[stefuel]

What results should one experience if they attempt to mig weld with straight argon?

[tweake]

welds like crap. (i'm assuming steel, not aluminum)
there is video's of it around of it tho can't remember who.
you need an active gas mix tho steel can be welded with 100% co2, so 100% active gas.

[Arno]

See:

https://www.youtube.com/watch?v=060NbYoOAio

Kinda works, but not great. Can be (ab)used on thin steel sheet with MIG to reduce the risk of blowing through.

Bye, Arno.

[cj737]

You could use 100% Argon to MIG but would have to switch to Silicon Bronze filler wire. Else, not a good choice.

[stefuel]

Can someone explain to me what exactly is happening with mild steel mig with 100% argon vs mild steel tig using 100% argon?
I't not just shielding gas. Some other molecular activity involved.

[Jack Ryan]

Can someone explain to me what exactly is happening with mild steel mig with 100% argon vs mild steel tig using 100% argon?
I't not just shielding gas. Some other molecular activity involved.

What sort of molecular activity are you seeing?

TIG uses DCEN and, even though the current in the ARC is made up of both electrons and IONs, there are many more electrons. When those electrons hit the work, their kinetic energy is converted to heat. There is much more heat at the work than there is in the tungsten. TIG cannot use an active or mixed inert/active gas because the tungsten will oxidise - sometimes violently.

MIG (GMAW & FCAW-G) (generally) uses DCEP so most of the heat is generated at the electrode. This is used to melt the electrode and the heat is then transferred to the work in the melted filler and in the shielding gas (plasma). This is a significantly different heat transfer process from that in TIG.

Pure Argon has a relatively high ionisation potential (is hotter) but a relatively low thermal conductivity - this leads to a pencil like penetration profile. The addition of an active gas such as CO2 or O2 increases the thermal conductivity and the weld bead widens.

Pure Argon is also not good at overcoming the surface tension of the puddle. The addition of CO2 or O2 improves that so that the weld becomes flatter and more easily wets at the toes.

There are other advantages to the use of an active gas in MIG welding. Active gases are oxidising agents and are used to help clean the weld. This is a balancing act though because it also oxidises alloying elements introduced via the filler, degrading the properties of the weld.

And then there is the stuff I have forgotten and the stull I never knew.

Jack

[tweake]

to add, mig (mild steel) is actually mag ie active gas.
co2 breaks down in the arc giving o2 to react with other things. here tri mix is the norm which has a small amount of o2 added to the argon/co2. so you get the activeness of high amounts of co2 but still retain the benefits of high amount of argon.
a small amount of o2 can be dealt with the deoxidants in the filler metal.
interestingly with stainless steel the gas has a much lower amount of co2, otherwise you end up with a hard black deposit which i think is a form of carbide.

[Jack Ryan]

to add, mig (mild steel) is actually mag ie active gas.

Yes, that's true. But you are not going to change the seemingly millions of people who call anything with a wire feeder "MIG". That's why I wrote "MIG (GMAW & FCAW-G)".

here tri mix is the norm which has a small amount of o2 added to the argon/co2

That's true here too. I tend to use Argoshield Light (C5O3) for most things mild steel. C25 is not even easy to find.

Jack