Guide
Welding Polarity: DCEP, DCEN and AC
DCEP puts the electrode positive and drives roughly two-thirds of the heat into the work for deep penetration; DCEN reverses that for shallower penetration and higher deposition; AC alternates and is required for aluminium TIG.
Polarity decides where the arc's heat goes, which in turn decides penetration depth and deposition rate. Getting it wrong is one of the few setup errors that makes a weld unmistakably bad rather than merely mediocre.
DCEP — direct current, electrode positive
Also called reverse polarity. Electrons flow from the work to the electrode, and roughly two-thirds of the arc heat ends up in the base metal. The result is deep penetration and a stable arc. DCEP is the default for most stick electrodes, all solid-wire MIG, and gas-shielded flux-cored wire.
DCEN — direct current, electrode negative
Also called straight polarity. Electrons flow from the electrode to the work, putting more heat into the electrode itself. Penetration is shallower and deposition rate is higher. DCEN is used for TIG on steel and stainless, for self-shielded flux-cored wire, and for some rutile stick electrodes on thin material.
AC — alternating current
The current reverses direction 60 times a second in North America, 50 in most of the rest of the world. Every reversal passes through zero, which is why an arc can go out unless the electrode coating or the machine keeps it alive. AC is required for aluminium and magnesium TIG, is used by E6011 and permitted by E6013, E7014, E7018 and E7024, and is useful on heavy plate because it reduces magnetic arc blow.
Quick reference
| Process or electrode | Polarity |
|---|---|
| E6010 | DCEP only |
| E6011 | AC or DCEP |
| E6013, E7014, E7024 | AC, DCEP or DCEN |
| E7018 | DCEP or AC |
| Stainless covered electrodes (-16) | DCEP or AC |
| Stainless covered electrodes (-15) | DCEP only |
| Solid MIG wire (GMAW) | DCEP |
| Gas-shielded flux core (E71T-1) | DCEP |
| Self-shielded flux core (E71T-11) | DCEN |
| TIG on steel, stainless, titanium | DCEN |
| TIG on aluminium and magnesium | AC |
Why aluminium TIG needs AC
Aluminium carries a tenacious oxide skin that melts around 3700 °F while the metal beneath it melts around 1200 °F. Welding through that skin requires removing it. The electrode-positive half of the AC cycle bombards the surface and strips the oxide away; the electrode-negative half puts heat into the joint. The balance control on a modern AC TIG machine sets how the cycle is split — more negative time for penetration, more positive time for cleaning.
Symptoms of wrong polarity
- E6010 on AC: the arc stutters, pops and goes out.
- Self-shielded flux core on DCEP: a wandering arc, heavy spatter and an ugly, porous bead.
- Solid MIG wire on DCEN: an erratic arc with poor fusion and excessive spatter.
- TIG on steel with DCEP: the tungsten overheats, balls up and may melt away within seconds.
Arc blow
Direct current creates a magnetic field around the arc, and on heavy plate or near a joint corner that field can push the arc sideways. Symptoms are a wandering arc, excessive spatter and undercut on one side of the bead. Switching to AC is the most effective cure, because the field reverses too fast to deflect the arc. Repositioning the work clamp, welding away from the ground connection, or using shorter arcs also help.
Frequently asked questions
What is the difference between DCEP and DCEN?
DCEP puts the electrode positive and drives roughly two-thirds of the arc heat into the work, giving deeper penetration. DCEN puts the electrode negative, putting more heat into the electrode itself for shallower penetration and higher deposition.
Is DCEP the same as reverse polarity?
Yes. DCEP is direct current electrode positive, also called reverse polarity. DCEN is direct current electrode negative, also called straight polarity.
What polarity is MIG welding?
DCEP for all solid-wire GMAW, and for gas-shielded flux-cored wire. Self-shielded flux-cored wire is the exception and runs DCEN.
Why does my flux core weld look terrible?
Check polarity first. Self-shielded wire such as E71T-11 needs DCEN, and most small machines ship wired for DCEP solid wire. The gun and work leads must be swapped at the terminals.
Can you weld aluminium with DC TIG?
DCEN TIG on aluminium is possible with helium shielding on thick sections, but it provides no oxide cleaning. For virtually all aluminium work, AC is the correct setting.