Master Class
An expert guide to using silicon bronze filler metal for coated materials, sheet metal fabrication, and artistic metalwork.
The Advantage of Silicon Bronze Filler Metal
Silicon bronze is a copper-based filler metal that can be used in several different welding applications. It is an alloy of copper and silicon, which contains 2.8 to 4.0 Si (silicon). The American Welding Society (AWS) classification of silicon bronze is AWS A5.7: ERCuSi-A.
Silicon bronze can be used for welding bronze and brass materials, dissimilar welds between copper alloys and steel or other alloys, and for braze-welding galvanized steels. Silicon bronze can also be used to add color to welded art or a metal sculpture, helping the project stand out compared with an average piece of stamped out sheet metal.
One important thing to remember: The strength of silicon bronze filler metal is lower than steel. The minimum tensile strength for silicon bronze is 50 ksi (kilopound per square inch). Common steel filler metals, such as Lincoln Electric’s ER70S-2 and ER70S-6, have a minimum tensile strength of 70 ksi.
This article addresses two applications using silicon bronze filler metal – brazing galvanized steel and welding on thinner sheet metal.
Coated Materials
Occasionally, a fabricator may have a need to weld on galvanized sheet metal. Removing the galvanized coating in the welding area is the best choice for welding the coated material. If the coating is not removed when using the TIG process, the tungsten will quickly become contaminated, causing an unstable arc (Figure A). Contamination is caused by the galvanized coating coming off the plate and attaching to the end of the tungsten (Figure B).
If removing the coating is not an option, it is possible to braze the sheets using a silicon bronze filler metal. The low melting point of the silicon bronze filler metal will allow the galvanized sheet to be joined without melting the base metal. The equipment set up to braze with silicon bronze is the same as welding steel: DC+ polarity and argon shielding gas.
Thinner Sheet Metal
Silicon bronze can be used to reduce distortion on thinner sheet metal. The sheet metal can be joined with silicon bronze using a lower current procedure when compared with welds made to carbon steel filler metals. The lower heat input reduces distortion and burn through.
Travel Speeds
Travel speeds can be increased on thinner metals when using silicon bronze filler metal. An example would be a fabricator using 3/32-inch ERCuSi-A (silicon bronze) filler metal at the same current setting used for a carbon steel filler metal when joining sheet metal. The travel speed would be much quicker because with the silicon bronze filler metal, less heat is needed to melt the wire when compared with carbon steel filler wire.
Tools
• Lincoln Electric Square Wave® TIG 200
• Harris Products Group silicon bronze filler metal, 3/32-inch diameter
• Argon gas
• Current, between 70 amps and 90 amps
• Lincoln Electric Pro-Torch™ PTA-9 air-cooled torch with gas lens
Personal Protective Equipment
• Welding helmet
• Safety glasses
• Welding gloves
• Fire-retardant clothing, including welding jacket and other protective layers to cover exposed skin
• Adequate ventilation and/or proper fume extraction
PREHEAT SAFELY
We always want to make sure we’re working safely when welding and working with torches. Refer to ANSI Z49.1: “Safety in Welding, Cutting, and Allied Processes,” which includes heating.
Make sure to wear the proper safety gear, including flame-retardant clothing, gloves and proper safety glasses. Make sure your jeans or pants are not frayed.
For proper torch setup and application, refer to the manufacturer’s guidelines. Make sure to have the correct check valves on the torch, flash arresters back at the regulator, hoses in good condition, and regulators set and operating properly.