[damae]

Does preheating aluminum with a propane torch contaminate the cleaned aluminum surfaces? I'm told that for TIG welding, cleaning is VERY important. Should I be cleaning the aluminum again after it is preheated? I have been using an angle grinder with stainless wire wheel to remove the annodized coating on my practice aluminum extrusions.

I'm starting to make decent looking lap-joint welds on clean 1/8" aluminum extrusion. (I'm also very good at coating tungsten with aluminum!)

I'm new to TIG welding and have practiced for a total of just a few hours. Recently, I attempted to butt weld two 1/2" thick aluminum plates of unknown aluminum grade (perhaps 6061?). I knew the thickness would be a problem, so I cleaned very carefully and preheated the pieces with a propane torch. Then I cranked the amperage up and proceeded to make a mess of the weld. The weld ended up very drossy and dull. It was hard to break the surface tension of the molten aluminum sitting on top of the butt weld, which is the way it acted when I was trying to weld dirty (not cleaned) aluminum.

Any ideas as to my problem? Could be that I'm welding on a 6xxx series aluminum with 4xxx wire? Or does the propane flame cause some contamination of the weld surfaces?