GB1561922A - High strength high conductivity copper alloys - Google Patents

Description

(54) HIGH STRENGTH, HIGH CONDUCTIVITY COPPER ALLOYS (71) We, OLIN CORPORATION, a corporation organised and existing under the laws of the State of Virginia, United States of America, of 427, N. Shamrock Avenue, East Alton, Illinois, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to high conductivity high strength copper alloys, and particularly to such alloys which are free from internal copper oxides.

Oxygen free copper must be used in applications where the alloy is to be annealed in a hydrogen containing atmosphere, as the presence of oxygen in either its elemental state or as copper oxide results in the formation of water vapor during the annealing process which causes embrittlement of the alloy.

Two major methods are used to reduce the oxygen level of copper so as to avoid embrittlement. The first method involves casting the alloy in an inert atmosphere and fluxing the molten copper with an inert gas to reduce the oxygen level. This is a complex process and difficult to perform satisfactorily. The other major method of deoxidizing copper consists of adding a reactive material to the melt which will form an oxide in preference to copper oxide. The reactive material is chosen so that its oxide will be stable and will not be reduced by hydrogen during annealing. Unfortunately, most of the reactive materials used have a highly deleterious effect on electrical conductivity if excess reactive material remains in solution in the deoxidized copper alloy. Because of the reactive nature of the materials used, it is difficult to accurately control the amount of reactive material which is actually needed to deoxidize the molten copper without causing a loss of conductivity.

In addition to the above, it is known that oxygen free copper has relatively low mechanical properties and it is highly desirable to improve these properties while simultaneously maintaining a high electrical conductivity. Further, oxygen free copper has a very low softening point and for many applications it would be highly desirable to maximize strength and conductivity and to increase the softening temperature. Finally, care must be taken in the processing of oxygen free copper to avoid the reintroduction of oxygen into the alloy. For example. when welding oxygen free copper, an inert atmosphere must be used so as to protect the molten material in the weld zone from oxidation.

Mischmetal has been used as a deoxidizing material in the production of oxygen free copper; however, when excess mischmetal is present a low melting point eutectic forms between Cu and CeCu6 compound which results in an alloy which is unsuitable for high temperature brazing and other similar applications where high temperatures are encountered.

In accordance with the present invention, there is provided a copper base alloy possessing high strength and high conductivity characterized by the presence of from 0.01 to 0.5% of an element selected from the lanthanide series of the Periodic Table or of mixtures of such elements, from 0.01 to 1.75% of phosphorus, from 0.007 to 3.3% of magnesium, and the presence of from 0.01% up to its maximum solubility in copper of an element which forms a precipitate with phosphorus, the percentage of the said element being sufficient to precipitate substantially all the phosphorus present so that the residual phosphorus does not exceed 0.025% of said alloy, the balance apart from impurities being copper. The phosphide precipitants useful herein comprise chromium, zirconium, titanium, cobalt, vanadium, niobium, manganese and iron, and are present in a range of from 0.01 to 5.or/,. The lanthanide element or component of the alloys of the present invention may, in a preferred embodiment, comprise mischmetal. The foregoing ranges of materials may be varied in order to emphasize properties desirable in particular applications of the alloys. Thus, for example, the alloys may be modified within said ranges to emphasize high strength and conductivity where the end use of the alloy primarily requires a high strength level. Conversely, conductivity may be accentuated without an appreciable loss of either strength or temperature stability.

The alloys of the present invention do not rely on specific stoichiometric ratios of precipitants because of the distinctiveness of the kinetics of precipitation. Thus, for example, the alloys of the present invention may attain improved conductivities and strengths without rigid adherence to particular stoichiometric ratios of elements, so long as the combination of precipitants results in essentially complete precipitation of phosphorus. The presence of any given element in the alloy is in part dependent upon the phosphorus available for precipitation therewith and the solubility of the given element in copper. Further, the ultimate properties of the alloys will also depend upon the specific processing employed.

The alloys of the present invention are characterized by a substantialy oxidation resistance in high temperature contact with air. As their preparation employs chemical deoxidizing techniques, the alloys are resistant to internal copper oxide formation and subsequent hydrogen embrittlement during hot processing or other elevated temperature exposure. This is a significant improvement over conventionally produced oxygen free copper and copper deoxidized with mischmetal alone. Increases of about 500C are observed in softening temperatures and improvements are noted in tensile properties.

The alloys of the present invention are copper base alloys which generally may contain up to and in excess of 99% copper and intentional alloying additions comprising one or more lanthanide elements, phosphorus, magnesium and at least one additional element which reacts with phosphorus to form a phosphide precipitate. Particularly, the alloys may comprise from 0.01 to 0.5%, and preferably from 0.012 to 0.5%, of the lanthanide component, from 0.01 to 1.75%, and preferably from 0.011 to 0.5% phosphorus, and from 0.007 to 3.3%, and preferably from 0.007 to 0.4% magnesium. The alloys may further comprise from 0.01% up to the maximum solubility in copper, of the phosphide precipitant. More particularly, the lanthanide component may comprise mischmetal, and the phosphide precipitants may comprise elements selected from the group consisting of chromium, zirconium, titanium, cobalt, vanadium, niobium, manganese, iron, and mixtures thereof.

As noted, the lanthanide component may comprise mischmetal which is a material composed largely of lanthanides comprising Elements Nos. 58-71 of the Periodic Table. A typical mischmetal composition is listed below: Cerium 50% Lanthanum 27% Neodymium 16% Praseodymium 5% Other Rare Earth Metals 2% However, as used in this application the term mischmetal is intended to include any material comprised predominantly of lanthanide regardless of the relative proportions thereof. For example, cerium alone could be used in place of mischmetal and would provide equally satisfactory results.

The phosphide precipitants will vary in their presence in relation to their respective solubilities in copper. Specifically, zirconium may be present in an amount rangingfrom 0.01 to 0.15%, chromium may be present in an amount ranging from 0.01 to 0.65%, titanium may be present in an amount ranging from 0.01 to .7 Ó, vanadium may be present in an amount ranging ftom 0.Ul to 0.64%, niobium may be present in an amount ranging from 0.01 to 1.5%, iron may be present in an amount ranging from 0.01 to 2.8%, manganese may be present in an amount ranging from 0.01 to 5.00,/, and cobalt may be present in an amount ranging from 0.01 to 3.5%.

The phosphide precipitant elements in accordance herewith preferably possess a low solubility in copper at relatively low temperatures such as 400 500 C so that if the element is added in an amount exceeding that capable of precipitating with phosphorus, the remainder of that element will precipitate during the annealing of the alloy to cause the electrical conductivity of the alloy to increase. Further as previously noted, the amounts of the precipitant element additions are related to the amount of phosphorus added to formulate the alloy. The precipitant elements are added in an amount sufficient to ensure that essentially all of the phosphorus added to the alloy is precipitated, whereby an excess of the precipitant element remains. Excess phosphorus may, however, be present up to 0.025%.

The amount of such excess which is either tolerable or desirable will depend upon the solubility of the particular precipitant element in copper at the aforenoted temperature range, and on the particular effects said element or elements may have on the electrical conductivity of the alloy. Thus, for example, a large excess of chromium or zirconium of 0.1% to 0.4%, would be tolerable and desirable, however, an excess of iron or cobalt beyond that combined with phosphorus should be less than 0.1%. Table I, below, shows the chemical formulas of the known phosphides which precipitate in the instance of each of the elements added in addition to phosphorus, including the lanthanide component, magnesium and the precipitant elements of the present invention, together with the corresponding weight ratios of the individual elements with respect to phosphorus. In the Table, cerium is presented as representative of the lanthanide component only, as it is contemplated that one or more of the lanthanides, including mischmetal, may be employed in mixture.

TABLE I Alloving Phosphide Metal: Phosphorus Element Formed Weight Ratio Mg Mg,Pz 1.18 Ce CeP 4.52 Ti Ti,P 4.64 Zr ZrP 2.95 V V,P 4.93 Nb NbP 3.00 Cr Cr P 5.04 Mn . Mn,P 5.32 Fe Fe,P 5.41 Co Co2P 3.51 Referring to Table I, the phosphorus content of a particular alloy desired, such as an alloy containing phosphorus, magnesium, cerium and chromium may thereby be determined by the following formula: Weight % of phosphorus is equal to or less than the sum of the weight % of magnesium divided by 1.18, the weight % of cerium divided by 4.52 and the weight % of chromium divided by 5.04. Adherence to the above suggested formulation will assure than excess phosphorus is not present in solid solution.

In addition to an excess of various phosphide precipitants, it is contemplated that an excess of phosphorus may be present in amounts ranging up to 0.025% without deleteriously affecting the properties of the alloy. Specifically, excess phosphorus will tend to increase strength while maintaining conductivity at an acceptable level.

During the course of the formation of the aforenoted phosphide compounds, small amounts of compounds containing mixtures of the various elements may be formed which contain other incidental elements. While these compounds may affect conductivity somewhat, they will not affect the strength of the resulting alloy.

The present invention also comprises the employment of optional additives for specific purposes. For example, deoxidizers such as aluminum boron or mischmetal if it is not one of the major alloy elements, may be added in small but effective amounts. Likewise, zirconium may be added in small amounts, if not already present, to improve resistance to softening. Lead, selenium or tellurium may be added in amounts effective to improve machinability. Arsenic and antimony, chemical congeners of phosphorus may be added in partial substitution for phosphorus on an equal atomic percentage basis, as they form compounds analogous to the phosphides. In addition, both arsenic and antimony may be added in small amounts along with phosphorus to improve resistance to corrosion or stress corrosion. The amounts in which the foregoing elements are added should be restricted to the minimum required to achieve the desired objectives, as amounts in excess of such minimum amounts will unnecessarily decrease electrical conductivity.

The preceding discussion has assumed that the compounds formed are based on cerium, however, it will be appreciated that because of the great chemical similarity between the lanthanides, analogous compounds will be formed based on the other lanthanides and these analogous compounds will have very similar characteristics.

The alloys of the present invention are generally prepared by conventional techniques. Because of the reactive nature of the additives comprising the present alloys, it is particularly desirable to add both mischmetal and zirconium in a continuous form immediately before the molten metal enters the mold. This form of addition is particularly practical in a continuous casting operation. Reference is made to U.S. Patent No. 3,738,827 which deals with this subject and which is assigned to the assignee of the present invention. Because of its reactivity, magnesium may be added in a similar fashion, however, this is not absolutely necessary. Likewise, the phsophorus and other alloying elements may be added in bulk form to the molten metal, or in the continuous fashion discussed above.

Subsequently, casting of the alloys of the present invention may be performed using conventional techniques and, in general, the methods used may be similar to those used for other high copper alloys.

The alloys of the present invention may be processed to final form using conventional processing techniques. The alloy should be hot rolled at a temperature in excess of 500"C, for example 500 to 900"C, to a desired intermediate gauge. After hot rolling is completed, the alloy may be subjected to an optional solution annealing treatment conducted at a temperature ranging from 500 to 10000C for a period of from 15 minutes to six hours, after which the alloy is rapidly cooled. If a solution anneal is not required, the alloy may alternatively be given a recrystallization anneal at a temperature of from 500 to 900"C, for a period of from one minute to one hour. As noted, both annealing treatments are strictly optional and not required.

The alloy should then be cold worked at a temperature of less than 200"C to obtain a reduction in excess of 10%, preferably in excess of 50%. The alloy may then be heat treated at a temperature from 250 to 600"C for a time of between 15 minutes and 24 hours. A particularly desirable combination of properties may be obtained by successively repeating the cold working and heat treating steps a plurality of times. If maximum strength is desired, the penultimate or final step should be cold working in excess of 10% and preferably in excess of 50%. A final stress relief annealing step conducted for from 15 minutes to 24 hours at a temperature of from 150 C to 350 C may be incorporated, if desired, to improve ductility without much loss in strength.

The present invention will be more readily understandable from a consideration of the following illustrative example.

EXAMPLE.

Alloys of varying compositions were produced by melting cooper and making additions of the desired elements under either a vacuum or an argon atmosphere.

The compositions of these alloys are listed in Tables II and III, below.

TABLE II PROPERTIES OF ALLOYS POSSESSING ONE PRECIPITATE Cold Work Nominal Solution Aging Before Electrical 0.2% Offset Elong. in Alloy Composition, Temp.* Temp.* Aging, Conductivity, YS, 2 Inches, Code wt. % C C % % IACS ksi % 62 0.10Mg-0.06P 900 400 75 87 67 3 65 0.17Mg-0.12P 900 400 75 82 77 2 80 0.24Mg-0.2P 900 400 75 74 88 < 1 80 0.24Mg-0.2P 900 500 75 87 71 3 69 0.27Mg-0.2P 1000 500 0 80 62 1 69 0.27Mg-0.2P 1000 500 75 78 75 2 60 0.5Cr 900 500 75 92 64 4 76 0.5Cr 1000 500 0 86 72 3 76 0.5Cr 1000 500 75 88 73 3 58 0.15Zr 900 400 75 84 74 2 *All alloys unless otherwise noted were solutionized and aged for 2 hours.

TABLE III PROPERTIES OF ALLOYS POSSESSING MORE THAN ONE PRECIPITATE Cold Work Solution Aging Before Electrical 0.2% Offset Elong. in Alloy Nominal Composition, Temp.* Temp.* Aging, Conductivity, YS, 2 Inches, Code wt % C C % % IACS ksi % 61 0.04Mg-0.06P-0.24mm+ 900 400 75 88 67 3 63 &num;61 + 0.5Cr 900 500 0 86 69 3 63 &num;61 + 0.5Cr 900 500 75 83 75 3 64 &num;62 + 0.5Cr 900 500 0 87 76 2 64 &num;62 + 0.5Cr 900 500 75 86 70 3 72 &num;69 + 0.5Cr 1000 500 0 65 75 < 1 72 &num;69 + 0.5Cr 1000 400** 75 70 82 3 73 &num;69 + 0.12Zr 1000 400 75 70 86 2 73 &num;69 + 0.12Zr 1000 600 0 75 65 1 73 &num;69 + 0.12Zr 1000 400** 75 80 75 2 81 &num;80 + 0.1mm 900 400 75 76 82 3 81 &num;80 +0.1mm 900 500 75 89 71 3 82 &num;81 + 0.5Cr 900 400 75 78 85 3 82 &num;81 + 0.5 Cr 900 500 75 82 74 3 83 &num;81 + 0.1Zr 900 400 75 68 92 2 83 &num;81 + 0.1 Zr 900 500 75 82 73 3 84 &num;81 + 0.5Cr + 0.1Zr 900 400 75 68 81 2 84 &num;81 + 0.5Cr + 0.1Zr 900 500 75 77 74 3 *All alloys unless otherwise noted were solutionized and aged for 2 hours.

**24 hours aging treatment.

+Mischmetal.

After casting, the above alloys were homogenized at temperatures ranging from 825"C to 950"C for two hours, and then hot rolled at temperatures of from 825"C to 900"C. Following hot rolling, the alloys were solutionized at temperatures of from 900"C to 10000C for two hours. The alloys were in most instances subsequently cold worked about 75%, after which they were subjected to an aging treatment at a temperature ranging from 400--6000C, for from two to 24 hours. All alloys were cold worked 75% after aging, after which they were tested for tensile properties and conductivity. The results of the tests are presented in Tables II and III, above.

Referring to Table II, the properties of alloy systems involving only one precipitate are shown. Alloy Code Nos. 62, 65, 80 and 69 illustrate the precipitation of the compound Mg,P, while Nos. 60, 76 and 58 illustrate the precipitations of chromium and zirconium with copper. Table II in total is presented for comparative purposes with the multiple precipitates presented in Table III.

Table III illustrates the changes in precipitation behaviour brought about by combining several alloy elements each of which individually, undergoes a precipitation reaction. It should be noted that the addition of elements such as Cr or Zr to a system already capable of precipitating Mg3P2 and (Ce, La)P does not just result in the additional precipitation of Cr or the Cu-Zr compound. In addition, phosphides of Cr or Zr would also be expected. When both Cr and Zr are added, additional intermediate phases are possible. The resultant properties are, thus, due to more than a simple superimposition of the individual ageing phenomena, since other reactions not possible in the individual systems come into play. Thus, alloys &num;62, &num;65, &num;69 and &num;80 which contain only Mg and P have good combinations of strength and conductivity, they are difficult to produce, since slight deviation from exact stoichiometry greatly reduces conductivity.

Many of the alloys shown exhibit attractive combinations of strength and conductivity. For example, alloy &num;82 had a 78% conductivity and a yield strength of 85 ksi with one heat treatment and 82% conductivity combined with a 74 ksi yield strength using another heat treatment. Alloy &num;63 which represents alloy &num;61 plus Cr exhibited even better combinations of properties. Alloy &num;83 containing Zr, Mg, P and mischmetal also had attractive properties.

The above examples of the invention are meant to be illustrative only. The essence of the invention in its most preferred form is the simultaneous precipitation of the compound Mg3P2 and one or more other precipitates. For example, a compound of the lanthanide elements comprised in mischmetal and phosphorus, chromium, a compound of copper and zirconium, phosphides of chromium and zirconium or intermediate phases comprising primarily Cr and Zr are all examples of the types of other prcipitates which may occur in alloys according to this invention.

From the above data, it can be seen that the alloys of this invention are capable of a wide variety of formulations and processing to prepare materials possessing properties suitable for diverse applications.

The alloys of the present invention are suitable for high temperature applications such as welding or brazing, as well as electrical applications such as receptacles, connectors and the like.

Throughout the specification, all percentages are expressed as percentages by weight.

Claims (12)

WHAT WE CLAIM IS:

1. A copper base alloy possessing high strength and high conductivity characterized by the presence of from 0.01 to 0.5% of an element selected from the lanthanide series of the Periodic Table or of mixtures of such elements, from 0.01 to 1.75% of phosphorus, from 0.007 to 3.3% of magnesium, and the presence of from 0.01% up to its maximum solubility in copper of an element which forms a precipitate with phosphorus, the percentage of the said element being sufficient to precipitate substantially all the phosphorus present so that the residual phosphorus does not exceed 0.025% of said alloy, the balance apart from impurities being copper.

2. An alloy according to Claim 1 in which the element forming said precipitate is selected from the group consisting of chromium, zirconium, titanium, vanadium, niobium, iron, manganese, cobalt, and mixtures thereof.

3. An alloy according to Claim 2 characterized in that chromium if used is employed in an amount ranging from 0.01 to 0.65%, zirconium if used is employed in an amount from 0.01 to 0.15%, titanium if used is employed in an amount from 0.01 to 4.7%, vanadium if used is employed in an amount from 0.01 to 0.64%, niobium if used is employed in an amount from 0.011.5%, iron if used is employed in an amount from 0.012.8%, cobalt if used is employed in an amount from 0.013.5%, and manganese if used is employed in an amount from 0.015.0%.

4. An alloy according to any one of Claims 1--3 characterized in that said element selected from said lanthanide series is provided by including mischmetal in the alloy.

5. An alloy according to any one of Claims 1--3 characterized in that said element selected from said lanthanide series comprises cerium.

6. An alloy according to any one of Claims 1--5 which includes up to 1% in total of an additive or additives selected from the group consisting of aluminum, boron, lead, selenium, tellurium, arsenic, antimony and mixtures thereof.

7. A copper base alloy according to Claim 1 in which the lanthanide series element is present in an amount 0.012 to 0.50%, the phosphorus is present in an amount from .011 to 0.5% and the magnesium is present in an amount of from 0.007 to 0.40%.

8. The alloy according to Claim 7 characterized in that the lanthanide series element is present in an amount ranging from 0.018 to 0.4%, the phosphorus is present in an amount ranging from 0.017 to 0.4% and the magnesium is present in an amount ranging from 0.01 to 0.32%.

9. A method for the preparation of a high strength, high conductivity copper base alloy characterized by the steps of: (A) providing a copper base alloy containing 0.01 to 0.5% of an element selected from the lanthanide series of the Periodic Table or of mixtures of such elements, 0.01 to 1.75% of phosphorus, 0.01% up to the maximum solubility thereof in copper of an element which forms a precipitate with phosphorus, and 0.007 to 3.3% of magnesium, balance apart from impurities copper, (B) hot working said alloy at a temperature in excess of 500"C, (C) cold working said alloy at a temperature of less than 2000C to a reduction of at least 10%, and (D) aging said cold worked alloy at a temperature of from 250--600"C for from 15 minutes to 24 hours.

10. The method according to Claim 9 wherein said element forming said precipitate is selected from the group consisting of chromium, zirconium, titanium, vanadium, niobium, iron, manganese, cobalt, and mixtures thereof.

11. The method according to Claim 10 characterized in that chromium if used is employed in an amount ranging from 0.01 to 0.65%, zirconium if used is employed in an amount ranging from 0.01 to 0.15%, titanium if used is employed in an amount from 0.01 to 4.7%, vanadium if used is employed in an amount from 0.01 to 0.64%, niobium if used is employed in an amount from 0.01 to 1.5%, iron if used is employed in an amount from 0.01 to 2.8%, manganese if used is employed in an amount from 0.01 to 5.0%, and cobalt if used is employed in an amount from 0.01 to 3.5%.

12. The method of Claim 9, 10 or 11 in which the element selected from said lanthanide series comprises cerium.