TIG problems -- AL and chromoly

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First, an introduction.  I've stick welded for years (25+), although it is not my profession.  I took a welding class at the local tech school 4 years ago to learn how to TIG & oxyfuel weld.  I learned to make some pretty good welds, although I focused more on oxyfuel than TIG.  I have a Syncrowave 180 SD (2% thoriated tungsten, 75% Ar, 25% CO2) machine and decided recently to do a couple of projects with AL and thin wall chromoly and/or steel tubing.For the chromoly I set the machine to DCEN and can't seem to avoid lots of splattering and blowing holes in the base metal.  I had a retired millwright friend come over to see if he could get any better results and he had the same problem as me.  With no other obvious things to try, I switched the machine to DCEP and the splattering subsided quite a bit and I was able to at least keep the tubing from melting away almost immediately.  Oh, with the original DCEN setup, I'm not talking high amperages -- any amperage high enough to start a puddle was enough to melt holes right into the tubing.  It's not paper thin tubing, so I'm a little perplexed as to why this would happen.Do I understand the hundreds of posts on this forum correctly when I read them to say that DCEN is recommended for TIG welding mild steel and chromoly, and AC for AL?  If so, what could be causing my chromoly & mild steel welding to be so poor (impossible) with DCEN?  Am I overlooking something?
Reply:You need to run 100 % argon instead of your Ar/CO2 mix.
Reply:yup..
Reply:Wow, thanks for the quick replies.  My gas bottle just ran out & I'll replace it with the right stuff tomorrow.
Reply:Originally Posted by rbranhamWow,
Reply:You guys (as expected) were exactly right.  I'm not sure how I ended up with a 75/25 argon/CO2 mix, but pure argon fixed the problem.  I bow before your greatness.Thanks again.
Reply:Originally Posted by rbranhamYou guys (as expected) were exactly right.  I'm not sure how I ended up with a 75/25 argon/CO2 mix, but pure argon fixed the problem.  I bow before your greatness.Thanks again.
Reply:Originally Posted by rbranhamI bow before your greatness.