Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SILVER SOLDER OR BRAZING ALLOYS AND THEIR USE
FIELD OF THE INVENTION
The present invention relates to silver solder or brazing alloys and to their
use in malting soldered joints in various grades of silver, particularly
silversmithing
grades. Silver brazing alloys are also lcnown in the silversmithing trade as
silver
solders or solders and these terms are used interchangeably herein.
BACKGROUND TO THE INVENTION
Various silver-based alloys of the silver-copper-zinc type are useful as
solders (brazing materials). Brazing has been defined as a joining process in
which
a filler metal is used which has a melting point of above 450°C, but
below that of
the parent metal and which is distributed in the joint by capillary
attraction.
Silver, copper and zinc form a ternary eutectic with a silver content of 56%
and melting at 665°C, see a ternary phase diagram which is given in
Fig. 2 of
Jacobson et al, Development. of ~zew silver free brazisZg alloys fog steel
tubula~°
assembly, supplement to the Welding Journal (sponsored by the American welding
Society/Welding Research Comlcil), August 2002, pages 149-S to 155-S
downloadable from http://www.aws.org/wj/supplement/OS-2002-JACOBSON-
s.pdf,. A commercially supplied silver alloy recommended by the AWS for
brazing
mild steel or copper has the composition of 44 wt % Ag, 30 wt % Cu and 26 wt
Zn. Such an alloy has too low silver content for use in silversmithing, where
solder
alloys of at least 55 wt % Ag are the noun.
Depending on their melting temperatures, brazing alloys for use in
silversmithing are classified as Easy, Medium and Hard, and the major UK
suppliers quote the values below:
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10
Thessco Solidus Liquidus
Easy 705C 725C
Medium 720C 765C
Hard 745C 778C
Johnson Matthey Solidus Liquidus
Easy 705C 723C
Medium 720C 765C
Hard 745C 778C
An alloy containing 75 wt % Ag, 22 wt % Cu and 3 wt % Zn is lcnown and
provides a good colour match for silver, but is high melting. An alloy with 70
wt
Ag, 20 wt % Cu and 10 wt % Zn is also of good colour and is lower melting, and
a
further alloy containing 65 wt % Ag, 20 wt % Cu and 15 wt % Zn is still lower
melting, see http://www.wlv.com/~ot inin~/silvabrazrefchart.xls. This is, of
course,
only one web page from one of the various suppliers of solder alloys for
silversmiths.
A corrosion-resistant silver solder for use in the electronics industry is
disclosed in JP 61078592 (Kyocera) and is based on Ag, 0.05-19 wt %, Ge, 0.01-
1.0
wt % Pd, and 0.01-2 wt % Li. An exemplified composition contains Ag 94 wt %,
Ge
4 wt %, Pd 0.5 wt %, Li 0.5 wt %, Fe 0.5 wt % and Ni 0.5 wt %, and another
exemplified composition has Ag 80%, Ge 11.95%, Pd 8% and Li 0.05%.
Recommended amounts of germanium are relatively high. For silversmithing, the
use of palladium is to be avoided, as is the use of lithium even in trace
amounts.
Although spreadability and wettability are said to be desirable properties,
colour
match to the material being soldered is not necessary.
Patent GB-B-2255348 (Rateau, Albert and Johns; Metaleurop Recherche)
discloses a novel silver alloy that maintains the properties of hardness and
lustre
inherent in Ag-Cu alloys while reducing problems resulting from the tendency
of the
copper content to oxidise. The alloys are ternary Ag-Cu-Ge alloys containing
at least
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92.5 wt% Ag, 0.5-3 wt % Ge and the balance, apart from impurities, copper.
Patents
US-A-6168071 and EP-B-0729398 (Johns) disclose a silver/germanium alloy which
comprises a silver content of at least 77 wt % and a germanium content of
between
0.4 and 7%, the remainder principally being copper apart from any impurities,
which
alloy contains elemental boron as a grain refiner at a concentration of
greater than 0
ppm. and less than 20ppm. Silver alloys according to the teaching of GB-B-
2255348
and EP-B-0729398 are now commercially available in Europe and in the USA under
the trade name Argentium (Ag 92.5 wt%, Cu 6.3 wt%, Ge 1.2 wt %), and the word
"Argentium" as used herein refers to these alloys.
SUMMARY OF THE INVENTION
In one aspect the invention provides a silver solder alloy of the Ag-Cu-Zn
family containing at least 55 wt % Ag and from 0.5 to 3 wt % Ge.
The above alloys can exhibit an advantageous combination of relatively low
melting point, high flowability and good colour. In particular, such alloys
may have
a solidus temperature in the range of about 700 to about 750°C and a
liquidus
temperature in the range of about 725°C to about 780°C. They can
be used for
soldering or brazing jewellery metals including grades of silver such as
Sterling.
They are particularly advantageous for soldering Argentium silver.
Other preferred features of the invention will be apparent from the appended
claims to which attention is directed. The alloys may contain 1.5-2.5 wt % Ge,
especially 2.0-2.5 wt % Ge and more especially about 2.0 wt % Ge. Addition of
Ge
has been found to improve colour and reduce melting point as well as to
increase
corrosion resistance.
The Ag-Cu-Zn alloy typically contains 55-77 wt % Ag, 10-30 wt% Cu
(preferably 56-75 wt %) and 8-15 wt % Zn. For flowability, it may fiu-ther
comprise
0.05-0.4 wt % Si especially about 0.1-0.2 wt % Si. Too large a proportion
gives
rise to brittleness. The alloy may further comprise 1-3 wt % Sn, especially
about 2
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wt % Sn which again reduces melting point and improves colour. It may further
comprise an amount of boron of e.g. 1 ppm-0.3 wt % boron, and more typically
0.1-
0.3 wt % of boron which reduces grain size and helps in rolling or drawizlg
the
composition.
Particular compositions comprise:
(a) 55-77 wt % Ag, 10-30 wt % Cu and 8-15 wt % Zn, 2-2.5 wt % Ge and
0.05-0.4 wt % Si,
(b) 55-77 wt % Ag, 10-30 wt % Cu and 8-15 wt % Zn, 2-2.5 wt % Ge and 1-
3 wt % Sn, or
(c) 55-77 wt % Ag, 10-30 wt% Cu and 8-15 wt% Zn, 2-2.5 wt % Ge, 0.05-
0.4 wt % Si and 1-3 wt % Sn.
The alloys of the invention may be provided any form that is convenient for
silversmithing, e.g. rod, strip, wire, fine particles or a paste in which
powdered
metal is suspended in a vehicle, and may be used with conventional fluxes. In
the
case of pastes, US-A-5443658 (Hermanek) discloses a vehicle which is an
aqueous
gel containing 78 weight percent water, 10 weight percent mineral oil, 10
weight
percent glycerin with the balance sodium carboxymethyl-cellulose. US-A-5120374
(Mizuhara) discloses gels containing 1-4 wt. % hydroxypropylcellulose, 40-80
wt.
1,2-propanediol, 18-58 wt. % 2-propanol or 1-4 wt. % hydroxypropylcellulose,
20-70 wt. % 1,2-propanediol, 26-76 wt. % water. US-A-4475959 discloses an
organic vehicle system based on resins dispersed in hydroxylic solvents. Low-
melting hydrocarbon vehicles may also be used. Useful materials include those
melting below room temperature to normally solid materials, e.g. C18-C6o
petroleum
hydrocarbon waxes melting from 28°C. to 100°C. Such materials
should have a low
ash or solid residue content and either melt and flow, sublime and/or
thermally
decompose below 500°C. Useful hydrocarbons may be paraffinic, aromatic,
or
mixed aromatic paraffmic or mixtures of compounds of such characteristics, and
include various mixtures of hydrocarbons, e.g., octadecane, mineral spirits,
paraffin
wax, and petrolatum (a colloidal system of non-straight-chain solid paraffmic
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hydrocarbons and high boiling liquid paraffinic hydrocarbons, in which most of
the
liquid hydrocarbons are held inside the micelles), e.g., Vaseline.
The alloys can be used in any conventional soldering or brazing method e.g.
5 using a hand torch, a fixed burner, induction or resistance heating or using
a brazing
furnace, preferably such a furnace which provides a protective atmosphere.
The invention is further illustrated in the following examples
Example 1
A brazing composition was prepared by melting together the following
materials:
Ag - 58%
Ge - 2%
Sn - 2.5%
Zn - 14.5%
Si - 0.1%
Cu - 22.9%.
The resulting composition rolled well from cast ingot (satisfactory to 40%
work hardened, then required annealing) and was evaluated as being a good
solder
when tested initially on gilding metal samples. The solder composition runs
well
along a 'T' join. Compared to known 56 and 60 silver solders (56 and 60 wt %
Ag),
the observed colour was good, and in particular it compared favourably to that
of
the 60 solder. On tarnish testing the present solder appeared brighter than
the 56 and
60 solders. Its melting point on gilding metal using a Degussa flux was below
that
of the conventional 56 silver solder.
Samples of Argentium Ag/Ge supplied by Thessco Ltd of Sheffield were
soldered using the above solder composition and the conventional 56 and 60
silver
solder and using various fluxes:
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Degussa Flux - the melting point of the above composition was slightly
below that of the 60 silver solder. Beading of the solder was observed before
dispersion. The resulting soldered joint exhibited good surface texture.
Superior 601 flux - The melting point of the above composition was lower
than using the Degussa Flux and no beading of the solder was observed
before dispersion. The resulting joint exhibited good surface texture.
Thessco Y Flux - The melting point of the above composition was lower
than with either the Degussa Flux or the Superior 601 flux and was observed
to be the same as the 56 silver solder No beading of solder before dispersion
was observed, and the resulting soldered joint exhibited good surface texture
when tested alongside the 60 silver solder but gave a slightly rough joint at
the melting temperature of the 65 silver solder suggesting that a slightly
higher temperature would be preferable.
The present solder was evaluated as being one of the best for use at
relatively low temperatures Its advantages and disadvantages were as follows:
~ Good colour in comparison to other lower M.P. solders including standard
56 silver solder.
~ Lowest M.P. in comparison to the other solders produced.
~ Solder runs well along a 'T' join.
~ Good results in tarnish test carried out at Thessco Ltd. - the solder of
this
Example was brighter than both 56 and 60 solders after test.
~ Surface of solder a little rough on some of the Argentium (Thessco) samples
(soldering temperature may have needed to have been pushed a little higher
with these samples).
Example 2
A brazing composition was prepared by melting together the following
materials:
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Ag - 58%
Ge - 2%
Sn - -
Zn - 14%
Si - 0.1%
Cu - 25.9%
The resulting composition rolled well from cast ingot and provided a good
solder that when tested on gilding metal samples was of good colour and ran
well
along a 'T' joint. However its melting point was above that of the 60 silver
solder.
When using Thessco F flux, beading of the solder before dispersion was
observed,
but the same beading occurred with the 60 silver solder.
Example 3
A brazing composition was prepared by melting together the following
materials:
Ag - 65%
Ge - 2%
Sn - -
Zn - 9%
Si - 0.1%
Cu - 23.9%
The resulting composition rolled well from cast ingot and provided a good
solder when tested on gilding metal samples but its colour was slightly
yellow.
When using Thessco F flux, the melting point was slightly above that of known
"Easy" silver solder and beading of the solder before dispersion was observed.
Beading was also observed with Superior flux 6. Using Superior flux 601, the
melting point was the same as that of Easy silver solder and beading of the
solder
before dispersion was not observed.
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Example 4
A brazing composition was prepared by melting together the following
materials:
Ag - 58%
Ge - 2%
Sn -
Zn - 14%
Si - 0.4%
Cu - 25.6%
The resulting composition rolled well fiom cast ingot and provided a good
solder that when tested on gilding metal samples was of good colour. Its
melting
point was closely below that of the 60 silver solder. When soldered onto a
flat
surface of gilding metal, the surface texture exhibited was slightly rough.
Example 5
A brazing composition was prepared by melting together the following
materials:
Ag - 58%
Ge - 2%
Sn - -
Zn - 17%
Si - 0.4%
Cu - 24.6%
The resulting composition exhibited a yellow colour and was not evaluated
further.
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Example 6
A brazing composition was prepared by melting together the following
materials:
Ag - 56%
Ge - 2%
Sn - -
Zn - 19.8%
Si - 0.2%
Cu - 22%
The resulting composition exhibited a yellow colour and was not evaluated
further.
Example 7
A brazing composition was prepared by melting together the following
materials:
Ag - 65%
Ge - 2%
Sn - -
Zn - 13.5%
Si - 0.1%
Cu - 19.2%
The resulting composition
exhibited a yellow colour
and the brazing beaded
before dispersion.
Example 8
A brazing composition was prepared by melting together the following
materials:
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Ag - 67%
Ge - 2%
Sn - -
Zn - 8%
5 Si - 0.1%
Cu - 22.9%
The resulting composition rolled well from cast ingot and provided a very
good solder when evaluated using Thessco F flux on gilding metal samples. It
exhibited good colour and no beading of the solder before dispersion. The
10 composition exhibited a melting point slightly above that of Easy silver
solder.
However, when re-tested on Argentium Ag/Ge material (Thessco) using Degussa
flux it exhibited a slightly better colour and a lower melting point than Easy
silver
solder. When soldering a 'T' joint in Argentium feeding the solder with a
sticl~ and
using a Degussa flux the solder flowed very well. The present solder was
judged to
be one of the best for use at higher soldering temperatures because of the
following
advantages:
~ Rolled well from cast ingot.
~ M.P. slightly lower than that of Example 10
~ Solder runs very well along a 'T' joint.
~ Good colour.
~ Good surface texture.
Example 9
A brazing composition was prepared by melting together the following
materials:
Ag - 60%
Ge - 2%
Sn - -
Zn - 13%
Si - 0.1%
Cu - 24.9%
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The resulting composition rolled well from cast ingot and provided a very
good solder when tested initially on gilding metal samples. It exhibited good
colour
and when using Degussa flux, no beading of the solder was observed before
dispersing. Using Thessco F flux, beading of the solder before dispersion was
observed, but known 60 silver solder also beaded on the same gilding metal
sample.
The above solder composition runs well along a 'T' joint and provides good
surface
texture. Its melting poiizt is fractionally above that of lcnown 60 silver
solder When
soldered onto Argentium (Thessco) the colour was fairly good and the solder
appeared greyer than Easy solder.
Example 10
A brazing composition was prepared by melting together the following
materials:
Ag - 70%
Ge - 2%
Sn - -
~n - 8%
Si - 0.1%
Cu - 19.9%
The resulting composition rolled well from cast ingot and provided a very
good solder when evaluated initially on gilding metal samples. When using
Degussa
flux no beading of the solder was observed before dispersion, but beading was
observed using Thessco F flux. The solder exhibited good surface texture and
had a
melting point slightly lower than Easy. When tested on Argentium (Thessco)
using
Degussa flux, its melting point was slightly higher than that of the solder of
Example 8, but its colour was slightly better. The present composition was
judged
to be one of the best for use at higher soldering temperatures because of the
following advantages:
~ Rolled well from cast ingot.
~ Good colour match with Argentium - slightly better colour than Example 8.
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~ M.P. slightly lower than Easy.
~ Solder runs well along a 'T' joint.
~ Generally good surface texture.
S Example 11
A brazing composition was prepared by melting together the following
materials:
Ag - 56%
Ge - 2%
Sn - -
Zn - 13%
Si - 0.2%
Cu - 28.8%
The resulting composition rolled well from cast ingot and provided a good
solder as evaluated on gilding metal samples, with good colour and good
surface
texture. The solder ran well along a 'T' join using Thessco flux. Also using
Thessco
flux, a large section of gilding metal spinning was soldered onto a base
without any
problems and with good solder flow. A sample was tested alongside 56 silver
solder
using different fluxes and was found to have a higher melting point. With
Thessco F
flux, both the present solder composition and the 56 silver solder exhibited
beading
before dispersion, whereas with Degussa flux beading results varied between
samples.
Example 12
A brazing composition was prepared by melting together the following
materials:
Ag - 74%
Ge - 2%
Sn - -
Zn - 8%
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Si - 0.1%
Cu - 15.9%
The resulting composition rolled well from cast ingot and provided a good
solder as evaluated on gilding metal samples, with good colour and good
surface
texture. The solder ran well along a 'T' joint using Thessco flux. Its melting
point
was slightly lower than Easy silver solder and fractionally lower than the
solder of
Example 10. Using Thessco F flux, beading of the solder before dispersion was
observed but the resulting joiilt had good surface texture. When tested on
Argentium (Thessco) an excellent colour match was achieved and the same
melting
temperature as Easy silver solder was obtained but with incomplete dispersion,
suggesting that a higher melting temperature is desirable.
Example 13
A brazing composition was prepared by melting together the following
materials:
Ag - 60%
Ge - 3%
Sn - -
Zn - 12%
Si - 0.1%
Cu - 24.9%
The resulting composition had a melting point lower than known 56 silver
solder but did not roll well from cast ingot.
Example 14
A brazing composition was prepared by melting together the following
materials:
Ag - 60%
Ge - 2.5%
Sn - -
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Zn - 12.5%
Si - 0.1%
Cu - 24.9%
The resulting composition rolled quite well from cast ingot (satisfactory to
40% work hardened, then required annealing).
Example 15
A brazing composition was prepared by melting together the following
materials:
Ag - 60%
Ge - 2.5%
Sn - -
Zn - 12.5%
Si - 0.1%
Cu - 24.9%
The resulting composition rolled quite well from cast ingot (satisfactory to
40% work hardened, then required annealing) and exhibited good colour. Samples
tested on gilding metal alongside known 56 and 60 silver solders using
different
fluxes exhibited beading before dispersion.
Example 16
A brazing composition was prepared by melting together the following
materials:
Ag - 74%
Ge - 2%
Sn - 1
Zn - 7.5%
Si - 0.2%
Cu - 15.3%
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The resulting composition rolled well from cast ingot and exhibited good
colour but its melting point was higher than Easy solder and than the solder
of
Example 12, and it does not disperse fully.
Example 17
A brazing composition was prepared by melting together the following
materials:
Ag - 74%
10 Ge - 2%
Sn - -
Zn - 13
S1 - 0.2%
Cu - 10.8%
15 The resulting composition did not roll well from cast ingot. It was tested
initially on gilding metal using Degussa Flux and exhibited better colour and
a
reduced melting point compared to Easy.
Example 18
A brazing composition was prepared by melting together the following
materials:
Ag - 74%
Ge - 2%
Sn _ _
Zn - 13%
Si - -
Cu - 11
The resulting composition rolled quite well from cast ingot (satisfactory to
40% work hardened, then required annealing). Solder tested initially on
gilding
metal using Degussa flux exhibited good colour and a lower melting point than
Easy silver solder. When tested on Argentium (Thessco ) Ag/Ge material
alongside
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Easy silver solder, the present composition exhibited lower melting point and
after
polishing provided a better colour match to the Argentium, malting the Easy
silver
solder look yellow. When tested on Argentium using Degussa flux alongside the
solder of Example 10, the melting point was similar or slightly lower and the
colour
match after polishing was slightly darker. When tested on Argentium using
Degussa
flux, the solder ran well along a T joint. The present solder was judged to be
one of
the best for use at higher temperatures for the following reasons:
~ Solder does not contain Si (one less constituent to add to the alloy).
~ M.P. fractionally lower than that of Example 10 (as seen with sample 2).
~ Solder runs well along a 'T' joint.
~ Good surface texture.
~ Rolled well from cast ingot.
Example 19
A brazing composition was prepared by melting together the following
materials:
Ag - 58%
Ge - 2%
Sn - 2.5%
Zn - 14.5%
Si - -
Cu - 23%
The resulting composition was the same as Example 1 except that the silicon
was omitted. It rolled quite well from cast ingot (satisfactory to 40% work
hardened, then required annealing). When tested on Argentium (Thessco)
material
alongside 56 silver solder using Degussa flux, it ran well along a T joint,
exhibited a
melting point slightly higher.than 56 silver solder, and exhibited better
colour.
When tested on samples of Argentium (Thessco) alongside the solder of Example
1
using Degussa the melting point was unchanged, the colour became fractionally
more yellow and the solder did not disperse so well.
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Example 20
A brazing composition was prepared by melting together the following
materials:
Ag - 74%
Ge - 2%
Sn - 1%
Zn - 11.4%
Si - 0.2%
Cu - 11.4%
The resulting composition was a very hard alloy, very brittle when rolled
from cast ingot and yellow in colour in comparison to Easy silver solder.
Example 21
A brazing composition was prepared by melting together the following
materials:
Ag - 68%
Ge - 2%
Sn - 2%
Zn - 8%
Si - 0.1%
Cu - 19.9%
The resulting composition rolled well from cast ingot, exhibited a melting
point slightly lower than Easy silver solder, and good colour, although it was
slightly more yellow than Easy silver solder.
Example 22
The brazing composition of Example 21 was re-melted with 3 wt % added tin. The
resulting composition rolled not as well as that of Example 21: it rolls down
to 40%
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then becomes brittle. Its melting point was lower than the composition of
Example
21, showing that addition of tin lowers the melting point, and its melting
point was
lower than that of 60 silver solder. Its colour was yellow compared to Easy
solder,
but it flowed well using F flux.
Example 23
A brazing composition was prepared by melting together the following
materials:
Ag - 58%
Ge - 2%
Sn - 1.4%
Zn - 14.5%
Si - 0.1%
Cu - 24%
The resulting composition rolled better than the solder of Example 1,
illustrating that tin additions tend to male silver solders harder and more
brittle.
When soldered onto gilding metal using Thessco F flux, the present composition
had a melting point lower than 60 silver solder but beaded before dispersing.
The
56 silver solder also beaded at the same time as the present solder but
dispersed
before the present solder. When soldered onto Argentium using F flux, the
present
solder dispersed well, melted fractionally below 56 silver solder and
exhibited
slightly better colour than that solder.
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Example 24
A brazing composition was prepared by melting together the following
materials:
Ag - 69%
Ge - 2%
Sn - 2%
Zn - 8%
Si - 0.1%
Cu - 18.9%
The resulting composition rolled well from cast ingot but melted at a
temperature significantly higher than easy silver solder. When soldered onto
Argentium (Thessco), both solders beaded before dispersion when heated from
above but dispersed without beading when heated from below.
Example 25
A brazing composition was prepared by melting together the following
materials:
Ag - 58%
Ge - 2%
Sn - 2.5%
Zn - 14.5%
Si - 0.1%
B - 0.14%
Cu - 22.76%
The resulting composition (which was the same as that of Example 1 except
for the addition of boron) rolled well from cast ingot (edge craclcing at 64%
reduction). When soldered onto Argentium (Thessco) using Thessco F flux it
melted below 56 silver solder but higher than Thessco MX12 silver solder,
exhibited similar colour to the solder of Example 1 and dispersed well. This
solder
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composition was evaluated as being one of the joiilt best for low temperature
uses,
and it had the following advantages:
~ Addition of boron allows the alloy to roll better than the solder of Example
1.
5 ~ M.P. lower than 56 solder.
~ Good colour in comparison to other lower M.P. solders including standard
56 silver solder.
A comparison of tarnish resistance was carried out using 'hard' and 'easy'
10 silver solders together with the solder of this example (Y solder). Hard,
Easy and Y
solders were soldered onto Argentium Silver. The soldered samples were
polished
using two types of polishing compounds, then degreased using a solvent cleaner
in
an ultrasonic cleaning tank and finally wiped with a silver polishing cloth.
An
accelerated tarnishing procedure was carried out by exposing the samples to
neat
15 ammonium polysulphide solution - 20% for 10 minutes. After 10 minutes
exposure,
the Y solder showed superior tarnish resistance in comparison to both the hard
and
easy silver solders as shown in Fig. l, which gives photographs of the
samples.
Example 26
A brazing composition was prepared by melting together the following
materials:
Ag - 63%
Ge - 2%
Sn - 1
Zn - 14%
Si - 0.1%
B - 0.14%
Cu - 19.76%
The resulting composition rolled well fiom cast ingot (edge cracking at 60%
reduction) and when soldered using F flux onto Argentium (Thessco) had a
melting
point significantly lower than 60 silver solder. It exhibited a melting point
between
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the solders of Examples 10 and 25, a better colour than 56 or 60 silver
solders and
beading on one sample tested but not on the other. It was considered the best
solder
composition for use at medium temperatures because of its combination of
rolling
properties, melting point and colour.
Example 27
A brazing composition was prepared by melting together the following
materials:
Ag - 63%
Ge - 2%
Sn - -
Zn - 15%
Si - 0.1%
B - 0.14%
Cu - 19.76%
The resulting composition (which was the same as Example 26 apart from
the absence of tin) rolled well from cast ingot (edge craclcing at 75%
reduction).
When soldered onto Argentium (Thessco) using Thessco F flux it exhibited a
melting point higher than that of the solder of Example 26, showing the effect
of Sn
in reducing the melting point.
Example 28
A brazing composition was prepared by melting together the following
materials:
Ag - 5~
Ge - 2%
Sn - 2.5%
Zn - 14.5%
Si - -
B - 0.14%
CA 02544861 2006-05-03
WO 2005/051593 PCT/GB2004/050027
22
Cu - 22.86%
The resulting composition which was the same as Example 25 except for the
absence of silicon) did not roll well from cast ingot (edge cracking at 32%
reduction) and appeared yellow. It was believed that the mold temperature used
was
too yellow, and on re-melting with a higher mould temperature the resulting
cast
ingot rolled better with edge cracking at 57% reduction.
Example 29
A brazing composition was prepared by melting together the following
materials:
Ag - 58%
Ge - 2%
Sn - 2.5%
Zn - 14.5%
Si - 0.3%
B - 0.14%
Cu - 22.56%
The resulting composition rolled fairly well from cast ingot (edge cracking
at 50% reduction).
