GB1593497A - Copper aluminium zinc and manganese alloy - Google Patents

Description

(54) COPPER, ALUMINIUM, ZINC AND MANGANESE ALLOY (71) WE, RAYCHEM CORPORATION, A Corporation organized according to the laws of the State of California, United States of America, of 300 Constitution Drive, Menlo Park, California 94025, United States of America, do hereby declare the invention, for which we prav 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 :- This invention relates to metal alloys capable of being rendered heat recoverable. In another aspect, it relates to heat recoverable metal articles.

Materials, both organic and metallic, capable of being rendered heat recoverable are well known. An article made from such materials can be deformed from an original, heat-stable configuration to a second, heat-unstable configuration. The article is said to be heat recoverable for the reason that, upon the application of heat, it can be caused to revert from its heat-unstable configuration to its original, heat-stable configuration.

Among metals, for example certain alloys of titanium and nickel, the ability to be rendered heat recoverable is a result of the fact that the metal undergoes a rPversihle transformation from an austenitic state to a martensitic state with PATENTS ACT 1949 SPECIFICATfON NO 1593497 The following amendments were allowed under Section 29 on 23 September 1982: Page 7, after line 3, insert Attention is drawn to claim 3 of U. S. Patent 2085416. No claim is made herein to an alloy per comprising 11% by weight zinc, 12% by weight manganese, 7% by weight aluminium and 70% by weight copper, although the following claims 8 and 9, respectively, include heat-recoverable articles made from, and processes for making heat-recoverable articles made from, that alloy.

Subject to the foregoing disclaimer, THE PATENT OFFICE 10 November 1982 Bas 93323/10 ,",.....,..~.....r,,.~~~~.~~~~~~ of the heat recoverable strain which an intervening substrate or other agency precludes recovery of, is referred to as unresolved recovery. Finally, any deformation which exceeds the maximum available heat recoverable strain is said to effect non-recoverable strain.

(54) COPPER, ALUMINIUM, ZINC AND MANGANESE ALLOY (71) WE, RAYCHEM CORPORATION, A Corporation organized according to the laws of the State of California, United States of America, of 300 Constitution Drive, Menlo Park, California 94025, United States of America, do hereby declare the invention, for which we prav 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 :- This invention relates to metal alloys capable of being rendered heat recoverable. In another aspect, it relates to heat recoverable metal articles.

Materials, both organic and metallic, capable of being rendered heat recoverable are well known. An article made from such materials can be deformed from an original, heat-stable configuration to a second, heat-unstable configuration. The article is said to be heat recoverable for the reason that, upon the application of heat, it can be caused to revert from its heat-unstable configuration to its original, heat-stable configuration.

Among metals, for example certain alloys of titanium and nickel, the ability to be rendered heat recoverable is a result of the fact that the metal undergoes a reversible transformation from an austenitic state to a martensitic state with changes in temperature. An article made from such a metal, for example a hollow sleeve, is easily deformed from its original configuration to a new configuration when cooled below the temperature at which the metal is transformed from the austenitic state to the martensitic state. This temperature, or temperature range, is usually referred to as the M, temperature. When an article thus deformed is warmed to the temperature at which the metal reverts back to austenite, referred to as the A, temperature or range, the deformed object will revert to its original configuration. Thus, when the hollow sleeve referred to above is cooled to a temperature at which the metal becomes martensitic, it can be easily expanded to a larger diameter, for example, by using a mandrel. If the expanded sleeve is subsequently allowed to warm to the temperature at which the metal reverts back to its austenitic state, the sleeve will revert to its original dimensions.

Ordinarily, such a sleeve would recover all or substantially all of the deformation, i. e., it would revert completely to its original dimensions. However, it should be noted that under certain circumstances the article might be deformed to such an extent that all of the deformation cannot be recovered on heating.

Alternatively, if something, e. g., an intervening rigid substrate having a greater external dimension than the internal pre-deformation dimensions of the sleeve is interposed within the sleeve, the sleeve cannot recover to its original dimensions.

Any dimensional change up to the maximum available which an article can recover absent any intervening substrate is called the heat recoverable strain. That portion of the heat recoverable strain which an intervening substrate or other agencv precludes recovery of, is referred to as unresolved recovery. Finally, any deformation which exceeds the maximum available heat recoverable strain is said to effect non-recoverable strain.

That the titanium nickel alloys referred to above possess the property of heat recoverability has been known for many years. More recently, for example in United States Patent No. 3,783,037, there is disclosed : a method for producing a heat recoverable article in which an alloy comprising an inter-metallic compound that undergoes a diffusionless transformation into a banded martensite upon cooling with or without working is deformed after appropriate heat treatment. On reheating the article, it at least partly resumes its original shape. The alloys indicated as preferred are copper based alloys which transform into a martensite of pseudo-cubic symmetry including: the binary copper-zinc and copper-aluminum systems and the ternary copperaluminum-zinc, copper-zinc-tin, copper-zinc-silicon, copper-aluminummanganese, copper-aluminum-iron and copper-aluminum-nickel systems.

In U. S. Patent No. 3,783,037 (Col. 8, In, 63 et seq.) it is noted in respect to the copper-aluminum-zinc system that"... as there is progressive increase in the aluminum content and decreases in the zinc content..., the maximum ductility that can be produced in the ternary alloys when deformed at or near the M. decreases." It is noted that as the aluminum level increases, the maximum obtainable heat recoverable strain decreases. For example, in alloys of the compositions (by weight) 72% copper, 22% zinc and 6% aluminum and 75.7% copper, 17% zinc and 7.5% aluminum, the maximum heat recoverable strain was reported to be 4.8 ó and 4.0% respectively.

The clear teaching of this patent is therefore that the aluminum content of the alloy should be reduced as much as possible to achieve maximum heat recoverable strain. Unfortunately, we have found that, unknown to the prior art, reducing the aluminum content has a severe adverse effect on the stability i. e., ability to avoid stress relaxation of the article under conditions of unresolved recovery.

Additionally, if one follows the teaching of the prior art and avoids ternary alloys containing significant. quantities of aluminum, limitations are encountered in hot working. In particular, low energy input hot working requires avoidance of a second phase in the structure. Unfortunately, low aluminum content alloys must be maintained at very high temperatures, e. g., at least in excess of 650 C, to be in the onephase beta condition the phase desired for hot workability. At such high temperatures, tool life is shortened and the avoidance of coarse grain size in the product is difficult.

If a heat recoverable article is recovered onto a substrate such that the substrate prevents full recovery of the article to its original configuration, i. e., under conditions of unresolved recovery, then the residual strain results in a stress in the article. We have now discovered that all copper alloy compositions having the A-brass structure are more or less unstable if complete recovery is prevented.

Thus, we find that at moderate temperatures such as would typically be seen during service, for example, in hydraulic or electrical applications in aircraft, the residual stress in incompletely recovered articles will decay steadily to zero such that after a certain period of time the recovered object, for example, a sleeve recovered about a substrate, can be easily removed from the substrate. Inasmuch as heat recoverable metals find their greatest utility in applications where they exert a high degree of compressive or other form of stress, it will be readily recognized by those skilled in the art that the stress relaxation process described above is a considerable impedement to the widespread use of these metals. For example, parts made from the binary alloys and the specific ternary alloys described in above mentioned U. S. Patent 3,783,037, when prevented from recovering completely to an initial configuration under conditions of about 4.0 " unresofvedrecovery, exhibit complete stress relaxation at 125 C, in less than l, 000 hours (equivalent to relaxation within 100 hours at 150 C) so that they are essentially useless in many applications.

Therefore, although a wide variety of p-brass type copper alloy compositions capable of being rendered heat recoverable are known to the prior art, those compositions possess serious shortcomings severely limiting their use.

Accordingly, one ob. ject of this invention is to provide improved !-brass type alloys.

Another object of this invention is to provide heat recoverable articles of p- brass type alloys that will exhibit long term stress stability when recovered under conditions so that a degree of unresolved recovery remains.

Yet another object of this invention is to provide heat recoverable articles of brass type alloys that will preferably maintain a stress for greater than 1 000 hours at 125 C or for greater than 100 hours at 150 C.

The present invention provides certain quaternary alloys of copper, aluminum, zinc and manganese which manifest good ductility and are easily worked by hot working techniques in addition to exhibiting excellent long term stress stability.

Both good ductility and hot workability are requisite for commercially useful materials. Neat recoverable articles made from the alloys of the present invention exhibit long term stress stability even when recovered under circumstances such that a level of unresolved recovery remains. In general, the stress stability of such heat recoverable articles is such that when they are caused partially to recover upon being warmed to the temperature at which the alloy reverts to the austentic state they exhibit a stress stability of at least 1, 000 hours at 125 C (or the equivalent of 100 hours at 150 C) The quaternary alloys of the present invention comprise by weight 70-82 / copper, 6-12% preferably 6-10 aluminum, 0. 1-24% zinc, and 0. 1 N, to 12% manganese.

The present invention will be described in more detail, by way of example only, with reference to the accompanying drawings, in which ; Figure I is a graph of the eutectoid line of copper-aluminum-zinc-manganese quaternary alloys having a M, of-50 C, Figure II is a graph showing the relationship between the manganese content and the long term stress stability of the quaternary alloys of this invention, Figure III is a graph showing the relationship between the aluminum content and the long term stress stability of the quaternary alloys of the present invention.

Figure IV is a graph showing the relationship between the M, temperature and the long term stress stability of the quaternary alloys of the present invention, and Figure V is a graph showing the preferred compositional limits for quaternary alloys of the present invention having an M, temperature-of-50 C.

As previously discussed, we have unexpectedly discovered that articles formed from the A-brass type compositions known to the prior art suffer the serious disadvantage of being unstable with respect to the maintenance of stress when the article has been exposed to modestly elevated temperatures for extended periods of time under condition of unresolved recovery. This phenomenon manifests itself in actual use situations when an article made from such an alloy is deformed when in its martensitic state to thereby render it heat recoverable, and then allowed to recover by warming it to a temperature at which the alloy reverts to austenite in a manner that precludes the article from completely recovering to its original configuration and thereafter exposed to temperatures above about 80 C. That portion of the strain which remains in the article after this partial recovery is, as already indicated, referred to as unresolved recovery.

We have discovered that articles made from p-brass type compositions known to the prior art are unstable with respect to maintaining adequate stress levels, i. e. the stress gradually decays to zero, the rate of decay increasing with temperature.

Attention is drawn to Patent Application No. 42949/79 (Serial No. 1, 593,498) and Patent Application No. 42950/79 (Serial No. t. 593, 499) each of which has been divided from the present application and which claim (3-brass type ternary alloys of copper, aluminum and manganese and copper, aluminum and zinc ; respectively.

The disclosures of both of these applications are incorporated herein by reference.

The alloys described and claimed in those divisional applications are also suitable for making heat-recoverable articles with good stress stability but there are certain practical consequences which impose limits on their usefulness. Firstly, in the Cu-AI-Zn ternary system, the composition range of maximum stability lies on or very near the eutectoid line even though the stability of the eutectoid composition can be equalled by moving into the gamma rich region, i. e., by increasing the aluminum content. However, as the alloy composition is moved into the gamma rich region, hot working and annealing at undesireably high temperatures becomes necessary to avoid significant precipitation of the gamma phase with concommitant embrittlement. In the case of Cu-AI-Mn ternary alloys, there is a level of stability which cannot be improved upon for any M. temperature.

However, because of the high aluminum content of the alloys which give the best stability, they may not be ductile enough for some uses.

The quaternary alloys of the present invention, overcome the shortcomings inherent in the ternary alloys, and provide alloys in which the stability ductility and M, can be optimised to meet a desired application. Thus, by virtue of the degree of freedom offered by the fourth metal, for each desired M. temperature there is a nearly infinite number of eutectoid compositions.

This is shown by way of exemplification in Figure I where there is plotted the eutectoid compositions for ailoys having an M, of-50 C as a function of the manganese and aluminum concentration. The zinc concentration along this eutectoidal line also varies and may be estimated from equations (b), (c), or (d) shown infra.

Another unexpected benefit of the use of these quaternary alloys is that the great majority of the alloys described herein do not form the a ory phase until cooled to temperatures of 550 C or even lower. By contrast, many of the unstable alloys contemplated by the prior art form the a or y phase even at temperatures in excess of 650 C Thus the quaternary alloys of the instant invention may advantageously be worked in the !-phase at much lower temperatures than those of the prior art with the consequence of greatly improved tool life. Yet another unexpected benefit of these alloys is that the kinetics of formation of the a and y phase is very significantly retarded when compared with any known prior art compositions. Thus in the majority of the quaternary alloys of the instant invention, air cooling is sufficiently rapid to retain substantially all the material in the A-phase.

A highly beneficial result of this is that the warpage which results from rapid quenching (as when using water as the quenchant) and variations in quenching rate across relative thick sections with a concommitant variation in phase composition can be avoided. The improvements obtained by the addition of combinations of either Mn or Zn, with other metals or pairs of other metals, to mixtures of Cu and Al, are minor when compared with the benefits accruing from the addition of Mn and Zn in combination.

A consideration of Figure I will show that the eutectoid composition for an M, of-50 C can be varied by substituting manganese for zinc (but not on equal weight basis).

For this reason, the aluminum content of the alloys can be increased with a corresponding increase in stability.

I have found that the stress stability of the quaternary alloys of this invention are influenced by: 1 : The position of the composition relative to the ; 2: The M, temperature ; 3: The aluminum content of the alloy.

The influence of these factors was found by the following procedure. Each alloy was quenched into water at 20 C from 650 C. A 3"long sample was cooled to below the M, temperature for the alloy and deformed 4.25'/n' by being bent into a U shape about a rod. The sample was heated to either 125 C or 150 C while being held in the deformed shape. Periodically the specimen was cooled to room temperature and the constraint was then removed. When this was done, the amount of springback, i. e., movement toward the original configuration, was measured. The specimen was then replaced in the constraint and held for a further period of time at either 125 C or 150 C. When upon removal of the constraint no springback was observed, the time that it took to reach that condition was taken as the stability limit. This is the time that is given in the tables of the Example.

The manner in which each of these factors affect the stress stability of these alloys can be seen from a consideration of Figures 1I-V. Referring now to Figure II there is shown the effect of varying the composition relative to the eutectoid for an alloy having an M, of-40 C and a constant aluminum content (10. , o by weight).

The eutectoid composition contains 4.6 / by weight of Figure III illustrates the effect of increasing aluminum content for alloys all having an M of about-30 C. From Figure VI it can be seen that stress stability increases with the increase in aluminum content.

Figure IV shows the effect of varying the M, temperature. The alloys used in the study for Figure IV all had tne same aluminium content (10 /,,). However, the relative proportions of the other elements were adjusted to obtain the desired M5.

From this Figure it can be seen that alloys of lower Ms are more stable.

In one aspect of the practice of the present invention one selects an M. temperature that is convenient for the application to which a heat recoverable article is to be put. Then, from curves like those in Figure II-IV, required levers of aluminum, manganese and zinc required for a desired life time can be estimated.

It will be appreciated that for a given M"there is an associated large family of eutectoid compositions. Thus for any given Mss the eutectoid line, as a function of Mn and Al content, is defined by the limiting ternary compositions of that Msz i. e., the compositions where the Mn and Zn content are respectively 0. In the case of alloys having an M, of-50 C, these'alloys are Cu (81.05 /n). AI (I 1. 75, . y), Mn (7.2 ; ;) and Zn (0*/,) and Cu (73.3%), A1 (7 /n). Mn (0 , and Zn () 9. 2). Referrinp now to Figure VIII, there is shown a graph of the line XY defined by the limiting ternary compositions described above. Thus, for all compositions on this line there is a coincidence between the eutectoid point and an M, of-50 C Similar lines can be obtained for alloys of M, other than-50 C. The following equation has been derived from which the line XY for other M, temperatures can be approximated:

The following equations have been derived to allow the estimation of the M temperature for a variety of alloys after having been quenched from 650 C into water at 20 C.

For alloys containing 6-10% AI and up to 4 /^ Mn : M, ( C) =2469-68 Zn (wt. %)-172 AI (wt. %)-89 Mn (wt. %) (b) For alloys containing 6-10 /A1 and 4-10% Mn: M ( C) =1814 52 Zn (wt. %)-133 AI (wt. %)-56 Mn (wt. %) (c) For alloys containing in excess of 10% Al : M, ( C) =1787-57 Zn (wt. %)-120 AI (wt. %)-60 Mn (wt. %) (d) As previously indicated, the compositions of maximum stability for any given aluminum content lie at or near the eutectoid. In some instances it may be desired to operate on the gamma or alpha side of the eutectoid. In the case of the former, relative Umited deviation is permissible as on the gamma side precipitation of the gamma phase is difficult to avoid and the compositions containing this phase have a significant tendency to be less ductile. Generally good stability and suitable ductility can be achieved on the gamma rich side up to a 3% deviation in Mn content from that of the eutectoid. However, it is preferred to stay within about a 1% deviation in the Mn content.

Moving to the alpha rich side does not lead to a substantial reduction in ductility but does tend to cause a reduction in stability. The maximum level of manganese addition is controlled by the line EF. The limiting composition of the two alloys E and F which are respectively ternary Cu-AI-Mn alloy and a ternary Cu-Al-Zn alloy are : 73% Cu, 6.6% Al, 20.4% Zn and 80.6% Cu, 9.1% Al,, and 10. 3% Mn.

Compositions with manganese levels in excess of that specified by the line EF will either have a stability of less than 1, 000 hours at 125 C or would require heating in excess of 650 C to remove the a-phase. However, it is preferred to stay within about 3 by weight of the eutectoid on the alpha side for best. result. The lines demarcating these bounds for alloys of M, =-50 C are shown in Figure V where line GH and AB, respectively show the 3% and 1% variance in manganese content on the gamma rich side of the eutectoid. By contrast, DC demarks the 3% variance in the manganese content and EF is the limiting level for high manganese content on the alpha side as explained above. Thus the highiv preferred alloys of Ms=50 C are found within the area bounded by the points ABYCDF.

For alloys of an M, other than-50 C, similar variance from the eutectoid also leads to alloys having an acceptable and even a highly desirable balance between stability and ductility. Graphs like that of Figure V for alloys of an M. of other than -50 C can be derived from equation (a) above for the eutectoid compositions. Line AB can be calculated from the following equation:

Line CD can be calculated from the equation :

Line GH can be calculated from the equation :

EXAMPLE I The following are examples of alloys according to the present invention having a long terin stress stability at 125 C for at least 1000 hours or at least 100 hours at 150 C. Each alloy was quenched into water at 20 C from 650 C. A 3"long sample was cooled to below the M, temperature for the alloy and deformed 4.25 /O by being bent into a U shape about a rod. The sample was heated to either 125 C or 150 C while being held in the deformed shape. Periodically the specimen was cooled to room temperature and the constraint was then removed. When this was done, the amount of springback, i. e., movement-toward the original configuration was measured. The specimen was then replaced in the constraint and held for a further period of time at either 125 C or 150 C. When upon removal of the constraint no springback was observed, the time that it took to reach that condition was taken as the stability limit.

Copper-Aluminum-Manganese-Zinc Quaternary Alloys Alloy Composition, Sample Cu Al Zn Mn M, Lifetimeat 125 C 1 79. 15. 10 8.25 2.6-39 14, 000 hours 2 79.3 10 7.3 3.4-42 18, 000 hours 3 79.3 10 6.4 4.3-41 20 000 hours 4 79.4 10 5.5 5.1-41 20, 000-hours 5 79.6 10 4. 4 6.0-38 19, 000 hours 6 79.6 10 3.5 6.9-36 13,000 hours 7 79.7 10 1. 7 8.6-43 8,500 hours 8 80.3 10 0 9.7-35 6, 000 hours 9 74.1 7 18 0.9-35 1,400 hours 10 78.1 9 9.5 3.4-35 4,700 hours 11 79.8 10 5.9 4.3-30 10,000 hours 12 78.7 10 7 4.3-78 50, 000 hours All the alloys of the instant invention, possessing as they do outstanding combinations of properties as hereinbefore described, are useful in many and diverse applications. Thus, they may be used to provide hydraulic couplings and electronic connectors as described in United States Patent No. 3,740,839.

The good hot workability of these alloys renders them particularly appropriate for use in extruded product. Thus they may be readily fabricated into wire, rod and various complex profiles. They may be readily stamped, swaged and formed by techniques well known to those skilled in the art.

Claims (10)

1. WHAT WE CLAIM IS: 1. An alloy having a ss-brass type structure capable of being rendered heat recoverable and capable of being cooled from a temperature at which it exists in an austenitic state to a temperature at which it exists in a martensitic state, said alloy being a quaternary alloy comprising 70. 82 hn by weight copper, 6-12 /by weight aluminum, 0.1-12% by weight manganese and 0. 1-24% by weight zinc.
2. 2. A quaternary alloy as claimed in claim 1, the components of which are present in an amount that corresponds substantially to that for a eutectoid composition of copper, aluminum, manganese and zinc.
3. 3. A quaternary alloy as claimed in claim 2, wherein the manganese content of the alloy deviates from the manganese content of the eutectoid composition by not more than about 3% by weight on the gamma rich side of the eutectoid.
4. 4. A quaternary alloy as claimed in claim 3, wherein the manganese content of the alloy deviates from that of the eutectoid composition by not more than 1% boy weight on the gamma rich side of the eutectoid.
5. 5. A quaternary alloy as claimed in claim 2, wherein the manganese content of the alloy deviates from the manganese content of the eutectoid composition by not more than about 3% by weight on the alpha rich side of eutectoid.
6. 6. A quaternary alloy as claimed in claim 5, wherein the manganese content of the alloy deviates from that of the eutectoid composition by not more than 1% by weight on the alpha-rich side of the eutectoid.
7. 7. An alloy as claimed in any one of claims I to 6, which, when deformed from an original configuration while in its martensitic state and caused partially to recover towards said original configuration upon being warmed to the temperature at which the alloy reverts to its austenitic state, exhibits stress stability of at least 1, 000 hours at 125 C.
8. 8. A heat recoverable article made from an alloy as claimed in any one of claims I to 7.
9. 9. A process for making a heat recoverable article that exhibits stress stability of at least 1, 000 hours at 125 C when allowed to recover so that a degree of unresolved recovery remains which comprises the steps of, (a) selecting an alloy as specified in any one of claims 1 to 6.

   (b) fabricating said article from the selected alloy into an original, heat-stable configuration.

   (c) cooling said article to a temperature at which the alloy exists in its martensitic state: and (d) deforming said article to a second, heat stable configuration from which recovery occurs when said article is warmed to a temperature at which the alloy reverts to austenite from said martensitic state.
10. 10. A process as claimed in claim 9, wherein said alloy has a substantially eutectoidal composition.