TIG Welding Aluminum at 50hz vs 250hz

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A more detailed article on the topic of AC frequency can be see here goo.gl/bPkfCt
This video is about tig welding aluminum on AC at 50hz and at 250hz.
there was a noticeable difference at the 2 different settings. 50hz got completed penetration and 250hz did not penetrate.
I tried to keep travel speed the same for both welds by using a motorized welding positioner turntable.
Ck worldwide mt200 ac/dc tig welder set at 90 amps, AC balance set to 6 using 3/32" (2.4mm) 2% lanthanated electrode and 4943 aluminum filler rod.