Tubular aluminum Pontoon boat frame TIG weld repair
A customer brought in a broken aluminum pontoon boat frame for me to weld repair. The tubing was probably about 1" diameter and maybe about .065" (1/16") wall thickness.
A side "arm" had a broken weld for unknown reason (possibly abuse) by the previous owner. However, the way it was manufactured (with the tube ends "pinched") also left the joint less rigid than it could have been. The owner who brought it to me said they had just bought it and got it for pretty cheap because of the damage. Here is what the broken joint looked like initially. It was definitely originally TIG welded:
Attachment 1781
I further prepped it by carbide burring out the crack a little bit, and using an aluminum oxide impregnated nylon bristle cup brush (good at conforming into crevices) to clean out all the remaining old finish. I also solvent cleaned it with some good (very strong) spray solvent that also very quickly evaporates.
There was also an area along the outer edge of a bent that had a crack which we figured must have been there from the original manufacture (the tubing might have been bent a little too much / too aggressively?) I can't figure how else it could have failed like this:
Attachment 1780
I figure this frame was probably if not 6061, an aluminum allow with primarily magnesium in it (5xxx series aluminum) as either are popular in marine applications. I used 5356 filler rod (aluminum with about 5% Mg) because it would give a nice, strong and also ductile weld in either scenario.
After preparing the surfaces, I danced an A/C TIG arc with light current (minimal to get a stable arc) over the weld joints, to ensure the solvents were completely evaporated and also to etch the surfaces clean. Then I TIG welded them using a footpedal and 3/32" tungsten (blunted end prep), #6 cup, 12 cfh argon gas flow. I did do a couple things differently than I usually do to try and get a different weld "look":
1. I used a higher than usual EP of about 35%EP, I selected it thinking it was about as high as I figure I could get away with without melting the tungsten tip (for the 2% lanthanated electrode.)
2. I used probably a little less stickout, and maybe a little more arc lengh than usual
3. I held the filler rod closer to the joint when not filling it, which may help keep the tip from oxidizing
The result is a really nice, clean weld beads with a "smooth" and shiny look.
Even though I did not go to great effort to weld in a comfortable position (due the large, awkward frame, I had the torch probably about 2 feet away from me and was hard to even see the puddle at times) and I did not keep an ideal torch angle all the time. But despite all that, I got really nice "wet", clean looking puddles. Fun stuff! I didn't go out of my way to smooth out the weld or anything, and there were some spots were I was not holding not the best torch angle.
Attachment 1778
The tubing joints were somewhat "pinched" and welded together rather than properly "bellmouthed", probably because it saved production time by the factory, although it did make the joint less rigid as a result.
So in addition to building the material up a bit on the side where it cracked, I also built up the back side with some extra material to stiffen and reinforce the overall joint. Although it is kind of a weave pattern, I just freehanded this one I didn't "walk the cup". I could have smoothed it out, but I was having fun with the wide, shiny weld beads.
Attachment 1779
Here is an overall shot of what the pontoon boat frame looked like when they were assembling it back together:
Attachment 1777
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Originally Posted by jakeru
