Welding Dissimilar Metals

Welding Dissimilar Metals with
Wisconsin Wire Works Copper-Base Filler Metals

Wisconsin Wire Works Inc. is an integrated U.S. manufacturer of copper and copper alloy welding wire. We manufacture our own wire to ensure that it satisfies what welders expect from made-in-the-USA quality. We insist that all of our products meet applicable standards and specifications for composition, cleanliness and properties.

Wisconsin Wire Works Products
PRODUCTS FOR DISSIMILAR METAL WELDING	APPLICABLE SPECIFICATION
WWW SIL-WELD	AWS A5.7/ER CuSi-A
WWW-A2 BRONZE WELD	AWS A5.7/ER CuAl-A2
WWW COPP-WELD	AWS A5.7/ER Cu
WWW PHOS-C-WELD	UNS C52100 (CDA 521)
Other WWW Products
WWW-A1 BRONZE WELD	AWS A5.7/ER CuAl-A1
WWW-A3 BRONZE WELD	AWS A5.7/ER CuAl-A3
WWW NI-AL BRONZE	AWS A5.7/ER CuNiAl
WWW MN-NI-AL BRONZE	AWS A5.7/ER CuMnNiAl
WWW LOW-FUMING BRONZE-C	AWS A5.27 & A5.8/RBCuZn-C

Disclaimer
The recommendations made in this publication are based on Wisconsin Wire Works Inc. experience. In some cases, these recommendations agree with recommended practices published in the technical literature while in others they go beyond those practices. In no case are the recommendations made in this publication to be construed as standards or specifications, nor should they be used in place of published standards, specifications and practices for use in work performed under accepted codes, standards or specifications or to other requirements as spelled out in engineering drawings. Questions of applicability should be resolved by thorough testing before placing weldments in service. Wisconsin Wire Works Inc. assumes no responsibility for damages or injuries resulting from application of the recommendations given in this publication.

Arc Welding Dissimilar Metals with WWW Copper Alloys

Welding dissimilar metals can be difficult, considering all the variables involved. Ideally, dissimilar metal welding should only be done with careful planning, perhaps even involving the welding of test coupons. Of course, extra caution is always needed when the welded components will be under high stress or pressure in service, or when there are codes, specifications, standards, engineering drawings and/or other safety issues to be considered. In such cases, a qualified welding engineer should be consulted before committing to a job.

On the other hand, successful and safe dissimilar metal weld joints can often be made if a reasonable amount of precaution is taken before and during welding. And, one thing that can make the job easier is to use high-quality welding consumables from Wisconsin Wire Works Inc.

Two alloys that are well suited for dissimilar metal welding are WWW-A2 BRONZE WELD aluminum bronze (AWS A5.7/ER CuAl-A2) and WWW SIL-WELD silicon bronze (AWS A5.7/ER CuSi-A). WWW PHOS-C-WELD and WWW COPP-WELD can also be used for certain dissimilar metal combinations, but they are not as versatile as either the silicon- or aluminum bronze alloys.

WWW-A2 BRONZE WELD is the stronger of the four alloys. It has a slightly higher thermal conductivity and slightly lower coefficient of thermal expansion than does WWW SIL-WELD. All copper alloys have good corrosion resistance.

Many Combinations Possible

WWW SIL-WELD and WWW-A2 BRONZE WELD can be used to weld ferrous and nonferrous metals and alloys to each other and in various combinations. The following is a partial list, based on Wisconsin Wire Works experience, of dissimilar metal pairs that can be welded successfully using the versatile WWW SIL-WELD and WWW-A2 BRONZE WELD consumables as filler metals. Other combinations not listed here can also be welded. For further information, contact Wisconsin Wire Works technical service.

Mild Steel - Galvanized Steel	Stainless Steel - Copper
Mild Steel - Stainless Steel	Stainless Steel - Copper-Nickel
Mild Steel - Cast Iron	Stainless Steel - Silicon Bronze
Mild Steel - Copper	Stainless Steel - Aluminum Bronze
Mild Steel - Copper-Nickel	Stainless Steel - Brass
Mild Steel - Silicon Bronze	Cast Iron - Copper
Mild Steel - Aluminum Bronze	Cast Iron - Copper-Nickel
Mild Steel - Brass	Cast Iron - Silicon Bronze
Galvanized Steel - Stainless Steel	Cast Iron - Aluminum Bronze
Galvanized Steel - Copper	Cast Iron - Brass
Galvanized Steel - Cast Iron	Copper - Copper-Nickel
Galvanized Steel - Copper-Nickel	Copper - Silicon Bronze
Galvanized Steel - Silicon Bronze	Copper - Aluminum Bronze
Galvanized Steel - Brass	Copper - Brass
Galvanized Steel - Aluminum Bronze	Copper-Nickel - Silicon Bronze
Silicon Bronze - Aluminum Bronze	Copper-Nickel - Aluminum Bronze
Silicon Bronze - Brass	Copper-Nickel - Brass

Things to Watch Out For

It's important to remember that we're talking about welding here, not brazing. In brazing, temperatures are lower and the base metals don't actually melt. In dissimilar metal welding the base metals do melt and partially dissolve in the filler metal and in one another to create a metallurgical bond. That bond makes for a stronger joint (in fact, the joint should be stronger than the base metals). But mixing of the different metals can also lead to problems.

For example, cracking can occur when the combination of base and filler metals produces a weak or brittle alloy in the fusion zone. Sometimes this happens because the base or filler metals become diluted or enriched in a certain element; other times it happens because reactions in the melt lead to the formation of brittle structures. One way to help avoid these sorts of problems is to lay down relatively light passes until the base metal has been thoroughly covered. Doing this reduces the amount of dilution and mixing of the alloy components. Avoiding any chance for these problems to arise calls for a thorough metallurgical analysis. Considering the large variety of possible base and filler metal combinations, we couldn't begin to cover the subject adequately in this booklet.

From a practical standpoint, cracking most often occurs when the base and filler metals (or both of the base metals) have widely different:

• Melting points,

• Thermal conductivities, or

• Thermal expansion coefficients.

The chance for problems grows worse when more than one of these conditions are present at the same time.

Table 1
Properties of WWW Filler Metals for Welding Dissimilar Metals

ALLOY	MELTING POINT OR RANGE	THERMAL CONDUCTIVITY AT 68°F (293K)	COEFFICIENT OF THERMAL EXPANSION 68-572°F (20-300°C)	TENSILE STRENGTH, AS DEPOSITED (NOMINAL)
WWW-A2 BRONZE WELD (AWS A5.7 ER CuAl-A2)	1904-1913°F (1040-1045°C)	37 Btu/ft²/hr/°F (64 W/m·°K)	9 min/in/°F (13.6 mm/m/°C)	60 ksi (380 Mpa)
WWW SIL-WELD (AWS A5.7 ER CuSi)	1866°F (1019°C)	20 Btu/ft²/hr/°F (35 W/m·°K)	10 min/in/°F (18 mm/m/°C)	50 ksi (345 Mpa)
WWW PHOS-C-WELD(a)	1920°F (1049°C)	20 Btu/ft²/hr/°F (35 W/m·°K)	10 min/in/°F (18 mm/m/°C)	38 ksi (134 Mpa)
WWW COPP-WELD(a)	1981°F (1019°C)	196 Btu/ft²/hr/°F (339 W/m·°K)	9.4 min/in/°F (17 mm/m/°C)	25 ksi (172 Mpa)

(a)These alloys can be used for some dissimilar metal combinations; however, they are considered to be less versatile in this regard than either WWW-A2 BRONZE WELD or WWW SIL-WELD.

Table 2
Properties of Alloys Often Found in Dissimilar Metal Combinations

ALLOY	MELTING POINT OR RANGE	THERMAL CONDUCTIVITY AT 68°F (293K)	COEFFICIENT OF THERMAL EXPANSION 68-572°F (20-300°C)	TENSILE STRENGTH, AS DEPOSITED (NOMINAL)
Mild Steel	2723-2777°F (1495-1525°C)	7.3 Btu/ft²/hr/°F (12.6 W/m·°K)	7.3 min/in/°F (13.0 mm/m/°C)	35 ksi (240 Mpa)
300-Series Stainless Steel	2550-2650°F (1400-1450°C)	16.2 Btu/ft²/hr/°F (9.4 W/m·°K)	9.6 min/in/°F (17.2 mm/m/°C)	70 ksi (480 Mpa)
Cast (Gray) Iron	2360°F (1295°C)	26.6 Btu/ft²/hr/°F (46 W/m·°K)	7.2 min/in/°F (13 mm/m/°C)	25 ksi (172 Mpa)
Copper	1981°F (1019°C)	196 Btu/ft²/hr/°F (339 W/m·°K)	9.4 min/in/°F (17 mm/m/°C)	25 ksi (172 Mpa)
Copper-Nickel	2093°F (1145°C)	26 Btu/ft²/hr/°F (45 W/m·°K)	9.3 min/in/°F (16.7 mm/m/°C)	47 ksi (324 Mpa)
Silicon Bronze	1866°F (1019°C)	20 Btu/ft²/hr/°F (35 W/m·°K)	10 min/in/°F (18 mm/m/°C)	50 ksi (345 Mpa)
Aluminum Bronze	1904-1913°F (1040-1045°C)	37 Btu/ft²/hr/°F (64 W/m·°K)	9 min/in/°F (13.6 mm/m/°C)	60 ksi (380 Mpa)
Yellow Brass	1660°F (904°C)	23 Btu/ft²/hr/°F (71 W/m·°K)	11.6 min/in/°F (21 mm/m/°C)	54 ksi (372 Mpa)

Suggested Problem-Solvers

The good news is that there are ways to overcome all three potential sources of trouble. It is helpful to have some information about the properties of filler metals and metals that are often found in dissimilar metal combinations. Properties of WWW filler metals used in dissimilar metal welding are listed in Table 1. Properties of some alloys that are commonly found in dissimilar metal combinations are listed in Table 2.

Melting Point. It's easy to understand how problems can arise when the two base metals have widely different melting points. Under the heat of the welding arc, one metal melts first, causing uneven heat flow and non-uniform dilution in the weld puddle. When the weld solidifies, the base metal with the higher melting point is already solid at the time when the lower-melting metal is still at least partially liquid or in a mushy state, or at least very weak. The result is that the lower melting metal is prone to cracking in the weld zone or in the nearby HAZ.

To help prevent this type of cracking you can use filler metal with a melting point that lies between those of the base metals. In some cases, it may be helpful to butter the filler metal onto the lower melting base metal before laying down the rest of the passes. That allows the buttered layer (one or more passes may be needed) to act as a thermal cushion to protect the lower melting base metal. Buttering also reduces dilution.

For example, say the two base metals are Type 304 stainless steel and a yellow brass. The steel melts around 2550-2650°F (1400-1450°C) while the brass melts between 1660 and 1710°F (904 and 932°C). Because brass has a considerably lower melting point than stainless, cracking is a possibility. Both WWW SIL-WELD (1866°F/(1019°C) and WWW-A2 BRONZE WELD (1904-1913°F/1040-1045°C) have melting points or ranges that lie about half-way between those of stainless and brass. Either filler metal would be a good choice to avoid problems due to the difference in melting points of the two base metals. The aluminum bronze is somewhat stronger than the silicon bronze, but the silicon bronze is considered to be the better choice because it is more compatible with the brass.

Thermal Conductivity. Differences in thermal conductivity between two base metals produce different heating and cooling rates on the two sides of the weld joint during and after the welding cycle. The metal with the higher conductivity will tend to draw heat away from the weld zone, and if the difference in conductivities of the two base metals is large enough, the uneven heat flow may prevent complete fusion of the low-conductivity metal. Uneven heat flow can also affect solidification of the weld metal and can lead to distortion in the finished assembly.

One way to deal with this situation is to preheat the base metal with the higher conductivity. Preheating causes more heat to flow to the lower-conductivity metal during welding (because of the larger temperature difference) and thus leads to a more even heating of the weld assembly. Heating the higher-conductivity base metal also reduces the cooling rate after welding, and this helps reduce post-weld thermal stresses. The degree of preheat may have to be arrived at by trial and error, although the temperatures listed in the tables below are good starting points. Thicker sections will require more preheat than thin ones because, during welding, they present a larger area to direct heat away from the weld zone. Care should be taken not to overheat the metals to the degree that they become softened or metallurgically altered.

Often, simply directing the arc toward the higher conductivity base metal can solve problems brought about by differences in base-metal conductivities. In the case of steels welded to copper-base alloys, it is usually the copper alloy that should receive most of the heat because the copper alloys' conductivities can be several times higher than steel's. On the other hand, some copper alloys, like copper-nickels, have thermal conductivities that are as low as those of highly alloyed or stainless steels. Preheating may not be necessary when joining such combinations of metals.

Coefficient of Thermal Expansion. When there are large differences in thermal expansion between two base metals (and between base metals and the filler metal) high stresses can arise during and after welding, and during service. The stresses can be high enough to cause cracking.

On cooling from the welding process, other factors being equal, the metal with the higher coefficient of thermal expansion will shrink more than the metal with the lower coefficient. Since the metals are rigidly bound together, this differential shrinking induces tensile stresses in the metal with the higher coefficient of thermal expansion and compressive stresses in the other. Again, tensile stresses are more damaging than compressive stresses because tensile stresses lead to cracking. The magnitude of the thermal stresses is determined by the geometry of the assembly and by the difference in thermal expansion coefficients of the dissimilar metals. The higher the difference the coefficients, the higher the stresses. It is easily possible for these thermal stresses to exceed the tensile strength of one of the metals involved (including the filler metal), and cause cracking.

Cracking sometimes occurs during or immediately after welding. This is called hot cracking or hot tearing, and it results from the normal weakness of metals at high temperatures. Cracking can also occur at room temperature if the stresses are not relieved. Cracking of this type is accelerated when the metals are cycled between low and high temperatures during service. There are two accepted methods to avoid cracking caused by differences in thermal expansion. The first method is to select a filler metal with a thermal expansion coefficient that is intermediate between those of the two base metals.

To use our previous example, the coefficient of thermal expansion of Type 304 stainless steel is 9.6 min/in/°F (17.2 mm/m/°C) while that of yellow brass is 11.3 min/ in/°F (20.4 mm/m/°C). The difference in this case is not large and the risk of cracking from this cause is low. On the other hand, if we had to weld a low alloy steels with a coefficient of thermal expansion as low as 6.6 min/in/°F (12 mm/m/°C) to a manganese bronze with a coefficient of 11.9 min/in/°F (21.4 mm/m/°C), we might expect to see cracking in the bronze.

The tendency to form cracks is lower in this case if you use WWW-A2 BRONZE WELD as a filler metal because its coefficient of thermal expansion (9 min/in/°F, 13.6 mm/m/°C) is intermediate between those of the two base metals.

The second "fix" is to apply preheat and, if necessary, post-heat in order to reduce the level of thermal stresses during and after welding. The use of heat in this manner can only provide partial relief of residual stresses since the choice of temperature will be a compromise between those needed to anneal both base metals. It is important not to overheat one base metal in an attempt to fully anneal the other.

Welding Practices

GTAW gives very good results when welding dissimilar metals in the flat position. Use 100% helium for thick sections; prep the joint as necessary for the degree of penetration needed. Use 100% argon for sheet and thin sections. Out-of-position welds are difficult because of the filler metals' high fluidity; however Wisconsin Wire Works welding experts can provide you with assistance if necessary.

The following tables, containing data taken in part from the AWS Welding Handbook, Vol. 3 and the ASM International Metals Handbook, Vol. 6, list recommended preheat and interpass temperatures for GTAW and GMAW processes using copper-base filler metals. In some cases, Wisconsin Wire Works recommendations with regard to filler metals, which are based on our experience, go beyond those proposed in other publications.

Suggested Preheat and Interpass Temperatures for GTA (TIG) Welding of Dissimilar Metal Combinations

(Data taken in part from AWS Welding Handbook, Vol. 3. and ASM International Metals Handbook, Vol. 6.)

FILLER METALS (AND PREHEAT AND INTERPASS TEMPERATURES) FOR WELDING METAL IN COLUMN 1 TO: (A)
FOR WELDING METAL IN COLUMN 1 TO: (A)	COPPERS	PHOSPHOR BRONZES	ALUMINUM BRONZES	SILICON BRONZES	COPPER-NICKELS
Low- carbon steel	WWW-A2 BRONZE WELD or WWW COPP-WELD or WWW SIL-WELD 1000°F (540°C)	WWW PHOS-C-WELD or WWW SIL-WELD or WWW-A2 BRONZE WELD 400°F (205°C)	WWW-A2 BRONZE WELD 300°F (150°C)	WWW-A2 BRONZE WELD or WWW SIL-WELD 150°F (65°C)max	WWW-A2 BRONZE WELD or WWW SIL-WELD 150°F (65°C)max
Medium- carbon steel	WWW-A2 BRONZE WELD or WWW COPP-WELD or WWW SIL-WELD 1000°F (540°C)	WWW PHOS-C-WELD or WWW SIL-WELD or WWW-A2 BRONZE WELD 400°F (205°C)	WWW-A2 BRONZE WELD 300°F (150°C)	WWW-A2 BRONZE WELD or WWW SIL-WELD 150°F (65°C)max	WWW-A2 BRONZE WELD or WWW SIL-WELD 150°F (65°C)max
High- carbon steel	WWW-A2 BRONZE WELD or WWW COPP-WELD or WWW SIL-WELD 1000°F (540°C)	WWW PHOS-C-WELD or WWW SIL-WELD or WWW-A2 BRONZE WELD 400°F (205°C)	WWW-A2 BRONZE WELD 300°F (150°C)	WWW-A2 BRONZE WELD or WWW SIL-WELD 150°F (65°C)max	WWW-A2 BRONZE WELD or WWW SIL-WELD 150°F (65°C)max
Low alloy steel	WWW-A2 BRONZE WELD or WWW COPP-WELD or WWW SIL-WELD 1000°F (540°C)	WWW PHOS-C-WELD or WWW SIL-WELD or WWW-A2 BRONZE WELD 400°F (205°C)	WWW-A2 BRONZE WELD 300°F (150°C)	WWW-A2 BRONZE WELD or WWW SIL-WELD 150°F (65°C)max	WWW-A2 BRONZE WELD or WWW SIL-WELD 150°F (65°C)max
Stainless steel	WWW-A2 BRONZE WELD or WWW COPP-WELD or WWW SIL-WELD 1000°F (540°C)	WWW PHOS-C-WELD or WWW SIL-WELD or WWW-A2 BRONZE WELD 400°F (205°C)	WWW-A2 BRONZE WELD 300°F (150°C)	WWW-A2 BRONZE WELD or WWW SIL-WELD 150°F (65°C)max	WWW-A2 BRONZE WELD or WWW SIL-WELD 150°F (65°C)max

(a) Filler metal selections shown are based on weldability, except where mechanical properties are usually more important. Preheating is ordinarily used only when at least one member is thicker than about 3.2 mm (1/8 in) or is highly conductive. Note that WWW PHOS-C-WELD is stronger than the lower-tin-content ERCuSn-A filler metal, which is occasionally recommended in instances where the WWW phosphor bronze is indicated above.

Preheat and interpass temperatures are subject to adjustment on the basis of the size and shape of the weldment.

Making dissimilar metal joints with GMAW is straightforward, too. For thick sections, it may be helpful to lay down a root pass using GTAW, then complete the joint with GMAW using 100% argon shielding. If more heat is needed, use a 75/25 mixture of argon and helium.

Suggested Preheat and Interpass Temperatures for GMA (MIG) Welding of Dissimilar Metal Combinations

(Data taken in part from AWS Welding Handbook, Vol. 3. and ASM International Metals Handbook, Vol. 6.)

ELECTRODES (AND PREHEAT AND INTERPASS TEMPERATURES) FOR WELDING METAL IN COLUMN 1 TO: (B)
METAL TO BE WELDED	COPPERS	LOW-ZINC BRASSES	HIGH-ZINC BRASSES, TIN BRASSES, SPECIAL BRASSES	PHOSPHOR BRONZES	ALUMINUM BRONZES	SILICON BRONZES	COPPER-NICKELS
Low- carbon steel	WWW-A2 BRONZE WELD or WWW COPP-WELD or WWW SIL-WELD 1000°F (540°C)	WWW PHOS-C-WELD or WWW SIL-WELD 600°F (315°C)	WWW-A2 BRONZE WELD 500°F (260°C)	WWW PHOS-C-WELD or WWW SIL-WELD 400°F (400°C)	WWW-A2 BRONZE WELD 300°F (150°C)	WWW-A2 BRONZE WELD or WWW SIL-WELD 150°F (65°C)max	WWW-A2 BRONZE WELD or WWW SIL-WELD 150°F (65°C)max
Medium- carbon steel	WWW-A2 BRONZE WELD or WWW COPP-WELD or WWW SIL-WELD 1000°F (540°C)	WWW PHOS-C-WELD or WWW SIL-WELD 600°F (315°C)	WWW-A2 BRONZE WELD 500°F (260°C)	WWW PHOS-C-WELD or WWW SIL-WELD 400°F (400°C)	WWW-A2 BRONZE WELD 300°F (150°C)	WWW-A2 BRONZE WELD or WWW SIL-WELD 150°F (65°C)max	WWW-A2 BRONZE WELD or WWW SIL-WELD 150°F (65°C)max
High- carbon steel	WWW-A2 BRONZE WELD or WWW COPP-WELD or WWW SIL-WELD 1000°F (540°C)	WWW PHOS-C-WELD or WWW SIL-WELD 600°F (315°C)	WWW-A2 BRONZE WELD 500°F (260°C)	WWW PHOS-C-WELD or WWW SIL-WELD 400°F (400°C)	WWW-A2 BRONZE WELD 300°F (150°C)	WWW-A2 BRONZE WELD or WWW SIL-WELD 150°F (65°C)max	WWW-A2 BRONZE WELD or WWW SIL-WELD 150°F (65°C)max
Low- alloy steel	WWW-A2 BRONZE WELD or WWW COPP-WELD or WWW SIL-WELD 1000°F (540°C)	WWW PHOS-C-WELD or WWW SIL-WELD 600°F (315°C)	WWW-A2 BRONZE WELD 500°F (260°C)	WWW PHOS-C-WELD or WWW SIL-WELD 400°F (400°C)	WWW-A2 BRONZE WELD 300°F (150°C)	WWW-A2 BRONZE WELD or WWW SIL-WELD 150°F (65°C)max	WWW-A2 BRONZE WELD or WWW SIL-WELD 150°F (65°C)max
Stainless steel	WWW-A2 BRONZE WELD or WWW COPP-WELD or WWW SIL-WELD 1000°F (540°C)	WWW PHOS-C-WELD or WWW SIL-WELD 600°F (315°C)	WWW-A2 BRONZE WELD 500°F (260°C)	WWW PHOS-C-WELD or WWW SIL-WELD 400°F (400°C)	WWW-A2 BRONZE WELD 300°F (150°C)	WWW-A2 BRONZE WELD or WWW SIL-WELD 150°F (65°C)max	ERCuAl-A2 or WWW SIL-WELD 150°F

(b) Filler metal selections shown are based on weldability, except where mechanical properties are usually more important. Preheating is ordinarily used only when at least one member is thicker than about 3.2 mm (1/8 in) or is highly conductive. Note that WWW PHOS-C-WELD is stronger than the lower-tin-content ERCuSn-A filler metal, which is occasionally recommended in instances where the WWW phosphor bronze is indicated above.

Wisconsin Wire Works has years of experience with dissimilar-metal welding, and our high-quality made-in-the-USA filler metals can make dissimilar- metal welding easier than you think. If you have a combination of metals you've never welded before, or if you need assistance with any dissimilar welding problems, call 262-679-8218, fax 266-679-8219 or email us at info@wisconsinwireworks.com. We're glad to help.