Which filler metals are used for arc brazing?
Almost always standardised copper-based solid wires to ISO 24373, usually 0.8 to 1.6 mm in diameter. The most common is CuSi3Mn1 for galvanised sheet, plus CuAl7 (formerly CuAl8) for aluminised sheet and visible seams, and tin bronzes for copper and brass parts.
The filler metals melt between about 900 and 1070 °C, well below the steel. They are made for arc brazing: silicon, aluminium or tin ensure good wetting, and there are hardly any elements that vaporise in the arc.
- Brass and nickel silver filler metals are only suitable in exceptional cases according to DVS 0938-1. Their zinc vaporises in the arc.
- Zinc-based filler metals with melting ranges of around 380 to 450 °C were being trialled in 2012, for example for very thin sheet or thick zinc layers.
- Non-standardised wires and flux-cored wires are less common.
The usual filler metals at a glance
At 980 to 1035 °C, CuSi3Mn1 has the lowest melting range of the common filler metals and reaches a tensile strength of over 340 MPa. CuAl7 is stronger at over 380 MPa, but melts at a higher temperature.
| Filler metal | ISO 24373 | Melting range | Rp0.2 | Rm | A5 | Main application |
|---|---|---|---|---|---|---|
| CuSi3Mn1 | Cu 6560 | 980–1035 °C | > 200 MPa | > 340 MPa | 40 % | galvanised steel car body parts |
| CuSi2Mn1 | Cu 6511 | 1030–1050 °C | > 100 MPa | > 290 MPa | 45 % | galvanised steel car body parts |
| CuAl7 | Cu 6100 | 1030–1040 °C | > 180 MPa | > 380 MPa | 40 % | galvanised steel car body parts |
| CuAl5Ni2Mn | Cu 6061 | 1040–1070 °C | > 200 MPa | > 360 MPa | 45 % | solenoid valves |
| CuSn1 | Cu 1898 | 1020–1050 °C | > 80 MPa | > 220 MPa | 25 % | copper vessel construction |
| CuSn6P | Cu 5180 | 910–1040 °C | > 150 MPa | > 260 MPa | 20 % | brass and bronze parts |
Extract from DVS 0938-1:2012, Table 5. The strength values are manufacturers’ data for the pure deposited filler metal and do not apply to the brazed joint. The table in the technical bulletin also gives the designations under ISO 17672 as well as filler metals for surfacing and zinc-based filler metals.
Copper-based wires are available in different heat treatment conditions. For robots with long hose packages, DVS 0938-1 recommends wires with higher strength, because they are easier to feed.
How do you read the standard designation under ISO 24373?
The designation ISO 24373 – S Cu 6560 (CuSi3Mn1) consists of three parts: S for solid wire or solid rod, Cu 6560 for the chemical composition and, optionally, the alloy symbol in brackets.
- ISO 24373: the standard for solid wires and solid rods of copper and copper alloys. It replaces DIN EN 14640 and, before that, DIN 1733.
- S: the product form. Wire and rod both carry the S; one product form can be used for several processes.
- Cu 6560: the numerical designation of the composition. It alone is binding.
- (CuSi3Mn1): the alloy symbol, for readability.
As a brazing filler metal under ISO 17672, the same alloy is designated Cu 541. On a drawing, a MIG-brazed seam is specified, for example, as ISO 4063-973 / ISO 24373 – S Cu 6560 (CuSi3Mn1), see Arc brazing processes at a glance.
Old and new designations of our brazing wires
The old DIN names still appear on drawings and orders. The table maps them to the current ISO designation and the American AWS classification.
| Wire | ISO 24373 | DIN 1733 (old) | Material no. | AWS A5.7 |
|---|---|---|---|---|
| ML CuSi3 | S Cu 6560 (CuSi3Mn1) | SG-CuSi3 | 2.1461 | ERCuSi-A |
| ML CuAl8 | S Cu 6100 (CuAl7) | SG-CuAl8 | 2.0921 | ERCuAl-A1 |
| ML CuSn | S Cu 1898A (CuSn1MnSi) | SG-CuSn | 2.1006 | ERCu |
| ML CuSn6 | S Cu 5180A (CuSn6P) | SG-CuSn6 | 2.1022 | ERCuSn-A |
ML CuSi28L has the same standard designation as ML CuSi3, S Cu 6560 (CuSi3Mn1). All wires: Copper welding and brazing wire.
CuAl8 or CuAl7: are they the same?
Essentially yes. For S Cu 6100 with the symbol CuAl7, ISO 24373 lists the old designation SG-CuAl8 (material no. 2.0921) as the corresponding national classification. It is the same wire type under a new name.
The analysis limits of the old and the new standard are not identical in every respect. ISO 24373 permits an aluminium content of 6.0 to 8.5 % for Cu 6100. The inspection certificate of the wire is decisive.
In everyday usage and on many drawings, CuAl8 has remained. Anyone ordering or testing to ISO will find it under Cu 6100.
CuSi3 or CuAl8: which filler metal for what?
CuSi3 for galvanised sheet; it is the standard filler metal and the most widely used. CuAl8 for aluminised sheet, when higher strength is needed or the seam should show fewer braze cracks.
- CuSi3Mn1: lowest melting range, wets galvanised sheet well and can be used with all arc brazing processes. Tolerates shielding gases with a little CO₂ or O₂.
- CuAl7 (CuAl8): for aluminised sheet, DVS 0938-1 recommends aluminium-containing filler metals. In the trials at SLV München, CuAl8 showed significantly less filler metal penetration than a tin bronze. Brazing is done under inert gas, argon or argon-helium.
- Limit for CuAl8: it is not suitable for TIG and plasma brazing because of poor wetting. See TIG and plasma brazing.
On the choice of gas: Shielding gas. On the base material: Base materials and coatings.
How hot may a brazed joint get in service?
Fluctuating temperatures up to 180 °C are not critical. For components that are permanently hotter, DVS 0938-2 currently does not recommend arc brazing.
According to DVS 0938-1, copper-based filler metals are creep-resistant up to about 250 °C; above that they begin to creep. They resist oxidation up to 450 °C. With temperature, diffusion also increases and with it the risk of braze cracks, see Seam defects and braze cracking.
What matters with brazing wire?
The geometry. The soft copper wire has to run through the hose package and contact tip without stuttering. DVS 0938-1 lists defects that must be avoided at all costs.
- longitudinal scores on the wire
- diameter outside tolerance
- waviness
- welds in the wire
In addition, cast and helix should be closely toleranced, and the surface clean. Dirt, grease and oil promote pores. More under Wire feeding.
Frequently asked questions
Is CuSi3 a welding wire or a brazing filler metal?
Both. CuSi3Mn1 is standardised in ISO 24373 as a welding consumable for copper materials. On steel, the same wire acts as a brazing filler metal, because only the wire melts and the steel stays solid.
What does Cu 6560 mean?
The numerical designation of the composition under ISO 24373, here copper with around 3 % silicon and 1 % manganese. The symbol CuSi3Mn1 is an optional addition to it.
Can you MIG braze with brass wire?
Only in exceptional cases. The zinc in the brass vaporises in the arc, which leads to pores, fumes and an unsteady arc.
Which wire diameter is used for brazing?
Usually 1.0 mm; 0.8 to 1.6 mm are used. Thinner wires for thin sheet and low currents, thicker ones for higher deposition rates.
What is the difference between SG-CuSi3 and CuSi3Mn1?
It is the same wire type. SG-CuSi3 is the old designation under DIN 1733, CuSi3Mn1 the symbol under ISO 24373, which lists it as an equivalent in its annex.
Further reading: articles on arc brazing
The series in the order in which the questions arise in practice: from the process via filler metal, gas and base material to the finished seam. For an overview, see Arc brazing.
About the author
Robert Lahnsteiner, Ing., is an International Welding Engineer (IWE) and managing director of MIGAL.CO GmbH. After training in telecommunications and electronics at HTL Braunau, he spent eighteen years in welding technology at Fronius from 1983. Since 2001 he has run MIGAL.CO, the aluminium welding wire manufacturer in Landau an der Isar, together with Martin Erl. His focus is aluminium filler metals, wire manufacturing and wire feeding, and the monitoring of welding processes. Within DVS, the German Welding Society, he has served for around 30 years on technical committee FA03 “Arc welding” and chairs working group 2.4.4 “MIG welding of aluminium”.