I ordered a bunch of aluminum parts from eBay and McMaster. I've spent a few afternoons just cutting the metal into random parts and TIG welding it back together
I've made a few coupons to test the five basic weld types:
* Open corner
* Lap joint
The above picture only shows a T-joint and open corner, since those are my best types.
This pipe doesn't do anything useful, unfortunately. I just made random cuts on my miter saw, rotated the two pieces 180*, then welded them.
I'm still working on getting nice, consistent beads, but they have good penetration, and I'm getting a lot more confident with aluminum.