>>>> Aluminum, no matter what alloy is used, develops a thick oxide layer when exposed to the atmosphere. If you scratch or grind it off, it will re-form in a few minutes. Unlike rusty steel, aluminum oxide is a good thing-it's a tough skin that protects the aluminum. It is also transparent, and that's why aluminum doesn't need to be painted to protect it from the elements-it is already coated with the oxide layer. Chancy told us this becomes problematic when welding or cutting, though, because the oxide layer melts at about 1,600 degrees F, roughly 30 percent higher than the temperature of the alloy underneath. See in the photo how it looks like the aluminum melted from the inside out? That's exactly what happened.
 Plasma-cutting worked much...  Plasma-cutting worked much better than a torch, but it left a big trail of slag behind that would need to be cleaned up before welding. In hindsight, we should have cleaned off the oxide layer from the sheet with a wire brush prior to cutting. That may have prevented some of this slag from forming. |  | |
<<<< The best way to cut aluminum is to use a saw with a serrated blade-one with teeth that will cut the aluminum in small chunks and put very little heat into the metal. You can buy metal-cutting blades for your chop saw or circular saw, but we made a trip to our local Lowe's and picked up a Skil jigsaw and a couple of packs of metal blades. We grabbed some for our Sawzall, too. The jigsaw blades are small and thin enough to cut shapes and curves. Check out the nice, clean cut made by the jigsaw versus the jagged edge left by the plasma cutter.
A bandsaw or a shear would work great, too, but we don't have either at our shop.
>>>> OK, so you've got your pieces cut and you're ready to start welding, but there's still a bunch of things you need to do before you strike an arc. First, you need to select the proper tungsten. Tungsten electrodes are available in several different formulations for welding various materials. Generally, aluminum is best welded with a pure tungsten electrode, indicated with a green band, or with a 2 percent ceriated (orange band) electrode.