Welcome to the forum Bkn !

Usually the color in the arc comes from a dirty/contaminated tungsten  :)

But yes... Magnesium does look a bit different when you weld it and most aluminum base metals and filler metals are alloyed with Mag.

Hello Bkndsdl, are you speaking of welding with the GMAW or the GTAW process? But, to somewhat answer your question, the color of the arc definitely has something to do with the various alloying elements present in the particular type of wire and grade of material that you are welding on.

I usually notice this "color" (the green) when I am welding with 5356 filler and when I am using 4043 the arc will have more of a purple tinge. The GMAW, in my estimation, is much more distinct in it's display of arc color and also displays more "smut", but both the color of the arc and the smut often have little to do with the quality of the resulting weld, although they could be indicative of the level of cleaning of the material prior to welding and that could be an indicator of weld quality. But these are just personal observations. Best regards, Allan

EDIT: I had one additional thought here, with GMAW the wire becomes the electrode and there is a certain amount of volatilization of the electrode as it is consumed and melted by the arc, thus displaying the "coloring" based on the alloys in the wire.

Bkndsdl,

WELCOME TO THE AWS WELDING FORUM!!

I hate to add to two very knowledgeable forum members in the aluminum arena especially with my limited exposure, experience, skill, and knowledge of it.

But, you can also look to your lens.  Different lenses will refract the rays differently.  Such as a standard lens, auto darkening, gold, etc.  They all work their magic in diverse ways. 

I find that many items purported to be alum have a high magnesium content which not only changes the color but can also add a degree of difficulty to the welding.  The higher the degree of cracking being the experienced, the higher the percentage of magnesium in the material.

He Is In Control, Have a Great Day,  Brent

I see the green arc on older aluminum castings that have more zinc & magnesium content and can usually tell before trying or testing it by it's heavier weight as well.  Brushing or dobbing on a little liquid Silver Nitrate and seeing it then turn black tells you the magnesium content is very high and you may not have success welding it.   I saw another older welder who is gone now use that on aluminum and asked about it on here years ago and I believe Allan or Lawrence were the knowlegable ones who told me to try silver nitrate.  Any really old aluminum casting on magnetos or motorcycles and such made during WWII era are going to have a higher zinc and magnesium content because the manufacturer couldn't get more pure aluminum then.

To my understanding, any difference in the color of the arc is A) the shielding gas used  and B) flourescence of the metal ions in the arc column.

It's basically an open circuit neon tube http://en.wikipedia.org/wiki/Neon_lighting

we use this change in flourescence to detect contamination of welding by looking at the shift in color when oxygen, nitrogen or CO2 is present.  It works and is automated but gas detectors are much more accurate.

Its not unless you have tainted your tungsten is some way your arc will look normal. Because there is no actual difference between the arcs of various metals besides the amount of amperage needed to melt them. Although, in some cases the light reflecting off of the metal can look different. You sold also make sure that your lens is not tented green (if you use different lenses to weld different metals due to the amperage difference, the lenses will make the arc look different then it is in reality).

For you information,
The Expert