Note: Descriptions are shown in the official language in which they were submitted.
CA 02639301 2009-03-02
LEAD-FREE FREE-CUTTING PHOSPHOROUS BRASS ALLOY AND ITS
MANUFACTURING METHOD
FIELD OF THE INVENTION
The present invention generally relates to a phosphorous brass alloy,
especially a
lead-free free-cutting phosphorous brass alloy which is applicable in forging
and castings for
a water supply system.
BACKGROUND OF THE INVENTION
It is well-known that lead-containing brass alloys such as CuZn40Pb1, C36000,
C3604 and C3771 usually contain 1.0-3.7 wt% Pb for ensuring excellent free-
cuttability.
Lead-containing brass alloys are still widely used in the manufacture of many
products due to their excellent cuttability and low cost. However, Pb-
contaminated steam
produced by the process of smelting and casting lead-containing brass alloy,
and Pb-
contaminated dust produced in the process of cutting and grinding the lead-
containing brass
alloy, are harmful to the human body and the environment. If the lead-
containing brass alloys
are used in drinking water installations such as faucets, valves and bushings,
contamination
of the drinking water by Pb is unavoidable. In addition, toys which are
produced by Pb-
containing brass alloys are more harmful, as they are touched frequently, thus
increasing
potential exposure to Pb.
Ingestion of lead by humans is harmful, so the use of lead is being strictly
banned by
law in many countries due to concerns for health and the environment. For
dealing with this
challenge, metallurgists and manufacturers of copper materials
CA 02639301 2008-09-30
-2-
actively research and develop lead-free free-cutting brass alloys. Some of
them use Si
instead of Pb, but the cuttability is not remarkably improved and the cost
increases
due to the high quantity of copper. Therefore, silicon brass alloys are not
commercially competitive at present. One commonly used type of lead-free free-
cutting brass alloy is a bismuth brass alloy, which uses bismuth instead of
Pb. Many
kinds of bismuth brass alloys with high or low zinc contents have been
developed,
and their formal alloy grades have been registered in the United States. These
kinds of
brass alloys contain valuable tin, nickel and selenium, as well as bismuth.
Although
their cuttability is 85%-97% of lead-containing brass alloy C36000, their cost
is far
higher than lead-containing brass alloy C36000. Therefore, these kinds of
bismuth
brass alloys are not competitively priced. Bismuth brass alloys also have been
researched and developed in Japan and China, and applications filed in their
Patent
Offices. Considering that bismuth is expensive, rare in the reserves and has
poor cold
and hot workability, using a bismuth brass alloy instead of a lead-containing
brass
alloy may be financially problematic. The invention of a free-cutting antimony
brass
alloy which uses Sb instead of Pb has been patented in China
(ZL200410015836.5). A
corresponding U.S. (US2006/0289094) application is currently pending.
DETAILED DESCRIPTION
One object of the present invention is to provide a phosphorous brass alloy
which will solve the limitations of conventional brass alloys discussed above,
especially the problem of lead contamination.
One object of the present invention is to provide a lead-free phosphorous
brass alloy which is excellent in cuttability, castability, hot and cold
workability and
corrosion resistance, and which is not harmful for the environment and the
human
body.
One object of the present invention is to provide a lead-free free-cutting
phosphorous brass alloy which is particularly applicable in forging and
castings for
components of water supply systems.
CA 02639301 2008-09-30
-3-
One object of the present invention is to provide a manufacturing method for a
phosphorous brass alloy.
The objects of the present invention are achieved as follows.
The present invention is intended to provide a lead-free free-cutting
phosphorous brass alloy. Considering that the solid solubility of P in the
matrix of
copper will be decreased rapidly with the temperature decrease, and forin the
brittle
intermetallic compounds Cu3P with Cu, the present invention elects P as one of
the
main elements for ensuring the excellent cuttability of the invented alloy and
solving
the limitations of conventional brass alloy discussed above, especially the
environmental problem. The lead-free free-cutting phosphorous brass alloy of
the
present invention comprises: Cu and Zn together having a combined wt% of
greater
than 97% and less than 99.5%, with at least 35 wt% Zn; 0.4 to 1.6 wt% P; and
other
elements in an amount 0.005 to 0.6 wt%, those other elements comprising at
least two
elements selected from the group consisting of Al, Si, Sb, Sn, Re, Ti and B;
and the
balance being unavoidable impurities.
The present invention is intended to provide a lead-free free-cutting
phosphorus brass alloy wherein the content of P is preferably among 0.5 and
1.35wt%, more preferably among 0.5 and 0.9wt% and most preferably among 0.5
and
0.8wt%. The said other elements are preferably selected from Al, Si, Sb, Ti
and B.
The phase compositions of the invented lead-free free-cutting phosphorus
brass alloy includes primarily alpha and beta phase, and a small quantity of
intermetallic compounds Cu3P.
In the invented alloy, Pb as an unavoidable impurity, its content is less than
0.02wt%. Fe as an unavoidable impurity, its content is less than 0.05wt%.
P is one of the main elements of the invented alloy. The beneficial effects of
P
include: ensuring the cuttability of the inventive alloy by the fracture of
the brittle
intermetallic compounds Cu3P, which is formed by elements P and Cu; improving
castability and weldability of the invented alloys as deoxidizers; and
improving
CA 02639301 2008-09-30
-4-
dezincification corrosion resistance of the invented alloy. The negative
effects of P
include: decreasing the plasticity of the invented alloy at room temperature;
if the
intermetallic compounds Cu3P disperse in the boundary of the crystal grain,
the
negative influence for plasticity will be larger.
The elements Re, Ti and B in the alloy have effects on deoxidization and grain
refinement. Re still can form intermetallic compounds with other elements,
disperse
intennetallic compounds in the interior of the crystal grain and reduce the
quantity
and aggregation degree of intermetallic compounds Cu3P in the boundary of the
crystal grain. The preferred content of Re, Ti and B is less than 0.02wt%.
The elements Al and Si in the alloy have the effects of deoxidization, solid
solution strengthening and corrosion resistance improvement. If the content of
Al and
Si is higher, however, castability will decrease due to the increase in the
quantity of
oxidizing slag. Higher content of Si also will form brittle and hard y-phase,
which
will decrease plasticity of the invented alloy. Thus, the content of Al and Si
is
preferably among 0.1 to 0.5wt%. A small quantity of Sn is added mainly to
improve
dezincification corrosion resistance. Sb can also improve dezincification
corrosion
resistance like Sn, and furthermore is beneficial for cuttability.
The features of the inventive alloy include: (a) the phase compositions of the
inventive alloy mainly include alpha phase, beta phase and intermetallic
compounds,
Cu3P; (b) P is one of the main elements for ensuring the cuttability of the
inventive
alloy; (c) Sb is complementary for the cuttability of the inventive alloy
through a
small quantity of brittle intermetallic compounds, Cu-Sb; and (d) multi-
component
alloying and grain refinement tends to uniformly disperse the intermetallic
compounds in the interior and boundary of the crystal grain, and improves
plasticity
of the alloy.
The cost of necessary metal materials of the invented alloy is lower than lead-
free free-cutting bismuth brass alloy and antimony brass alloy, and is
equivalent to
CA 02639301 2008-09-30
-5-
lead-containing brass alloy, as a result of the selection of alloy elements,
and the
design of element contents.
The manufacturing process of the invented alloy is as follows:
The raw materials used in the alloy in accordance with the invention include:
electrolytic Cu, electrolytic Zn, brass scraps, Cu-P master alloy, Cu-Si
master alloy,
Cu-Ti master alloy, Cu-B master alloy, and optionally pure Sb, Sn, Al and Re.
The
raw materials are combined in a non-vacuum intermediate frequency induction
electric furnace, having a quartz sand furnace lining, in the following order:
First, electrolytic Cu, brass scraps, and covering agent that enhances slag
removal efficiency are added to the furnace. These materials are heated until
they
have melted. Then the Cu-Si master alloy, Cu-Ti master alloy, and the Cu-B
master
alloy are added. Thereafter, pure Sb, Sn, Al and Re are optionally added.
These
materials are again heated until melted, and are thereafter stirred. Then
electrolytic
Zn is added. The melt is stirred, and slag is skimmed from the melt. The Cu-P
master
alloy is then added, and the melt is stirred further. When the melt reaches a
temperature of 980 to 1000 degrees Celsius, it is poured into ingot molds.
The alloy ingots may be processed in different ways according to the method
of the invention. First, the ingot may be extruded at a temperature among 550
to 700
degrees Celsius for about 1 hour with an elongation coefficient of greater
than 30 to
be formed, for example, into bar. Second, the ingot may be forged at a
temperature
among 570 and 680 degrees Celsius, to be formed, for example, into a valve
body, or
for manufacturing other water supply system components. Third, the ingot may
be
remelted and cast at a temperature among 980 to 1010 degrees Celsius at a
pressure of
0.3 to 0.5 Mpa for manufacturing faucets.
Smelting is processed in the atmosphere when protecting with the covering
agent. Casting is processed at a temperature among 980 to 1000 degrees
Celsius. The
ingot is extruded at a temperature among 550 and 700 degrees Celsius with an
elongation coefficient of greater than 30, and forged at a temperature among
570 to
CA 02639301 2008-09-30
-6-
710 degrees Celsius, or remelted to be cast at a temperature among 990 and
1010
degrees Celsius by low pressure die casting.
The advantages of this manufacturing process include the following. Casting
ingots (rather than extruding bars) are used directly for hot-forging, and can
thus
reduce manufacturing costs. Ingot remelting is favorable to control the
addition of the
contents when in low pressure die casting. Extruding at a greater elongation
coefficient could further refine grain and intermetallic compounds such as
Cu3P and
uniformly disperse intermetallic compounds and consequently decrease the
negative
effect on plasticity.
The inventive lead-free free-cutting phosphorus brass alloy uses P instead of
Pb and has been improved on cuttability, weldability and corrosion resistance;
Furthermore, by multi-component alloying, grain refinement, large deformation
degree and heat-treating, the intermetallic compounds Cu3P in granular fonn is
dispersed in the interior and boundary of the crystal grain thereby improving
workability and mechanical properties of the invented alloy. The invented
alloy is
applicable in spare parts, forging and castings which require cutting and
particularly
in forging and castings for a water supply system that requires cutting,
grinding
(polishing), welding and electroplating. The ingot (~ 37mm, h 60mm) may be
forged at different temperatures among 570 and 700 degrees Celsius, into
valves with
complex structures for water supply system. The production yield by disposable
mold
forging is 98.6%. The results from the research of mold forging indicate the
invented
alloy has excellent hot workability.
BRIEF DESCRIPTION OF THE DRAWINGS
To understand the present invention, it will now be described by way of
example, with reference to the accompanying drawings in which:
FIG 1 shows the shapes of the cutting chips formed in Examples 1, 2 and 3.
FIG 2 shows the shapes of the cutting chips formed in Examples 4, 5, 6, 7 and
8.
CA 02639301 2008-09-30
-7-
FIG 3 shows the shapes of the cutting chips formed in Examples 9 and 10.
FIG. 4 shows the shapes of the cutting chips formed in cutting lead-containing
brass alloy C36000, for comparison.
EXAMPLES
The alloy composition of examples 1 to 10 is shown in Table 1. The alloy
ingots are for applications including forging, remelting and low pressure die
casting,
and for extruding into bar. The cuttability, castability, dezincification
corrosion
resistance and mechanical properties have been tested. Forging is processed at
a
temperature among 570 to 700 degrees Celsius. The extruding is processed at a
temperature among 560 to 680 degrees Celsius. The low pressure die casting is
processed at a temperature among 980 to 1000 degrees Celsius. Stress relief
annealing
is processed at a temperature among 350 to 450 degrees Celsius.
Table 1 Composition of lead-free free-cutting phosphorus brass alloy (wt%)
=
Examplesl Cu P Sb Si Al Sn ? Ti B Re Zn
1 60.13 0.42 0.20 0.24 <0.001 -~- 0.005 0.003 Balance
:........................................................
.........................................
.................................:......................................t......
............................................
........... .....................
..............I.......................................L........................
. ........:................................. 5..................
................I._.......... .................................
e
Balance
2 60.11 0.59 0.10 0.25 <0.001 0.05 0.02 0.0008 -
..
..................: .........
.... ..;..... .....
..................... .........._ .._........................._............
............
_. ..............._-~--~--_ ........................ . ....
~_.................. ...... ,_.. Balance
3 57.51 0.690.01 0.04 0.19 0.04 - 0.006 -
............._
.......... ................................. .... ...........
...........................p...................... .......... ..............
.................. ....................... .........
..;._.......................... _. ................................
.................v_...!.............. __...... .............
_..__...;............... .................._..........
Balance
4 59.180.990.01 0.33 0.05 0.050.01 0.0006 -
. .. ....' ............
...............................................................................
...:............................................:..............................
................................:..............................................
................;................................. ......................
..................................... ..
Balance
5 59.31 1.00 0.59 0.28 1<0.02 - -' 0.006 -
__........... .._. _
..........................~..................__....._....................
......................._... ............_ . ........ ......
....
_ ._...... ...................
i_ ------- ....t......_... ..... Balance
6 57.100.960.540.43 0.21 - - 0.007 -
..................................... .......... ........................
.:................................. .......................... ......
......................... . ....;. ......... .... . .... ... ......_ ..... .
......................;....................... ...,..............
..................................... . ...........................
................
;.....Balance
7 57.94 0.92 0.01 0.27 0.16 - 0.01 0.0008 ............. ......
....................................... .__._.._............
..._.....__..._.._.._.._................. ......
.....;.................................... ...... ....... ...............
..... :...... ........... ..................... .......... ........... .... .
....... ......................
Balance
- ; -
8 58.871 0.900.11 0.26 0.05 0.03 0.004
....................._ ...................... __............................
................ __.... ........ ....
............... ...... ....... ............... ................. _ ........
..................... __._...........
.................:....... ~-... Balance
9 : 60.01 1.35 0.11 0.25 0.23 - - 0.004 0.004
..............................:.................................
.............................. ...:....... ....................
........:............. ......... ........................
:................................_i...............................;............
....
..............................................!................................
......i.................................................
Balance
10 ~57.53 1.570.010.28 0.10 0.06 0.01 0.0004 0.002i
The lead-free phosphorus brass alloy of the present invention has been tested,
with results as follows:
CA 02639301 2008-09-30
-8-
Cuttability test:
There are several indexes and methods for testing the cuttability of the
alloy.
The present invention tests the cuttability by measuring the cutting
resistance and
comparing the shapes of cutting chips. The samples for test are in the half-
hard state.
The same cutting tool, cutting speed and feeding quantity (0.6mm) is
approached. The
relative cutting ratio is calculated by testing the cutting resistance of
alloy C36000,
and of the invented alloy:
Cutting resistance of alloy C36000
x 100% = relative cutting ratio
Cutting resistance of the invented alloy
It's assumed that the cutting ratio of alloy C36000 is 100%. FIG. 4 shows the
shapes of the cutting chips formed in cutting lead-containing brass C36000
Then the
cutting ratio of examples 1, 2 and 3 is ?80% by testing the cutting resistance
of alloy
C36000 and examples 1, 2 and 3 of the invented alloy. FIG. 1 shows the shapes
of the
cutting chips formed in Examples 1, 2 and 3. The cutting ratio of examples 4,
5, 6, 7
and 8 is ?85% by testing the cutting resistance of alloy C36000 and examples
4, 5, 6,
7 and 8 of the invented alloy. FIG. 2 shows the shapes of the cutting chips
formed in
Examples 4, 5, 6, 7 and 8. The cutting ratio of examples 9 and 10 is >90% by
testing
the cutting resistance of alloy C36000 and examples 9 and 10 of the invented
alloy.
FIG. 3 shows the shapes of the cutting chips formed in Examples 9 and 10.
Dezincification corrosion test:
Considering the invented phosphorus brass alloy will be mass produced to be
castings by low pressure die casting, the samples for test are in the cast
state. The
samples of alloy C36000 for test are in the stress relief annealing state. The
test for
dezincification corrosion resistance is conducted according to PRC national
standard
GB10119-88. The test results are shown in Table 2.
CA 02639301 2008-09-30
-9-
Table 2 The results show dezincification corrosion resistance
of lead-free free-cutting phosphorus brass alloy
Examples 1 2 3 4 5 6 7 8 9 10 C36000
Dezincification
90 100 120 120 50 60 110 120 140 180 610
layer depth/ m;
Castability test:
Several indexes can be used to measure the castability of the alloy. The
present invention uses the standard samples in volume shrinkage, cylindrical,
strip
and spiral for testing the castability of the lead-free free-cutting
phosphorus brass
alloy. For volume shrinkage samples, as may be seen in Table 3, if the face of
the
concentrating shrinkage cavity is smooth, and no visible shrinkage porosity in
the
bottom of the concentrating shrinkage cavity, it indicates castability is
excellent and
will be shown as "o" in Table 3. If the face of the concentrating shrinkage
cavity is
smooth but the height of visible shrinkage porosity in the bottom of the
concentrating
shrinkage cavity is less than 5mm, it indicates castability is good, and will
be shown
as "A" in Table 3. If the face of the concentrating shrinkage cavity is not
smooth and
the height of visible shrinkage porosity in the bottom of the concentrating
shrinkage
cavity is more than 5mm, it indicates castability is poor, and will be shown
as "x" in
Table 3. For strip samples, the linear shrinkage rate is not more than 1.5%.
For
cylindrical samples, as may be seen in Table 3, if no visible shrinkage crack
is shown,
it indicates castability is excellent and will be shown as "o" in Table 3. If
the visible shrinkage crack is shown, it indicates the castability is poor,
and will be shown as "x"
in Table 3. Spiral samples are for measuring the flowability of the invented
alloy. The
pouring temperature of each alloy is about 1000 degrees Celsius. The results
are
shown in Table 3. It indicates the castability of the phosphorus brass alloy
is excellent.
CA 02639301 2008-09-30
-10-
Table 3 The results show the castability of the lead-free
free-cutting phosphorus brass alloy
Examples 1 2 3 4 5 6 7 8 9 10 C36000
....... ........................... . : .... .. ....... ..........
................. ...:.................... : ........ ... . ....... ......
........ ........ ............ Volume
shrinkage o 0 0 0 0 0 0 0 o Q: o
samples
................................................................
............................. .......... ....................
,............................... ..............................
............................... ...............................
...................... .........:...............................
................................ .............................................
.... ................ . .................
Cylindrical
0 0 0 0 0 0 0 0 0 0 0
samples
Melt fluid
450 460 470 480 470 470 480 505 533 545 460
length/mm
.......................... ...................................... . . . . . .
. . . . : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . :
................................ .....................
....................................................... .....................
............................................................ . . . . :
........................... . . . . . : . . . . . . . . . . . . . . . . . . .
. . . . . . . . . ... ........................... . ..........................
...................... . . . . . . . . . . .
Linear
shrinkage <1.5 1.95-2.15
rate/%
2. Mechanical properties test:
The samples for test are in the half-hard state. The specification is ~6mm
bar.
The test results are shown in Table 4.
Table 4 The results show the mechanical properties of the
lead-free free-cutting phosphorous brass alloy
Examples 1 2 3 4 5 6 7 8 9 10 C36000
Tensile
503 510 505 520 540 530 515 520 510 500 485
strength/MPa
0.2%Yield
360 360 350 370 395 385 380 390 385 380 340
strength/MPa
Elongation/ % 11.4 12.5 12.7 12.1 10.3 10.0 11.0 10.8 9.5 8.9 9
3. Stress corrosion test:
The samples for test are from extruded bar, castings and forging. Stress
corrosion test is conducted according to PRC's national standard GB/T10567.2-
1997,
CA 02639301 2008-09-30
-11-
Ammonia fumigation test. The test results show no crack appears in the face of
the
samples.
