Note: Descriptions are shown in the official language in which they were submitted.
CA 02688994 2010-09-10
LEAD-FREE FREE-CUTTING ALUMINUM BRASS ALLOY AND ITS
MANUFACTURING METHOD
FIELD OF THE INVENTION
[ 0002] The present invention generally relates to a lead-free free-cutting
aluminum brass
alloy, in particular a lead-free free-cutting aluminum brass alloy and its
manufacturing
method which is applicable in low pressure die castings and forgings.
BACKGROUND OF THE INVENTION
[ 0003] Currently, when people search and develop lead-free or low lead free-
cutting brass
alloys, they typically follow two routes to find the elements which could
replace Lead: one
route is to select the elements which hardly form solid solutions in Cu and
can't form
intermetallic compounds with Cu, such as Bi, Se and Te, etc; the other route
is to select the
elements which will form solid solutions in Cu wherein the solid solubility is
reduced with
decreasing temperature, so as to form intermetallic compounds with Cu, and
with Sb, P,
Mg, Si, B and Ca, etc. The first route has been well-known for some time. The
second route
is a more recent development.
[ 0004] In the process of research and development, considering the process
properties,
and comparing properties versus market cost requirements, the selection of
elements for an
alloy, and their range, will vary. Therefore, varied lead-free free-cutting
brass alloys have
been invented. The bismuth brass alloy invention is the most common of these
alloys.
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[0005] For example, Pub. No. CN101225487A to Xuhong Hu discloses an arsenic-
containing
low-lead brass alloy which comprises (wt%) 57-62 Cu, 36-43 Zn, 0.01-1.0 Al,
0.05-2.5 Bi,
0.005-0.3 As, <0.2 Pb and <0.65 Sri, wherein small amounts of Ni, Fe and S and
minimum
amounts of Si, Mg, Mn and Re (Rhenium) are selectively added. No P is added.
Arsenic is one
of the main elements of such an alloy. If its As content is in the middle to
upper limits of the
above-specified range, and if the content of Pb is in the range of 0.1-0.2wt%,
then both As and
Pb are released into the water in amounts that will exceed the upper limits of
the NSF standard.
Therefore, such brass alloys cannot be used in the components for drinking
water supply
systems, such as faucets and valves.
[0006] Pat. No. CN1045316C to Kohler discloses a low-lead bismuth brass alloy
which
comprises (wt%) 55-70 Cu, 30-45 Zn, 0.2-1.5 Al, 0.2-0.3 Bi, <1.0 Pb, <2.0 Ni,
<1.0 Fe, <0.25
In, and 0.005-0.3 Ag, further comprising minimal amounts of one or more of the
elements Ta,
Ga, V, B, Mo, Nb, Co, and Ti. Zr is selectively added. No Si or P is added.
[0007] Pub. No. CN1710126A to Powerway discloses a lead-free free-cutting low-
antimony
bismuth brass alloy and its manufacturing method which comprises (wt%) 55-65
Cu, 0.3-1.5
Bi, 0.05-1.0 Sb, 0.0002-0.05 B, wherein elements such as Ti, Ni, Fe, Sn, P and
rare earth
elements are selectively added and the balance is Zn and impurities. No Si or
Al is added. If
the content of Sb is >0.1, the amount of Sb released in the water will exceed
the requirements
of the NSF standard.
[ 0008] JP2000-239765A to Joetsu discloses a lead-free brass alloy with
corrosion resistance
for castings, which comprises (wt%) 64-68 Cu, 1.0-2.0 Bi, 0.3-1.0 Sri, 0.01-
0.03 P, 0.5-1.0 Ni,
0.4-0.8 Al, <0.2 Fe and the balance being Zn and impurities. The content of Bi
is higher and no
Si is added.
[ 0009] With the increasingly extensive application of bismuth brasses, their
negative effects
are also increasingly notable, such as susceptibility to hot and cold
cracking, poor weldability,
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the necessity to slowly heat and cool when annealing, etc. The cause of these
negative effects
has a common thermodynamic reason: the large differential between the surface
tension of
bismuth (350 dyne/cm) and that of copper (1300 dyne/cm), and the fact that
bismuth cannot
form a solid solution in copper and cannot form intermetallic compounds with
copper. As a
result, liquid bismuth has good wetting with a and 0 grains of copper and
brass. The dihedral
angle between bismuth and copper or brass tends to zero. After solidification,
bismuth is
distributed in the grain boundary in the form of a continuous film.
[0010] Nowadays, the developed bismuth brasses are mainly deformation alloys
and
comprise more than 0.5wt% bismuth. The public casting bismuth brasses, such as
C89550
(which comprises 0.6-4.2wt% Bi), have high tendencies to experience hot
cracking during low
pressure die casting, and are not easily welded.
[0011] Lead-free or low-lead free-cutting antimony brass has excellent
castability,
weldability, hot working formability, and dezincification corrosion
resistance. However,
antimony is more toxic than lead. The NSF/ANSI61-2007 standard requires that
Sb is released
in drinking water in amounts <0.6 g/L and that Pb is released in amounts <1.5
g/L
(NSF61-2005 requires that Pb release is <5 g/L).. Antimony brass is not
suitable for
components used in drinking water supply system.
[0012] Lead-free free-cutting silicon brass is a brass which has certain good
developing
prospects. Currently researched and developed lead-free free-cutting silicon
brasses are mainly
low-zinc deformation silicon brass. Most of them comprise small amounts of
bismuth and the
cost of raw material is rather higher.
[0013] Aluminum brass has good corrosion resistance, but its cuttability is
inadequate. Few
patents and other literature exists relating to lead-free free-cutting
aluminum brasses. United
States Patent No. 3,773,504 (1973) discloses a Cu-Zn-Al-P series alloy having
wear resistance.
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Japanese Patent 2003-253358 discloses a lead-free free-cutting low-zinc
aluminum brass
(containing vanadium and boron, etc.)
BRIEF DESCRIPTION OF THE DRAWINGS
[ 0014] Figures 1 A, 1 B and 1 C show the chip shape of example alloy 1
obtained at a cutting
speed of 40 m/minute, at feeding quantities of 0.1, 0.2, and 0.3
mm/revolution, respectively.
[0015] Figures ID, I E and IF show the chip shape of alloy CuZn40Pb 1 A 10.6
obtained at a
cutting speed of 40 m/minute, at feeding quantities of 0.1, 0.2, and 0.3
mm/revolution,
respectively.
[ 0016] Figures 2A, 2B and 2C show the chip shape of example alloy 1 obtained
at a cutting
speed of 60 m/minute, at feeding quantities of 0.1, 0.2, and 0.3
mm/revolution, respectively.
[0017] Figures 2D, 2E and 2F show the chip shape of alloy CuZn40Pb1A10.6
obtained at a
cutting speed of 60 m/minute, at feeding quantities of 0.1, 0.2, and 0.3
mm/revolution,
respectively.
[ 0018] Figures 3A, 3B and 3C show the chip shape of example alloy 1 obtained
at a cutting
speed of 80 m/minute, at feeding quantities of 0.1, 0.2, and 0.3
mm/revolution, respectively.
[0019] Figures 3D, 3E and 3F show the chip shape of alloy CuZn40Pb1Al0.6
obtained at a
cutting speed of 80 m/minute, at feeding quantities of 0.1, 0.2, and 0.3
mm/revolution,
respectively.
[ 0020] Figures 4A, 4B and 4C show the chip shape of example alloy 1 obtained
at a cutting
speed of 100 m/minute, at feeding quantities of 0.1, 0.2, and 0.3
mm/revolution, respectively.
[0021] Figures 4D, 4E and 4F show the chip shape of alloy CuZn40Pb1A10.6
obtained at a
cutting speed of 100 m/minute, at feeding quantities of 0.1, 0.2, and 0.3
mm/revolution,
respectively.
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DETAILED DESCRIPTION
[ 0022] The object of the present invention is to solve the technical problems
of current
aluminum brass alloys, including bad cuttability, a tendency of hot cracking
and difficulty in
welding. The object of the invention also includes the provision of an
environment-friendly
lead-free free-cutting aluminum brass alloy, which is applicable for low
pressure die casting,
gravity casting, horizontal continuous casting, forging and welding.
[ 00231 The object of the present invention is realized by selection of the
following elements
and their composition design. The present invention provides a lead-free free-
cutting aluminum
brass alloy which comprises (wt%): 57.0 - 63.0 Cu, 0.3 - 0.7 Al, 0.1 - 0.5 Bi,
0.1 - 0.4 Sn, the
balance being zinc and unavoidable impurities. The present invention also
provides another
alloy which comprises (wt%): 57.0 - 63.0 Cu, 0.3 - 0.7 Al, 0.1 - 0.5 Bi, 0.1 -
0.5 Si, 0.1 - 0.4
Sn, 0.01 - 0.15 P, and which further comprises at least two elements selected
from Mg, B and
rare earth elements, with the balance being Zn and unavoidable impurities. The
at least two
selected elements are present in amount of 0.01 - 0.15wt% Mg, 0.001 - 0.05wt%
rare earth
elements and 0.0016 - 0.0020wt% B.
[ 0024] When bismuth content is in the middle to upper limits of the specified
range, a phase
and a small amount of (3 phase dominate the matrix phase of the alloy. When
bismuth content
is in the lower to middle limits of the specified range, (3 phase and small
amounts of a phase
and y phase dominate the matrix phase of the alloy.
[ 0025] In the inventive alloy, aluminum is the main alloy element, except for
zinc. Al can
improve corrosion resistance and strength of common brass. During the melting
and casting
process, bismuth can form compact oxide film for preventing melt oxidation,
and for reducing
the loss of zinc, which is prone to volatilize and oxidize. However, oxidation
characteristics of
aluminum are unfavorable for castability and weldability. In addition,
aluminum will coarsen
CA 02688994 2009-12-22
the grain of common brass. The zinc equivalent coefficient of aluminum is
rather great, and
can substantially enlarge the (3 phase zone. If combined with silicon,
aluminum is prone to
increase the (3 phase rate, and promote the formation of the y phase.
Therefore, it is beneficial
for improving the cuttability of brass. The surface tension of aluminum (860
dyne/cm) is less
than that of copper. It can form solid solutions in copper resulting in
decreasing the surface
tension of copper. It is favorable for spherifying bismuth, which is
distributed in the grain
boundary. The surface tension of zinc (760dyne/cm) is less than that of
copper. It can form
solid solutions in copper. It is also favorable for spherifying bismuth which
is distributed in the
grain boundary. In this inventive alloy, aluminum content is lower than common
commercialized aluminum brass, and is limited in the range of 0.3-0.7wt%, more
preferably in
the range of 0.4-0.6wt%. Higher aluminum content is not beneficial for
castability and
weldability.
[ 0026] Bismuth is added to improve the cuttability of aluminum brass.
However, as
mentioned above, bismuth will increase the hot and cold cracking tendency of
copper alloys.
The thermodynamic reason for this is the large differential between the
surface tension of
bismuth and copper, with the result that the dihedral angle between liquid
bismuth and solid
copper grain tends to be zero. Bismuth will fully wet copper grains. After
solidification,
bismuth will be distributed in the grain boundary in the form of a continuous
film. In order to
promote bismuth spheroidization and reduce its unbeneficial effect, the
present invention
selects the elements which can form solid solutions in copper and decrease the
surface tension
of copper, such as the above-mentioned main alloy elements, zinc and aluminum.
Other
optional elements are P, Sri, In, Ga, Ge, Mg, B, Ca, etc. On the other hand,
the elements which
can form solid solutions in bismuth, and which have surface tension greater
than bismuth, such
as Pb, Se, Ti, etc, can also promote bismuth spheroidization. The first of the
above-mentioned
elements, In, Ga and Ge, are very expensive, so only a few bismuth brasses
selectively add
them. Among the second group of the above-mentioned elements, Pb's pollution
to the
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environment and harmfulness to the human body have been a concern. Selenium
and thallium
are also toxic. NSF61 standard requires that in drinking water, Se release
should be <5.0 g/L
(equal to Pb) and Ti release should be <0.2gg/L (equal to Hg). Ingestion of
trace amounts of
selenium is not harmful, but in excessive amounts, will damage the skin.
Selenium and
thallium are also very expensive. In this inventive alloy, selenium and
thallium are not added,
and thus thallium cannot leach into the water. In this inventive alloy,
bismuth content is limited
in the range of 0.1-0.5wt%. Higher bismuth content will not only increase the
tendency of hot
cracking, which makes castings crack from time to time during low pressure die
casting, but
also increase cost, reduce corrosion resistance and increase the risk of
thallium as an impurity
in amounts beyond the standard. The content of Bi is limited in the range of
0.1- 0.5wt%, more
preferably in the range of 0.1-0.3wt%, so that it can achieve castability,
weldability, cuttability
and low cost.
[ 0027] The effects of Tin mainly include strengthening the solid solution,
and improving
dezincification corrosion resistance of the alloy. If y phase is formed in the
alloy, small
amounts of tin will make y phase more effectively dispersed, uniformly
distributed, and
decrease the harmful effects of y phase on plasticity, and further improve
cuttability. The
surface tension of tin is 570 dyne/cm. The effect of zinc in promoting bismuth
spheroidizing is
greater than the spheroidizing effect of zinc and aluminum. Tin content is
limited to the range
of 0.1-0.4wt%. Higher content of tin is helpful for bismuth spheroidizing, but
cost will
increase, and together with silicon and aluminum, more y phase will be
produced resulting in
increasing hardness, decreasing plasticity and unbeneficial effects for
cutting and forming.
[ 0028] The effects of silicon include improving castability, weldability and
corrosion
resistance of the alloy, and remarkably enlarging (3 phase zone. Under certain
zinc content,
silicon is the main element for adjusting the composition of matrix phase. If
there is an
appropriate matching ratio among silicon and zinc and aluminum, silicon will
promote the
formation of y phase in the alloy and then improve the cuttability. With the
increasing of
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silicon content, y phase will increase and cuttability will be improved.
However, the plasticity
will gradually decrease and tendency of hot cracking will increase. It is not
beneficial for
casting forming, especially for low pressure die casting forming.
[ 0029] In the case that cuttability is guaranteed by bismuth, silicon content
is limited in the
range of 0.1-0.5wt%, and is more preferably limited in the range of 0.2-
0.5wt%. When
bismuth content is in the middle to upper limits of the specified range and
silicon content is in
the middle to lower limits of the specified range, the matrix phase of the
alloy is a phase and
minor amount of (3 phase.
[0030] When bismuth content is in the middle to lower limits of the specified
range and
silicon content is in the middle to upper limits of the specified range, the
matrix phase of the
alloy is [3 phase and minor amount of a phase and y phase.
[0031] Phosphorus is one of the main elements of the alloy. Its effects
include deoxidation,
improving castability and weldability of the alloy, reducing the oxidation
loss of beneficial
elements such as aluminum, silicon, tin and bismuth, and refining brass
grains. If phosphorus
content in the brass exceeds 0.05wt%, intermetallic compound Cu3P will be
formed. It is
beneficial for improving the cuttability of the alloy, but meanwhile, the
plasticity will be
decreased. Excessive Cu3P resulting from excessive phosphorus will increase
the tendency of
hot cracking during low pressure die casting.
[ 0032] In addition, the surface tension of phosphorus is 70 dyne/cm and
phosphorus has
bigger solid solubility in copper at high temperature; therefore it will
obviously decrease the
surface tension of copper and improve the effect of bismuth spheroidization.
It is a
"plasticizer" of bismuth-contained brass.
[ 0033] In the presence of phosphorus, tin, aluminum and zinc, bismuth will be
spherically
distributed in grain and in grain boundary. It will obviously decrease its
unbeneficial influence
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for cold and hot plasticity and improve castability and weldability.
Meanwhile, as bismuth is
spherically, uniformly and dispersedly distributed, it is favorable for
bismuth to play its
beneficial influence on cuttability.
[0034] Phosphorus content is limited in the range of 0.01-0.15wt%. If it is
used for
horizontal continuous castings or forgings, its content is in the middle to
upper limits of the
specified range. If it is used for low pressure die casting products (such as
the bodies of a
faucet), its content is in the middle to lower limits of the specified range.
[ 0035] Magnesium is a selectively added element. Its main effects include
further
deoxidizing before horizontal continuous casting and preventing castings from
cracking during
low pressure die casting and welding. If magnesium content exceeds 0.1 wt%,
the effect on
preventing castings from cracking is still obvious. However, the elongation
rate will be
decreased. This effect also appears in lead-free free-cutting high-zinc
silicon brass. Magnesium
also has the effect of grain refinement with the result that bismuth and hard-
brittle intermetallic
compounds grain is more dispersedly and uniformly distributed and is
beneficial for improving
cuttability, castability and weldability.
[0036] If magnesium content is larger than 0.1 wt%, it will form intermetallic
compound
Cu2Mg with copper and is also beneficial for improving cuttability. If
magnesium is added, its
content is preferably limited in the range of 0.01-0. 1 5wt%.
[0037] The main effect of selectively adding boron and rare earth metal is for
grain
refinement. The solid solubility of boron in copper is very small, but it will
be reduced with the
temperature decrease. Precipitated boron also has the effect of improving
cuttability. Boron
also could suppress dezincification. In addition to grain refinement, rare
earth metal also can
clean the grain boundary and reduce the unbeneficial effects resulting from
the impurities in
the grain boundary. Cerium and bismuth can form intermetallic compound BiCe
whose
melting point reaches up to 1525 C so that bismuth can enter into the grain
boundary in the
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form of such intermetallic compound. It is favorable for eliminating the hot
and cold brittleness
caused by bismuth, but meanwhile the contribution of bismuth on cuttability is
reduced.
[0038] Magnesium, boron, and the rare earth elements are added in small
amounts.
[0039] In the inventive alloy, Zr and C are present only as unavoidable
impurities. Zr and C
are not required in the alloy. If Zr is present as an unavoidable impurity,
the amount of Zr at
most at 0.0007wt%. If C is present as an unavoidable impurity, the amount of C
will be less
than 0.0015wt%. The alloy does not require Ni.
[ 0040] In the inventive alloy, lead, iron and antimony may be present as
unavoidable
impurities, but their content should be limited in the range of <0.1wt%,
<0.lwt% and
<0.03wt%, respectively. If Pb>0.2wt%, Pb released will exceed government
standards. If
Sb>0.05wt%, Sb released will exceed the standard. Therefore, the alloy
containing such larger
content is not applicable for the components used in drinking water systems.
[0041] Trace antimony can improve dezincification corrosion resistance of the
alloy, like tin
and arsenic. In the common casting copper alloys, the allowed iron content is
larger than
0.2wt%. In the inventive alloy, aluminum and silicon are present and iron will
form hard-brittle
iron-aluminum intermetallic compounds and iron silicide, which will decrease
the plasticity,
corrosion resistance and castability. In addition, if the hard particles
formed by these
intermetallic compounds are placed on the surface of the products, after
polishing and
electroplating, a "hard spots" defect characterized by inconsistent brightness
will appear. Any
such products must be scrapped.
[ 0042] Alloys containing small amounts of such impurities are beneficial for
collocation
using lead brass, antimony brass, phosphorus brass, magnesium brass and other
old brass
materials, saving resource and cost.
CA 02688994 2009-12-22
[ 0043] The features of selection of the above alloy elements and their
composition design
include making bismuth be spherically, uniformly and dispersedly distributed
in the grain and
in the grain boundary, instead of continuous film distribution in the grain
boundary. One
should generally consider the high standard requirements of processing
properties (casting,
welding, cutting, plating and etc.). One should also consider using
performance criteria
(dezincification corrosion, stress corrosion, salt spray corrosion, metal
release amount in water,
leakage, hardness, strength, elongation rate, consistent brightness on the
electroplating surface)
and the cost.
[ 0044] The invented alloy and old bismuth brass alloy can be recycled. Lead
brass, antimony
brass, phosphorus brass, magnesium brass and other old brass materials can be
used for saving
resources and cost.
[ 0045] The manufacturing method is easily operated, and current lead brass
manufacturing
equipment can be used.
[ 0046] In order to take all processing properties and using performance into
consideration,
the volume shrinkage samples should ensure that the surface of concentrating
shrinkage
cavities is smooth, there is no porosity in depth, the elongation rate of as-
cast is larger than 6%,
the hardness HRB is in the range of 5575, and the bending angle of the strip
samples is larger
than 55 .
[ 0047] The inventive alloy is a new environment-friendly aluminum brass,
especially
applicable for low pressure die casting or gravity casting or forging products
which are subject
to cutting and welding, such as components for drinking water supply systems.
[ 0048] The manufacturing method of the inventive alloy is as follows:
[ 0049] Materials proportion - melting in main-frequency induction furnace and
being
protected by the covering agent - tapping at 1000 C, and pouring to be ingots -
remelting -
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low pressure die casting (980 - 1000 C) or horizontal continuous casting (990 -
1030 C) -
forging (650 - 710 C)
EXAMPLES
[ 0050] The alloy composition in examples is shown in Table 1.
Table 1 Alloy composition in examples (wt%)
Examples Cu Al Bi Sn Si Mg B Re P Zn
1 60.13 0.52 0.48 0.275 0.12 - 0.0017 0.005 0.0653 Balance
2 58.72 0.38 0.41 0.165 0.23 0.09 0.0016 - 0.093 Balance
3 59.60 0.49 0.30 0.133 0.182 0.07 0.0017 - 0.0128 Balance
4 61.06 0.42 0.24 0.242 0.13 0.105 - 0.01 0.051 Balance
61.27 0.43 0.29 0.251 0.27 0.133 - 0.03 0.062 Balance
6 60.82 0.39 0.23 0.318 0.24 0.08 0.01 0.075 Balance
7 60.26 0.42 0.37 0.327 0.31 0.07 0.019 0.04 0.082 Balance
[ 0051] 1. Castability
[ 0052] Castability of the inventive alloy is measured by four kinds of common
standard test
samples for casting alloys.
[ 0053] Volume shrinkage test samples are used for measuring the shrinkage
condition. If the
face of the concentrating shrinkage cavity is smooth, and there is no visible
shrinkage porosity
in depth, it will be shown as "0." It indicates the alloy has good fluidity,
strong feeding
capacity and high casting compactability. If the face of the concentrating
shrinkage cavity is
smooth but the height of visible shrinkage porosity is less than 3mm in depth,
it indicates
castability is good, and will be shown as "^." If the face of the
concentrating shrinkage cavity
is not smooth and the height of visible shrinkage porosity is more than 5mm in
depth, it will be
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shown as "x." It indicates the alloy has bad fluidity, weak feeding capacity
and bad casting
compactability. Leakage will appear if water test is done.
[ 0054] Strip samples are used for measuring linear shrinkage rate and bending
angle of the
alloy. If the bending angle is larger than 55 , it indicates it is excellent.
If it is less than 40 , it
indicates the plasticity of the alloy is too low and it is poor. If it is
larger than 100 and even
unpliant, it indicates the plasticity of the alloy is good and is not
beneficial for cutting.
[ 0055] Circular samples are used for measuring shrinkage crack resistance of
the alloy. If
there is no crack, it is rated as excellent, and will be shown as "0." If
there is a crack, it is rated
as poor, and will be shown as "x."
[ 0056] Spiral samples are used for measuring the melt fluid length and
evaluating the fluidity
of the alloy.
[ 0057] All samples are hand poured and the pouring temperature is 1000 C.
Test results are
shown in Table 2.
Table 2 Castability of the examples and comparative alloys
Examples 1 2 3 4 5 6 7 C36000 CuZn40Pb 1 A10.6
Volume shrinkage 0 0 0 0 0 0 0 0
Linear shrinkage
1.5-1.9 1.9-2.1 1.7-1.9
rate/%
Fluid length/mm 400 - 420 420 - 440 440 430
Wall 2.5 0 0 0 0 0 0 0 0 0
thickness of
3.0 0 0 0 0 0 0 0 0 0
circular
samples/mm 3.5 0 0 0 0 0 0 0 0 0
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[ 0058] 2. Weldability
[ 0059] The pieces for welding are low pressure die castings and CuZn37 brass
pipes and are
processed by brazing and flame heating at a temperature of 350^-400 C.
Weldability
measuring standards relate to whether cracks and porosity appear in the
welding seam and the
heat affected zone. If there is no crack and no porosity, it is qualified;
otherwise it is
unqualified.
[ 0060] Fifty (50) pieces are taken from the same type of faucet body of each
alloy. Test
results are shown in Table 3.
Table 3 Weldability of the examples and comparative alloys
Examples 1 2 3 4 5 6 7 CuZn40Pb l A10.6
After welding Qualified Qualified Qualified Qualified
After welding and Small part
Qualified Qualified Qualified
polishing unqualified
After welding,
polishing and Qualified Qualified Qualified Small part
ammonia-fumigating unqualified
[ 0061] 3. Cuttability
[ 0062] Several methods can be used for measuring the materials cuttability.
The common
method is fixing the cutting process parameters, measuring the cutting
resistance, energy
consumption or spindle torque of the machine motor and so on, comparing with
free-cutting
lead brass such as C36000 and finally obtaining the relative cutting rate.
Actually, good or poor
materials' cuttability is very closely related to the cutting process
parameters. In actual
production, the cuttability of the material is "good" or "poor," is always
judged by the shape
and size of the chips, smooth degree of chip discharging and wear speed of the
tools. The
cutting process parameters can be adjusted on the base of different materials
or different states
of the same material for getting successful cutting operation. The influence
of the cutting
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process parameters on chip shape is shown in Table 4. This shows that feeding
quantity has
great influence on chip shape and size, while linear speed has little
influence on chip shape and
size. If feeding quantity is 0.2mm/rev. and 0.3mm/rev., the chip shape of
example alloy 1 is a
thin sheet or thin tile. It indicates cuttability is good, but not better than
lead brass which
contains lwt% Pb. Cutting depth is 4mm.
Table 4 Influence of cutting process parameters on chip shape
Cutting Example alloy 1 CuZn40PblA10.6
speed/m feeding quantity/mm-r- 1 feeding quantity/mm-r"1
.Min -1 0.1 0.2 0.3 0.1 0.2 0.3
40 See Fig. IA See Fig. lB See Fig. 1C See Fig. 1D See Fig. 1E See Fig. IF
60 See Fig. 2A See Fig. 2B See Fig. 2C See Fig. 2D See Fig. 2E See Fig. 2F
80 See Fig. 3A See Fig. 3B See Fig. 3C See Fig. 3D See Fig. 3E See Fig. 3F
100 See Fig. 4A See Fig. 4B See Fig. 4C See Fig. 4D See Fig. 4E See Fig. 4F
[ 0063] 4. Corrosion resistance
[ 0064] All test samples are taken from low pressure die castings. The results
are shown in
Table 5.
[ 0065] Dezincification corrosion testing is carried out according to GB 10119-
1988 standard.
[ 0066] Stress corrosion testing is carried out according to GS0481.1.013-2005
standard.
[ 0067] Salt-spray corrosion testing is carried out according to ASTMB368-97
standard.
[ 0068] Release amount Value Q is measured according to NSF/ANSI61-2007
standard.
CA 02688994 2009-12-22
Table 5 Corrosion Test results of the examples and comparative alloy
Examples 1 2 3 4 5 6 7 CuZn40Pb
1 A10.6
Depth of Average 0.24 - 0.27 - 0.25- 0.24- 0.23-
0.30-0.35
dezincificat value 0.32 0.38 0.33 0.31 0.28
ion
Maximum 0.43- 0.47- 0.40- 0.40- 0.41-
layer/mm. 0.45 0.51
value
0.50 0.55 0.48 0.50 0.49
Stress corrosion Qualified Qualified
Salt spray corrosion Qualified Qualified
All
Release amount Value Q Zn<300,Bi<50.0,Pb<1.5,Sb<0.6, qualified
/ g/L Tl<0.2,Cd<0.5, As<1.0, Hg<0.2, All qualified except for
Pb>5.0
[ 0069] 5. Mechanical Properties
[ 0070] Tensile test samples are processed by low pressure die casting.
Hardness test samples
are processed by hand pouring. The test results are shown in Table 6.
Table 6 Mechanical properties of the examples and comparative alloy
Examples 1 2 3 4 5 6 7 CuZn40Pb l A10.6
Tensile
Strength /MPa 378 365 380 430 410 442 445 370
Elongation
Rate /% 7.5 9.5 11 16 14 16 17 10
Hardness HRB 69 62 61 57 72 70 70 55
16
