I'm just learning to TIG weld and am about to try my hand at welding some aluminum. One of the books I have says to use the 2% Thoruim Alloyed tungsten for steel but to use pure tungsten for aluminum. Why is this and is it really necessary?

yes, in an ideal world you would and if you were going to x ray the weld you would want to. for the most part i use 2% for everything, but again not on critical welds.

Just backing up ede, but I only have 2% too...now I don't do work with my tig that will up for any lawsuits, but have never had a failure on anything either.

I also use 2%.......never had anything come apart yet

on the flip side i've worked nukes and 2% will trip the lud meters used to check for contamination so we used pure and never had any problems with it. most of the metal was monel and nickel, but some steel, stainless, and aluminum too.

when i was at skool and now at the shop im workin at we use both. at skool i was taught to use the red (2%) on alumin and green (pure) on steel and stainless. and it works great. at my shop it kinda doesnt matter but we use mainly pure on either alumin or stainless, dont get alot of jobs where we would need to tig steel.