TIG Brazing With Silicon Bronze
April 4, 2019
Welder/fabricator Josh Welton of Brown Dog Welding explains how to use silicon bronze when TIG brazing.
Versatile filler material
Silicon bronze is pretty versatile as a filler material. With a TIG torch, you can put it to use on a number of tasks that range from difficult to impossible with a typical steel filler rod.
Of course, using this filler material is not exactly welding — not in the traditional sense at least. Instead, you’re brazing with a softer filler utilizing capillarity, while still using a TIG setup instead of a gas torch. It’s a process sometimes known as TIG or electric brazing. Brazing is done at lower temperatures without melting the base metals; the filler material flows into any and all microscopic crevices in the metal and pulls the pieces together, similar to a permanent Velcro. Because of this, you don’t need the base metals to be similar, so it’s possible to TIG braze copper to stainless steel, as an example.
Lower melting point
The silicon bronze rod’s lower melting point makes it ideal for joining together thin sheet metal, galvanized steel, and nuts and bolts, too. It’s nice for sheet metal work because the lower melting temps means less heat, which equals less warping when compared to TIG with, say, an ER70 rod. And you can still sand and paint it just like the surrounding metal.
Additionally, you won’t get the “popping” and tungsten blowouts that are normally associated with welding galvanized steel because the silicon bronze flows at a temperature lower than the zinc-heavy coating. Zinc is relatively nasty stuff that causes a mess.
Silicon bronze actually has outstanding wear properties, too. My dad had some worn cast-iron gears that needed the teeth built up. I didn’t have the time to do the preheat/postheat a weld would require, so I decided to braze it “cold” instead, getting the material just warm enough to take the silicon bronze. I did the buildup, dad filed them down to fit, and they’ve been working perfectly in his snow blower for the past five or six seasons.
Joining dissimilar metals
The ability to join dissimilar metals is huge in a lot of arenas, including art. For my sculptures, it opened up a new world to me years ago when I found I could use it to attach copper to steel. The contrast in colors, the tactile difference in materials, it all adds to the character of the pieces.
In reality, I do go back and forth between calling it TIG brazing and welding. It’s too easy to call it TIG welding, because it’s essentially the same process. The differences in how the filler reacts to the base metal are subtle. You have a smaller window for the rod to melt into the puddle; if you’re too cold, the joint won’t accept the filler and the end will ball up. If you’re too hot, you melt into the base metal too much and find out the hard way why it’s called a “hot cracking” rod.
Melting into the base metal a little is ok, but excessive melting will fracture the joint down the middle. Still, overall, it’s a lot like TIG welding steel when it comes to machine settings, consumables, and hand-eye coordination. The filler is pretty much the only variable that changes from a process standpoint.
DC vs. AC polarity
I should note that while I typically use DC negative polarity (just like I’d use on steel) to weld/braze with silicon bronze, you can use AC, too. Alternating current’s cleaning process helps when brazing some materials. The Multimatic® 220 AC/DC multiprocess welder from Miller offers both AC and DC TIG — which I used to compare the two. Your best bet is to experiment with the different settings to find what works best for your situation.
As with any kind of welding or brazing you’ll want to work with good ventilation — like a fume extraction system.
If you can TIG weld and want to try TIG brazing, just grab some silicon bronze and go to town. You'll notice the slight differences in laying a bead that I mentioned earlier, but overall, it's a pretty simple process.
About Josh Welton
Josh Welton, owner of Brown Dog Welding LLC fabrication and art studio in Detroit MI, is an established welder, fabricator, teacher, artist, writer, social media influencer, entrepreneur and automotive enthusiast. He is a contributing writer to TheFabricator.com and The WELDER Magazine (FMA Publications), as well as DodgeGarage.com. He was honored as the 2018 recipient of the WEMCO/AWS Foundation Excellence in Welding Award in the Media category for his contributions to promote welding.