TIG, silicon bronze and galvanised

I have come across some vague references to this combination working out well, with no spatter or contamination of the tungsten. But no-one will definitively say how well it works. Does/Has anyone here use(d) it? I don't want to fork out for silicon bronze rods for no reason but if you can do this combo without really grinding away the galvanised coating and not having to post-treat for rust then I will happily pay the difference. I'm talking about dura/supagal, not hot-dipped and just structures like backyard furniture, joining galvanised or zincanneal sheet to light SHS/RHS.

Not sure how that would work. I've TIG'd zinc plated tubes (tent knuckles) and while the zinc would melt away, it was messy because the zinc fumed and so the nozzle got coated in yellow zinc oxide. If I have to weld zinc plated tube these days I try to stay with stick.

Michael

I've found vague reference to it being a brazing process and the silicon bronze melts very cold, well before the parent metal. I guess the question is, does it melt at a lower temp than the zinc either melts or sublimates or oxidises or vaporises or whatever it does that causes it to contaminate tungsten. Zinc melts at about half the temperature of silicon bronze, it boils at about the same temperature that bronze melts.

Stuff I read suggests using about half the amps you'd use for welding the parent steel and even at those settings the bronze flows readily and the process is fast.

The rods are very expensive but eliminating prep would make the cost well worthwhile.

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Originally Posted by Legion

I've found vague reference to it being a brazing process and the silicon bronze melts very cold, well before the parent metal. I guess the question is, does it melt at a lower temp than the zinc either melts or sublimates or oxidises or vaporises or whatever it does that causes it to contaminate tungsten. Zinc melts at about half the temperature of silicon bronze, it boils at about the same temperature that bronze melts.

Stuff I read suggests using about half the amps you'd use for welding the parent steel and even at those settings the bronze flows readily and the process is fast.

The rods are very expensive but eliminating prep would make the cost well worthwhile.

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I haven't tried it but I'd really interested in the answer. I'd gladly pay more for something that would allow me to tig over duragal. I'm skeptical that it would work - the issue being that the arc temperature is way over the boiling temp for zinc, and the zinc is the first thing that is encountered by the arc - so unless you can add the filler straight away AND the filler additives somehow mop up all the zinc before it vapourises, then I think it is inevitable that you're going to get zinc condensing on your tungsten and oxides everywhere. With brazing you aren't dealing with such fierce arc temperatures - so I can imagine how that would work. I'm not sure how you could get away with half amps tig welding? what about penetration, etc.?

I've found that if I'm tigging and I get SOME zinc contamination I can keep going fine, but the weld metal (not just a coating) gets this funny black look ... not sure what that is?

Cheers

- Mick

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Originally Posted by WelderMick

... unless you can add the filler straight away ...

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That's it though - someone on some google search said you don't form a puddle, don't melt the parent, you just go and the rods melt very quickly with such small heatsink mass. Brazing and soldering are the common analogies mentioned, definitely not welding.

I was thinking of e.g. a BBQ table for a ceramic cooker I have. Frame out of welded dura/supagal rhs with galv thin sheet as panels. The alternative was stainless, but I've never done that and certainly getting the cosmetics right would be a big ask. Not to mention materials and consumables cost more than silicon bronze anyway. The sheet would be too thin (to be cost effective, maybe 0.95mm) for stick welding. I'd prefer the cosmetics of silicon bronze to e.g. riveting or glueing. And if it is a process where no pre or post treatment has to happen, well that would make my decision easy.

I might eventually pick up a 1kg pack of rods and give it a shot out of interest.

I was lucky enough to come across a roll of mig wire which I think is silicon bronze (first picture), in a scrap yard a couple of years ago.
I'm not a proper welder but I tried some tests as best I could.
I tried it on hot dip galv, but no way (using TIG) 2nd Picture. The bronze wouldn't stick at all and far to much fumes and spitting.
I'm not sure what duragalv is but I have some 12mm rod which is coated in a gold coloured plate which I think is a form of zinc, so I tried it on that.
The third picture was weld with just steel welding rod, heating up the rod slowly (bottom bar in the picture). It spit quite a bit and I wouldn't want to do this because it messed up my gas lens, but it probably would work. Welding had much more spitting than with the bronze.
Fourth picture top bar, at the right was my first attempt and I melted the steel into the bronze but it's quite easy to avoid this once you know. The longer run on the left was after I had blobbed on big chunk of bronze, so I could heat up the rod, and then the arc was only onto the bronze. You still need to get the steel red hot or the bronze won't wet out, if that's a proper term. You can see the heating to get red hot has blistered the plating nearby. probably heated too slow but you don't want to melt the steel. Once it got going though, I could run the bead quite quickly to the left and it has wetted in ok I think. While doing this, there is a steady stream of white fumes pouring off, but its the plate coming off at the edge of the red hot area, and not directly in your arc. Kind of works then, but still quite a lot of spitting. When you start there always seemed to be spitting. I probably don't have good technique.
The last photo shows how I started by melting only the bronze onto the rod, no wetting (top left). Then I could put some heat into the rod through the blob of bronze to minimise zinc boiling. There was some spitting and a stream of fumes but it wets out and you can run a bead with less spitting but with fumes (bottom left). Right picture is the same blob after wire brushing. You wouldn't want to use a gas lens although I did, to my regret. Not sure if this was any use to you. All I can say is that for me, there is too much fumes and too much spitting so I would rather take the zinc off.

sossity, that's a great post.

Duragal is the factory coated zinc stuff that just has a thin smooth polished galv coating. It's nothing like hot-dipped. In my stick welding experience, hot-dipped galv is impossible to weld through, requires the whole lot ground off whereas duragal and supagal you can just weld straight through with no problems at all as long as you have good ventilation and don't breathe the fumes.

I do lots of stuff with thin-walled SHS and RHS in the 25-150mm size range and duragal and supagal are very common coatings while hot-dipped doesn't happen. I guess hot-dipping would warp these thin-sections and cost too much for what they are.

Anyway, your post was food for thought and makes me wonder with practice if this is reliably achievable. Maybe without gas lens or with extra steel wool protection in the lens, as per Jody.

I can't remember hearing of TIG brazing being used on galvanised product, (duragal may be worse because of the clear polymer coating applied over the zinc), but I have heard reference to silicon bronze MIG being used.
Looking at their melting points, silicon bronze is over double that of Zinc and 100 Deg C over the boiling point of Zinc. I reckon you would be running on a real knife edge at best, your travel speed, amperage, gas coverage and heat input would need to be near perfect.
I checked a few spec sheets for silicon bronze TIG filler and none mention use on Galv. None of the numerous youtube clips that I found mention galvo either.
If you are making items from an aesthetic point of view then I would have thought that the finished product would look decidedly off if not post treated in some way.
I like your Stainless Steel option better for your cooktop project or perhaps just fabricate the whole thing with galv, weld as normal and then powdercoat or 2 pack paint?
Come to think of it, I don't ever remember seeing any commercially made items using silicon bronze for joining Galv product, although I have seen several stools and chairs made of black ERW tube using the process, (presumably MIG), so this too could be a clue.

I have no info on TIG, although silicon bronze is very commonly used with the MIG process in the fence manufacturing industry