Just looking for some advice on what to practice in order to get better at welding.

For stainless I was using 3/32 tungsten and 1/16 rod on a miller econotig and 70 amps

For aluminum I used 1/16 tungsten and 1/16 rod and 70 amps

 

Undercut. on the 1st pic cant really see on the 2nd. but looks like you just need to add more material or turn down the amps.

 

Ditch the 1/16" tungsten. It's a poor choice, especially for aluminum work. With AC welding, your tungsten will get much hotter than with DC. Therefore, you need to use tungsten a bit larger, within reason. In most cases, I use 3/32, but if it is getting so hot that the end melts, I move up to 1/8".

As mentioned above, you need more filler to reduce the undercut. Actually, it's hard to tell if it's really undercut or if your bead is just concave. Neither is a good thing.

Also, when you end your bead, taper off the heat slowly, and then leave the torch there a few seconds so that arcon shields the crater as it cools. That will avoid the dark spot you have where you stopped.

 

judging by how the stainless looks.. You started on the right side and ended on the left.. From what I can see.. you started welding the part then once it heated up you didn't compensate for it.. It'll take a little while for that 3/8" plate to get hot.. Once the part heats up you'll need to work faster, back off on the footpetal (if you have one) and/or add more filler wire to avoid getting a concave weld. As far as the aluminum I can't really see it too great.. As mentioned above ditch that 1/16 tungsten.. I think 3/32 would be ideal but I dont know how thick you're welding