The most commonly used electrode for GTAWing of Al is plain tungsten. As you are welding AC, the tungsten will become very hot, and tends to form a "ball" on the end of the electrode. (In other words, it actually melts!) You therefore do not have to actually sharpen the tungsten to any great degree.

I understand that Lanthenated tungsten is also useable, but in South Africa we seldom use it. For AC welding we use plain W and for DCEN we use Thoriated.

Hope this helps

Regards
Niekie Jooste

http://www.aws.org/cgi-bin/mwf/topic_show.pl?id=1460 This is a link to a discussion on your subject which took place in this very forum earlier this year. If you look it up you will have the reasoning behind my selection of Zirconium alloyed tungsten electrodes for GTAW Aluminum A/C operations along with discussion of technique and process control. There are also several links in that discussion to Electrode vendors and articles which will educate you on this important topic. If after reading this you have more specific questions just fire away..


Good Luck

Lawrence

Are you sure you are useing AC? Your symptoms sound like DC reverse.

To answer you question most folks prefer pure Tugsten for Aluminum, it is Green on one end.

There seems to be a lot of cross talk in the postings of this forum about which electrode is best or most preferred for welding of A/C Aluminum . Yes we have choices, and rather than argue, lets share some facts and suggestions that seem to need repeating. Here is a list.

Pure tungsten electrodes (EWP) Green color, are the electrodes that have the LOWEST current capicity of all electrodes, this means they melt sooner than all other electrodes

Pure tungsten electrodes are the WORST emitters of all tungsten electrodes, having the worst work function, they also display poor arc-transfer characteristics

Zirconium Alloyed Electrodes (EWZr) Brown Color code, have been the #1 recommendation for the last 15 years at least by most institutions, textbooks and vendors.

Cerium alloyed Electrodes (orange) are also now employed in AC aluminum operations due to their higher current carrying capacity and excellent arc transfer qualities.

Lanthanum (Black) is a great emitter and has excellent current carrying capicity however, it will not hold an AC arc at the electrode tip, this instability which produces "arc wander" usually knocks it righ out of the running for Aluminum operations

With the advent of square-wave technology 20 years ago, and more recently Asymmetric power sources, Miller Electric and the Hobart School of welding (to name but a few) have put new emphasis on AC Aluminum welding with a pointed tip prep rather than the balled tip formerly used. Directional Arc control in thin fillets and maniuplation of bead profile being the most obvious benefits. Pure Tungsten electrodes will not sustain a pointed tip prep.

It can be stated with confidence backed by both education and industry, that if your specification or textbook mandates pure tungsten electrodes as a first option, it's time to look at making a revision or buying an updated textbook.

For purposes of advice in this forum its important that we impart what is best first. Only then followed by options that still may work.

Now for particulars, 125 amps is a lot of juice, Equipment wise at the absolute minimum you will require a "WP-20" or equivalent water-cooled torch and a Full-length electrode 3/32" Dia. to manage that kind of heat. If your torch is not water-cooled you will need an even larger diameter electrode. Also at 125 amps you might try boosting your argon flow to around 25-30 CFH unless you are using a very small cup.

PS. a # 11 or 12 filter lens would be a good Idea too. Start with the darker


Let us know how you fare.

check this out and tell me what you think!!

http://www.millerwelds.com/pdf/techart/Aluminations_Ad_Package.pdf