Pure tungsten (green band) has no operational advantage over Cerium (orange) or Zerconium (brown) doped electrodes for AC aluminum using an inverter such as the one you describe.

Here is the most accurate, most detailed AC aluminum arc/wave shaping info available. Mike Sammons, the author, is simply the best when it comes to publishing easy reference for GTAW. My advice is to read sections one and two of the link below.
http://www.millerwelds.com/education/tech_articles/articles42.php

Check the bottom of page 1 of the Aluminations article for a link to a quicktime video of GTAW aluminum at several different AC frequencies.


Here are basics from Miller for GTAW and good electrode info.
http://millerwelds.com/education/tech_tips/TIG_tips/hints_tips.html

Lawrence is on the money, I use strickly 2%ceriated on my Dynasty 200DX, the manfacturer recomends not using the pure on these machines due to the balling of the tip makes the machine work harder than a pointed electrode at the same amperage. The recomended tungstens are 1.5% and 2% ceriated or lanthanated, I know guys on both sides of the ceriated or lanthanated argument. I see slight differences, but for most of the work I do ceriated is the best overall.

Here is the page I refer to about recomended tungstens,
http://www.millermotorsports.com/products/dynasty200_sd_dx.html

Hope this helps,

Many thanks for the information.My local suppliers don't carry anything but 2% and pure so,I think I will place an order
tomorrow.