: from 0.071% to 0.073% by weight chromium; 0.08% by weight silicon; 0.13% by weight silver; from 0.011% to 0.028% by weight titanium; from 0.02% to 0.034% by weight zirconium; and from 99.1% by weight to 99.7% by weight of copper, with the amounts of impurities being controlled to be less than or equal to 0.01% by weight of nickel and less than or equal to 0.01% by weight of iron.

[0040] In specific embodiments, the copper alloy may comprise: 0.53% to 0.58% by weight chromium; from 0.036% to 0.043% by weight silicon; from 0.142% to 0.145% by weight silver; from 0.09% to 0.019% by weight titanium; from 0.023% to 0.028% by weight zirconium; and from 98.7% by weight to 99.2% by weight of copper, with the amounts of impurities being controlled to be less than or equal to 0.01% by weight of iron.

[0041] In specific embodiments, the copper alloy may comprise: from 0.74% to 0.77% by weight chromium; from 0.062% to 0.077% by weight silicon; from 0.139% to 0.143% by weight silver; from 0.013% to 0.042% by weight titanium; 0.022% by weight zirconium; and from 98.9% by weight to 99.3% by weight of copper, with the amounts of impurities being controlled to be less than or equal to 0.01% by weight of nickel and less than or equal to 0.01% by weight of iron.

[0042] It is noted the zirconium may be added to act as a deoxidizer and should not be considered an impurity. Zirconium silicides can affect the yield strength, are desirably not present in the copper alloys of the present disclosure. The copper alloys of the present disclosure should be substantially devoid of such zirconium silicides. Preferably, the zirconium is present in the form of zirconium oxides. Desirably, such oxides are in the form of small particles, and are not present as a continuous stringer.

[0043] The zirconium in the Cu-Cr-Si-Ag-Ti-Zr alloy is used as a deoxidizer because it does not melt at low temperatures, does not generally detrimentally affect the electrical conductivity in the final alloy, does not tend to stay in solution with the copper, and usually improves the yield strength. In comparison, magnesium fades quickly, can cause the melt to “spit”, and melts at a low temperature, which can cause difficulty during hot rolling. Manganese does not fade fast enough, and can detrimentally affect the electrical conductivity. Cadmium can cause issues during hot rolling and is also toxic. Lithium is relatively expensive.

[0044] After processing, the Cu-Cr-Si-Ag-Ti-Zr alloys may have certain properties. The strengthened copper alloy may have a 0.2% offset yield strength of 550 MPa or more, e.g., 575 MPa or more, 600 MPa or more, 625 MPa or more, 650 MPa or more, or 700 MPa or more. In terms of ranges, the strengthened copper alloy may have a 0.2% offset yield strength from 550 MPa to 850 MPa, e g., from 550 MPa to 800 MPa, from 575 MPa to 750 MPa, from 575 MPa to 725 MPa, or from 600 MPa to 700 MPa. The 0.2% offset yield strength may be measured according to ASTM E8.

[0045] The strengthened copper alloy may have an ultimate tensile strength of 475 MPa or more, e.g., 515 MPa or more, 550 MPa or more, or 600 MPa or more. In one embodiment, the strengthened copper alloy may have an ultimate tensile strength up to 620 MPa. The ultimate tensile strength may be measured according to ASTM E8.

[0046] The strengthened copper alloy may have an elastic modulus of 130 GPa or more, e.g., 140 GPa or more, or 150 GPa or more. In one embodiment, the strengthened copper alloy may have an elastic modulus up to 175 GPa. The elastic modulus is measured according to ASTM El 11-17.

[0047] The strengthened copper alloy may have a % total elongation to break of at least 7%, or at least 7.5%, or at least 8%, or at least 9%, and/or up to 12%. The % total elongation may be measured according to ASTM E8.

[0048] The strengthened copper alloy may have a formability ratio of at least 1.0/1.0, and may have a ratio of 0.0/0.0 R/t. Formability may be measured by the formability ratio or R/t ratio (i.e. bend strength). This specifies the minimum inside radius of curvature (R) that is needed to form a 90° bend in a strip of thickness (t) without failure, i.e. the formability ratio is equal to R/t. Materials with good formability have a low formability ratio (i.e. low R/t), in other words a lower R/t is better. The formability ratio can be measured using the 90° V-block test, wherein a punch with a given radii of curvature is used to force a test strip into a 90° die, and then the outer radius of the bend is inspected for cracks. The formability ratio can also be reported as the ratio of the formability in the longitudinal (good way) direction to the formability in the transverse (bad way) direction, or as GW/BW.

[0049] The strengthened copper alloy may have an electrical conductivity of 80% or more IACS, e.g., 81% or more IACS, 82% or more IACS, 83% or more IACS, 84% or more IACS or 85% or more IACS. In terms of ranges the strengthened copper alloy may have an electrical conductivity from 80% IACS to 90% IACS, e.g., from 81% IACS to 90% IACS, from 82% IACS to 90% IACS, from 83% IACS to 90% IACS, from 84% IACS to 90% IACS or from 85% IACS to 90% IACS. Conductivity of copper alloys may be expressed as %IACS, which is short for International Annealed Copper Standard. 100% IACS is defined as the conductivity corresponding to a volume resistivity at 20°C of 17.241 nfl«m, which was based on the expected typical conductivity of commercial “pure” annealed copper at the time the standard was adopted by the International Electrotechnical Commission in 1914.

[0050] Continuing now with reference to FIG. 1, a process 100 for method for strengthening a copper alloy is illustrated in accordance with one embodiment of the present disclosure. The process 100 begins at step 110, with a melt casting to form a copper casting. In some embodiments, the melt casting may produce a copper ingot. The composition as described above is melted and casted to produce copper casting in a crucible or a casting furnace. A degassing process may be used to remove gases from the melt, such as hydrogen and oxygen. In one embodiment, the copper casting comprises a Cu-Cr-Si-Ag-Ti-Zr alloy, also referred to as the initial copper alloy, has initial properties such as, for example, an initial 0.2% offset yield strength, an initial ultimate tensile strength, an initial formability ratio, an initial % total elongation to break, and/or an initial electrical conductivity (i.e. % IACS), prior to any processing according to the present disclosure.

[0051] In step 110, copper may be melted at temperature of 1200°C or more and the alloying elements of chromium, silicon, silver, titanium and zirconium are added to the melt. The melt casting may be a continuous process to produce the copper casting having a thickness suitable for mechanical processing. Accordingly, the copper casting may be in the form of a strip, rod, wire, or tube.

[0052] In one embodiment, the initial copper alloy can be provided in the form of a casting. Alternatively, the initial copper alloy may undergo one or more additional pre-processing steps, including, for example, casting, cropping, milling, hot rolling, slab milling, to obtain a desired shape. These pre-processing steps generally do not change the properties of the copper alloy. [0053] Following the melt casting in step 110, the copper casting is mechanically deformed in step 120. The mechanically deformed in step 120 may comprise at least one of rolling, drawing, or forging. In one embodiment, mechanically deforming may be achieved by cold rolling, cold drawing or other suitable cold working process. These mechanically deforming process may to form dislocations. Accordingly, step 120 may be performed in the absence of heat. Cold working is a metal forming process typically performed near room temperature, in which an alloy is passed through rolls, dies, or is otherwise cold worked to reduce the section of the alloy and to make the section dimensions uniform. This increases the strength of the alloy. The degree of cold working performed is indicated in terms of a percent reduction in thickness, or percent reduction in area, and is referred to in this disclosure as a percentage of cold working (%CW). In particular embodiments, the copper casting may be cold worked to a %CW from about 60 %CW to about 95 %CW, including from about 80 %CW to about 95 %CW, and from about 82 %CW to about 92 %CW. Cold working within the %CW may increase the dislocations within the grains and to lead to further strengthening.

[0054] In step 130, the deformed copper alloy may be solution annealed. Solution annealing involves heating a precipitation hardenable alloy to a high enough temperature to convert the microstructure into a single phase. A rapid quench to room temperature leaves the alloy in a supersaturated state that makes the alloy soft and ductile, helps regulate grain size, and prepares the alloy for aging. Subsequent heating of the supersaturated solid solution enables precipitation of the strengthening phase and hardens the alloy. After any solution annealing, a water quench should be performed to “lock in” the results. The quench rate should be a minimum of l°C/second, and quench rates up to 30°C/second are acceptable. The solution annealing of step 130 may be performed at a temperature from 900°C to 1100°C, e.g., from 950°C to 1050°C or from 980°C to 1000°C. The solution annealing may be performed for a time period of from about 1 minute to about 10 minutes, including from about 2.5 minutes to about 5 minutes or from about 1.3 minutes to about 4 minutes.

[0055] In step 140, the heated deformed copper alloy may be cold worked. In one embodiment, the cold working step 140 may achieve a second percentage of cold working from 30 %CW to 80 %CW, e.g., from 35 %CW to 70 %CW or from 40 %CW to 65 %CW. In embodiment, additional dislocations may be formed during step 140.

[0056] Following step 140, the deformed copper is heat treated in a partial aging step 150. Aging is a heat treatment technique that produces ordering and precipitates of an impurity phase that impedes the movement of defects in a crystal lattice. This hardens the alloy. In step 150, the deformed copper is heated to a temperature from 300°C to 500°C for a period not to exceed 1 hour. In one embodiment, the heat treatment is conducted at a temperature from 325°C to 475°C, and more preferably from 325°C to 450°C. The period of time preferably does not exceed 0.75 hours, e.g., does not exceed 0.5 hours or does not exceed 0.25 hours. Shorter times for the heat treatment are preferred to form a sufficient amount of precipitates without coarsening. Under such conditions, precipitates may be formed. In one embodiment, the heat treatment step forms precipitates may be distributed along the dislocations. This may allow the precipitates to pin the dislocations and increase the strength of the copper alloy.

[0057] In one embodiment, the precipitates comprise at least one element selected from the group consisting of chromium, silicon, silver, titanium, and zirconium. Preferably, the precipitates comprise at least chromium silicide and/or titanium silicides.

[0058] In one embodiment, the precipitates have an average diameter (D50) of less than or equal to 5 microns, e.g., less than or equal to 4 microns, less than or equal to 3 microns, less than or equal to 2 microns, less than or equal to 1 micron, or less than or equal to 0.5 microns. In one embodiment, the precipitates may be super fine and have average diameter of about 100 nm. The precipitates may have a morphology that is irregular, rounded, spherical, ellipsoid, cylindrical, cubic, flake-shaped or combination thereof. In one embodiment, spherical or near-spherical precipitates are preferred.

[0059] In step 160, the copper alloy may be cold worked to a percentage of cold working (%CW). In particular embodiments, the %CW in step 160 may be from about 30 %CW to about 80 %CW, including from about 40 %CW to about 80 %CW. The minimum cumulative cold working for all the cold working steps may be at least 85 %CW. To achieve greater performance, the heat treatment step 150 occurs between cold working steps 140 and 160.

[0060] It is noted that in some situations where the initial copper alloy casting is especially thick, an additional solution annealing and/or cold working may be desired. In such cases, the additional solution annealing may be performed according to the parameters described for step 130, and the cold working may be performed according to the parameters described for step 140/160.

[0061] Then, in step 170, the cold-worked copper alloy is aged for a period to obtain the copper alloy with improved 0.2% offset yield strength. Step 170 may further harden the alloy. In particular embodiments, the alloy is aged at a temperature of up to 500°C, e.g., up to 490°C, up to 475°C or up to 450°C. The aging may be performed for a period not to exceed 12 hours, e.g., not to exceed 10 hours or not to exceed 8 hours. In one embodiment, the aging period may be from 2 hours to 12 hours, or from 4 hours to 10 hours, or from 6 hours to 8 hours. It is noted that the aging can be performed at multiple different temperatures within these temperature ranges. [0062] Usually, when multiple different temperatures are used for aging, the successive aging temperature is lower than the previous aging temperature. [0063] The copper alloy may be aged in steps 150 and/or 170 in a full hydrogen atmosphere. The term “full” means that the atmosphere in which the aging occurs is 100% hydrogen (H2). For comparison, dry air contains roughly 0.5 ppm to 1 ppm hydrogen (H2). Aging in a full hydrogen atmosphere is significant because the thermal conductivity of hydrogen is greater than that of air. [0064] After steps 170, the copper alloy may be subjected to one or more post-processing steps. For example, the copper alloy may be pickled and/or brushed.

[0065] The copper alloys obtained after step 170 has improved 0.2% offset yield strength, and can be considered a “final” copper alloy. In one embodiment, the final Cu-Cr-Si-Ag-Ti-Zr alloy may have one or more final properties such as, for example, a final 0.2% offset yield strength, a final ultimate tensile strength, a final formability ratio, a final % total elongation to break, and a final electrical conductivity (i.e. % IACS), as described above.

[0066] In accordance with an aspect of the present disclosure, articles formed from these Cu- Cr-Si-Ag-Ti-Zr copper alloys are described. The copper alloys of the present disclosure have a combination of good 0.2% offset yield strength, high formability, and high electrical conductivity. The alloys can be formed into articles such as billet, plate, strip, foil, wire, rod, tube, or bar. For purposes of the present disclosure, billet is a solid metal form, usually having a large cross-sectional area. Plate is a flat surfaced product of generally rectangular cross-section with the two sides being straight and having a uniform thickness greater than 4.8 millimeters (mm), and with a maximum thickness of about 210 mm, and a width of greater than 30 mm. Strip is a flat surfaced product of generally rectangular cross-section with the two sides being straight and having a uniform thickness of up to 4.8 millimeters (mm). This is generally done by rolling an input to reduce its thickness to that of strip. Bar is as a flat surfaced product of generally rectangular cross-section and having a uniform thickness greater than 0.48 mm, and with a maximum width of 30 mm. Wire is a solid section other than strip, furnished in coils or on spools or reels. Rod is a round, solid section furnished in straight lengths. Tube is a seamless hollow product with round or other cross section. Foil is a very thin flat surfaced product, typically having a uniform thickness of 0.04 mm or less. It is noted there may be some overlap between these various articles.

[0067] The copper alloys of the present disclosure can also be used to make particular articles of varied shape for various applications, for example, a heat sink in a cellphone, or a wide range of electrical and electronic devices, components, and parts, such as wire, cabling, electrical connectors, electrical contacts, electrical ground plates, Faraday shield walls, heat spreaders, wire harness terminal contacts, processor socket contacts, backplane, midplane, or card-edge server connectors, and so forth.

Embodiments

[0068] The following embodiments, among others, are disclosed.

[0069] Embodiment 1. A method for strengthening a copper alloy, the method comprising the steps of melt casting to form a copper casting containing copper and at least one element selected from the group consisting of chromium, silicon, silver, titanium, and zirconium; mechanically deforming the copper casting to form dislocations in the absence of heat; solution annealing the deformed copper alloy to a temperature of greater than 900°C; cold working the solution annealed copper alloy with a reduction of 30% or more; heating the cold-worked copper alloy to a temperature from 300°C to 500°C for a period not to exceed 1 hour to form precipitates that are at least distributed along the dislocations, wherein the precipitates comprise at least one element selected from the group consisting of chromium, silicon, silver, titanium, and zirconium; cold working the heated copper alloy with a reduction of 30% or more; and heat aging the cold- worked copper alloy at a temperature of up to 500°C for a period not to exceed 12 hours to form a strengthened copper alloy.

[0070] Embodiment 2. The method of embodiment 1, wherein the mechanically deforming step comprises at least one of rolling, drawing, or forging.

[0071] Embodiment 3. The method of any one of embodiments 1 or 2, wherein the mechanically deforming step with a reduction of 60% or more.

[0072] Embodiment 4. The method of any one of embodiments 1-3, wherein the precipitates comprise chromium silicide or titanium silicide.

[0073] Embodiment 5. The method of any one of embodiments 1-4, wherein the strengthened copper alloy has a 0.2% offset yield strength of 550 MPa or more.

[0074] Embodiment 6. The method of any one of embodiments 1-5, wherein the strengthened copper alloy has a 0.2% offset yield strength of is from 550 MPa to 850 MPa. [0075] Embodiment 7. The method of any one of embodiments 1-6, wherein the strengthened copper alloy has an electrical conductivity of 80% IACS or more.

[0076] Embodiment 5. The method of any one of embodiments 1-7, wherein the strengthened copper alloy has an electrical conductivity from 80% to 90% IACS. [0077] Embodiment 5. The method of any one of embodiments 1-8, wherein the strengthened copper alloy has a % total elongation to break of at least 7 %.

[0078] Embodiment 10. The method of any one of embodiments 1-9, wherein the copper alloy comprises from 0 to 1% by weight of chromium, from 0.02% by weight to 0.1% by weight of silicon, from 0.1% by weight to 0.2% by weight of silver, from 0.015% by weight to 0.05% by weight of titanium, from 0.02% by weight to 0.06% by weight of zirconium, and the balance being copper, preferably from 97.5% by weight to 99.995% by weight of copper.

[0079] Embodiment 11. The method of any one of embodiments 1-10, wherein in the copper alloy does not contain beryllium, phosphorous, tin, boron, magnesium, manganese, or zinc.

[0080] Embodiment 12. The method of any one of claims 1-11, wherein in the copper alloy contains less than 0.02% by weight of any one of cobalt, iron, nickel, beryllium, phosphorous, tin, boron, magnesium, manganese, or zinc, preferably any one of cobalt, iron, or nickel.

[0081] Embodiment 13. An article formed from the strengthened copper alloy produced by the method of any one of claims 1-12.

[0082] Embodiment 14. A method for strengthening a copper alloy, the method comprising the steps of melt casting to form a copper casting containing copper, from 0.5 to 1% by weight of chromium and at least one element selected from the group consisting of silicon, silver, titanium, and zirconium; mechanically deforming the copper casting to form dislocations in the absence of heat; solution annealing the deformed copper alloy to a temperature of greater than 900°C; cold working the solution annealed copper alloy with a reduction of 30% or more; heating the cold- worked copper alloy to a temperature from 300°C to 500°C for a period not to exceed 1 hour to form precipitates that are at least distributed along the dislocations, wherein the precipitates comprise at least one element selected from the group consisting of chromium, silicon, silver, titanium, and zirconium; cold working the heated copper alloy with a reduction of 30% or more; and heat aging the cold-worked copper alloy at a temperature of up to 500°C for a period not to exceed 12 hours to form a strengthened copper alloy.

[0083] Embodiment 15. The method of embodiment 14, wherein the mechanically deforming step involves rolling, drawing, or forging.

[0084] Embodiment 16. The method of any one of embodiments 14 or 15, wherein the mechanically deforming step with a reduction of 60% or more. [0085] Embodiment 17. The method of any one of embodiments 14-16, wherein the precipitates comprise chromium silicide or titanium silicide.

[0086] Embodiment 18. The method of any one of embodiments 14-17, wherein the strengthened copper alloy has a 0.2% offset yield strength of 550 MPa or more.

[0087] Embodiment 19. The method of any one of embodiments 14-18, wherein the strengthened copper alloy has a 0.2% offset yield strength of is from 550 MPa to 850 MPa.

[0088] Embodiment 20. The method of any one of embodiments 14-19, wherein the strengthened copper alloy has an electrical conductivity of 80% IACS or more.

[0089] Embodiment 21. The method of any one of embodiments 14-20, wherein the strengthened copper alloy has an electrical conductivity from 80% to 90% IACS.

[0090] Embodiment 22. The method of any one of embodiments 14-21, wherein the strengthened copper alloy has a % total elongation to break of at least 7 %.

[0091] Embodiment 23. The method of any one of embodiments 14-22, wherein the copper alloy comprises from 0.65 to 1% by weight of chromium, from 0.02% by weight to 0.1% by weight of silicon, from 0.1% by weight to 0.2% by weight of silver, from 0.015% by weight to 0.05% by weight of titanium, from 0.02% by weight to 0.06% by weight of zirconium, and the balance being copper, preferably from 97.5% by weight to 99.995% by weight of copper.

[0092] Embodiment 24. The method of any one of embodiments 14-23, wherein in the copper alloy does not contain beryllium, phosphorous, tin, boron, magnesium, manganese, or zinc.

[0093] Embodiment 25. The method of any one of embodiments 14-24, wherein in the copper alloy contains less than 0.02% by weight any one of cobalt, iron, nickel, beryllium, phosphorous, tin, boron, magnesium, manganese, or zinc, preferably any one of cobalt, iron, or nickel.

[0094] Embodiment 26. An article formed from the strengthened copper alloy produced by the method of any one of embodiments 14-25.

[0095] Embodiment 27. A copper alloy comprising from 0 to 1% by weight of chromium, from 0.02% by weight to 0.1% by weight of silicon, from 0.1% by weight to 0.2% by weight of silver, from 0.015% by weight to 0.05% by weight of titanium, from 0.02% by weight to 0.06% by weight of zirconium, and the balance being copper, wherein the copper alloy is produced by the method comprising: melt casting to form a copper casting; mechanically deforming the copper casting to form dislocations in the absence of heat; solution annealing the deformed copper alloy to a temperature of greater than 900°C; cold working the solution annealed copper alloy with a reduction of 30% or more; heating the cold-worked copper alloy to a temperature from 300°C to 500°C for a period not to exceed 1 hour to form precipitates that are at least distributed along the dislocations, wherein the precipitates comprise at least one element selected from the group consisting of chromium, silicon, silver, titanium, and zirconium; cold working the heated copper alloy with a reduction of 30% or more; and heat aging the cold-worked copper alloy at a temperature of up to 500°C for a period not to exceed 12 hours to form a strengthened copper alloy.

[0096] Embodiment 28. The copper alloy of embodiment 27, wherein the copper alloy has a 0.2% offset yield strength of 550 MPa or more.

[0097] Embodiment 29. The copper alloy of any one of embodiments 27 or 28, wherein the copper alloy has a 0.2% offset yield strength of is from 550 MPa to 850 MPa.

[0098] Embodiment 30. The copper alloy of any one of embodiments 27-29, wherein the strengthened copper alloy has an electrical conductivity of 80% IACS or more.

[0099] Embodiment 31. The copper alloy of any one of embodiments 27-30, wherein the strengthened copper alloy has an electrical conductivity from 80% to 90% IACS.

[0100] Embodiment 32. The copper alloy of any one of embodiments 27-31, wherein the strengthened copper alloy has a % total elongation to break of at least 7 %.

[0101] Embodiment 33. The copper alloy of any one of embodiments 27-32, wherein the copper alloy comprises from 0.5 to 1% by weight of chromium.

[0102] Embodiment 34. The copper alloy of any one of embodiments 27-33, wherein the copper alloy comprises from 0.65 to 1% by weight of chromium.

[0103] While the invention has been described in detail, modifications within the spirit and scope of the invention will be readily apparent to those of skill in the art. In view of the foregoing discussion, relevant knowledge in the art and references discussed above in connection with the Background and Detailed Description, the disclosures of which are all incorporated herein by reference. In addition, it should be understood that aspects of the invention and portions of various embodiments and various features recited below and/or in the appended claims may be combined or interchanged either in whole or in part. In the foregoing descriptions of the various embodiments, those embodiments that refer to another embodiment may be appropriately combined with other embodiments as will be appreciated by one of skill in the art. Furthermore, those of ordinary skill in the art will appreciate the foregoing description is by way of example only and is not intended to limit.

Claims

We Claim:

1. A method for strengthening a copper alloy, the method comprising the steps of: melt casting to form a copper casting containing copper and at least one element selected from the group consisting of chromium, silicon, silver, titanium, and zirconium; mechanically deforming the copper casting to form dislocations in the absence of heat; solution annealing the deformed copper alloy to a temperature of greater than 900°C; cold working the solution annealed copper alloy with a reduction of 30% or more; heating the cold-worked copper alloy to a temperature from 300°C to 500°C for a period not to exceed 1 hour to form precipitates that are at least distributed along the dislocations, wherein the precipitates comprise at least one element selected from the group consisting of chromium, silicon, silver, titanium, and zirconium; cold working the heated copper alloy with a reduction of 30% or more; and heat aging the cold-worked copper alloy at a temperature of up to 500°C for a period not to exceed 12 hours to form a strengthened copper alloy.

2. The method of claim 1, wherein the mechanically deforming step comprises at least one of rolling, drawing, or forging.

3. The method of any one of claims 1 or 2, wherein the mechanically deforming step with a reduction of 60% or more.

4. The method of any one of claims 1-3, wherein the precipitates comprise chromium silicide or titanium silicide.

5. The method of any one of claims 1-4, wherein the strengthened copper alloy has a 0.2% offset yield strength of 550 MPa or more, preferably from 550 MPa to 850 MPa.

6. The method of any one of claims 1-5, wherein the strengthened copper alloy has an electrical conductivity of 80% IACS or more, preferably from 80% to 90% IACS.

7. The method of any one of claims 1-6, wherein the strengthened copper alloy has an electrical conductivity.

8. The method of any one of claims 1-7, wherein the strengthened copper alloy has a % total elongation to break of at least 7 %.

9. The method of any one of claims 1-8, wherein the copper alloy comprises from 0 to 1% by weight of chromium, from 0.02% by weight to 0.1% by weight of silicon, from 0.1% by weight to 0.2% by weight of silver, from 0.015% by weight to 0.05% by weight of titanium, from 0.02% by weight to 0.06% by weight of zirconium, and the balance being copper.

10. The method of any one of claims 1-9, wherein in the copper alloy does not contain beryllium, phosphorous, tin, boron, magnesium, manganese, or zinc.

11. The method of any one of claims 1-10, wherein in the copper alloy contains less than 0.02% by weight of any one of cobalt, iron, nickel, beryllium, phosphorous, tin, boron, magnesium, manganese, or zinc, preferably any one of cobalt, iron, or nickel.

12. The method of any one of claims 1-11, wherein the melt casting uses from 0.5 to 1% by weight of chromium.

13. A copper alloy produced by the method of any one of claims 1-12, wherein the copper alloy comprises: from 0 to 1% by weight of chromium, from 0.02% by weight to 0.1% by weight of silicon, from 0.1% by weight to 0.2% by weight of silver, from 0.015% by weight to 0.05% by weight of titanium, from 0.02% by weight to 0.06% by weight of zirconium, and the balance copper.

14. The copper alloy of claim 13, wherein the copper alloy comprises from 0.5 to 1% by weight of chromium, preferably from 0.65 to 1% by weight of chromium.

15. An article formed from the strengthened copper alloy produced by the method of any one of claims 1-14.