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PostPosted: December 11, 2012, 12:02 am 
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Location: Novato, CA
I ordered some cold roll 1/8" steel plate from my usual supplier. I didn't notice at first that it didn't have the usual smooth gray surface. It was silver, though, not hot roll. I cut a piece from it, ground and filed the edges to shape and didn't notice anything different. I welded it to the car and it puddled just fine.

When I went to wire brush the piece it gave off a fine white powder, and I noticed for the first time that the surface wasn't smooth, but had a very fine wrinkle finish, like some kind of rough plating. I'm guessing zinc. I don't think I should've welded it. I guess I'll know in a couple of days. At least the part won't rust.


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PostPosted: December 11, 2012, 12:32 am 
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Could be satin coat or galvanized.


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PostPosted: December 11, 2012, 8:15 am 
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Nick
The save thing to do is to take your 4" grinder with a fine disc or wire bush and remove the plating before welding. The edge of the fillet weld can set on top of the plating which has lifted from the heat. This makes it a lot easier to start a crack in the weld, plus depending on the plating it will cause what is call dislocation in the microstructure.
Dave W


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PostPosted: December 11, 2012, 11:43 pm 
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Was there a whitish powder on the back side of the metal after welding? If so then it was probably galvanized or satin coat, which IIRC is a type of galvanizing.


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PostPosted: December 12, 2012, 12:39 am 
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Definitely a whitish powder. The metal didn't have a patchy, galvanized look to it, but I could believe some kind of zinc coating.


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PostPosted: December 12, 2012, 10:09 am 
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Could be electroplated zinc. It has a non-spangled look.

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PostPosted: December 12, 2012, 10:49 pm 
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Sounds like satin coat, could be called other things in different areas of the world, but its basically as said above electro-plated zinc. Just gently sand it off where you are going to weld and you should have no problems.


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PostPosted: December 12, 2012, 11:11 pm 
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You should have no problem welding zinc coated steels with no prep. according to http://www.nakedwhiz.com/weldinggalvanized.pdf:

Quote:
Welding of galvanized steel is done almost exactly the same way as welding of the bare steel of the same composition; the
same welding processes, volts, amps, travel speed, etc. can be used with little modification when the switch is made from
uncoated steel to galvanized steel -- unless the zinc coating is unusually thick.
The difference between welding galvanized steel and welding uncoated steel is a result of the low vaporization temperature of
the zinc coating. Zinc melts at about 900°F and vaporizes at about 1650°F. Since steel melts at approximately 2,750°F and
the welding arc temperature is 15,000 to 20,000°F, the zinc that is near the weld does not stand a chance -- it's vaporized!
By the time the weld pool freezes, the zinc is gone. This has two immediate consequences:
• The vaporized zinc increases the volume of welding smoke and fumes.
• The zinc at and near any welds is actually burned off by the heat of the arc, removing the protective zinc coating.


Read the full article to further learn methods of reducing the possible effect of "“metal fume fever”. Some people are resistant to it. Personally, I have welded small amounts of zinc-coated steels with no ill effects. Just have to remove that cloudy white residue afterwards.

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PostPosted: December 13, 2012, 1:22 am 
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Thanks, Chuck, that's good to know. I did a test weld with a couple of scraps, and couldn't get the weld to crack, even with my biggest hammer. I cut through the bead and the weld goes all the way down, so I'm okay with it. I was a little worried about the metal fume fever, but the 48 hours passed with no symptoms, so I'm either immune, or having the garage door wide open helped.

Image

I dropped a piece of the stuff in a cup of water a few days ago, and just pulled it out. Got some discoloration, but no rust. The discoloration is in patches, so it almost does look galvanized now. At one point I thought it might be stainless, but it's magnetic, so unlikely.

I'm good with leaving the piece I already welded on the car, but I'm not using the stuff again.


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