Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Copper/zinc/silicon alloy, use and production thereof
The invention relates to a copper-zinc-silicon alloy
and to the use and production of a copper-zinc-silicon
alloy of this type.
A priority requirement of copper-zinc-silicon alloys is
that they be resistant to dezincification and
machineable. Hitherto, good machining properties of
brass alloys of this type has been realized by the
addition of lead, as described, for example, in
EP 1 045 041 Al. Recently, however, lead-free brass
alloys with good machining properties have been
developed, as described, for example, in
EP 1 038 981 Al and DE 103 08 778 B3. Both lead-free
and lead-containing Cu-Zn-Si alloys have a tendency to
be oxidized and form a layer of scale at temperatures
between 300 C and 800 C. This layer of scale is only
loosely bonded to the metal and can easily become
detached from it, so that it is then dispersed through
the production facilities, with the result that this
layer has a disruptive contaminating effect. The
production facilities are expensive to clean, making
production costs high. A further drawback of the known
Cu-Zn-Si alloys is that the mechanical properties of
the material change over long workpieces, since the
material lacks homogeneity.
In view of these facts, the present invention is
therefore based on the problem of providing a copper-
zinc-silicon alloy which is improved in terms of its
homogeneity and, furthermore, is less prone to the
formation of scale, and to provide the use and
production of a brass alloy of this type.
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The first aspect, relating to an alloy, is achieved according
to the invention by a copper-zinc-silicon alloy comprising, in
% by weight, 70 to 80% of copper, 1 to 5% of silicon, 0.0001 to
0.5% of boron, 0 to 0.2% of phosphorus and/or arsenic,
remainder zinc plus inevitable impurities.
In one embodiment of the first aspect, the invention relates to
a Cu-Zn-Si alloy, comprising, in % by weight: 70 to 80% of
copper; 1 to 5% of silicon; 0.0001 to 0.004% of boron; at least
one of: 0 to 0.5% of gold, 0 to 0.3% of cadmium, 0 to 0.3% of
selenium, 0 to 0.3% of tellurium, 0 to 0.3% of bismuth, 0
to 0.2% arsenic; 0 to 0.2% of phosphorus; and remainder zinc
plus inevitable impurities.
In a further embodiment of the first aspect, the invention
relates to a Cu-Zn-Si alloy, comprising, in % by weight: 70
to 80% of copper; 1 to 5% of silicon; 0.0001 to 0.0004% of
boron; 0 to 0.2% of phosphorus; and remainder zinc plus
inevitable impurities.
The copper content is between 70 and 80%, since copper contents
of below 70% or above 80% would have an adverse effect on the
machining properties of the alloy. The same applies if the
silicon concentration departs from the indicated range of 1%
to 5%. The boron concentration in the alloy is between 0.0001
and 0.5%. Surprisingly, it has now been found that the
addition of boron within the concentration range claimed on the
one hand reduces the formation of scale and on the other hand
significantly improves the bonding of the remaining scale to
the material. Furthermore, it is also surprising that the
addition of boron improves the homogeneity of the
microstructure and thereby prevents fluctuations in the
mechanical properties. Phosphorus and arsenic may each be
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present in the alloy in a concentration of up to 0.2%, and can
be substituted for one another. Phosphorus and arsenic have a
beneficial effect on the formation of the initial cast
microstructure and the corrosion properties, and furthermore
improve the flow properties of the melt and reduce the
susceptibility to stress corrosion cracking. The remaining
main component of the alloy is zinc.
In addition to the advantages listed above of avoiding easily
detached layers of scale which increase production costs and
improving the mechanical properties and, furthermore, good
machining properties and shaping properties in combination with
a high resistance to corrosion are provided, the resistance to
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dezincification and stress corrosion cracking are also
particularly pronounced in the invention.
Dezincification tests carried out in accordance with
ISO 6509 give dezincification depths of only up to
26 m.
The second aspect, relating to the use of a copper-
zinc-silicon alloy of this type, is achieved by its use
for electrical engineering components, for sanitaryware
components, for vessels for transporting or storing
liquids or gases, for torsionally loaded components,
for recyclable components, for drop-forged components,
for semi-finished products, for strips, for sheets, for
profiled sections, for plates or as a wrought, rolled
or cast alloy.
The Cu-Zn-Si alloy is used for contacts, pins or
securing elements in electrical engineering, for
example as stationary contacts or fixed contacts,
including clamping and plug connections or plug-in
contacts.
The alloy has a high resistance to corrosion with
respect to liquid and gaseous media. Moreover, it is
extremely resistant to dezincification and stress
corrosion cracking. Consequently, the alloy is
particularly suitable for use for vessels for
transporting or storing liquids or gases, in particular
for vessels used in refrigeration or for pipes, water
fittings, valve extensions, pipe connectors and valves
in sanitaryware.
The low corrosion rates also ensure that the metal
leaching, i.e. the property of losing alloying
constituents through the action of liquid or gaseous
media, is inherently low. In this respect, the material
is suitable for application areas which require low
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pollutant emissions in order to protect the
environment. Therefore, the alloy according to the
invention can be used in the field of recyclable
components.
The lack of susceptibility to stress corrosion cracking
means that the alloy is recommended for use in screwed
or clamped connections in which for technical reasons
high elastic energies are stored. Therefore, the alloy
is particularly suitable for all components which are
subject to tensile and/or torsional loads, in
particular for nuts and bolts. After cold-forming, the
material achieves high values for the proof stress.
Consequently, greater tightening torques can be
realized in screw connections which must not be
plastically deformed. The yield strength ratio of the
Cu-Zn-Si alloy is lower than in the case of free-
machining brass. Screw connections which are tightened
only once and in the process are deliberately over-
extended therefore achieve particularly high holding
forces.
Possible uses of the Cu-Zn-Si alloy result for starting
materials in both tube and strip form. The alloy is
also eminently suitable for strips, sheets and plates
which can be milled or punched, in particular for keys,
engravings, for decorative purposes or for leadframe
applications.
The third aspect relating to production of a copper-
zinc-silicon alloy, of this type is achieved by
conventional continuous casting and hot-rolling at
between 600 and 760 C with subsequent deformation, in
particular cold-rolling, preferably with the addition
of further annealing and deformation steps.
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T h e aspect relating to production of a copper-zinc-
silicon alloy of this type is also achieved by
conventional continuous casting and extrusion at up to
760 C, preferably between 650 and 680 C, followed by
cooling in air.
In an advantageous refinement of the Cu-Zn-Si alloy,
the alloy comprises 75 to 77% of copper, 2.8 to 4% of
silicon and 0.001 to 0.1% of boron, as well as 0.03 to
0.1% of phosphorus and/or arsenic, as well as zinc as
remainder element plus inevitable impurities.
In a preferred alternative, the copper-zinc-silicon
alloy comprises at least one element, in % by weight,
selected from the group consisting of 0.01 to 2.5% of
lead, 0.01 to 2% of tin, 0.01 to 0.3% of iron, 0.01 to
0.3% of cobalt, 0.01 to 0.3% of nickel and 0.01 to 0.3%
of manganese. The addition of lead has a positive
influence on the machining properties.
The alloy in this case advantageously comprises at
least one element, in % by weight, selected from the
group consisting of 0.01 to 0.1% of lead, 0.01 to 0.2%
of tin, 0.01 to 0.1% of iron, 0.01 to 0.1% of cobalt,
0.01 to 0.1% of nickel and 0.01 to 0.1% of manganese.
In a preferred refinement, the Cu-Zn-Si alloy in
addition comprises at least one element, in % by
weight, out of up to 0.5% of silver, up to 0.5% of
aluminium, up to 0.5% of magnesium, up to 0.5% of
antimony, up to 0.5% of titanium and up to 0.5% of
zirconium, and preferably selected from the group
consisting of 0.01 to 0.1% of silver, 0.01 to 0.1% of
aluminium, 0.01 to 0.1% of magnesium, 0.01 to 0.1% of
antimony, 0.01 to 0.1% of titanium and 0.01 to 0.1% of
zirconium.
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In an advantageous alternative, the Cu-Zn-Si alloy in
addition comprises at least one element, in % by
weight, selected from the group consisting of up to
0.3% of cadmium, up to 0.3% of chromium, up to 0.3% of
selenium, up to 0.3% of tellurium and up to 0.3% of
bismuth, preferably selected from the group consisting
of 0.01-0.3% of cadmium, 0.01-0.3% of chromium, 0.01-
0.3% of selenium, 0.01-0.3% of tellurium and 0.01-0.3%
of bismuth.
An exemplary embodiment is explained in more detail
with reference to the drawing and with reference to the
following description. In the drawing:
Fig. 1 shows the formation of a layer of scale after
annealing for 2 h at 600 C on a CuZn21Si3P
alloy without the addition of boron (a), a
CuZn21Si3P alloy containing 0.0004% of boron
(b), and a CuZn21Si3P alloy containing 0.009%
of boron (c), and
Fig. 2 shows the formation of the cast microstructure
of a CuZn21Si3P alloy without the addition of
boron (a), a CuZn21Si3P alloy with 0.0004% of
boron (b), and of a CuZn21Si3P alloy containing
0.009% of boron (c).
The CuZn21Si3P alloys on which the exemplary embodiment
is based have variations in concentration of the
components, with copper amounting to between 75.8 and
76.1%, silicon amounting to between 3.2 and 3.4% and
phosphorus amounting to between 0.07 and 0.1%, together
with zinc as the remainder plus inevitable impurities.
The alloy examples have different boron contents, at
0%, 0.004% and 0.009%. The alloys are produced by
continuous casting followed by extrusion at
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temperatures below 760 C, preferably between 650 and
680 C, followed by rapid cooling.
All the alloys have an excellent resistance to
dezincification. A dezincification test carried out in
accordance with ISO 6509 reveals dezincification depths
of only less than 26 m.
If CuZn21Si3P alloys are exposed to temperatures of
300-800 C, for example during hot-working, scale is
formed, and this scale can easily become detached and
contaminate the production facilities. An extensively
scaled surface of a boron-free CuZn21Si3P alloy is
illustrated in Fig. la. The surface of the specimen
appears predominantly grey in Fig. la. This grey colour
reveals the scaled surface of the CuZn21Si3P alloy.
Only a few individual bright spots without any regular
distribution are visible on the surface of the alloy.
By contrast, the CuZn21Si3P alloy with a boron content
of 0.0004% in Fig. lb has a very much greater number of
white spots on the surface of the alloy than the boron-
free alloy. These white spots represent bright metallic
regions of the alloy. These bright metallic regions,
i.e. regions without any scale, are distributed
uniformly over the surface of the alloy. The proportion
of the surface on which scale has formed is
considerably reduced and the remaining scale is more
securely bonded to the metal than in the case of the
boron-free alloy. Fig. lc illustrates a CuZn21Si3P
alloy containing 0.009% of boron. This figure clearly
reveals that the number of bright metallic surfaces,
i.e. of white spots, has increased further. In some
areas, there are relatively large continuous regions of
bright metallic material, and the figure also reveals a
very regular distribution on the surface of the alloy.
The proportion of the surface on which scale has formed
has decreased further, and the remaining scale is
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securely bonded to the metal. Therefore, it has
surprisingly emerged that low boron concentrations of
0.0001 - 0.5% restrict the formation of scale on Cu-Zn-
Si alloys and at the same time considerably increase
the bonding of the scale to the metal, with the result
that undesirable contamination of the production
facilities is avoided.
A similar result was also found for Cu-Zn-Si-P alloys
with different lead content, such as for example 0.01%,
0.05%, 0.1% or 2.5%.
In addition to reducing the susceptibility to scaling
of Cu-Zn-Si alloys, boron also has a positive effect on
the mechanical properties, since boron makes the
microstructure of the alloy more homogeneous. This
change to the microstructure of the alloy is
illustrated in Fig. 2 as a function of the boron
concentrations. Whereas a CuZn21S13P alloy without the
addition of boron has a coarse, inhomogeneous
microstructure (Fig. 2a), a CuZn21Si3P alloy containing
0.0004% of boron has a significantly more homogeneous
microstructure which already has very uniform grain
sizes (Fig. 2b). A further increase in the boron
content to 0.009% results in an even more uniform
CuZn21Si3P alloy of even greater homogeneity, in which
the grains of the microstructure can no longer be seen
by the naked eye (Fig. 2c).
In addition to optical changes to the microstructure,
the addition of boron also has beneficial effects on
the mechanical properties. This is particularly
apparent on rods which have been extruded from Cu-Zn-Si
alloys. To determine the mechanical properties, samples
were taken at the start and end of such rods. The
tensile strength of a rod made from a CuZn21Si3P alloy
without the addition of boron differs by more than
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60 N/mm2 at the start of the rod compared to the end of
the rod. A corresponding alloy with a boron content of
0.0004%, by contrast, has a tensile strength difference
of only less than 40 N/mm2 between the start and end of
the rod. If 0.0096 of boron is added to a CuZn21Si3P
alloy, the difference in the tensile strength between
the start and end of the rod is less than 5 N/mm2.
Therefore, the material has identical mechanical
properties throughout. Accordingly, a uniform strength
is achieved over the entire extruded length. The reason
for this is the grain-refining action of boron.
The table reveals the relationship between the boron
content of a Cu-Zn-Si alloy and the increasing
homogeneity of the alloy microstructure or the
decreasing strength differences within an extruded
workpiece.
Alloy Position Tensile
strength
in N/mm2
CuZn21Si3P Start of extrusion 514
End of extrusion 578
CuZn21Si3P containing Start of extrusion 507
0.0004% of boron
End of extrusion 545
CuZn21Si3P containing Start of extrusion 508
0.009% of boron
End of extrusion 512
