US3788902A - Process for improving the elongation of grain refined copper base alloys - Google Patents

Abstract

A PROCESS FOR IMPROVING THE ELONGATION OF COPPER BASE ALLOYS BY CONTROLLED GRAIN COARSENING. COPPER BASE ALLOYS CONTAINING FROM ABOUT 2 TO ABOUT 9.5% ALUMINUM, LESS THAN 1% ZINC,AND A GRAIN REFINING ELEMENT SUCH AS IRON, CHROMIUM, ZIRCONIUM, OR COBALT ARE SUBJECTED TO FINAL COLD REDUCTION OF FROM ABOUT 8% TO ABOUT 22% AND A FINAL ANNEAL OF FROM ABOUT 550 TO ABOUT 715* C. ALTERNATIVELY, THE ALLOY CAN BE SUBJECTED TO A SEQUENCE OF DECREASING REDUCTIONS INTERSPREAD WITH HIGH TEMPERATURE ANNEALS, FOLLOWED BY THE ABOVE FINAL REDUCTION AND ANNEAL.

Description

United States Patent 6 3,788,902 PROCESS FOR IMPROVING THE ELONGATION OF GRAIN REFINED COPPER BASE ALLOYS Eugene Shapiro, Hamden, Jacob Crane, Woodbridge, and George H. Eichelman, Jr., Cheshire, Conn., assignors to Olin Corporation, New Haven, Conn. No Drawing. Filed Nov. 24, 1972, Ser. No. 309,345 Int. Cl. C22f I/08 U.S. Cl. 14811.5 R

ABSTRACT OF THE DISCLOSURE A process for improving the elongation of copper base alloys by controlled grain coarsening. Copper base alloys containing from about 2 to about 9.5% aluminum, less than 1% zinc, and a grain refining element such as iron, chromium, zirconium, or cobalt are subjected to a final cold reduction of from about 8% to about 22% and a final anneal of from about 550 to about 715 C. Alternatively, the alloy can be subjected to a sequence of decreasing reductions interspersed with high temperature anneals, followed by the above final reduction and anneal.

BACKGROUND OF THE INVENTION It is common practice to add grain refiners to various solid solution, single-phase alloys for the purpose of maintaining a fine grain material during processing from the original cast material to the final wrought condition. The grain refiner may be added to improved processing and/ or to improve properties. In most cases, the grain refiner serves to maintain uniform properties over a compositional range and over a range of processing conditions. In many cases, such as for copper base alloys containing aluminum and a grain refining element such as cobalt, the grain refiners are not completely stable over the full range of temperatures :up to the melting point of the alloys because of decomposition or varying solubility.

Copper base alloys containing grain refiners maintain a fine grain size over a range of commercially suitable annealing temperatures and over a range of commercially acceptable solute concentrations. These alloys maintain a relatively small variation in mechanical properties over these temperature and composition ranges. This, of course, is a very desirable feature commercially. It does, however, cause certain restrictions in the normally available ductility of the alloy. In contrast thereto, as a solid solution, single-phase alloy without grain refiners is heat treated to higher annealing temperatures, the grain size and the ductility of the alloy increase and the strength decreases.

It is common practice to anneal at the highest temperature consistent with strength requirements to obtain material which requires unusually high ductility in forming operations such as stretch forming. The annealing temperature is further limited for fabricating parts which require a highly polished surface in that above a certain grain size, an orange peel condition occurs during fabrication which detracts from the appearance of the polished surface.

It is an undesirable feature of many grain refined cop per base alloys that any attempt to coarsen the grain size above the stable level imposed by the grain refining addition results in an uncontrolled mixed grain size consisting of very small and abnormally large grains. This irregular grain growth is caused by factors such as secondary recrystallization which are a direct result of the effect of the second phase particles on the matrix during cold working and subsequent annealing. Material subjected to irregular grain growth is not suitable for fabrication into parts re- 15 Claims Patented Jan. 29, 1974 quiring smooth surfaces for bufling and electroplating and causes nonuniformity of mechanical propertles.

SUMMARY OF INVENTION In accordance with this invention, a process has been developed which permits certain grain refined copper base alloys to achieve uniform ductility with a controlled grain size. The process comprises a final cold reduction of annealed metal of from about 8 to 22 percent, followed by a high temperature anneal or a sequence of decreasing cold reductions interspersed with relatively high temperature anneals. The process in accordance with this invention is particularly applicable to copper base alloys containing from about 2 to about 9.5 percent aluminum, less than about 1 percent zinc, and a grain refining element selected from the group consisting of iron .001% to 5.0%, chromium .001% to 1%, zirconium 001% to 1.0%, co balt 001% to 5.0%, and mixtures of these grain refining elements. Preferably, the aforenoted alloys also contain from about .001 to about 3 silicon.

The alloys processed in accordance with this invention provide markedly improved elongation with a suitably small grain size.

Therefore, it is an object of this invention to provide a process for improving the ductility of grain refined copper base alloys without subjecting them to irregular grain growth.

It is a further object of this invention to provide a proc-' DETAILED DESCRIPTION In accordance with this invention, a process has been developed which permits certain grain refined copper base alloys to achieve improved ductility with a uniformly coarsened grain size.

The process is particularly applicable to copper base alloys containing from about 2 to about 9.5% aluminum, less than 1% zinc, and a grain refining element selected from the group containing iron .001 to 5.0%, chromium .001 to 1%, zirconium .001 to 1.0%, cobalt .001 to 5.0%, and mixtures of these elements and the balance copper. Preferably, the alloy also contains from about .001 to about 3% silicon, and the aluminum range is from about 2 to about 5%. It has been found that the processing of this invention is particularly applicable to CDA Alloy 638 containing 2.5% to 3.1% aluminum, 1.5% to 2.1% silicon, 0.25% to 0.55% cobalt, and the balance copper.

It is desirable in accordance with this invention to provide the aforenoted copper base alloys in the wrought condition with improved ductility, as, for example, at least 40% elongation for CDA Alloy 638, without their being subject to irregular grain growth.

In accordance with one embodiment of this invention, an alloy within the aforenoted ranges of composition is provided in the annealed condition, the alloy having been annealed at a temperature of less than 600 C. The annealed alloy is subjected to a final cold reduction of from about 8% to about 22%, and preferably from about 10% to about 20%. The cold worked alloy is then subjected to a final anneal at a temperature of from about 550 C. to about 715 C., and preferably from about 650 C. to about 700 C.

It has been found that the elongation increases with increasing temperatures in the final annealing step. The

aforenoted process yields a wrought alloy having a substantially uniform grain size of less than 0.025 millimeters, an ultimate tensile strength of at least 70 k.s.i., a 0.2% yield strength of at least 30 k.s.i., and an elongation of at least 40%. It has been possible to achieve with CDA Alloy 638 elongations as high as about 45% with an ultimate tensile strength of about 74 k.s.i., and a 0.2% yield strength of about 40 k.s.i.

In accordance with preferred embodiments of this invention, the process is carried out in a sequence of cold reductions interspersed with relatively high temperature anneals.

In accordance with one preferred embodiment, an alloy within the aforenoted ranges of composition is subjected to an amount of cold work suflicient for it to recrystallize at less than about 600 C. Generally, this comprises cold reducing the alloy at least and preferably at least 30%. The maximum amount of cold work performed is governed by the gage requirements for the alloy. The cold worked alloy is then subjected to an intermediate anneal at a temperature of from about 400 to about 600 C., and preferably from about 450 to about 575 C. The intermediate annealed alloy is then subjected to a final cold reduction of from about 8% to about 22%, and preferably from about 10% to about 20%. The finally cold worked alloy is then subjected to a final anneal at a temperature of from about 550 to about 715 C., and preferably from about 650 to about 700 C.

As with the process of the preceding embodiment, elongation increases with the temperature of the final anneal. Similar properties are obtained as those set forth for the process of the previous embodiment. It has been found, however, that the intermediate annealing temperature is in every sense critical in that temperatures exceeding about 600 C. result in irregular grain growth in the alloy, if the alloy has previously been subjected to a cold reduction of at least about 22%.

In accordance with a still further embodiment of the invention, an alloy within the aforenoted ranges of composition is subjected to a cold reduction of at least 10%, and preferably at least 30%, depending on gage requirements; the cold worked alloy is then intermediate annealed at a temperature of from about 400 to about 600 C., and preferably at a temperature of from about 450 to about 575 C.

The annealed alloy is then subjected to a cold reduction of from about 25 to about 40% and then to an intermediate anneal at a temperature of from about 400 to about 600 C., and preferably at a temperature of about 450 to about 575 C. The intermediate annealed alloy is then subjected to a final cold reduction of from about 8% to about 22%, and preferably from about 10% to about 20%. The finally cold worked alloy is then subjected to a final anneal at a temperature of from about 550 to about 715 C., and preferably at a temperature from about 650 to about 700 C. This embodiment of the invention provides greater flexibility in meeting gage requirements in accordance with this invention, and should give more uniform recrystallization of the alloy and more uniform properties.

As with the previous embodiment, the intermediate an- .nealing temperatures are critical if the alloy has previously been subjected to a cold reduction of at least 22%.

In all of the embodiments discussed in accordance with this invention, the final cold working and final annealing steps are critical to obtain a wrought alloy having improvide elongation without irregular grain growth. The processes of this invention provide uniform grain coarsening and substantially uniform grain sizes of less than .025 millimeters. If the upper limit for the final annealing temperature is exceeded in accordance with this invention, the alloy is subject to irregular grain growth. This is similarly the case with respect to the final cold Working step, since a reduction of greater than 22% will produce the onset of irregular grain growth.

While the invention has been described with respect to specific embodiments, it is possible that other processing steps can be performed in addition to the processing of this invention so long as the limitations on the intermediate annealing temperature and final cold working and final annealing are adhered to.

The times at temperature and the heat up and cool down rates for the annealing steps of this invention are not critical and may be set as desired in accordance with conventional practice for these types of alloys.

The following discussion is believed to set forth the mechanisms which govern the critical nature of the processing of this invention. The mechanisms set forth are not meant to be limitative of the invention.

In alloys of low stacking fault energy containing dispersed second phase particles, e.g. Alloy 638, a 50% cold reduction results in a strong {ll0} ll2 deformation texture or preferred orientation. When Alloy 638 is recrystallized at 500 to 600 C., it contains newly formed recrystallized strain-free grains of very small size. The strong pinning effect of the CoSi dispersed second phase insures retention of fine grains. At higher annealing temperatures above 600 C., the pinning force diminishes as the CoSi agglomerates and/ or resolutionizes. Under these conditions, newly recrystallized grains which have a {ll0} ll2 annealed texture or preferred orientation grow preferentially into the l-10} 112 texture of the still deformed regions. Preferential grain growth continues even after recrystallization, since the larger grains of preferred orientation have more rapid growth rates than their smaller neighbors of different orientations. This preferential grain growth constitutes the undesired irregular grain growth and yields a duplex microstructure.

The {ll0} ll2 type texture has been found to be the stable end texture in cold rolled, low stacking fault energy alloys, such as Alloy 638. Irregular grain growth results in a {ll0} ll2 type annealed texture. It is believed that the development of the irregular grain growth and the 112 annealed texture is related to the presence of a critical amount of {ll0} ll2 deformation texture before the final recrystallization anneal.

The terms texture or preferred orientation as used in this application refer to the planes of the grains which are parallel to the strip surface.

It has been found in accordance with this invention that if the final cold working step is maintained within the aforenoted ranges of reduction, the amount of {110} 1l2 deformation texture is maintained below the critical level so that irregular grain growth will not occur during final annealing within the specified temperature ranges. Therefore, the processes of this invention provide uniform grain coarsening without duplex or irregular grain growth.

The processes of the invention will now be illustrated by reference to specific examples.

In the examples in all the final anneals and intermediate lalnneals, the samples were held at temperature for one our.

The annealing temperature, as the term is employed in this application, refers to the temperature of the metal rather than the furnace temperature.

Example I Samples of CDA Alloy 638 having a composition of 1.98% silicon, 2.5% aluminum, 0.42% cobalt, and the balance copper were prepared by commercial means to 0.090 inch gage. The samples were then processed in accordance with the process sequences in the table following. The mechanical properties and grain sizes for the samples are shown in the table.

Processing sequences A GR 507, Ann. 575 (l/CR 507 Ann. 575 C B 0325i Anne. 575 CJCR 30 Ann. 575 0.] CR 15%,

C CR 45%, Ann. 575 0 /CR 30%, Ann. 575 C./CR 15%,

Ann. 700 C N own-G R=cold roll; Ann. =anneal.

This example shows that a range of elogation and strength properties and uniform grain coarsening which results in a suitably small grain size can be obtained by the processes of this invention.

Process Sequence A corresponds to conventional processing for this alloy and is not in accordance with the process of this invention. It is presented by way of comparison.

Processing Sequences B and C illustrate that if the final cold working step is kept within the range of reduction in accordance with this invention, uniform grain coarsening and marked improvements in elongation can be obtained upon final annealing over a range of annealing temperatures.

Example II Samples of CDA Alloy 638 having a composition of 1.98% silicon, 2.5% aluminum, 0.42% cobalt, and the balance copper were prepared by commercial means to 0.080 gage- The samples were given varying final cold reductions and were annealed at varying final annealing temperatures. The resulting relationships are tabulated below.

Deformation, percent 0. 005 and 0. 030. 0. 060.

1 Duplex microstructure. t 9 Grain size after development of the high temperature gram growth exture.

Samples of CDA Alloy 638 having a composition of 1.98% silicon, 2.5 aluminum, 0.42% cobalt, and the balance copper were prepared by commercial means to 0.090 inch gage. The samples were processed in accordance with the following sequence, wherein the intermediate annealing temperature was varied. The results are tabulated below.

PROCESS SEQUENCE OR 45%, Ann. 575 0.; CR 30%, I. Ann.; CR 15%, Ann. 700 C.

UIS, 0.2% Ye, E, Grain I. ann., C. k.s.i. k.s.i. percent size, mm.

' Mostly 0.0050010 mm. grains, but 0.030 mm. grains were observed indicating exaggerated grain growth.

This example clearl illustrates the critical nature of the intermediate annealing temperature. The example shows that if the intermediate annealing temperature after a cold reduction of at least about 22% exceeds about 600 C., one can expect the onset of exaggerated grain growth.

+Samp1es in annealed condition anealed at less than 600 C.

Grain UTS, 0.2% YS, size,

k.s.i. k.s.i. percent mm.

Example IV Temperature, C.

Percent cold work:

15 U D U D D D D D 1 An almost entirely uniform structure, 1 or 2 isolated coarse grains.

Norn.-D=Duplex grain structure; U=Uniform grain structure These results indicate that final reductions within the ranges of this invention will result in a uniform grain structure, whereas reductions outside the mange of this invention, as, for example 25%, will result in irregular grain growth and a consequent duplex grain structure. The results further indicate that for final anneals at temperatures outside the range of the instant invention, namely above 715 0., a uniform grain structure cannot be assured for any of the degrees of cold reduction shown.

The aforenoted examples illustrate clearly the criticalnature of the intermediate annealing temperature, the final cold reduction, and final annealing temperature in accordance with the processes of this invention.

While the invention has been described with reference to a single final cold reduction and anneal, it should be evident from the above that a series of cold reductions and anneals within the ranges of the final cold reduction and anneal could be employed Without subjecting the alloy to irregular grain growth. This invention, therefore, also covers such a sequence of a plurality of reductions and anneals within the ranges of the final reduction and anneal.

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 come within the meaning and range of equivalency are intended to be embraced therein.

What is claimed is:

1. A process for improving the elongation of copper base alloys by controlled grain coarsening comprising:

providing a copper base alloy containing from about 2 to about 9.5% aluminum, less than about 1% zinc, a grain refining element selected from the group consisting of iron from about .001% to about 5.0%, chromium from about .001% to about 1%, zirconium from about 001% to about 1.0%, cobalt from about .001% to about 5.0%, and mixtures of these elements, and the balance copper, said alloy being in the annealed condition;

+Samples in annealed condition anealed at less than 600 C.

subjecting said alloy to a final cold reduction of from about 8% to about 22%; and

then final annealing said alloy at a temperature of from about 550 to about 715 C.

2. A process as in claim 1 wherein said alloy further contains from about .001 to about 3% silicon, and wherein the aluminum content is from about 2 to about 3. A process according to claim 2 wherein said alloy contains 2.5 to 3.1% aluminum, 1.5% to 2.1% silicon, 0.25% to 0.55% cobalt, and the balance copper.

4. A process according to claim 3 wherein the final cold reduction is from about to about 20%.

5. A process according to claim 4 wherein the final annealing temperature is from about 650 C. to about 700 C.

6. A process for improving the elongation of copper base alloys by controlled grain coarsening comprising:

(A) providing a copper base alloy containing from about 2 to about 9.5% aluminum, less than about 1% zinc, a grain refining element selected from the group consisting of iron from about .001% to about 5.0%, chromium from about 001% to about 1%, zirconium from about 001% to about 1.0%, cobalt from about .001% to about 5.0% and mixtures of these elements, and the balance copper, said alloy being in the annealed condition;

(B) cold reducing said alloy at least 10% so that it will recrystallize at a temperature of less than about 600 C.;

(C) then intermediate annealing said alloy at a temperature of from about 400 to about 600 C.;

(D) then finally cold reducing said alloy from about 8% to about 22%; and

(B) then finally annealing said alloy at a temperature of from about 550 to about 715 C.

7. A process as in claim 6 wherein said alloy further contains from about .001 to about 3% silicon, and wherein the aluminum content is from about 2 to about 5%.

8. A process according to claim 7 wherein said alloy contains 2.5% to 3.1% aluminum, 1.5% to 2.1% silicon, 0.25 to 0.55 cobalt, and the balance copper.

9. A process as in claim 8 wherein the cold reduction in Step B comprises at least 30% and the intermediate annealing temperature in Step C is from about 450 to about 575 C.

10. A process as in claim 9 wherein the final cold reduction of Step D is from about 10% to about 20% and wherein the final annealing temperature of Step E is from about 650 to about 700 C.

11. A process for improving the elongation of copper base alloys by controlled grain coarsening comprising: (A) providing a copper base alloy containing from about 2 to about 9.5% aluminum, less than about 1% zinc, a grain refining element selected from the group consisting of iron from about .001% to about 5.0%, chromium from about .001% to about 1%, zirconium from about .001% to about 1.0%, cobalt from about 001% to about 5.0%, and mixtures of these elements, and the balance copper, said alloy being in the annealed condition;

(B) cold reducing said alloy at least 10% so that it will recrystallize at a temperature of less than about 600 C.;

(C) then intermediate annealing said alloy at a temperature of from about 400-to about 600 C.;

(D) then cold reducing said alloy from about 25 to about 40%;

(E) then intermediate annealing said alloy at a temperature of from about 400 to about 600 C.;

(F) then finally cold working the alloy from about 8% to about 22%; and

(G) then finally annealing said alloy from Step F at a temperature of from about 550 to about 715 C.

12. A process as in claim 11 wherein said alloy further contains from about .001 to about 3% silicon, and where the aluminum content is from about 2 to about 5 13. A process according to claim 12 wherein said alloy contains 2.5% to 3.1% aluminum, 1.5% to 2.1% silicon, 0.25 to 0.55 cobalt, and the balance copper.

14. A process as in claim 13 wherein the cold reduction in Step B is at least 30% and wherein the annealing temperatures in Step C and Step E are from about 450' to about 575 C.

15. A process as in claim 14 wherein the cold reduction in Step E is from about 10% to about 20% and wherein the annealing temperature in Step F is from about 650 to about 700 C.

References Cited UNITED STATES PATENTS 2,210,672 8/1940 Kelly -162 2,669,534 2/1954 Richardson 148-11.5 R 3,253,911 5/1966 Cairns 75-162 3,475,227 10/1969 Caule et al 14811.5 R 3,656,945 4/1972 Eichelman, Jr. 14811.5 R 3,725,056 4/1973 Ingerson 75162 WAYLAND W. STALLARD, Primary Examiner UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,7 ,9 Dated January 9, 197

Inventor(s) Eugene piro et a1.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In Column 1, line 31, the word "improved" should read ---improve---.

In Column 5, line 8; under the heading Grain Size, mm, -"0. 912'" should read -0 .012---;

In Column 5-, line 10, the word "elogation" should read --elongati onv v v Signed and sealed this 10th day of September 197A.

'(SEAL) Attest:

MCCOY M. GIBSON, JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents USCOMM-DC 60376-P69 FORM po-wso (10-69) I 11.5. GOVERNMENT PRINTING OFFICE: 1969 0-366-331