Current Type for welding Aluminum

[kwb74]

I have been researching welding units both MIG and TIG. Something has struck me as odd everywhere I read that you must have AC to weld aluminum when discussing generalities but then getting into specs of weld units and I see DC mig machines that are quite good at Aluminum. What is it about MIG that lets DC work for it but to TIG you need AC?

 

[EgyDesign]

hi kbw74,
i beleive that welding alum must be with dc reverse polarity ......because alum forms oxides too fast and that causes internal cracks.......and because alum is a very good conductor of heat and not very high melting point ...because of all this u must weld it with dc reverse polarity....and i beleive that tig and mig makes no big dfferences.regards

 

[rnd2]

Reverse polarity is required to disperse the aluminium (aluminum?) oxide surface. This is easy with MIG because the moving wire elctrode is consumed in the process. On the other hand TIG uses a non-consumable electrode and that will get mighty hot running on pure DC reverse polarity. A very good compromise for TIG welding ally is to run AC. This reduces heat building too much at the tungsten electrode and at the same time provides sufficient reverse polarity to disperse ally oxides forming on the molten weld pool.
I understand it is possible to weld thin aluminium with pure DC reverse polarity but have never seen it done.

 

[rnd2]

Last sentence should read: I understand it is possible to TIG weld thin aluminium with pure DC reverse polarity but have never seen it done.

 

[EgyDesign]

thanks rnd2 i think i didnt concentrate while saying that i beleive that tig and mig same to me......anyway reverse polarity will make high tension on the tungesten elec. but u know how alum. forms oxides too fast....anyway i think that ur right about that.

 

[metengr]

If you want more information regarding welding of aluminum, the web site below is from esab. Once you enter their web site you can navigate your way around to obtain all sorts of interesting information on welding of aluminum;

http://www.esab.com/index.asp?item=14

 

[21121956]

Hello everybody:

In order to perform a good welding job on aluminium, besides an experienced and certified welder, it is needed to have an alternating current welding machine with a HIGH FREQUENCY UNIT built-in.

That high frequency unit basically helps to start the electric arc without any contact between the non consumable Tungsten electrode and the base material (working piece), keeping the electrode from contamination.

In addition, this high frequency alternating current allows the electric arc to disperse and pierce the aluminium oxide that forms on the working piece surface.

As an option for welding aluminium, a direct current welding machine, reverse polarity can be used.

Ricardo

 

[MetalsInc]

Many AC machines have settings listed as "Max Cleaning" and "Max Penetration". MC is weighted more heavily to DC+ and MP more to DC-.

I have been involved with studies that showed MC actually got better penetration. The balance was ~70%DC+. Theory being that the workpiece heated up as it is far more difficult to emit an electron from Al then from W. Therefore the base metal was much hotter, resulting in deeper welds.

Slightly off topic, but Ricardo's post mentioned the cleaning issue.