Yes, you can GMAW galvanized steel. I recommend grinding away the area to be welded first. If you choose not to, the welding procedures are similar to those for bare carbon steel. Travel speed should be slower on galvanized steel to allow the zinc coating to volatize ahead of the weld pool. The required reduction in speed depends on the thickness of the galvanized coating, the joint design, and the welding position. Root openings must be greater than those for bare steel to obtain good joint penetration and to provide a path for vaporized zinc to escape. Slight weaving of the arc is required to control excessive melt thru with groove welds.
With GMAW especially, remove as much of the galvanized coating as possible(it's not as forgiving as SMAW in regards to porosity when welding over galvanizing). If you run ahead of the puddle occasionally with a forward/backward whip like Scott suggested, any glavanized that you weren't able to grind off should boil off ahead of the puddle. John Wright
Call me a retart. I get shielded metal and gas metal all mixed up. I meant GMAW. Since I am out of practice, I usually have best results when using GMAW.
I will be cutting the galvanized with a plasma cutter, then welding square steel tubing to it. Most of the welds will be pipe to square tubing. The plasma cutter should give me the best result. I plan to make a template and then vice grip it to the pipe where I need to cut it.
I guess I will need to go to a local ship to find spools of the correct wire. I would guess the metal would be about 3/16 think. Should I use .035 wire to weld with? I have regular .045, but think that would probably blow through even with the voltage turned down.
I wouldn't buy .035 if you have .045. I don't know what type of shielding gas you are using, but typical parameters for welding 3/16 steel using 98/2 is a current range of around 180-190, around 24-25 volts, with a wire feed speed of around 185-195.
Don't forget plenty of ventilation if you're going to weld (and it welds fine, but dirty) straight on the galvanized. The stuff is nasty and metal flu sucks.
With GMAW especially, remove as much of the galvanized coating as possible(it's not as forgiving as SMAW in regards to porosity when welding over galvanizing).
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