US 3778318 A
Description (OCR text may contain errors)
Dec. 11, 1973 w.1 FLNLAY m1 3,778,318
COPPER BASE COMPOSITION Original Filed Feb. 24, 1969 FIG. I
United States Patent 3,778,318 COPPER BASE COMPOSITION Walter L. Finlay, New York, N.Y., and Henry J. Fisher, Wellesley Hills, and Donald A. Hay, Medfield, Mass., assignors to Cooper Range Company, New York, NY. Original application Feb. 24, 1969, Ser. No. 802,330, now Patent No. 3,677,745. Divided and this application June 7, 1972, Ser. No. 260,379
Int. Cl. C22c 9/00; C22f 1/08 US. Cl. 14812.7 11 Claims ABSTRACT OF THE DISCLOSURE A copper-magnesium-phosphorous alloy (optionally containing silver and/or cadmium) wherein the magnesium is present in amounts from 0.01 to 5.0 weight percent, the phosphorous from .002 to 4.25 weight percent with copper making up the remainder. When silver or cadmium are employed, they are employed in amounts of from 0.02 to 0.2 weight percent and from 0.01 to 2.0 weight percent, respectively. These alloys have unexpectedly good combinations of mechanical heat resistance and conductivity properties.
BACKGROUND OF THE INVENTION This is a division, of application Ser. No. 802,330, filed Feb. 24, 1969 now US. Pat. No. 3,677,745.
The present invention relates to copper-base alloys and more particularly to the copper-magnesium family of alloys.
As is Well known, various copper base alloys have been developed in an attempt to satisfy the need for high thermal and electrical conductivity alloys having good mechanical properties and/or characteristics over a rather wide range of temperatures. Exemplary of the copper based alloys developed to satisfy this need are the copper- Zirconium family of alloys, disclosed in US. Pat. Nos. 2,842,438; 2,847,303; 3,019,102; 3,107,998 and 3,194,655. Each of these alloys was developedfor a specific purpose and, in general, each of them has performed satisfactorily when used for its intended purpose. However, each of them, like most other materials, has certain shortcomings and these shortcomings militate against their use for some high volume, commercial applications where cost is an important consideration, e.g., automotive radiators. For example, with the exception of the alloys disclosed in US. Pat. No. 2,847,303, each of the other alloys is advantageously prepared from the copper which is substantially devoid of oxygen, e.g., oxygen free copper or copper prepared in an inert atmosphere or a vacuum. Alloys prepared from such high purity coppers are relatively expensive which seriously inhibits their use for many applications, particularly in high volume industries such as the automotive industry or electrical conductor industry where cost per unit is very important.
The alloys disclosed in US. Pat. No. 2,847,303 are similarly disadvantageous. For example, the copper-zirconium alloys containing phosphorous described therein do not consistently exhibit good conductivity characteristics when produced in accordance with the usual commercial methods since the amount of phosphorous added to the melt must be stoichiometrically related to the amount of oxygen present in order to prevent an excess of phosphorous in the alloy. If too much is used, the strength of the alloy may be reduced. If too little is used, complete deoxidation is not achieved. Consequently, industry, when melting phosphorous containing copper-zirconium alloys, has been faced with the difficult problem of carefully controlling the oxygen content of the charge. These controls are clearly objectionable from a practical or economic standpoint.
Patented Dec. 11, 1973 p CC Of course, it has been possible to produce high strength copper alloys without using high purity starting materials or without purging the oxygen from impure starting ma the conductivity of the alloy may be decreased significantly. For example, one of the largest uses for high strength copper is in the fabrication of automobile radiators and electrical components. The thin fins of the radiators are easily deformed during assembly of the radiator and of the automobile. The automobile companies, therefore, are requiring high strength alloys for use in radiator construction. Strength, however, is not the only criterion; copper alloys for use in automobile radiators must possess high thermal conductivity, i.e., preferably above 95% IACS and at least above IACS (a direct correlation exists between electrical and thermal conductivity). An inexpensive alloy having good mechanical properties at room and elevated temperatures and after exposure to elevated temperatures together with good conductivity is, therefore, greatly needed.
Although attempts have been made to provide such an alloy, none, as far as we are aware, has been entirely successful when carried into practice commercially on an industrial scale. Furthermore, it is very important in the automotive industry as well as in the aerospace industries, Where metals are usually joined by welding, brazing or soldering, that as noted previously the alloy be capable of withstanding high temperature without softening appreciably.
It has now been discovered that inexpensive coppermagnesium-phosphorous alloys having excellent mechanical properties in combination with unexpected but desirable high conductivities, typically between 90 and 94% IACS in the cold-rolled condition and from about 95 to approximately 98 or even 99% in the properly thermomechanically treated condition may now be economically produced. It is an object of the present invention to provide such alloys.
The high strength and conductivity properties of the alloys of the present invention make them, in addition to radiator -fins, particularly useful for the production of electrical components such as bus bars or resistance welding electrodes such as welding tips or welding wheels, and the like.
The alloys of the present invention provide inexpensive copper-magnesium-phosphorous alloys having good mechanical properties and/or characteristics and heat resistance together with good conductivities over a wide range of temperatures. The alloys of the present invention advantageously also contain silver and/or cadmium and such alloys are considered to be part of this invention and the expression copper magnesium phosphorous alloy when used generically is meant to include alloys containing silver and/or cadmium.
These new copper-magnesium-phosphorous alloys comprised of a unique combination of ingredients, in special proportions, when properly thermo-mechanically processed, are characterized by being resistant to softening after being exposed for normal soldering cycles to temperatures in the range offrom 700 to 800 F. The alloys of the present invention are especially useful in fabricating heat-transfer apparatus where the components must retain their strength and conductivity after being subjected to an elevated temperature joining operation.
The high conductivity properties of the alloys of the present invention are not only unexpected, they are contrary to the teachings of the prior art. Technical Survey- OFHC Brand Copper, American Metal Co., Ltd. (1957),
page 90, teaches that the addition of phosphorous or magnesium to copper increases the electrical resistivity, which results in decreased electrical conductivity of the alloy. The present invention, however, is directed to a copper alloy containing phosphorous and magnesium and exhibiting high conductivity properties.
. These properties are obtained, it has been discovered, by controlling the amount of phosphorous relative to that of the magnesium present in the alloy; an alloy is produced which exhibits an electrical conductivity between 90 and 97% IACS. The optimum conductivity is achieved when the phosphorous is present in an amount equivalent to about 85% by weight with respect to the magnesium, i.e., a phosphorous-magnesium ratio of about 0.85 to 1. Moreover, the strengthening effect of the magnesium on the tensile strength of the alloy is not materially diminished by the addition of phosphorous in an amount equivalent to about 85% of the magnesium. While cold working has a tendency to lower the electrical conductivity somewhat, as it does with copper alloys in general, the advantages obtained by controlling the ratio between the amounts of phosphorous and magnesium in the alloy as indicated above are also present in the coldworked condition.
The unexpected properties exhibited by the present invention are believed to result from the formation of intermetallic compounds within the copper matrix.
It is believed that the phosphorous and magnesium combine to form an intermetallic compound approximating the formula Mg P or a complex mixture of compounds formed between copper, magnesium and phosphorous, such as Cu Mg and Cu P. The existence of a chemical interaction between the magnesium and the phosphorous is indicated by the fact that when phosphorous is added in an amount equal or close to the stoichiometric ratio of about 0.85 to 1, which exits between the relative weights of the phosphorous and the magnesium in the compound Mg P then the electrical conductivity reaches a peak value with the more simple thermo-mechanical treatments such as those outlined in the subsequent Example 1. When the relative weight ratio of phosphorous to magnesium is materially less than or materially greater than 0.85 to l, the electrical conductivity is also less than the 95-99% IACS peak value attainable using the aforementioned simple thermomechanical treatment. It is postulated that this decrease in conductivity is caused by the free phosphorous or magnesium which is in excess of the amount utilized in the formation of the intermetallic compound(s) and the free magnesium or phosphorous behaves as if it were alone in the copper and reduces the electrical conductivity accordingly. As discussed earlier, we have discovered that Cu-Mg-P alloys which also contain silver as an alloying element seem capable of producing a desirable combination of high conductivity and high tensile strength over a wider range of phosphorous-to-magnesium ratios than in the absence of the silver.
The premise that the magnesium is reacting with the phosphorous is further supported by the fact that the presence of only phosphorous in the amount of 0.85% in pure copper increases the electrical resistivity of copper to a value of 2.90 microhm-cm. This resistivity is equivalent to only 59.5% IACS in electrical conductivity. (The resistivity of the International Annealed Copper Standard at C. being 1.7241 microhm-cm.).
It has been found that in order to achieve electrical conductivity values of from 90% IACS to 99% IACS and to develop high mechanical strength at the same time, it is desirable to control the temperature and the time of the final annealing treatment. A good balance of properties is obtained by finally annealing the alloy at between about 700 to 1000 F. for from about one to about three hours. The alloy is then taken to its final dimensions by cold-working, e.g., cold-rolling, wire-drawing,
swaging, cold-heading, etc. The increased properties are believed to be due to a combination of strengthening mechanisms including the coherency and the dispersion strengthening caused by the fine dispersion of intermetallic compound or compounds resulting from agehardening (or precipitation-hardening), and cold work strengthening.
Thus it appears that, when silver is added to this alloy system, the precipitation mechanism is rendered more controllable, particularly as the strength and conductivity properties are affected by modifications in the thermomechanical processing. For example, with silver, the better combinations of strength and electrical conductivity can be attained over a somewhat wider range of alloy composition than in the absence of silver. Thus, alloys containing silver, e.g., .02 to .09% by weight can achieve high conductivity and mechanical strengths with the phosphorous-to-magnesium-ratio ranging from 0.3 to as high as 1.4.
In order to achieve these good results, it is necessary to vary the thermo-mechanical processing in some cases and this is usually more diflicult in the absence of silver. We have found that many thermo-mechanical processing variations can be used to give this alloy system a wide range of electrical conductivity and mechanical strength combinations and this versatility is one of the outstanding attributes of this Cu-Mg-P-base alloy. Techniques which are suitable include warm-rolling (pseudo-ausforming), zerolling, shock-loading, cryogenic cooling, stress aging, pseudo-maraging (quenching directly to the aging temperature from the solution-treatment temperature), multiple-aging treatments in succession at the same or various different temperatures (with or without interposing warm or cold-rolling in between the aging treatments), and 'various amounts of cold or warm-working prior to the aging treatment. The unifying feature of all these thermomechanical treatments is believed to be the etfect they have in establishing the size, shape, interparticle spacing, distribution, degree of coherency and other controlling characteristics of the precipitate particles. A majority of these precipitate particles (say in excess of 50%) are characterized by diameter less than 1 micron in extent.
To demonstrate the large effects that prior thermomechanical processing, such as the amount of cold-work, has on final electrical conductivity two different amounts of cold work, 69%, and 91%, were introduced into previously hot-rolled material, prior to receiving the precipitation-aging treatment. The results shown below indicate how higher electrical conductivity can be attained by increasing the amount of cold-work prior to the precipitation treatment for an alloy containing copper, .041% silver, .09% magnesium 'and .09% phosphorous:
Electrical conductivity after 3 hrs. at 800 F. preeipitation-aging Percent, treatment, percent IACS Gauge cold reduction .160" 69% (.500" to .160)--- .027" 91% (.300" to .027")-.- 99
GENERAL DESCRIPTION OF THE DRAWINGS GENERAL DESCRIPTION OF THE INVENTION The present invention contemplates the production of unique low cost copper-magnesium-phosphorous alloys.
Each of the alloys of this invention, after being subjected to appropriate thermo-mechanical processing has good electrical and thermal conductivity together with high mechanical strength, e.g., an ultimate tensile strength (UTS) in excess of 60,000 pounds per square inch (p.s.i.) despite elevation to temperatures of 700 F. or higher for about 3 minutes. Alloys within the contemplated scope of the present invention having the foregoing desirable properties and/or characteristics contain, in weight percentages, .002 to 4.25 phosphorous, 0.01 to 5.0 percent magnesium with the balance, apart from the usual impurities and residual elements, copper. In order to obtain optimum properties, the phosphorous and magnesium are employed in amounts sufficient to establish a ratio by Weight in the range of 0.3 to 1.3, preferably in the neighborhood of 0.85. The alloys of the present invention can also contain from 0.02 to 0.2 weight percent silver and from 0.01 to 2.0 weight percent cadmium.
Unlike comparable prior art alloys, the copper-base alloys of this invention can be produced from coppers containing by weight as much as 600 parts per million (p.p.m.), i.e., 0.06% of oxygen without materially and detrimentally altering the advantageous properties and/ or characteristics of these alloys. This is a very desirable economic advantage since it permits the use of the less expensive grades of copper in the manufacture of these alloys. Accordingly, tough pitch copper, which is a copper containing 0.02% to 0.05% oxygen and which is obtained by melting electrolytically obtained cathode copper or by fire refining, can be successfully used in producing the alloys of the present invention. Of course, it is to be appreciated that high purity, substantially oxygen-free coppers may also be employed in the manufacture of the alloys of the present invention if cost is not an important consideration. Thus, cathode copper is suitable starting material as is copper which has been produced in a reducing atmosphere such as OFHC brand copper (which is 99.99% or more pure), copper prepared in an inert atmosphere, under a charcoal cover or in a vacuum and chemically deoxidized coppers such as lithium-deoxidized copper. The use of phosphorous deoxidized copper (DLP-deoxidized low phosphorous and DHP-deoxidized high phosphorous) is, of course, acceptable and in some cases preferable because it may eliminate the step of adding phosphorous to the copper if sufiicient phosphorous remains in solution in the copper.
The alloys of this invention containing the aforementioned ingredients, i.e., copper, phosphorous, magnesium and optionally silver or cadmium, in the aforementioned specially proportioned amounts are characterized by being cold-workable to strengths in exces sof 60,000 p.s.i. These alloys are further characterized by having good eastability. Phosphorous is employed in an amount corresponding to from 0.002 to 4.25 weight percent of the total weight of the alloy. The phosphorous when employed in such amounts together with magnesium has a number of beneficial effects including alloying as well as deoxidizing eifects. The magnesium is employed in amounts sufiicient to constitute from 0.01 to 5.0 weight percent of the total weight of the alloy. The inclusion of magnesium has an important effect upon the unexpected tensile strength and electrical and thermal conductivity properties of the alloy. The optimum balance of mechanical and electrical and thermal conductivity properties is obtained when the phosphorous and magnesium are employed with respect to each in a weight ratio of about 0.85 to 1. When employed in proportions substantially equivalent to this ratio, the phosphorous and magnesium have a synergistic effect on the thermal and electrical conductivity and on the mechanical properties. Material deviations from this ratio may result in a decrease in the strength of the alloy, a decrease in the thermal and electrical conductivity or a decrease in both properties although in most cases this tendency can be counteracted by appropriate changes in the thermo-mechanical processing;
also, as noted elsewhere, the presence of silver minimizes this decrease. It has been found that increasing the proportion of phosphorous with respect to the magnesium has a greater deleterious effect on the properties of the alloy than increasing the proportion of magnesium with respect to the phosphorous. When the magnesium content of the alloy is from 0.01 to about 0.5 weight percent, the desired strength and conductivity properties are obtained without using special processing; however, when the amount of magnesium is in excess of 0.5 weight percent, special thermo-mechanical processing steps are recommended to obtain optimum properties. The special thermomechanical processing steps are believed to be made necessary by the relatively large amount of intermetallic compound or compounds present in the copper matrix.
Such versatility and good control of a wide range of desirable properties has long been sought and, until the present discovery, has eluded metallurgists. While the atomistic mechanisms which effect the excellent combinations of properties achieved by this discovery have not yet been completely elucidated, the following hypothetical model will be instructive to those skilled in the art and will assist them in the practice of the invention:
(A) At temperatures above about 1200-1400 F., it appears that P and Mg go into solid solution to the extent of their solid solubility in Cu at the solution annealing temperature employed.
(B) It appears further that both P and Mg tend to stay in solid solution even when the temperature is lowered so that the solid solution state becomes a nonequilibrium condition rather than to precipitate out readily as Cu Mg and Cu P, respectively. Thus, rapid cooling such as water quenching, or even air cooling, maintains a substantial part of all, of the P and Mg in solid solution. This gives low conductivity and solid solution strengthening. When this super-saturated solid solution structure is cold worked, quite high strengths are obtained e.g. the 90,000 psi. ultimate tensile strength (and 70% IACS). This cold working does not appear per se to cause precipitation of Cu-Mg and Cu-P compounds but it does condition the copper matrix to precipitate such compounds if thereafter the material is heated; additional cycles of cold working and elevated temperatures aging further promote the precipitation of such compounds.
(C) In order to secure high conductivities, eg 99% IACS, rather than the 70% IACS noted above, it is necessary to precipitate the Mg and P from solid solution. As indicated above in paragraph (B) the binary equilibrium diagrams of Cu-Mg and of Cu-P suggest that these precipitations might be Cu- Mg and Cu P. The precipitation may, however, be a complex of these or other compounds. Moreover, as is well known in the case of carbide compounds in tool steels where simple carbides precipitate first-then by interdiifusion form very complex carbides during tempering, two or more compounds may form separately and then subsequently may form the final precipitation-this is particularly true in the alloys of this invention where Ag and/or Cd may advantageously be present to modify the kinetics and/or compositions of the precipitations. The alloys of this invention thus are characterized by a relatively controlled rate of precipitation. This is very fortunate: standard, low-cost rolling and heating schedules for which existing production equipment is well adapted can be employed While maintaining the Mg, P, Ag and/or Cd in solution; then, again by standard, low-cost processing in existing production equipment, a metallurgist skilled in the art and following the teachings of this specification can select optimum combinations of strength and conductivity by starting at the high strength made possible by the solid solution plus cold work and gradually, under excellent production control, can increase the conductivity by suitable thermo-mechanical processing. The atomistic mechanism for this is controlled precipitation of compounds made possible by the critical amounts and ratios, as taught herein, of Mg, P, Ag and/or Cd in conjunction with appropriate thermo-mechanical processing. This controlled precipitation yields a most important benefit, surprisingly high in its degree of effectiveness-high resistance to softening by heat as noted in the following paragraph (D).
(D) A first factor resides in the fact that fundamentally, Cu contributes high conductivity and high coldwork-strengthenability. Mg and P, optionally with Ag and/or Cd, first contribute an important increase in the cold-work-strengthenability of Cu via solid solution but at some cost in conductivity; then, within the critical limits taught herein, the Mg, P, Ag and/or Cd can be precipitated under excellent control to give a dispersion of precipitate particles throughout the Cu matrix above the softening temperature of the Cu matrix-thus the cold- Work-strengthening is sacrificed while the conductivity is increased by precipitating the Mg, P, Ag and/or Cd out of solid solution. A second factor resides in the discovery that the matrix containing the precipitate can now be cold-worked to regain the cold-work strengthening with only a small loss of electrical conductivity. The matrix containing the precipitate work-hardens at a more rapid rate than the solution-annealed and quenched alloy, and, therefore, higher strengths may be obtained for an equivalent amount of cold work. A third factor resides in the discovery that the precipitate so formed now inhibits the atomic movements which are necessary to dissipate cold-work-strengthening i.e. the precipitate particles block recrystallization and softening. The result is that the properly processed alloy can, without serious or complete softening, be heated and used at temperatures and time considerably higher than any hitherto known material with comparable conductivity and strength.
Silver when present in the amounts hereinbefore set forth, i.e., 0.02 to 0.2%, together with proper amounts of magnesium and phosphorous (whether cadmium is present or not) as previously mentioned, has a number of beneficial effects upon the mechanical and conduction properties. In addition to greater latitude in permissible P to Mg ratios, noted earlier, silver raises the softening temperatures and increases the strength of the alloy. Secondly, silver retards recrystallization of wrought copper significantly. Thirdly, it is believed that silver inhibits grain growth. Further, the desirability of silver in the aforementioned ranges permits the use of the base-copper containing silver such as Copper Range White Pine silver-bearing coppers, when making the alloys of the present invention, and these commercially available grades of copper can be used without sacrificing such desirable properties and/or characteristics as electrical or thermal conductivity.
As pointed out hereinbefore, the alloys of this invention may contain up to 2.0% cadmium by weight. The addition of cadmium to the copper-magnesium-phosphorous or copper-magnesium-phosphorous-silver alloys of the invention results in the retention of strengths higher after exposure to elevated temperatures without detrimentally decreasing the conductivity and/or the mechanical properties for many important commercial applications.
In carrying the invention into practice, particularly significant results are obtained when the alloys contain approximately in weight percentages, 0.05 to 0.3% magnesium, 0.04 to 0.25% phosphorous, 0.03 to 0.09% silver and 0.02 to 0.10% cadmium, with the balance, apart from the usual impurities and residual elements, copper. Such alloys have a superior combination of physical, mechanical and/or metallurgical properties and/or characteristics in combination with being inexpensively produced.
Alloys within the broad and advantageous ranges are resistant to thermal softening after they have been subjected to cold-working operations. Advantageously, the alloys are cold-worked at least 40% to obtain greater strength and hardness. More advantageously, they are cold-worked at least 60 to As those skilled in the art will readily appreciate, the softening temperature is a function of the amount of cold work, to wit, the lower the amount of cold work, the higher the softening temperature, and conversely. In any event, the half-hardness temperature of the cadmium-free alloys of this invention lies between 725 F. to 750 F. When cadmium is present in the amounts heretofore mentioned, the half-hardness temperature for 30 minutes is between about 750 and 800 F.
The unique copper-magnesium-phosphorous and copper-magnesium-phosphorous-silver alloys of this invention are prepared in accordance with known procedures. In representative operations, the copper is melted and the alloying ingredients added thereto. The melting of the copper can be carried out in air under a protective cover or in a vacuum. Special refractories such as aluminum oxide, magnesium oxide and the like can be employed in the production of the alloy. It is advantageous, particularly when using tough pitch or other relatively high oxygen containing coppers, to add the phosphorous before or simultaneously with the silver and the magnesium or cadmium to be added after the deoxidation in order to minimize magnesium and cadmium losses. The established melt is then preferably cast in a non-oxidizing atmosphere such as N; or argon.
It is advantageous, particularly because of the small amounts used, to add, in terms of weight percent, the magnesium as a copper-10 to 20% magnesium alloy, phosphorous as 15% phosphorous-copper and cadmium as a copper-5% cadmium alloy. Silver may, on the other hand, be added in the elemental form or as a master alloy.
The alloys of the present invention can be worked using a variety of techniques. Good balance between the mechanical and conductivity properties of the alloys containing from about 0.01 to about 1 weight percent magnesium and from about 0.002 to 0.85 weight percent phosphorous (with or without silver and cadmium) is obtained when the alloys are worked as follows. Cast rolling slabs are hot-rolled at temperatures from about 1000 to 1600 F. to a metal thickness of about 0.30 to 0.50 inch. Further reduction in thickness is achieved by conventional cold-rolling and annealing procedures. In fact these alloys can be intermediately annealed in the readily available continuous annealing lines.
In those alloys where the magnesium and phosphorous are present in amounts equivalent to from about 1.0 to about 2.0 and from about 0.85 to about 1.70 weight percent, respectively, good mechanical and conductivity properties are obtained by deforming the primary cast ingot structure by hot-forging operations at temperatures between 1200" and 1400 F. Following the initial hotforging steps additional reduction is carried out by coldworking.
When employing an alloy having a magnesium and phosphorous content of from about 2.0 to 5.0 and about 1.7 to about 4.25 weight percent, respectively, a wrought product is produced by reducing the cast blank or intermediate at a temperature below about 1200 F. in order to avoid rupturing the cast blank.
It is, of course, understood that the alloys of the present invention can be sold in the as-cast state or after any degree of reduction (hot or cold). They can also for some applications be produced and processed by power metallurgical techniques. The fabricator can then age-harden and/or work-harden the material at the desired stage in his fabrication procedure.
The adaptability of these alloys for producing high electrical conductivity and hardness from an as-cast condition, or from an as-cast and solution-annealed condition, by means of a simple precipitation heat treatment is shown by the data below for an alloy containing copper with 0.041% silver, 0.16% magnesium, and 0.148%
phosphorous, which was aged at 800 F. for the times indicated:
percent IACS after exposure to a temperature of 800 F. for 3 minutes. One use for such an alloy is its employ- Aging time at 800 F.
SPECIFIC EXAMPLES The following examples are merely illustrative and are not deemed to be limiting.
Example 1 The alloys of the present invention having the composition set forth in Table I were prepared by melting ETP copper, at about 2000 F. Carbon was added to the melt to deoxidize the copper partially. Fifteen percent phosphorous-copper was then added to the melt to complete the deoxidization of the copper; however, enough phosphorous must be added to provide, after the deoxidation is complete, an amount of phosphorous equivalent to the desired phosphorous content of the alloy. Following the addition of the phosphorous copper, the magnesium was added to the melt in the form of a copper-magnesium alloy containing about percent magnesium. (The silver, if not already present, is added before or after the deoxidizing process. It is, of course, possible and convenient to use a copper which already contains silver.) The entire melting and compounding process was carried out under an atmosphere of non-oxidizive protective gas such as nitrogen or the like. The melt was poured into cakes while at a temperature of about 2150 F. Cakes of each alloy were then hot-rolled at a starting temperature of 1500 F. to 0.30 inch and allowed to cool to room temperature. The 0.300 inch strip was then scalped to 0.285 inch and thereafter cold-rolled to 0.0275 inch. This 0.0275 inch strip was then annealed at from 800 to 1000 F. The annealing or aging cycle was three hours heating, three hours at temperature and six hours cooling to room temperature. The 0.0275 inch strip was finally cold-rolled 90% to 0.003 inch. The strips thus produced were tested to determine their ultimate tensile strength. Electrical conductivity (percent IACS) was determined on strips which were cold-rolled to a thickness of 0.050 inch. The results of these tests are tabulated in Table 1.
As was pointed out hereinbefore, there is a demand for a low cost copper alloy which will retain an UTS of 50,000 to 60,000 p.s.i. and a conductivity of at least 90 ment as the structural material for heat transfer fins for automobile and other vehicle radiators as exemplified by the radiator assembly depicted in FIG. 1 of the drawings. Referring now thereto, the drawing is a perspective view, partially broken, of a typical fin and tube type radiator assembly having a plurality of large surface area fins 22 or heat transfer surfaces and coolant tubes 20 for water passage.
The reason for the strength requirements stems from the amount of handling, particularly during assembly and installation, to which the apparatus is subjected coupled with a requirement that the fins be quite thin. Being so thin, they must be strong enough to resist the multiple stresses to which they are subjected during fabrication, installation and use. In addition, the strength as well as the conductivity requirements take into effect the temperature at which the soldering operation is conducted.
FIG. 2 illustrates a pair of metal sheets 24, 26 being spot welded as at 28 by a pair of welding tips 30, 32, composed of a copper alloy of the present invention. FIG. 3 illustrates a pair of metal sheets 34, 36 being resistance Welded along a seam 38 by a pair of Welding Wheels 40, 42, composed of a copper alloy of the present invention. FIG. 4 illustrates a coiled compression spring 44, composed of copper alloy of the present invention.
Example 2 In further operations, other alloys of the present invention are prepared. These alloys are prepared from ETP copper as described in Example 1. Each alloy thus prepared is hot-rolled at 1450 F. and reduced from 1 inch to /2 inch. The /2 inch material is placed in the annealing furnace for 30 minutes at 1450 F. and then waterquenched. The water-quenched material is cold-rolled 50 percent to produce a 4 inch strip which was cold-rolled further to obtain a strip 0.024 inch thick. This strip is annealed at 750 F. in molten salt for from 10 to 30 minutes, and then colded-rolled again (87 /2%) to obtain a strip 0.003 inch thick. This strip is made into tensile samples and tested as cold-rolled after a 3-minute anneal at 710 F. (in molten salt). The composition of these alloys and their properties are listed in Table II.
TABLE I Tensile strength and electrical conductivity in as-rolled strip .003 thick after resclarglwng the following annealing conditions a Annealing Annealing temperature, 1,000 F. temperature, 800 F. for 3 hours for 3 hours Composition, weight percent UTS Percent UTS Percent Ag Mg P Cu (kips) LACS 1 (ln'ps) IACS l Alloy- A 0. 041 0. 1 008 61. 5 88 78. 1 87 B 0. 041 0. 1 024. 76. 6 90 75. 8 87 C"--. 0.041 0. 1 044 75. 7 90 77. 9 90 D 0. 041 0.1 060 76. 4 91 76. 9 E 0. 041 0. 1 085 74. 9 90 81. 9 89 F--." 0. 041 0. 1 10 76. 6 93 80. 5 92 0.050 thick strip (cold-rolled 69%). 2 Remainder.
In order to illustrate the novel and desirable effects due to the inclusion of cadmium in the alloys of the present invention, alloys X and Y were prepared in the same manner as the alloy described in Example 1. These alloys were prepared as a 0.10 inch strip which had been cold-worked 60 percent prior to being heated in a salt bath at 710 F. The strip was then tested for hardness. The results which show the retention of the asrolled hardness, which is indicative of the strength, are listed below in Table III.
TABLE III Hardness, Rockwell B Composition, percent After heating 1 As- P Cd Cu rolled Ag Mg 3 min. 90 min.
Alloy- 1 In molten salt at 710 F. 2 Remainder.
Example 4 An alloy having a composition of 0.041% silver, 0.53% magnesium, 0.32% phosphorous with the remainder being copper was cast into 1-inch thick slabs for hotrolling in accordance with the method of Example 1. The alloy was hot-rolled at 1650 F. from 1 inch to 0.480 inch with reheat after each pass, and waterquenched from 1650 F. Cold-rolling was then carried out to reduce the strip 68% from 0.48 inch to .160 inch. Very good retention of hardness is possessed by this alloy as indicated when the alloy is heated at 700 F. for
200 minutes, and shown by the data below.
TABLE IV Composition, percent Hardness, Ag Mg P Cu Rockwell B Alloy- Condition 1 Hot-rolled from 1" to 0.480" water quenched 84. 5 from 1,650 F. then cold-rolled 68% from 0.480 to 0.160 2. Aged at 700 F. for the following times-- 3 minutes... 94. 0 minutes. 95. 0 60 minutes. 92.0 100 minutes. 91.0 200 minutes 92. 0
CONCLUSION Thus the additives of the present invention do not appreciably adversely alTect two basic properties of pure copper, viz high conductivity, both electrical and thermal; and (2) high strengthenability by cold work with very little loss in conductivity, e.g. only a drop from 100% IACS to 97-98% IACS by 60-90% cold reduction, which can increase the yield strength by a factor as high as five and can more than double the ultimate tensile strength. Moreover, employing two of the lowestcost and most abundant elementsphosphorus and magnesium-within critical percentage ranges and in critical ratios, four important objectives are accomplished at will and under good control:
(1) Achieving high strength with good conductivity e.g. 90,000 psi. ultimate tensile strength (compared to a pure Cu maximum of 65,00070,000 p.s.i.) with 70% IACS;
(2) Achieving moderate strength, even after elevated temperature fabrication such as soldering for 3 minutes at 800 F. with excellent conductivity e.g. 55,000 p.s.i. ultimate tensile strength (compared to a pure Cu, or even a silver-bearing copper, maximum of 30,000-35,000 p.s.i.) with 95% IACS;
(3) Combinations of strength and conductivity intermediate between (1) and (2) above; and
(4) Higher resistance to heat softening as described above.
Since certain changes may be made in the above disclosure without departing from the scope of the drawings herein, it is intended that all matter contained in the above description and shown in the accompanying drawings be interpreted in an illustrative and not in a limiting sense.
What is claimed is:
1. A copper base alloy consisting essentially of by total weight, 0.002 to 4.25% phosphorous and 0.01 to 5.0%
magnesium with the remainder copper, the approximately stoichiometric ratio of phosphorous to magnesium ranging from 0.3 to 1.4 by weight, said alloy being characterized by a dispersion of precipitate particles which impart combinations of tensile and conductivity properties that are superior to (1) 80,000 UTS with 70% IACS and (2) 55,- 000 UTS with IACS, the strength-conductivity minima being consistent with and intermediate to the limits of (1) and (2) aforesaid, said alloy being characterized by dispersed particles, a majority of which are less than one micron in extent.
2. A copper base alloy consisting essentially of, by total weight, 0.002 to 4.25% phosphorous, 0.01 to 5.0% magnesium and 0.02 to 0.2% silver with the remainder copper, the approximately stoichiometric ratio of phosphorus to magnesium ranging from 0.3 to 1.4 by weight, said alloy being characterized by a dispersion of precipitate particles which impart combinations of tensile and conductivity properties that are superior to (1) 80,000 UTS with 70% IACS and (2) 55,000 UTS with 90% IACS, the strength-conductivity minima being consistent with and intermediate to the limits of 1) and (2) aforesaid, said alloy being characterized by dispersed particles, a majority of which are less than one micron in extent.
3. A copper base alloy consisting essentially of, by total weight, 0.002 to 4.25 phosphorous, 0.01 to 5.0% magnesium, 0.02 to 0.2% silver, and cadmium in an amount no greater than 2% with the remainder copper, the approximately stoichiometric ratio of phosphorous to magnesium ranging from 0.3 to 1.4 by weight, said alloy being characterized by a dispersion of precipitate particles which impart combinations of tensile and conductivity properties that are superior to (1) 80,000 UTS with 70% IACS and (2) 55,000 UTS with 90% IACS, the strengthconductivity minima being consistent with and intermediate to the limits of 1) and (2) aforesaid, said alloy being characterized by dispersed particles, a majority of which are less than one micron in extent.
4. A copper-base material of claim 1 consisting essentially of from 0.01 to 1.0 percent magnesium, from 0.003 to 1.0 percent phosphorous with the remainder being copper.
5. A copper-base material of claim 2 consisting essentially of from 0.01 to 1.0 percent magnesium, from 0.003 to 1.0 percent phosphorous, 0.02 to 0.2 percent silver with the remainder being copper.
6. A copper base material of claim 1 consisting essentially of from 2 to 5 percent magnesium, from 0.6 to 4.25 percent phosphorous with the remainder being copper.
7. A copper base material of claim 1 consisting essentially of from 1.0 to 2.0 percent magnesium, from 0.3 to 2.0 percent phosphorous with the remainder being copper.
8. The copper base material claimed in claim 1 having an electrical conductivity of at least 90 percent IACS.
9. A radiator fin comprised of the copper material claimed in claim 8.
10. An electrical conductor comprised of the copper material claimed in claim 8.
11. A process of thermo-mechanically working a copper material consisting essentially of from 0.002 to 4.25 percent by weight phosphorous, 0.01 to 5.0 percent by weight magnesium with the remainder being copper, the approximately stoichiometric ratio of phosphorous to magnesium ranging from 0.3 to 1.4 by weight, said material being characterized by dispersed particles, a majority of which are less than one micron in extent, said process comprising deforming the primary ingot structure by hot- 14 working and thereafter annealing the reduced material at from 700 to 1315 F. for from one to three hours followed by slow-cooling to room temperature before finally cold-working the material.
5 References Cited UNITED STATES PATENTS 2,123,628 7/1938 Hansel et al. 75-153 2,171,697 9/1939 Hansel et al. 75-153 10 2,243,276 5/1941 Hansel et al 75-153 2,268,938 1/ 1942 Hansel 75-152 FOREIGN PATENTS 577,850 6/1959 Canada 75-153 5 915,392 7/ 1954 Germany 75-153 CHARLES N. LOVELL, Primary Examiner US. Cl. X.R. 20 148-325