What are the limitations of tig welding aluminum on DCEN?

What are the limitations of tig welding aluminum on DCEN?

Summary

Usually AC is better for these situations. also, if you have large gaps to fill AC is usually better.

What are the limitations of tig welding aluminum on DCEN?

dirty, oily, or heavily oxidized aluminum does not respond well.  

Usually AC is better for these situations. also, if you have large gaps to fill AC is usually better.