U.S. patent application number 08/885930 was filed with the patent office on 2001-05-24 for grain refined tin brass.
This patent application is currently assigned to Dennis R. Brauer et al. Invention is credited to BRAUER, DENNIS R., BREEDIS, JOHN F., CARON, RONALD N., DEPPISCH, CARL.
Application Number | 20010001400 08/885930 |
Document ID | / |
Family ID | 27126508 |
Filed Date | 2001-05-24 |
United States Patent
Application |
20010001400 |
Kind Code |
A1 |
BRAUER, DENNIS R. ; et
al. |
May 24, 2001 |
GRAIN REFINED TIN BRASS
Abstract
There is provided a tin brass alloy having a grain structure
that is refined by the addition of controlled amounts of both zinc
and iron. Other metallic elements that undergo peritectic
decomposition in a tin brass alloy, such as cobalt, iridium,
niobium, vanadium and molybdenum may substitute for from a portion
to all of the iron. Direct chill cast alloys containing from 1% to
4%, by weight of tin, from 0.8% to 4% of iron, from an amount
effective to enhance iron initiated grain refinement to 20% of zinc
and the remainder copper and inevitable impurities are readily hot
worked. The zinc addition further increases the strength of the
alloy and improves the bend formability in the "good way",
perpendicular to the longitudinal axis of a rolled strip.
Inventors: |
BRAUER, DENNIS R.;
(BRIGHTON, IL) ; BREEDIS, JOHN F.; (TRUMBULL,
CT) ; CARON, RONALD N.; (BRANFORD, CT) ;
DEPPISCH, CARL; (HAMDEN, CT) |
Correspondence
Address: |
GREGORY S ROSENBLATT
INTELLECTUAL PROPERTY LAW SECTION
WIGGIN & DANA
ONE CENTURY TOWER
NEW HAVEN
CT
065081832
|
Assignee: |
Dennis R. Brauer et al
|
Family ID: |
27126508 |
Appl. No.: |
08/885930 |
Filed: |
June 30, 1997 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
08885930 |
Jun 30, 1997 |
|
|
|
08844478 |
Apr 18, 1997 |
|
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|
5853505 |
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Current U.S.
Class: |
148/433 ;
420/471 |
Current CPC
Class: |
C22C 9/04 20130101 |
Class at
Publication: |
148/433 ;
420/471 |
International
Class: |
C22C 009/02; C22C
009/01 |
Claims
We claim:
1. A copper alloy, consisting essentially of: from 1% to 4% by
weight of tin; from an amount effective to enhance peritectic
initiated grain refinement to 20% by weight of zinc; up to 0.4% by
weight of phosphorous; a combination of iron and cobalt present in
an amount satisfying the equation: Fe+MCo=0.8%-4.0% by weight;
where M is between 0.45 and 0.65; and the remainder copper and
inevitable impurities, said alloy having a refined as-cast average
crystalline grain size of less than 100 microns.
2. The copper alloy of claim 1 wherein said zinc is present in an
amount of from 5% to 15% by weight.
3. The copper alloy of claim 2 wherein said zinc is present in an
amount of from 8% to 12% by weight.
4. The copper alloy of claim 3 wherein a portion of said zinc is
replaced at a 1:1 atomic ratio with an element selected from the
group consisting of aluminum, manganese and mixtures thereof.
5. The copper alloy of claim 2 wherein Fe+MCo=1.6%-2.2%
6. The copper alloy of claim 5 wherein Fe+MCo=1.6%-1.8%.
7. The copper alloy of claim 2 wherein a portion of said
iron+cobalt is replaced with one or more peritectic reaction
initiators selected from the group consisting of iridium, niobium,
vanadium and molybdenum.
8. The copper alloy of claim 5 wherein a portion of said zinc is
replaced at a 1:1 atomic ratio with an element selected from the
group consisting of aluminum, manganese and mixtures thereof.
9. The copper alloy of claim 6 wherein said tin content is from
1.2% to 2.2%.
10. The copper alloy of claim 9 wherein said phosphorous content is
from 0.03% to 0.3%.
11. The copper alloy of claim 9 further containing an addition
selected from the group consisting of nickel, magnesium, beryllium,
silicon, zirconium, titanium, chromium and mixtures thereof,
wherein each component of said addition is present in an amount of
less than 0.4% by weight.
12. The copper alloy of claim 9 being wrought to a thickness of
from 0.005 inch to 0.015 inch and having an average final gauge
grain size of from 3 microns to 20 microns.
13. An electrical connector formed from the alloy of claim 9.
14. A spring formed from the alloy of claim 12.
15. A copper alloy, consisting essentially of: from 1% to 4% by
weight of tin; a peritectic reaction initiator selected in an
amount effective to provide said copper alloy with a fine grain
microstructure without an excessive degradation in electrical
conductivity and strength selected from the group consisting of
cobalt, iridium, vanadium, molybdenum and mixtures thereof; from an
amount effective to enhance peritectic initiated grain refinement
to 20% by weight of zinc; up to 0.4% by weight of phosphorous; and
the remainder copper and inevitable impurities, said alloy having a
refined as-cast average crystalline grain size of less than 100
microns.
16. The copper alloy of claim 15 wherein said peritectic reaction
initiator is cobalt present in an amount of from about 3.2% to
about 4.4%
17. The copper alloy of claim 15 wherein said peritectic reaction
initiator is iridium present in an amount of from about 10% to
about 20%
18. The copper alloy of claim 15 wherein said peritectic reaction
initiator is niobium present in an amount of from about 0.01% to
about 5%
19. The copper alloy of claim 15 wherein said peritectic reaction
initiator is vanadium present in an amount of from about 0.01% to
about 5%
20. The copper alloy of claim 15 wherein said peritectic reaction
initiator is molybdenum present in an amount of from about 0.5% to
about 5%
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This patent application is a continuation-in-Part of U.S.
patent application Ser. No. 08/844,478 entitled "Iron Modified Tin
Brass" by D. R. Brauer et al. that was filed on Apr. 18, 1997.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to copper alloys having high
strength, good formability and relatively high electrical
conductivity. More particularly, grain refinement of a tin brass is
obtained by a controlled addition of iron, cobalt or other element
that initiates a peritectic reaction during solidification.
[0004] 2. Description of Related Art
[0005] Throughout this patent application, all percentages are
given in weight percent unless otherwise specified.
[0006] Commercial tin brasses are copper alloys containing from
0.35%-4% tin, up to 0.35% phosphorous, from 49% to 96% copper and
the balance zinc. The alloys are designated by the Copper
Development Association (CDA) as copper alloys C40400 through
C49080.
[0007] One commercial tin brass is a copper alloy designated as
C42500. The alloy has the composition 87%-90% of copper, 1.5%-3.0%
of tin, a maximum of 0.05% of iron, a maximum of 0.35% phosphorous
and the balance zinc. Among the products formed from this alloy are
electrical switch springs, terminals, connectors, fuse clips, pen
clips and weather stripping.
[0008] The ASM Handbook specifies copper alloy C42500 as having a
nominal electrical conductivity of 28% IACS (International Annealed
Copper Standard where "pure" copper is assigned a conductivity
value of 100% IACS at 20.degree. C.) and a yield strength,
dependent on temper, of between 45 ksi and 92 ksi. The alloy is
suitable for many electrical connector applications, however the
yield strength is lower than desired.
[0009] It is known to increase the yield strength of certain copper
alloys through controlled additions of iron. For example, commonly
owned U.S. patent application Ser. No. 08/591,065 entitled "Iron
Modified Phosphor-Bronze" by Caron et al. that was filed on Feb. 9,
1996, discloses the addition of 1.65%-4.0% of iron to phosphor
bronze. The Caron et al. alloy has an electrical conductivity in
excess of 30% IACS and an ultimate tensile strength in excess of 95
ksi.
[0010] U.S. patent application Ser. No. 08/591,065 is incorporated
by reference in its entirety herein.
[0011] Japanese patent application number 57-68061 by Furukawa
Metal Industries Company, Ltd. discloses a copper alloy containing
0.5%-3.0%, each, of zinc, tin and iron. It is disclosed that iron
increases the strength and heat resistance of the alloy.
[0012] While the benefit of an iron addition to phosphor-bronze is
known, iron causes problems for the alloy. The electrical
conductivity of the alloy is degraded and processing of the alloy
is impacted by the formation of stringers. Stringers form when the
alloy contains more than a critical iron content, which content is
dependent on the alloy composition. The stringers originate when
properitectic iron particles precipitate from liquid prior to
solidification and elongate during mechanical deformation.
Stringers are detrimental because they affect the surface
appearance of the alloy and can degrade the formability
characteristics.
[0013] In high copper (in excess of 85% Cu) tin brasses, the
maximum permissible iron content, as an impurity, is typically
0.05%. This is because iron is known to reduce electrical
conductivity and, through the formation of stringers, deteriorate
the bend properties.
[0014] Other metallic additions to the alloy that induce the
formation of a peritectic phase during solidification may
substitute for the iron, either in whole or in part. One particular
addition is cobalt, while other suitable additions include
vanadium, niobium, iridium and molybdenum.
[0015] There exists, therefore, a need for an iron modified tin
brass alloy that does not suffer from the stated disadvantages of
reduced electrical conductivity and stringer formation.
SUMMARY OF THE INVENTION
[0016] Accordingly, it is an object of the invention to provide a
tin brass alloy having increased strength. It is a feature of the
invention that the increased strength is achieved by an addition of
controlled amounts of a combination of iron and zinc. It is another
feature of the invention that by processing the alloy according to
a specified sequence of steps, a fine microstructure is retained in
the wrought alloy.
[0017] Among the advantages of the alloy of the invention are that
the yield strength is increased without a degradation in electrical
conductivity. The microstructure of a refined as-cast alloy, grain
size less than 100 microns, and a wrought alloy, grain size of
about 5-20 microns, is fine grain. Still another advantage is that
the electrical conductivity is about equal to that of copper alloy
C42500 with a significant increase in yield strength.
[0018] In accordance with the invention, there is provided a copper
alloy. This alloy consists essentially of from 1% to 4% by weight
of tin, from 0.8% to 4.0% by weight of iron, from an amount
effective to enhance iron initiated grain refinement to 20% by
weight of zinc, up to 0.4% by weight of phosphorus and the
remainder is copper, as well as inevitable impurities.
[0019] The grain refined alloy has an average as-cast grain size of
less than 100 microns and an average grain size after processing of
between about 5 and 20 microns.
[0020] The above stated objects, features and advantages will
become more apparent from the specification and drawings that
follow.
IN THE DRAWINGS
[0021] FIG. 1 is a flow chart illustrating one method of processing
the alloy of the invention.
[0022] FIG. 2 graphically illustrates the effect of iron content on
the yield strength.
[0023] FIG. 3 graphically illustrates the effect of iron content on
the ultimate tensile strength.
[0024] FIG. 4 graphically illustrates the effect of tin content on
the yield strength.
[0025] FIG. 5 graphically illustrates the effect of tin content on
the ultimate tensile strength.
[0026] FIG. 6 graphically illustrates the effect of zinc content on
the yield strength.
[0027] FIG. 7 graphically illustrates the effect of zinc content on
the ultimate tensile strength.
DETAILED DESCRIPTION
[0028] The copper alloys of the invention are an iron modified tin
brass. The alloys consist essentially of from 1% to 4% of tin, from
0.8% to 4.0% of iron, from 5% to 20% of zinc, up to 0.4% of
phosphorus and the remainder is copper along with inevitable
impurities. As cast, the grain refined alloy has an average
crystalline grain size of less than 100 microns.
[0029] When the alloy is cast by direct chill casting, in preferred
embodiments, the tin content is from 1.5% to 2.5% and the iron
content is from 1.6% to 2.2%. 1.6% of iron has been found to be a
critical minimum to achieve as-cast grain refinement. Most
preferably, the iron content is from 1.6% to 1.8%.
[0030] Tin
[0031] Tin increases the strength of the alloys of the invention
and also increases the resistance of the alloys to stress
relaxation.
[0032] The resistance to stress relaxation is recorded as percent
stress remaining after a strip sample is preloaded to 80% of the
yield strength in a cantilever mode per ASTM (American Society for
Testing and Materials) specifications. The strip is heated to
125.degree. C. for the specified number of hours and retested
periodically. The properties were measured at up to 3000 hours at
125.degree. C. The higher the stress remaining, the better the
utility of the specified composition for spring applications.
[0033] However, the beneficial increases in strength and resistance
to stress relaxation are offset by reduced electrical conductivity
as shown in Table 1. Further, tin makes the alloys more difficult
to process, particularly during hot processing. When the tin
content exceeds 2.5%, the cost of processing the alloy may be
prohibitive for certain commercial applications. When the tin
content is less than 1.5%, the alloy lacks adequate strength and
resistance to stress relaxation for spring applications.
1 TABLE 1 Electrical Conductivity Composition (% IACS) Yield
Strength (ksi) 88.5% Cu 26 75 9.5% Zn 2% Sn 0.2% P 87.6% Cu 21 83
9.5% Zn 2.9% Sn 0.2% P 94.8% Cu 17 102 5% Sn 0.2% P
[0034] Preferably, the tin content of the alloys of the invention
is from about 1.2% to about 2.2% and most preferably from about
1.4% to about 1.9%.
[0035] Iron
[0036] Iron refines the microstructure of the as-cast alloy and
increases strength. The refined microstructure is characterized by
an average grain size of less than 100 microns. Preferably, the
average grain size is from 30 to 90 microns and most preferably,
from 40 to 70 microns. This refined microstructure facilitates
mechanical deformation at elevated temperatures, such as rolling at
850.degree. C.
[0037] When the iron content is less than about 1.6%, the grain
refining effect is reduced and coarse crystalline grains, with an
average grain size on the order of 600-2000 microns, develop. When
the iron content exceeds 2.2%, excessive amount of stringers
develop during hot working.
[0038] The effective iron range, 1.6%-2.2%, differs from the iron
range of the alloys disclosed in Caron et al. patent application
Ser. No. 08/591,065. Caron et al. disclose that grain refinement
was not optimized until the iron content exceeded about 2%. The
ability to refine the grain structure at lower iron contents in the
alloys of the present invention was unexpected and believed due to
a phase equilibrium shift due to the inclusion of zinc. To be
effective, this phase shift interaction requires a minimum zinc
content of about 5%.
[0039] Large stringers, having a length in excess of about 200
microns, are expected to form when the iron content exceeds about
2.2%. The large stringers impact both the appearance of the alloy
surface as well as the properties, electrical and chemical, of the
surface. The large stringers can change the solderability and
electro-platability of the alloy.
[0040] To maximize the grain refinement and strength increase
attributable to iron without the detrimental formation of
stringers, the iron content should be maintained between about 1.6%
and 2.2% and preferably, between about 1.6% and 1.8%.
[0041] Zinc
[0042] The addition of zinc to the alloys of the invention would be
expected to provide a moderate increase in strength with some
decrease in electrical conductivity. While, as shown in Table 2,
this occurred, surprisingly, with a minimum of 5% zinc present, the
grain refining capability of the iron addition was significantly
enhanced, as illustrated in Table 3.
2 TABLE 2 Electrical Conductivity Tensile Strength Composition (%
IACS) (ksi) 1.8 Sn 33 99 2.2 Fe balance Cu 1.8 Sn 29 99 2.2 Fe 5 Zn
balance Cu 1.8 Sn 25 108 2.2 Fe 10 Zn balance Cu (Tensile strength
measured following 70% cold reduction)
[0043]
3 TABLE 3 Composition Grain Size 1.9 Fe Coarse 1.8 Sn 0.04 P
balance Cu 5 Zn Medium 1.9 Fe 1.8 Sn 0.04 P balance Cu 7.5 Zn Fine
1.9 Fe 1.8 Sn 0.04 P balance Cu 10 Zn Fine 1.9 Fe 1.8 Sn 0.04 P
balance Cu 15 Zn Fine 3.3 Co Fine 1.8 Sn 0.04 P balance Cu
[0044] Preferably, the zinc content is from that effective to
enhance iron initiated grain refinement to about 20%. More
preferably, the zinc content is from about 5% to about 15% and most
preferably, the zinc content is from about 8% to about 12%.
[0045] Peritectic Reaction for Cast Grain Refinement
[0046] It is believed that the grain refining effectiveness of the
iron addition is due to the iron separating from the melt first,
during solidification, as numerous, relatively fine, dendritically
shaped particles of fcc (face centered cubic) gamma iron. With
continued cooling, these properitectic iron particles effectively
nucleate cast grains of the alloy via the peritectic solidification
reaction:
Fe+L.rarw..fwdarw.Cu (alloy),
[0047] effectively raising the nucleation rate, in turn resulting
in cast grain refinement.
[0048] Other metallic elements that undergo a similar peritectic
decomposition reaction with elemental or intermetallic
properitectic particles in a tin brass may also be used, subject to
the proviso that the peritectic composition does not require such a
large amount of the addition that the desirable properties of the
tin brass, such as processing capability, conductivity or bend
formability, are severely degraded.
[0049] Cobalt is a suitable substitute for either a portion, or
all, of the iron as shown in Table 4.
4 TABLE 4 Composition Grain Size 10 Zn Coarse 2.7 Co 1.8 Sn 0.04 P
balance Cu 10 Zn Coarse 3.0 Co 1.8 Sn 0.04 P balance Cu 10 Zn Fine
3.3 Co 1.8 Sn 0.04 P balance Cu
[0050] From Table 4, the cobalt content, when used as the primary
grain refiner, should be in excess of about 3.0%. Preferably, the
cobalt content is between about 3.2% and 4.4% and most preferably
from between 3.2% and 3.6%. Excessive amounts of cobalt should be
avoided because coarse stringers of excess properitectic cobalt
particles may occur and degrade alloy properties.
[0051] Cobalt may be added as a partial substitute for iron. Cobalt
less effectively refines the grain structure of the alloys of the
invention and the substitution should satisfy the equation:
Fe+MCo=iron ranges specified above.
[0052] M is between 0.45 and 0.65, and preferably from 0.5 to 0.6.
Most preferably, the substitution is in the higher range, about 0.6
for lower contents of cobalt and about 0.5 for higher contents of
cobalt with an approximate delineation between the lower contents
and the higher contents being a 2% cobalt.
[0053] Other suitable properitectic particle formers include
iridium in an amount of from about 10% to about 20% and preferably
in an amount of from about 11% to 15%; niobium in an amount of from
about 0.01% to about 5% and preferably in an amount of from about
0.1% to about 1%; vanadium in an amount of from about 0.01% to
about 5% and preferably in an amount of from about 0.1% to about
1%; and molybdenum in an amount of from about 0.5% to about 5% and
preferably in an amount of from about 1% to about 3%.
[0054] One or more of these other peritectic reaction initiators
may substitute, in whole or in part, for cobalt or iron.
[0055] Other additions
[0056] Phosphorous is added to the alloy for conventional reasons,
to prevent the formation of copper oxide or tin oxide precipitates
and to promote the formation of iron phosphides. Phosphorous causes
problems with the processing of the alloy, particularly with hot
rolling. It is believed that the iron addition counters the
detrimental impact of phosphorous. At least a minimal amount of
iron must be present to counteract the impact of the
phosphorous.
[0057] A suitable phosphorous content is any amount up to about
0.4%. A preferred phosphorous content is from about 0.03% to
0.3%.
[0058] Other elements that remain in solution when the copper alloy
solidifies may be present in amounts of up to 20% and may
substitute, at a 1:1 atomic ratio, for either a portion, or all, of
the zinc. The preferred ranges of these solid-state soluble
elements are those specified for zinc. Among the preferred elements
are manganese and aluminum.
[0059] Less preferred are additions of elements that affect the
properties of the alloy. Although, less preferred, additions such
as nickel, magnesium, beryllium, silicon, zirconium, titanium,
chromium and mixtures thereof may be included.
[0060] For example, nickel additions severely reduce electrical
conductivity. As a result, the less preferred additions are
preferably present in an amount of less than about 0.4% and most
preferably, in an amount of less than about 0.2%. Most preferably,
the sum of all less preferred alloying additions is less than about
0.5%.
[0061] Processing
[0062] The alloys of the invention are preferably processed
according to the flow chart illustrated in FIG. 1. An ingot, being
an alloy of a composition specified herein, is cast 10 by a
conventional process such direct chill casting. The alloy is hot
rolled 12, at a temperature of from about 650.degree. C. to about
950.degree. C. and preferably, at a temperature of between about
825.degree. C. and 875.degree. C. Optionally, the alloy is heated
14 to maintain the desired hot roll 12 temperature.
[0063] The hot rolling reduction is, typically, by thickness, up to
98% and preferably, from about 80% to about 95%. The hot rolling
may be in a single pass or in multiple passes, provided that the
temperature of the ingot is maintained at above 650.degree. C.
[0064] After hot rolling 12, the alloy is, optionally, water
quenched 16. The bars are then mechanically milled to remove
surface oxides and then cold rolled 18 to a reduction of at least
60%, by thickness, from the gauge at completion of the hot roll
step 12, in either one or multiple passes. Preferably, the cold
roll reduction 18 is from about 60%-90%.
[0065] The strip is then annealed 20 at a temperature between about
400.degree. C. and about 600.degree. C. for a time of from about
0.5 hour to about 8 hours to recrystallize the alloy. Preferably,
this first recrystallization anneal is at a temperature between
about 500.degree. C. and about 600.degree. C. for a time between 3
and 5 hours. These times are for bell annealing in an inert
atmosphere such as nitrogen or in a reducing atmosphere such as a
mixture of hydrogen and nitrogen.
[0066] The strip may also be strip annealed, such as for example,
at a temperature of from about 600.degree. C. to about 950.degree.
C. for from 0.5 minute to 10 minutes.
[0067] The first recrystallization anneal 20 causes additional
precipitates of iron and iron phosphide to develop. These
precipitates control the grain size during this and subsequent
anneals, add strength to the alloy via dispersion hardening and
increase electrical conductivity by drawing iron out of solution
from the copper matrix.
[0068] The bars are then cold rolled 22 a second time to a
thickness reduction of from about 30% to about 70% and preferably
of from about 35% to about 45%.
[0069] The strip is then given a second recrystallization anneal
24, utilizing the same times and temperatures as the first
recrystallization anneal. After both the first and second
recrystallization anneals, the average grain size is between 3 and
20 microns. Preferably, the average grain size of the processed
alloy is from 5 to 10 microns.
[0070] The alloys are then cold rolled 26 to final gauge, typically
on the order of between 0.010 inch and 0.015 inch. This final cold
roll imparts a spring temper comparable to that of copper alloy
C51000.
[0071] The alloys are then relief annealed 28 to optimize
resistance to stress relaxation. One exemplary relief anneal is a
bell anneal in an inert atmosphere at a temperature of between
about 200.degree. C. and about 300.degree. C. for from 1 to 4
hours. A second exemplary relief anneal is a strip anneal at a
temperature of from about 250.degree. C. to about 600.degree. C.
for from about 0.5 minutes to about 10 minutes.
[0072] Following the relief anneal 28, the copper alloy strip is
formed into a desired product such as a spring or an electrical
connector.
[0073] The advantages of the alloys of the invention will become
more apparent from the examples that follow.
EXAMPLES
Example 1
[0074] Copper alloys containing 10.5% zinc, 1.7% tin, 0.04%
phosphorous, between 0% and 2.3% iron and the balance copper were
prepared according to the process of FIG. 1. Following the relief
anneal 28, the yield strength and the ultimate tensile strength of
sample coupons, 2 inch gauge length, were measured at room
temperature (20.degree. C.).
[0075] The 0.2% offset yield strength and the tensile strength were
measured on a tension testing machine (manufactured by Tinius
Olsen, Willow Grove, Pa.).
[0076] As shown in FIG. 2, increasing the iron from 0% to 1% led to
a significant increase in yield strength. Further increases in the
iron content had only a minimal effect on strength,but increased
the likelihood of stringers.
[0077] FIG. 3 graphically illustrates a similar relationship
between the iron content and the ultimate tensile strength.
Example 2
[0078] Copper alloys containing 10.4% zinc, 1.8% iron, 0.04%
phosphorous, between 1.8% and 4.0% tin and the balance copper were
processed according to FIG. 1. Test coupons in the relief anneal
condition 28, were evaluated for yield strength and ultimate
tensile strength.
[0079] FIG. 4 graphically illustrates that increasing the tin
content leads to an increase in yield strength. While FIG. 5
graphically illustrates the same effect from tin additions for the
ultimate tensile strength.
[0080] Since the strength increase is monatomic with the amount of
tin while the conductivity decreases, the tin content should be a
trade-off between desired strength and conductivity.
Example 3
[0081] Copper alloys containing 1.9% iron, 1.8% tin, 0.04%
phosphorous, between 0% and 15% zinc and the balance copper were
processed according to FIG. 1. Test coupons in the relief anneal
condition 28, were evaluated for yield strength and ultimate
tensile strength.
[0082] FIG. 6 graphically illustrates that a zinc content of less
than about 5% does not contribute to the strength of the alloy, and
as discussed above, does not enhance the grain refining capability
of the iron. Above 5% zinc, the alloy strength is increased,
although a decrease in electrical conductivity is experienced.
[0083] FIG. 7 graphically illustrates the same effect from zinc
additions for the ultimate tensile strength of the alloy.
Example 4
[0084] Table 5 illustrates a series of alloys processed according
to FIG. 1. Alloy A is an alloy of the type disclosed in Caron et
al. Ser. No. 08/591,065. Alloys B and C are in accordance with the
present invention and alloy D is conventional copper alloy C510.
All properties were measured when the alloy was in a spring temper
following a 70% cold roll reduction in thickness.
5TABLE 5 Elec. Tensile Yield Conduct. Strength Strength Alloy
Composition % IACS (ksi) (ksi) A 1.8 Sn 33% 99 96 2.2 Fe 0.06 P
balance Cu B 1.8 Sn 29% 99 94 2.2 Fe 0.06 P 5.0 Zn balance Cu C 1.8
Sn 25% 108 101 2.2 Fe 0.06 P 10.0 Zn balance Cu D 4.27 Sn 17% 102
96 0.033 P balance Cu
[0085] Table 5 shows that the addition of 5% zinc did not increase
the strength of the alloy and slightly reduced electrical
conductivity. A 10% zinc addition had a favorable impact on the
strength.
[0086] The benefit of the zinc addition is more apparent in view of
Table 6 where the strength to rolling reduction is compared.
6 TABLE 6 MBR/t MBR/t Alloy % Red. YS TS GW BW A 25 80 83 1.0 1.3 C
25 84 88 0.8 1.6 A 33 83 86 1.0 1.3 C 33 89 94 0.9 2.1 A 58 96 99
1.7 3.9 C 60 96 102 1.6 6.4 A 70 100 104 1.9 6.3 C 70 101 108 1.9
.gtoreq.7 % Red. = percent reduction in thickness at the final cord
step (reference numeral 26 in FIG. 5). YS = Yield strength in ksi.
TS = Tensile strength in ksi. MBR/t (GW) = Good way bends about a
180.degree. radius of curvature. MBR/t (BW) = Bad way bends about a
180.degree. radius of curvature.
[0087] A further benefit of the zinc addition is the improved good
way bends achieved with alloy C. Bend formability was measured by
bending a 0.5 inch wide strip 180.degree.about a mandrel having a
known radius of curvature. The minimum mandrel about which the
strip could be bent without cracking or "orange peeling" is the
bend formability value. The "good way" bend is made in the plane of
the sheet and perpendicular to the longitudinal axis (rolling
direction) during thickness reduction of the strip. "Bad way" is
parallel to the longitudinal axis. Bend formability is recorded as
MBR/t, the minimum bend radius at which cracking or orange peeling
in not apparent, divided by the thickness of the strip.
[0088] Usually, an increase in strength is accompanied by a
decrease in bend formability. However, with the alloys of the
invention, an addition of 10% zinc increases both the strength and
the good way bends.
Example 5
[0089] Alloys of the compositions indicated in Table 7, with the
balance being copper, were processed according to Process 1. Table
7 shows the effectiveness of cobalt as a partial substitute for
iron in the tin brass alloys of the invention.
7TABLE 7 CR 22% CR 65% As-cast (RA) (RA) Grain YS/UTS/EL) YS/UTS/EL
Zn Sn Fe Co P Size (ksi/ksi/%) (ksi/ksi/%) 10.4 1.80 1.5 0.5 0.04
fine (83/87/7) (101/108/4) 10.4 1.80 1.78 -- 0.04 fine (81/85/11)
(102/108/2) 10.4 1.80 1.5 -- 0.04 coarse -- -- YS = yield strength
UTS = ultimate tensile strength EL = elongation CR = cold roll RA =
relief anneal
[0090] Table 8 illustrates the magnetic permeability of hot rolled
plate when formed from cobalt containing tin brass is higher than
the magnetic permeability of the same alloy when an equivalent
amount of iron is present, using 0.6Co=Fe as the equivalency
relationship.
8TABLE 8 Magnetic Permeability As-cast (Hot Rolled Zn Sn Fe Co P
Grain Size Plate) 10.2 1.87 2.02 -- 0.03 fine 1.05-1.10 10.5 1.80
-- 3.3 0.04 fine 1.2
[0091] While described particularly in terms of direct chill
casting, the alloys of the invention may be cast by other processes
as well. Some of the alternative processes have higher cooling
rates such as spray casting and strip casting. The higher cooling
rates reduce the size of the properitectic iron particles and are
believed to shift the critical maximum iron content to a higher
value such as 4%.
[0092] It is apparent that there has been provided in accordance
with the invention an iron modified phosphor bronze that fully
satisfies the objects, means and advantages set forth hereinabove.
While the invention has been described in combination with
embodiments thereof, it is evident that many alternatives,
modifications and variations will be apparent to those skilled in
the art in light of the foregoing description. Accordingly, it is
intended to embrace all such alternatives, modifications and
variations as fall within the spirit and broad scope of the
appended claims.
* * * * *