Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Copper-zinc alloy, production method and use
Description
The invention relates to a copper-zinc alloy, to
methods for producing tubes or rods from the copper-zinc
alloy and to its use.
= Owing to the greatly increasing stress on
materials for friction bearings and the rising operating
pressures and temperatures in modern machines, engines and
equipment, the demands on the properties of the alloys
suitable for use are increasing.
For this reason there is a need to further
develop the operating properties of materials for
bearings. This entails on the one hand increasing the
strength properties, the heat resistance of the structure
and the complex wear resistance while simultaneously
having sufficient ductility properties. On the other hand,
the friction bearing alloy must have a sufficient
performance in the event of lubrication supply failure,
which avoids seizure of the bearing partners. To date,
copper alloys containing lead have been used for this
purpose.
Documents DE 10 2004 058 318 B4 and DE 10 2005
015 467 Al disclose the application possibilities of a
copper-zinc alloy for use as a valve guide and friction
bearing with high thermal and wear stability. The alloy
consists of 59 - 73 wt% copper, 2.7 - 8.5 wt% manganese,
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1.5 - 6.3 wt% aluminum, 0.2 - 4 wt% silicon, 0.2 - 3 wt% iron, 0
- 2 wt% lead, 0 - 2 wt% nickel, 0 - 0.4 wt% tin and the
remainder zinc.
Increasing the thermal and wear stability for these
alloys with an extremely high alloy content of manganese and
aluminum generally entails a 13-matrix, in which a-precipitates
and hard phases are incorporated. Although the wear and heat
resistance of these alloys may be regarded as sufficient, this
unilateral orientation of the structural adjustment
detrimentally affects the ductility properties of the material.
Furthermore, DE 29 19 478 C2 discloses the use of a
similar alloy for synchronous rings. In respect of this use, it
is regarded as advantageous that there is an improved wear-
resistance and at the same time a significantly increased
coefficient of friction. The semifinished products made from the
alloy furthermore have good processability; they can readily be
cold-formed owing to the relatively high aluminum content,
although an increase in hardness at room temperature is to be
noted compared with the previously conventional special brasses.
The aluminum content lies in the range of from 4 to 6 wt%.
The further document US Patent No. 3,773,504 discloses
a copper-based alloy which is wear-resistant at high temperature
for a valve seat in combustion engines, which likewise has a
comparatively high aluminum content of from 5 to 12 wt%. The
aluminum content in the specified range improves the corrosion
resistance in addition to the effect of reinforcing the matrix.
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A further increase in the wear resistance occurs through the
formation of an intermetallic phase of manganese and silicon.
The patent application published for opposition DE 1
194 592 discloses a method for producing synchronous rings,
which are distinguished by a high and constant coefficient of
friction, a high wear resistance and good machining
processability. To this end annealing treatments of the alloy,
consisting substantially of 0-phase at between 200 and 500 C,
are proposed in order to achieve from 5 to 50% a-precipitation.
A certain lead content is usually provided in said
documents for better machining processability.
It is an object of the invention to provide a copper-
zinc alloy having improved cold formability, higher hardness and
heat resistance.
In one aspect of the invention there is provided a
copper-zinc alloy, consisting of, in wt.%: from 28.0 to 36.0%
Zn; from 0.5 to 1.5% Si; from 1.5 to 2.5% Mn; from 0.2 to 1.0%
Ni; from 0.5 to 1.5% Al; from 0.1 to 1.0% Fe; optionally up to
0.1% Pb, up to 0.1% P. and up to 0.08% S. with the balance being
Cu and inevitable impurities, the copper-zinc alloy having
Incorporated therein mixed suicides of iron-nickel-manganese, a
hard phase of the mixed suicides of iron-nickel-manganese being
incorporated in an a-matrix and contributing to improving the
resistance of the alloy against abrasive and adhesive wear; and
after a post-processing step which involves hot-forming and
further annealing steps, the alloy structure comprises both
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body-centered cubic crystal type p-phase inclusions in an amount
of from 5-45 vol.% and the mixed suicides of iron-nickel-
manganese present in an amount not exceeding 20 vol.%
incorporated in the a-matrix, a portion of the mixed suicides
of the iron-nickel-manganese having a columnar shape and a
proportion of the iron-nickel-manganese mixed suicides having a
globular configuration.
The invention includes the technical teaching that a
copper-zinc alloy consists of (in wt%):
from 28.0 to 36.0% Zn,
from 0.5 to 2.3% Si,
from 1.5 to 2.5% Mn,
from 0.2 to 3.0% Ni,
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from 0.5 to 1.5% Al,
from 0.1 to 1.0% Fe,
optionally also up to at most 0.1% Pb,
optionally also up to at most 0.2% Sn,
optionally also up to at most 0.1% P,
optionally also up to 0.08% S,
remainder Cu and inevitable impurities,
with mixed suicides of iron-nickel-manganese
incorporated in the matrix.
The invention is based on the idea of providing
a copper-zinc alloy which has incorporated mixed silicides
of iron-nickel-manganese and can be produced with the aid
of the continuous or semicontinuous extrusion casting
method. Owing to the mixed silicide formation, the copper-
zinc alloy has a high hard phase content which contributes
to improving the material resistance against abrasive
wear. Owing to their low susceptibility to seizure, the
high content of suicides furthermore entails a better
resistance against adhesive wear.
The alloy thus has high hardness and strength
values but a requisite degree of ductility is nevertheless
ensured, as expressed by an elongation at break value in a
tensile test. With this combination of properties, the
subject of the invention is particularly suitable for Pb-
free friction bearing elements in engines, for example
piston bore liners, and in transmissions.
When casting the alloy, early precipitation of
iron- and nickel-rich mixed suicides initially takes
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place. During further growth, these precipitates can
develop to form mixed suicides of iron-nickel-manganese
with a considerable size, often with a columnar shape.
Furthermore, a considerable proportion also remains rather
small with a globular configuration, which is finely
distributed in the matrix. In particular, the finely
distributed suicides are regarded as the reason why
stabilization of the 13-phase takes place. This makes an
important contribution to increasing the heat resistance
and complex wear resistance.
The particular advantage of the alloy according
to the invention is due to a combination of properties,
optimized for an application purpose, in the form of
increasing the strength, the heat resistance of the
structure and the complex wear resistance while
simultaneously having sufficient ductility properties.
Furthermore, the alloy has good performance in the event
of lubrication supply failure for friction bearing
applications, which avoids seizure of the bearing
partners. Owing to the substituted lead content compared
with conventional alloys, the claimed material solution
also accommodates the need for an environmentally friendly
lead-free alloy alternative.
This material is furthermore intended for
particular applications in which a requisite degree of
plasticizability is important, despite
stringent
requirements for the hardness and strength. This is the
case for example in the field of hydraulic equipment, the
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sliding pad of which is partly produced by pressing
together the respective connection partners. Particularly
in this field of hydraulic mechanical engineering, for
example for axial piston machines, future developments are
likely to entail increasing operating pressures which
place greater demands on the strength properties of the
materials being used.
In a preferred configuration, the alloy
according to the invention may contain
from 28.0 to 36.0% Zn,
from 0.5 to 1.5% Si,
from 1.5 to 2.5% Mn,
from 0.2 to 1.0% Ni,
from 0.5 to 1.5% Al,
from 0.1 to 1.0% Fe.
Owing to the somewhat reduced elementary
contents of silicon and nickel, the iron-nickel-manganese
mixed silicide formation can be specially oriented toward
an optimized combination of properties, particularly in
relation to the requisite degree of ductility.
In another preferred configuration, the alloy
according to the invention may contain
from 28.0 to 36.0% Zn,
from 1.0 to 2.3% Si,
from 1.5 to 2.5% Mn,
from 1.5 to 3.0% Ni,
from 0.5 to 1.5% Al,
from 0.1 to 1.0% Fe.
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The ratio Mn/Ni of the elementary contents of
the elements manganese and nickel may preferably lie
between 0.7 and 1.3. With a higher silicon content,
particularly in conjunction with the preferred Mn/Ni
ratio, this material has good plasticizability. This is
important particularly for friction bearing elements which
need to receive their bearing partners by producing a
press-fit connection just before operation.
Advantageously, the structure comprises a 3-
phase content of up to 50 vol.% in the cast state. This is
regarded as a necessary prerequisite for sufficiently good
hot formability of the copper alloy by extrusion.
In a preferred configuration of the invention,
after post-processing which involves at least hot forming
or cold forming and further annealing steps, the structure
comprises a 3-phase content of up to 45 vol.%, the mixed
suicides of Fe-Ni-Mn up to 20 vol.% and a remainder of a-
phase.
With these 3-inclusions and hard phases of
different size distribution in an a-matrix, this alloy
ensures advantageous heat resistance of the structure with
sufficient ductility properties as well as a suitable
complex wear resistance of the components. In particular,
owing to the low cold seizure susceptibility of silicides,
the high suicide content contributes to improving the
frictional and lubricant-failure properties in bearing
elements, so that the omission of the Pb content can be
compensated for. The demand for improved environmental
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compatibility of these machine and system components has
therefore likewise been accommodated.
The ratio Rp0.2/R,, of the values for the yield
point and tensile strength of the alloy may advantageously
lie between 0.5 and 0.95.
In the field of another application, i.e.
hydraulic machine and system technology, future
developments are likely to entail increasing stress on the
friction bearings due to increasing operating pressures.
Besides a strength increase, this configuration ensures
the required ratio Rp0.2/Rm in the range of between 0.5 and
0.95. This is an important prerequisite for the production
of a bearing seat by press-fit connection of the friction
bearing partners.
Another aspect of the invention relates to a
method for producing tubes or rods made of the copper-zinc
alloy according the invention, wherein a post-processing
of the alloy comprises the following steps:
- extrusion in a temperature range of from 600
to 800 C,
- at least one cold forming.
These tubes and rods may be used as starting
material for the machining manufacture of friction bearing
elements.
Another alternative aspect of the invention
relates to a method for producing tubes or rods made of
the copper-zinc alloy according the invention, wherein a
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post-processing of the alloy comprises the following
steps:
- extrusion in a temperature range of from 600
to 800 C,
- a combination of at least one cold forming
with at least one anneal in a temperature range of from
250 to 700 C.
By means of a combination of cold forming by
drawing and one or more intermediate anneals of the rods
and tubes in the temperature range of from 250 to 700 C,
it is possible to set up a fine distribution of the
heterogeneous structure.
The demand for improving the complex operating
properties of the bearing materials will thereby have been
satisfied, since modern machines, engines, transmissions
and equipment entail greatly increasing stress on the
friction bearing elements. A significant increase in the
tensile strength R, yield point Rp0.2 and hardness of the
material are achieved with this particular configuration
of the copper-zinc alloy. The elongation at break of the
alloy likewise moves to a sufficiently high level, so that
the required ductility properties are achieved. The
extraordinarily high content of hard phases, in particular
the mixed silicides of iron-nickel-manganese and the
heterogeneous matrix structure of a- and 3-phases, ensures
a suitable complex wear resistance of the components made
of this material.
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The relationship between the level and
distribution of the 3-phase content and the heat
resistance of the structure is already known. Yet since
this body-centered cubic crystal type fulfills an
indispensable strength-increasing function in the copper-
zinc alloys, minimizing the 13-content should not
exclusively be paramount. By means of the manufacturing
sequence of extrusion/drawings/intermediate anneals, the
structure of the copper-zinc alloy can be modified in its
phase distribution so that it also has a sufficient heat
resistance besides a high strength.
In a preferred configuration, the forming may be
followed by a stress-relieving anneal in a temperature
range of from 250 to 450 C.
In the manufacturing procedure, it is necessary
to reduce the level of residual stresses with the aid of
one or more stress-relieving anneals. Reducing the
residual stresses is also important for guaranteeing a
sufficient heat resistance of the structure, and for
ensuring sufficient straightness of the rods and tubes.
Furthermore, as already mentioned above, the
copper-zinc alloy according to the invention may be used
for friction bearing elements in combustion engines,
transmissions or hydraulic equipment.
Further exemplary embodiments of the invention
will be explained in more detail with the aid of the
table. Cast bolts made of the copper-zinc alloy according
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to the invention were produced by ingot casting. The
chemical composition of the castings is shown in Tab. 1.
Table 1: Chemical composition of the cast bolts
(embodiment A)
No. Cu Zn Si Mn Ni Sn Al Fe
[96] [96] [96] [96] [96] [%] [%]
[%]
Alloy type 64.1 31.2 1.20
1.76 0.40 <0.01 0.92 0.30
1
Alloy type 63.6 31.7 1.17
1.75 0.55 <0.01 0.87 0.33
2
Alloy type 59.3 33.4 1.7 2.0 2.3 <0.01 0.9
0.5
3
Manufacturing sequence for alloy types 1 and 2:
= extrusion to form tubes at a temperature of
700 C
= combination of cold forming/intermediate
anneals (650 C/50-60 min)/rectifying/stress-relieving
anneals (300-350 C/3 h)
At the end of manufacturing, the mechanical
properties of the tubes are at the level which is
represented as numerical values in Tab. 2.
Table 2: Mechanical properties of the tubes
p.
(alloy type 1 and alloy type 2) R02
No. 8-content Grain Rm Rp0.2/ A5 HE
[%] size [MPa] [MPa] Rm [%]
[Pm]
Alloy 5 5-10 715 656
0.92 12.0 222
type
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1
Alloy 5-10 10-15 660 577 0.87 13.2
207
type
2
Manufacturing sequence:
= Hot rolling at a temperature of 750 C on
the laboratory scale
= Combination of cold forming/intermediate
anneals (300-400 C/2-3 h)
At the end of manufacturing, the mechanical
properties of the tubes are at the level which is
represented as numerical values in Tab. 3.
Table 3: Mechanical properties (alloy type 3)
No. p- Grain Rm Rp0.2 R02/ A5 HB
Alloy type content size [MPa [MPa Rm Po]
3 [%] [Pm] ] ]
Treatment 1 30-40 10 674 399 0.59 7.3 222
(300 0/2 h)
Treatment 2 30-40 10 621 424 0.68 13.1 206
(400 C/2 h)
