The arc brazing processes are generally used for joining of uncoated or coated steel fine sheets in a thickness range of up to 3.0 mm. With higher tensile strength of the steel sheets it must be considered that the strength of the brazing alloy is usually lower than the strength of the base metal.
A speciality is brazing of different base materials i.e. of Copper alloys with steel. These joints show two different characteristics – brazing on the steel side and welding on the Copper side.
Even stainless steel can be joined with arc brazing. In particular the low heat input can be of great advantage with long seams and thin materials, because distortion of the work pieces is greatly reduced. Due to a higher susceptibility for soldering cracks it needs to be tested in every single case. The improved gap-bridging capability is responsible for a higher tolerance on work piece dimensions. ML CuAl8 is the recommended filler wire. The colour difference between base material and filler wire must be obeyed.
Surface coatings and preparation
Sheets with a coating thickness of up to 15 µm can generally be used without any problems. In case that i.e. hotgalvanized work pieces with greater thicknesses are used additional investigations may be required. For base metals covered with Aluminium also Aluminium containing brazing alloys shall be used. Additional organic coatings may need specially adapted parameters.
In order to obtain a metallurgical interaction between the base material and the wetting liquid braze the border area should be clean and pure metal. Dirt, grease, residuals from machining, wax, adhesives or oil may reduce the joint quality (Porosity, lack of fusion etc.) and shall be removed by either chemical and/or mechanical surface treatment processes.
Consumables and auxiliary materials
Brazing consumables For arc brazing mainly the two alloys ML CuSi3 and ML CuAl8 are used as wires or rods. With MIG brazing a wire diameter of 1.0 mm is commonly used. Traditionally for Germany the ML CuSi3 is applied, whilst in other countries the alloy ML CuAl8 is used for similar applications. ML CuAl8 is also used for joints in the furniture industry where the optical look of the seam surface is essential. MIGAL.CO consumables are optimized for GMA brazing. The wires have an ideal hardness and provide the best gliding characteristic. Shielding gases For arc brazing usually Argon or Ar-mixes with additions of CO2 or O2 are used. Together with filler metals containing Si or Sn low active additions of CO2 or O2 may be of advantage. These gases stabilize the arc, reduce porosity, however, increase the heat input into the work piece. N2 additions stabilize the arc and give a wider seam, however, may produce considerable amounts of porosity. H2 additions increase the speed of brazing, but may also lead to porosity. In order to optimize the shielding gas composition to the brazing job it is recommended to use the experiences from gas manufacturers.