Butt welding on aluminum

Im using a miller syncrowave 200 to weld two pieces of heat sink together and am not getting good penetration - without warping it to no end.

I'm running 100% argon, 9 on the balance and put a small bevel on both sides with a tiny air gap.

What would you suggest to get better penetration?

Great site by the way!

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I know i am late in posting this, but a little preheat using a propane torch and less argon flow on the cup will help.
turn the argon down to less than 15cfh and use a small cup like a 5 or 6

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