US3816187A - Processing copper base alloys - Google Patents

Abstract

A process for obtaining improved strength properties and improved stress corrosion resistance in copper base alloys including the steps of hot rolling, annealing, cold rolling, and stress relief annealing.

Description

O United States Patent 1191 1111 3,816,187 Smith et al. June 11, 1974 [54] PROCESSING COPPER BASE ALLOYS 2.101.087 12/1937 Munson 1. 75/1575 2.3 .208 2 9 4 t .5 1 1 Rkhard Dale 81111115111111 1.122.095 851921 fic'h'il fl... 1 121157.? Rd-1Madisomconn- O6443;Irwi" 7.663.311 5/1972 Chin etal. 148/115 R Broverman, 7337/8 S. Shore Dr., A t. 1017, Ch' .111. 60649 p FOREIGN PATENTS OR APPLICATIONS [22] Fledi July 1972 578.873 7/1946 Great Britain 75/1575 [21] Appl. No.: 274,807

7 Related Application Data Primary Examiner-W. W. Stallard [60] Division of Ser. No. 115,839, Feb. l6 1971. Anomey, Agent, or Fi,m RObert Bachman abandoned which is a continuation of Ser. No. 800,354, Feb l() 1969, abandoned, which is a continuation of Ser. No. 530,942, March 1, 1966,

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a 57 ABSTRACT 52 us. c1 l48/ll.5 R

[51] Int. Cl. C22f l/08 A process for obtaining improved strength properties [58] Field of Search l48/1l.5 R, 12.7 and improved stress corrosion resistance in copper base alloys including the steps of hot rolling, anneal- [56] References Cited ing, c0ld rolling, and stress relief annealing.

UNITED STATES PATENTS 8/1935 Price 75/1575 3 Claims, 2 Drawing Figures PATENTEnJun 1 1 m4 CROSS REFERENCE TO RELATED APPLICATIONS This application is a division of application Ser. No. 115,839, filed Feb. 16, 1971, by Richard Dale Smith and lrwin Broverrnan for Copper Base Alloys, now abandoned, which in turn is a Continuation of application Ser. No. 800,354, filed Feb. 10, 1969, by Richard Dale Smith and lrwin Broverman for Copper Base Alloys," now abandoned, which in turn is a Continuation ofapplication Ser. No. 530,942, filed Mar. 1, 1966, by Richard Dale Smith and lrwin Broverman for Copper Base Alloys, now abandoned.

The present application relates to new and improved copper base alloys. More particularly, the present invention resides in greatly improved copper base alloys containing zinc, aluminum and nickel, said alloys having greatly improved physical properties and being suitable for a wide range of applications, including castings, forgings, extrusions, and hot or cold rolled or drawn products. The improved alloys of the present invention are particularly suitable for use in wrought products.

Over the years, numerous attempts have been made to improve the strength characteristics of ductile brass withoutsacrifice of formability. These attempts have concentrated on utilizing a great variety of alloying additions in order to achieve this goal. Some of these alloying additions are quite expensive and add considerably to the-cost of the alloy.

in addition, the art has thoroughly explored manyunusual thermo-mechanical processesin order to improve the strength characteristics without sacrificing formability.

The high strength brasses which have been developed in the art generally are multiphase alloys having limited ductility and cold formability. Such alloys are most suitable for application as castings or hot worked products.

Despite these extensive investigations, 70/30 brass has prevailed over the years as the best and most economical copper base alloy for severe forming applications.

Accordingly, it is a principal object of the present invention to provide an improved copper base alloy.

It is an additional object of the present invention to provide a copper base alloy having improved strength levels in either the fully annealed or cold workedtempers.

It is an additional object of the present invention to provide improved copper base alloys as aforesaid which achieve improved strength characteristics with minimal sacrifice in formability.

It is an additional object of the present invention to provide an improved copper base alloy as aforesaid, said alloy being characterized by relatively low cost so that it is economically suitable on a large scale.

Further objects and advantages of the present invention will appear hereinafter.

In accordance with the present invention, it has now been found that-the foregoing objects may be readily and conveniently achieved. The improved alloy of the present invention consists essentially of the following ingredients in the following ranges, wherein all percentages are weight percentages: copper from'66 to 80.0

percent, zinc from 15.0 to 32.5 percent, aluminum from 1.5 to 5.0 percent, and nickel from 0.2 to 5 percent.

It has been found that the foregoing alloy achieves greatly improved physical properties with minimal sac range of 50,000 to 75,000 psi.

In addition, and importantly the alloys of the present invention are characterized by a high formability. Using the highly formable /30 brass as a standard, the alloys of the present invention have comparable formability. This is particularly surprising in view of the high strength of the alloys of the present invention.

These surprising characteristics .in an inexpensive alloy are particularly unexpected in view of the extensive art in this field attempting to approximate these characteristics.

The alloys of the present invention are known as modified aluminum-brasses and basically have either of the following structures: (1) an alpha (face-centered cubic) structure; or (2) an alpha plus a limited amount of beta (body-centered cubic) structure.

The addition of aluminum to copper-zinc alloys has long been known for its strengthening effect on such alloys. The disadvantage of the aluminum addition is that in saturated alpha phase alloys, which have highest strengths, small variation in aluminum content generally results in large variations in ductility and strength. These large variations are a result of the structure of the saturated alloy changing markedly with aluminum content. For example a change in aluminum content of one percent may cause an increasein beta phase content of up to 33 percent.

In accordance with the present invention it has been surprisingly found that the addition of nickel in the range of 0.2 to 5 percent by weight overcomes the disadvantages of the ternary copper-aluminum-zinc alloys such that properties and structure are more uniform over a practical range of aluminum content. In addition, a very marked grain refining effect occurs upon the addition of nickel, which is highly advantageous.

In accordance with the present invention the alloying ingredients must critically fall within the foregoing ranges. The copper content must fall within the range of 66 to percent by weight and preferably from 70 to 76 percent by weight. Below 66 percent by weight the strength falls off markedly and above 76 percent by weight in saturated alloys an additional phase, termed gamma-having a complex cubic crystal structure, may be encountered which limits the ductility of the alloy.

Similarly, the zinc content is within the range of 15.0 to 32.5 percent by weight and preferably from 21 to 28 percent. The aluminum content should be maintained in the range from 1.5 to 5.0 percent by weight and preferably 2.5 to 4.5 percent and the nickel content should be maintained in the range 0.2 to 5 percent and preferably 0.4 to 2.0 percent.

For maximum ductility-formability at any given copper-aluminum level, the nickel content should be betweenv 0.2 and'l.0 percent while for greater strength and lesser ductility the nickel may approach higher levels up to 5 percent. At higher nickel levels ductility is reduced to such an extent that usefulness as a wrought product isimpaired.

In general, the lower nickel content alloys are high strength, high ductility materials; whereas the higher nickel content alloys provide even higher strengths, but lower ductility.

The composition of specific alloys within the above ranges are subject to the further internal restriction that at about the 71.5 percent level of copper the aluminum content should preferably be in the range of 1.5

to 4.0 percent in order to insure high ductility-strength characteristics and at about the 74 percent level of copper the aluminum content should preferably be between 2.5 and 5.0 percent for the same reasons. Proportionate adjustments of aluminum content for the various copper contents between the specified limits should preferably be made.

Furthermore, in order to attain the preferred properties the aluminum content should preferably be related to the zinc content in accordance with the following equation:

Weight %'AI 0.30 wt% Zn 10.3 i 1.25 The subject alloys are represented in the attached I drawings which are isothermal (932F), constant nickel (0.5%) sections of the quaternary phase diagram. FIG. I shows the relative location of the alloys of the present invention on the ternary phase diagram. FIG. 2 shows the shaded section of FIG. 1. In FIGS. 1 and 2 the solid line represents the alpha phase boundary. In FIG. 2, the dotted line represents the alloys of the present invention at constant 0.5 percent nickel. Similar diagrams may be readily constructed for other nickel levels.

The structure of the alloys of the present invention in the cold worked and annealed condition is either l) a matrix of fine grained, face-centered cubic, alpha phase (saturated or very nearly so), or. (2) saturated alpha plus beta phase, with both structure l) and structure (2) having very fine intermetallic compound and/or precipitate particles dispersed throughout.

The alloys of the present invention may include in addition to the foregoing materials conventional impurities typically found in commercial copper base alloys. In addition, various other alloying ingredients may be added to achieve particularly desirable results. Common impurities may include: lead; tin; phosphorus; iron; manganese; and silicon. Forminimizing dezincification in corrosive environments, the addition of arsenic, antimony or phosphorus may be desirable in an.

amount from 0.02 to 0.10 percent.

In general, the alloys of the present invention have an alpha plus particulate phase or an alpha plus beta plus particulate phase structure and are utilizable in a wide variety of applications. In view of their high strength and high formability, they are preferably provided in the wrought form. The oxidation resistance and castability of the alloys of the present invention are excellent suggesting wide spread application as high strength, low cost foundry alloys while their excellent hot forming properties also make them desirable for forgings as well as extrusions. In general, better combinations of mechanical properties at low costs are obtainable with the alloys of the present invention than are available in any currently produced. copper base alloys regardless of price.

Processing of the subject alloys requires no unusual treatment. As an example, the processing to sheet is as follows. Melting and casting are performed under similar conditions as brass alloys. Direct chill (DC) casting is particularly suitable. Hot rolling is easily accomplished using normal brass mill procedures. Under rapid coolingconditions a non-equilibrium structure may be obtained which reduces initial cold rollability. This may be overcome by an anneal in the range of lO0O to l200F wherein practically equilibrium proportions of alpha and beta phases are attained.

It has been observed in the processing of the subject alloys that they exhibit an unusually high response to low temperature stress relief annealing following cold working. Normally, copper base alloys which have been heavily cold worked may respond with an increase in yield strength of up to 15v percent when annealed at temperatures below the recrystallization temperature. This increase also normally is of practical consequence only within a relatively narrow range of annealing temperatures (50 to' F). In the alloys of this invention, increases in yield strength of 30 to 40 percent have been noted upon low temperature annealing of material cold rolled 50 percent. Further, this response occurs over a wider range of temperature 1 50 to 200F span), thereby increasing its commercial applicability. The magnitude of improvement in strength properties will be illustrated in the examples which form a part of the present specification.

A further outstanding characteristic of the subject alloys is a very marked improvement in stress corrosion resistance. The copper-zinc brasses are highly susceptible to stress corrosion'cracking when exposed to certain corrosive environments; This susceptibility is proportional to zinc content and hence alloys containing more than 15% zinc are rarely chosen for stressed applications in corrosive environments. It has been found that the nickel modified aluminum brasses have greatly improved resistance to stress corrosion cracking when compared with the binary copper-zinc alloys. This behavior will be apparent'from the ensuing examples. Coupled with this stress corrosion resistance is a high level of resistance to general corrosion.

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

EXAMPLE I Alloys having the compositions listed below were prepared from cathode copper, slab zinc, nickel metal, and aluminum metal pellets. Preparation followed the ensuing sequence. Cathode copper chunks and nickel chunks were melted under charcoal, the desired aluminum content was added and stirred in, zinc chunks Table [11 Alloy Limiting Draw Ratio Olsen Bulge Height 11 2.240 0.380" 1V 2.225 0.370" V 2.225 0.391" V1 2.260 0.420"

EXAMPLE IV Resistance to stress corrosion cracking is of importance in many applications. The improved alloys of the present invention have demonstrated a marked superiority over common brasses in-this respect. In an accel- Table I Alloy Composition Cold Rolled 50% An Hit H wt Yield Yield Percent Yield Yield Percent Strength Strength Elongation Strength Strength Elongation psi psi psi psi 1 75.9Cu 19.4Zn 4.0Al 0.7Ni 95,500 124,000 1.7 49,500 79,000 38 ll 74.2Cu 21.8Zn 3.5Al 0.5Ni 86,000 125,000 2.0 49,000 78,000 36.5 111 71.3Cu 21.7Zn 4.0Al 3.0Ni 91,000 128,000 2.0 62,000 89,000 26 1V 72.0Cu 25.0Zn 2.5Al 0.5Ni 91,000 122,000 3.0 53,000 83,000 34 V 76Cu Zn 4A1 89,000 1 14,000 2.0 27,000 65,000 57 *41,000 72,000 39 V1 70Cu Zn 74,500 90,000 Y 3.5 *2l,800 53,000

' Annealed at 800F EXAMPLE 11 Alloy V from Example [was given the following erated test in a solution containing (Nl-1 (SO.,), Cu(- S0 and NH OH, highly stressed strip samples retreatment after the final cold roll: 1 hour anneal at 30 375F. The properties were as follows:

Table IV Alloy Time to Failure in Atmosphere Time to Failure in Accelerated Test or Amount of relaxation in 500 Hrs.

(70/ 30 brass) 85/15 brass 14% relaxation 500 hrs. 43% relaxation 500 hrs. complete failure 4 hrs.

No failures at 4 mos. no failures at 10 mos. 8 to 15 weeks complete failure 48-72 hrs. no failures at 12 mos.

Table 11 Cold Rolled 5071 Cold Rolled 50% 1 hour at 375F Yield Strength 91,000 psi 114,500 psi Tensile Strength 128,000 psi 132,000 psi Elongation 2.0% 1.2%

EXAMPLE 111 Several of the alloys prepared in Example I were evaluated for formability using two common measurements, i.e., limiting draw ratio determination for evaluating deep drawability, and Olsen cup testing to check This invention may be embodied in other forms or carried out in other ways without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered as in all respects illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and all changes which some within the meaning and range of equivalency are intended to be embraced therein.

What is claimed is:

l. A process for obtaining improved strength properties and improved stress corrosion resistance in copper base alloys consisting essentially of copper from 66 to 76 percent by weight, zinc from 15.0 to 32.5 percent by weight, aluminum from 2.5 to 4.5 percent by weight and nickel from 0.2 to 5.0 percent by weight, consisting essentially of the steps of:

B. annealing said alloy at a temperature of from 'l000 to 1200F;

group consisting of arsenic, phosphorus and antimony in an amount from 0.02 to 0.10 percent by weight.

'3. A process according to claim 1 wherein said material is stress relief annealed at a temperature of 375F for one hour.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 7 Dated June 11, 197 1 Inventor(5) Richard Dale Smith and Irwin Broverman It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:-

In the heading, aft er "Richard Dale Smith, 51 Twin Cones Rd. Madison, Conn. 06 4 13; Irwin Broverman, 7337/B 1017, Chicago, Ill. 606 19" insert 8'. Shore Dr. vApIz. ---assignors to Olin Mathieson Chemical Corporation, a

corporation of Virginia---.

Signed and sealed this 29th day of October 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Commissioner of Patents Attesting Officer USCOMM-DC 60376-P69 n uis. GOVERNMENT PRINTING OFFICE I959 0366-33l F ORM PC3-1050 (1069)

Claims (2)

1. 2. A process according to claim 1 wherein said copper base alloy contains a material selected from thE group consisting of arsenic, phosphorus and antimony in an amount from 0.02 to 0.10 percent by weight.
2. 3. A process according to claim 1 wherein said material is stress relief annealed at a temperature of 375*F for one hour.

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