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Introduction:
Copper and Copper alloys remain to this day among the most important
engineering materials due to their good electrical and thermal
conductivity, corrosion resistance, metal-to-metal wear resistance and
distinctive aesthetic appearance. Copper and most copper alloys can be
joined by welding, brazing and most copper alloys can be joined by
welding, brazing and soldering. The major markets for copper and its alloys
include the building industry, electrical and electronic products,
industrial machinery and equipment and transportation. This section
outlines the different types of copper alloys and gives guidance on
processes and techniques to be used in fabricating copper alloy
components without impairing their corrosion or mechanical properties or
introducing weld defects.
1) Types of Copper Alloys:
The eight major groups of
copper and copper alloys are:
i)Copper - 99.3% minimum Copper
content.
ii) High copper alloys - up to
5% alloying elements.
iii) Copper-Zinc alloys
(Brass).
iv) Copper-Tin alloys (Phosphor
Bronze).
v) Copper-Aluminum alloys
(Aluminum Bronze).
vi) Copper-Silicon alloys
(silicon bronze).
vii) Copper-Nickel alloys.
viii) Copper-Nickel-Zinc alloys
(Nickel silver).
i) Pure Copper: 99.3%
minimum Copper content- Copper is normally supplied in one of three
forms:
(a) Oxygen free copper.
(b) Oxygen-bearing copper (tough pitch and fire-refined grades) - the
impurities and residual oxygen content of oxygen-bearing copper may cause
porosity and other discontinuities when these coppers are welded or
brazed.
(c) Phosphorous deoxidized copper.
ii) High Copper Alloys:
(a) Free machining copper - Low alloying additions of sulphur or
tellurium can be made to improve machining. These grades are considered
to be unweldable due to a very high susceptibility to cracking. Free
machining coppers are joined by brazing and soldering.
(b) Precipitation - hardenable copper alloys - Small additions of
beryllium, chromium or zirconium can be added to copper and then given a
precipitation hardening heat treatment to increase mechanical properties.
Welding or brazing of these alloys will over-age the exposed area
resulting in degradation of mechanical properties.
iii) Copper-Zinc Alloys
(Brass):
Copper alloys in which zinc is the major alloying element are generally
called brasses. Brass is available in wrought and cast form, with the
cast product generally not as homogeneous as the wrought products.
Additions of zinc to copper decreases the melting temperature, the
density, the electrical and thermal conductivity and the modulus of
elasticity. The additions of zinc will increase the strength, hardness,
ductility and coefficient of thermal expansion. Brasses can be separated
into two weldable groups, low zinc (up to 20% zinc) and high zinc (30-40%
zinc). The main problems encountered with brass is due to zinc
volatilization which results in white fumes of zinc oxide and weld metal
porosity. The lower zinc alloys are used for jewelry and coinage
applications and as a base for gold plate and enamel. The higher zinc
alloys are used in applications where higher strength is important.
Applications include automotive radiator cores and tanks, lamp fixtures,
locks, plumbing fittings and pump cylinders.
iv) Copper-tin Alloys (Phosphor
Bronze):
Copper alloys which contain between 1 percent and 10 percent tin. These
alloys are available in the wrought and cast forms. These alloys are
susceptible to hot cracking in the stressed condition. The use of high
preheat temperatures, high heat input, and slow cooling rates should be
avoided. Examples of specific applications include bridge bearings and
expansion plates and fittings, fasteners, chemical hardware and textile
machinery components.
v) Copper-Aluminum Alloys
(Aluminum Bronze):
Contain from 3-15 percent aluminum with substantial additions of iron,
nickel and manganese. Common applications for Aluminum Bronze alloys
include pumps, valves, other water fittings and bearings for use in
marine and other aggressive environments.
vi) Copper-Silicon Alloys
(Silicon Bronzes):
Available in both wrought and cast forms. Silicon Bronzes are
industrially important due to their high strength, excellent corrosion
resistance, and good weldability. The addition of silicon to copper
increases tensile strength, hardness and work hardening rates. Low
silicon bronze (1.5% Si) is used for hydraulic pressure lines, heat
exchanger tubes, marine and industrial hardware and fasteners. The high
silicon Bronze (3% Si) is used for similar applications as well as for
chemical process equipment and marine propeller shafts.
vii) Copper Nickel Alloys:
The cupronickel alloys containing 10-30% Ni have moderate strength
provided by the nickel which also improves the oxidation and corrosion
resistance of copper. These alloys have good hot and cold formability and
are produced as flat products, pipe, rod, tube and forgings. Common
applications include plates and tubes for evaporators, condensers and
heat exchangers.
viii) Copper Nickel Zinc Alloys
(Nickel Silvers):
Contain zinc in the range 17-27% along with 8-18% Nickel. The addition of
nickel makes these alloys silver in appearance and also increases their
strength and corrosion resistance, although some are subject to
dezincification and they can be susceptible to stress corrosion cracking.
Specific applications include hardware, fasteners, optical and camera
parts, etching stock and hollowware.
2) Weldability of Copper and
Copper Alloys:
Welding processes such as Gas Metal Arc Welding and Gas Tungsten Arc
Welding are commonly used for welding copper and its alloys, since high
localized heat input is important when welding materials with high
thermal conductivity. Manual Metal Arc Welding of Copper and Copper
alloys may be used although the quality is not as good as that obtained
with the gas shielded welding processes. The weldability of copper varies
among the pure copper grades (a) (b) and (c). The high oxygen content in
tough pitch copper can lead to embitterment in the heat affected zone and
weld metal porosity. Phosphorus deoxidized copper is more weldable, with
porosity being avoided by using filler wires containing deoxidants (Al,
Mn, Si, P and Ti). Thin sections can be welded without preheat although
thicker sections require preheats up to 60°C. Copper alloys, in contrast
to copper, seldom require preheating before welding. The weldability
varies considerably amongst the different copper alloys and care must be
taken to ensure the correct welding procedures are carried out for each
particular alloy to reduce the risks of welding defects.
2.1 Weld joint designs for
Joining Copper and Copper alloys:
The recommended joint designs for welding copper and copper alloys are
shown in Figures 1 & 2. Due to the high thermal conductivity of
copper, the joint designs are wider than those used for steel to allow
adequate fusion and penetration.
NOTE A = 1.6mm, B = 2.4mm, C = 3.2mm, D = 4.0mm, R = 3.2mm, T=thickness
Figure 1. - Joint designs for Gas Tungsten Arc Welding and Manual Metal
Arc welding of Copper and Copper Alloys.
2.2 Surface Preparation:
The weld area should be clean and free of oil, grease, dirt, paint and
oxides prior to welding. Wire brushing with a bronze wire brush followed
by degreasing with a suitable cleaning agent. The oxide film formed
during welding should also be removed with a wire brush after each weld
run is deposited.
2.3 Pre-heating:
The welding of thick copper sections requires a high preheat due to the
rapid conduction of heat from the weld joint into the surrounding base
metal. Most copper alloys, even in thick sections, do not require
pre-heating because the thermal diffusivity is much lower than for
copper. To select the correct preheat for a given application,
consideration must be given to the welding process, the alloy being
welded, the base metal thickness and to some extent the overall mass of
the weldment. Aluminum bronze and copper nickel alloys should not be
preheated. It is desirable to limit the heat to as localized an area as
possible to avoid bringing too much of the material into a temperature
range that will cause a loss in ductility. It is also important to ensure
the preheat temperature is maintained until welding of the joint is
completed.
3) Gas Metal Arc Welding (GMAW)
of Copper and Copper alloys:
3.1 GMAW of Copper:
ERCu copper electrodes are recommended for GMAW of copper. Aufhauser
Deoxidized Copper is a versatile 98% pure copper alloy for the GMAW of
copper. The gas mixture required will be largely determined by the
thickness of the copper section to be welded. Argon is generally used for
6mm and under.
The helium-argon mixtures are used for welding of thicker sections.
The filler metal should be deposited with stringer beads or narrow weave
beads
using spray transfer. Table 1 below gives general guidance on procedures
for GMAW
of Copper.
|
Metal
Thickness
|
Joint
Design*
|
Electrode
Diameter
|
Preheat#
Temperature
|
Welding
Current
|
Voltage
Rate
|
Gas
Flow Rate(l/min)
|
Travel
Speed
|
|
1.6mm
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A
|
0.9mm
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75°C
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150-200
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21-26
|
10-15
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500
mm/min
|
|
3.0mm
|
A
|
1.2mm
|
75°C
|
150-220
|
22-28
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10-15
|
450
mm/min
|
|
6.0mm
|
B
|
1.2mm
|
75°C
|
180-250
|
22-28
|
10-15
|
400
mm/min
|
|
6.0mm
|
B
|
1.6mm
|
100°C
|
160-280
|
28-30
|
10-15
|
350
mm/min
|
|
10mm
|
B
|
1.6mm
|
250°C
|
250-320
|
28-30
|
15-20
|
300
mm/min
|
|
12mm
|
C
|
1.6mm
|
250°C
|
290-350
|
29-32
|
15-20
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300
mm/min
|
|
16mm +
|
C,D
|
1.6mm
|
250°C
|
320-380
|
29-32
|
15-25
|
250
mm/min
|
*refer to figure 2
Recommended Shielding Gases for
the GMA welding of Copper and Copper Alloys:
- Welding Grade Argon.
- Ar + >0-3% O2 or equivalent shielding gases.
- Ar + 25% He or equivalent shielding gases.
- He + 25% Ar or equivalent shielding gases.
3.2 GMAW of Copper Silicon
Alloys:
ERCuSi-A type welding consumables plus argon shielding and relatively
high travel speeds are used with this process. Aufhauser Silicon Bronze
is a copper based wire recommended for GMAW of Copper Silicon Alloys. It
is important to ensure the oxide layer is removed by wire brushing between
passes. Preheat is unnecessary and interpass temperature should not
exceed 100 C.
3.3 GMAW of Copper Tin Alloys
(Phosphor Bronze):
These alloys have a wide solidification range which gives a coarse
dendritic grain structure, therefore care must be taken during welding to
prevent cracking of the weld metal. Hot peening of the weld metal will
reduce the stresses developed during welding and the likelihood of
cracking. The weld pool should be kept small using stringer beads at high
travel speed.
4) Gas Tungsten Arc Welding
(GTAW) of Copper and Copper Alloys:
4.1 Gas Tungsten Arc Welding of
Copper:
Copper sections up to 16.0mm in thickness can be successfully welded
using the Gas Tungsten Arc Welding process. Typical joint designs are
shown in Figure 1. The recommended filler wire is a filler metal whose
composition is similar to that of
4) Gas Tungsten Arc Welding (GTAW) of Copper and Copper Alloys cont.: the
base metal. For sections up to 1.6mm thick Argon shielding gas is
preferred and helium mixes is preferred for welding sections over 1.6mm
thick. In comparison to argon, argon/helium mixes permit deeper
penetration and higher travel speeds at the same welding current. A 75%
Helium-25% Argon mixture is commonly used to give the good penetration
characteristics of helium combined with the easy arc starting and
improved arc
stability properties of Argon.
Forehand welding is preferred for Gas Tungsten Arc Welding of Copper with
stringer beads or narrow weave beads. Typical conditions for manual GTAW
of
copper is shown in Table 2 below.
|
Metal
|
Joint
|
Shielding
|
Tungsten
Type &
|
Welding
Rod
|
Preheat#
|
Welding
|
|
Thickness
(mm)
|
Design*
|
Gas
|
Welding
Current
|
Diameter
|
Temperature
|
Current
|
|
0.3-0.8
|
A
|
Argon
|
Thoriated/DC-
|
__
|
_.
|
15-60
|
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1.0-2.0
|
B
|
Argon
|
Thoriated/DC-
|
1.6 mm
|
__
|
40-170
|
|
2.0-5.0
|
C
|
Argon
|
Thoriated/DC-
|
2.4 -
3.2 mm
|
50°C
|
100-300
|
|
6.0
|
C
|
Argon
|
Thoriated/DC-
|
3.2 mm
|
100°C
|
250-375
|
|
10.0
|
E
|
Argon
|
Thoriated/DC-
|
3.2 mm
|
250°C
|
300-375
|
|
12.0
|
D
|
Argon
|
Thoriated/DC-
|
3.2 mm
|
250°C
|
350-420
|
|
16.0
|
F
|
Argon
|
Thoriated/DC-
|
3.2 mm
|
250°C
|
400-475
|
*refer to Figure 1
4.2 Gas Tungsten Arc Welding of
Copper-Aluminum alloys:
The ERCuAl-A2 filler rod can be used for GTAW of Aluminum Bronze Alloys.
Alternating Current (AC) current with argon shielding can be used to
provide an arc cleaning action to assist in removing the oxide layer
during welding. Direct Current (DC-)
electrode negative with Welding Grade Argon or Argon-Helium mixes can be
used in applications requiring deeper penetration and faster travel
speed. Preheat is only required on thicker sections.
4.3 Gas Tungsten Arc Welding of
Silicon-Bronze:
Aufhauser Silicon Bronze Rod (ERCuSi-A) can be used to weld Silicon
Bronze in all positions. The Aluminum Bronze welding rod ERCuAl-A2 may
also be used. Welding can be performed with DC- using argon or argon/helium
shielding or AC using argon shielding gas.
5) Manual Metal Arc Welding
(MMAW) of Copper & Copper Alloys:
5.1 Manual Metal Arc Welding of
Copper:
MMAW is normally used for the maintenance and repair welding of copper,
copper alloys and bronzes. Aufhauser AC-DC electrode (ECuSn-C) can be
used
for the following:
A Minor repair of relatively thin sections.
A Fillet welded joints with limited access.
A Welding copper to other metals.
Joint designs should be similar to that shown in Figure 1. Direct Current
electrode positive (DC+)
should be used with a stringer bead technique. Sections over 3.0mm
require a preheat of 250°C or greater.
5.2 Manual Metal Arc Welding of
Copper Alloys:
Bronzecraft AC-DC (ECuSn-C) can be used to weld Copper-Tin and
Copper-Zinc alloys. Large butt angles are required and the weld metal
should be deposited using the stringer bead technique.
|
Copper
Alloy
|
Recommended
AWS Electrode Code
|
Aufhauser
Welding Electrode
|
Electrode
Polarity
|
Joint
Design
|
|
Brasses
|
ECuSn-A
or ECuSn-C
|
Aufhauser
PhosBronze AC-DC
|
DC+
|
C in
Figure 1
|
|
Phosphor
Bronze
|
ECuSn-A
or ECuSn-C
|
Aufhauser
Phos Bronze AC-DC
|
DC+
|
C in
Figure 1
|
Table 3 - Recommendations for MMAW of Brasses and Phosphor
Bronzes.
6) Brazing of Copper and Copper
Alloys:
The principle of brazing is to join two metals by fusing with a filler
metal. The filler metal must have a lower melting point than the base
metals but greater than 450°C (use of a filler metal with a melting point
less than 450°C is soldering). The filler metal is usually required to
flow into a narrow gap between the part by capillary action.
Brazing is used widely for the joining of copper and copper alloys, with
the exception of Aluminum bronzes containing greater than 10 percent
aluminium and alloys containing greater than 3 percent lead. Brazing of
copper is used extensively in the electrical manufacturing industry, and
in the building mechanical services, heating, ventilation and
air-conditioning fields.
To achieve an adequate bond during brazing, the following points should
be considered:
1. The joint surfaces are clean and free of oxides etc.
2. The provision of the correct joint gap for the particular brazing
filler metal.
3. The establishment of the correct heating pattern so that the filler
metal flows up the thermal gradient into the joint.
6.1 Surface Preparation:
Standard solvent or alkaline degreasing procedures are suitable for
cleaning copper base metals. Care must be taken if mechanical methods are
used to remove surface oxides. To chemically remove surface oxides, an
appropriate pickling solution such as Chrome Bright‚ should be
used.
6.2 Joint Design
Considerations:
1. The distance between the joints to be joined must be controlled to
within certain tolerances which depend upon the brazing alloy and the
parent metal used. The optimum joint gap typically lies between 0.04 and
0.20mm.
6) Brazing of Copper and Copper
Alloys:
2. Generally a joint overlap of three or four times the thickness of the
thinnest member to be joined is sufficient. The aim is to use as little
material as possible to achieve the desired strength.
Figure 3-Common Joint Design For Silver Brazing
6.3 Flame
adjustment
Use a neutral flame. A neutral flame is where equal amounts of oxygen and
acetylene are mixed at the same rate. The white inner cone is clearly
defined and shows no haze.
6.4 Flux Removal:
If flux has been used, the residue must be removed by one of the
following methods:
A Dilution in hot caustic soda dip.
A Wire brushing and rinsing with hot water.
A Wire brushing and steam.
Incomplete flux removal may cause weakness and failure of the joint.
7) Braze Welding of Copper:
Braze welding is a technique similar to fusion welding except with a
filler metal of lower melting point than the parent metal. The Braze
welding process derives its strength from the tensile strength of the
filler metal deposited as well as the actual bond strength developed
between the filler metal and parent metal. Oxy-acetylene is usually
preferred because of its easier flame setting and rapid heat input.
7.1 Choice of alloy:
The alloy most suited to the job requirement depends on the strength
required in the joint, resistance to corrosion, operating temperature and
economics. Alloys commonly used are:
Aufhauser Low Fuming Bronze or Aufhauser Low Fuming Bronze (Flux Coated).
7.2 Joint Preparation:
Typical joint designs are shown in figure 4 below.
Figure 4 -
Typical joint designs for Braze welding of copper.
7.3 Flame adjustment
Use slightly oxidizing flame.
7.4 Flux:
Use Aufhauser Copper and Brass Flux, mix to a paste with water and apply
to both sides of joint. Rod can be coated with paste or heated and dipped
in dry flux.
7.5 Preheating:
Preheating is recommended for heavy sections only.
7.6 Blowpipe and rod angles:
Blowpipe tip to metal surface 40° to 50°. Distance of inner cone from
metal surface 3.25mm to 5.00mm. Filler rod to metal surface 40° to 50°.
|
Plate
Thickness(mm)
|
Filler
Rod(mm)
|
Blowpipe
Acetylene Consumption (Cu. L/Min)
|
Tip
Size
|
|
0.8
|
1.6
|
2.0
|
12
|
|
1.6
|
1.6
|
3.75
|
15
|
|
2.4
|
1.6
|
4.25
|
15
|
|
3.2
|
2.4
|
7.0
|
20
|
|
4.0
|
2.4
|
8.5
|
20
|
|
5.0
|
3.2
|
10.0
|
26
|
|
6.0
|
5.0
|
13.5
|
26
|
Table 5 Data for the Braze welding of Copper
7.7 Welding Technique:
After preheating or after the joint is raised to a
temperature sufficient to permit alloying of the filler rod and copper,
melt a globule of metal from the end of the rod and deposit it into the
joint, wetting or tinning the surface. When tinning occurs, begin welding
using forehand technique. Do not drop filler metal on untinned surfaces.
See figure 5.
Figure 5 - Braze welding forehand technique.
7.8 Flux Removal:
Any of the following methods may be used to remove flux residue:
A Grinding wheel or wire brush and water.
A Sand blasting
A Dilute caustic soda dip.
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