Look in the EDUCATION pages for a string started by MATHIUS and I do belive you will find the answers you need with explanations.

The most frequent mistake I see with those trying to weld aluminum is the lack of understanding relative to the required cleanliness of the base metal. The formation of oxide on all exposed aluminum surfaces is a problem. This oxide layer actually has a higher melting temperture than the base metal, so by the time heating is sufficient to establish a puddle a large hole can develope. Cleaning can be accomplished with a variety of methods including a stainless steel wire brush or by using a carbide rotary cutter to lightly skim over the surface.
You did not mention the thickness of the material you are beginning your experiment with, but I suggest a minimum of .090 for you to get the feel of the process. Then you can progressively move to thinner stuff.
When you are clean and ready, don't fool around playing the torch in circles or other nonsense. Get the amperage up to a level which will allow bead formation almost immediately and then be prepared to move swiftly along the joint and use the foot-pedal to prevent overheating. It is helpful on thin stuff to use the filler to help those stubborn little molecules to join together from both base pieces. After you learn to get the initial start, you will find that continuing is less difficult.
If this information does not apply to your situation, just say so, and someone will give additional info.

Hey WeldPunk87,

When I first started, it took me a while to figure out that the rod cannot be allowed outside of the shielding gas envelope of the weld while welding, otherwise the rod gets the oxide layer in between dips and will look like the pile of fecal matter that you are seeing. Keep the rod close enough to the arc to stay shielded as you are plugging along, then when you have to re-adjust your hand on the filler metal, pull your foot off the petal a little bit (just enough to keep the metal hot) and slowly pull the filler metal out of the area that you are welding in, readjust the filler, and go again.

Hope that helps!
G. L.

if it's not shiny, don't dip the rod. if the rod melts before the base metal is melted you'll end up w/ a pile of crap. Alum. is more sensetive to the size tungsten you use than steel. 100-170 amps = 3/32" pure tungsten. Alum. likes to be welded hotter and faster than steel. if the base metal isn't melted within 4 seconds of you starting the arc on 1/8" material, the amps are probably too low. Once the base metal is melted don't waste any time...dip that rod to keep the puddle cool or you'll burn holes in the plate