TIG Welding: How Does AC Clean Oxide Layer?

[patshek]

Hello,
I know AC is used for welding of Aluminum or materials that have oxide layer on the surface
Books also tell me that the oxide layer is cleaned by AC
However, what is the exact mechanism of this cleaning action? Besides, where does the oxide gone? Vaporized? Dissolved?
Thanks

 

[nucleus]

There are other metals that have oxide layers that are not welded with AC. The oxide layer on Al melts at a higher temperature than the base metal and should be removed mechanically or chemically before welding. Lincoln has a good site on welding:
http://www.lincolnelectric.com/knowledge/articles/content/alum.asp