Sputtering action in Tig welding of aluminium using AC and argon gas

[waqasmalik]

Hi all, For TIG welding of aluminum i use AC and argon gas. I have learnt that oxide layer must be removed prior to welding and during welding. During welding, oxide layer is removed by sputtering phenomenon,which is that during the positive half cycle of electrode, heavy argon ions knock off the atoms from the work-piece surface.

My question is where these atoms go after being sputtered? Obviously, atoms will be oxygen and aluminum, does they go out into atmosphere? stay inside? in the weld metal? to the electrode?

Any response shall highly acknowledged.

 

[waqasmalik]

any one plz respond

 

[berkshire]

They go to the gas stream and are carried off.
B.E.


You are judged not by what you know, but by what you can do.

 

[waqasmalik]

Thanx for responding Berkshire, i shall ask one more question plz.

If they go to gas stream do they have potential to cause any defect/discontinuity or any related problem?

Thanx in advance

 

[berkshire]

waqasmalik
Not to the metal being welded.
Metal oxides and fumes are a well known industrial hazard, government regulations limiting the exposure to welders, and other people working in the area are well defined. Failure to adhere to the relevant guidelines and regulations can expose the employer and the welder to legal action, particularly if they expose other people to the welding fumes.
B.E.

You are judged not by what you know, but by what you can do.

 

[waqasmalik]

Thanx sir.

 

[Tmoose]

The linked article mentions fumes from manual metal arc ( shielded metal arc or "stick" )or oxy-acetylene welding.
FWIW I did not see any references to MIG or TIG welding.

 

[berkshire]

T Moose,
You are right, That did not have specific references to TIG. Here is a Safety Poster that does. see attachment.
B.E.

You are judged not by what you know, but by what you can do.

 

[gtaw]

Welding with AC produces an arc where the electrons are traveling from the electrode (cathode) to the work piece (anode) on one half the cycle and then from the work piece (cathode) to the electrode (anode) on the other half cycle. The most heat is produced when the electrons liberated from the tungsten electrode (cathode) are attracted to and accelerated toward the positively charged work piece (cathode spot). The reverse portion of the cycle, when the electrode is the cathode), the electrons travel from the work piece to the electrode, causing the electrode to heat up. It is during the that portion of the arc cycle (when the electrode is the cathode) when the electrons are propelled toward the electrode that the ions traveling from the electrode toward the work piece bombards the aluminum work piece and blasts off the aluminum oxide. The phenomena is called cathodic etching.
The AWS Handbooks and the book Modern Welding Technology by H. Cary and S. Helzer can provide some additional insight on cathodic etching (cathodic cleaning).


Best regards - Al