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ER70S-2 vs ER70S-6: the short answer
For TIG welding clean mild steel, both ER70S-2 and ER70S-6 can produce strong, good-looking welds. ER70S-2 is usually the better choice when the steel is clean and you want precise control over the puddle. ER70S-6 is more forgiving when the material has light mill scale, surface oxidation, or small amounts of contamination.
The difference is in the wire’s chemistry. ER70S-2 contains small additions of aluminum, titanium, and zirconium. These are deoxidizers that help the molten weld metal handle minor surface contaminants. ER70S-6 contains higher silicon and manganese, which improve wetting and deoxidation. In practical terms, ER70S-6 often flows out more readily, while ER70S-2 tends to produce a slightly crisper, more controlled puddle.
Neither filler rod makes dirty steel safe to weld. Remove oil, paint, rust, and heavy mill scale before striking an arc. A filler rod can tolerate limited contamination; it cannot replace proper preparation.
Side-by-side comparison
| Feature | ER70S-2 | ER70S-6 |
|---|---|---|
| Best use | Clean mild steel, precision TIG work | General fabrication and less-than-perfect surfaces |
| Deoxidizers | Aluminum, titanium, zirconium | Primarily higher silicon and manganese |
| Puddle behavior | Controlled and relatively clean | More fluid, with strong wetting |
| Surface tolerance | Good, but still needs cleaning | Better with light mill scale and oxidation |
| Typical appearance | Neat bead with controlled reinforcement | Smooth, flowing bead; can be more fluid |
| Common drawback | Less forgiving of contamination and poor cleaning | Can make a puddle run ahead on thin material |
When ER70S-2 is the better choice
Choose ER70S-2 when you are welding clean, freshly prepared mild steel and want a filler that responds predictably to torch movement. It is a strong choice for visible TIG welds, tubing, brackets, automotive work, and small fabrication projects where bead shape matters.
ER70S-2 is also useful when you need to avoid adding more silicon to the weld pool. Its chemistry is designed for clean weld metal and controlled arc behavior. On properly prepared steel, it can produce a narrow bead with less tendency to spread than ER70S-6.
Use it with a tight arc and enough shielding gas to keep the puddle protected. A long arc can cause porosity, oxidation, and excessive heat input regardless of which rod you buy. If the finished weld has pinholes or a gray, sugared surface, inspect gas flow, leaks, drafts, cup size, and cleaning before blaming the filler.
For most mild-steel TIG work, a 1/16-inch ER70S-2 TIG filler rod is a practical starting size. It works well on thin tubing and sheet when the joint is fitted tightly.
When ER70S-6 makes more sense
ER70S-6 is the better all-around choice for general-purpose mild-steel fabrication, especially when the material is not perfectly clean. It handles light mill scale and surface oxidation better than many basic filler wires, and its higher silicon content helps the molten metal wet the joint.
That extra fluidity is useful for lap joints, fillets, and parts with slightly uneven fit-up. It can help the bead flow into the toes instead of sitting on top of the joint. The trade-off is that it may be less comfortable on very thin sheet, where the puddle can spread quickly and increase burn-through risk.
ER70S-6 is not a license to weld over paint, oil, galvanized coating, or heavy rust. These contaminants can cause porosity, inclusions, fumes, and an unreliable joint. Grind or wire-brush the weld area, wipe it with a suitable solvent, and let the surface dry before welding.
If you want one economical rod for repairs and mixed mild-steel projects, 3/32-inch ER70S-6 TIG filler rod covers a wide range of work. It is particularly useful when 1/16 inch feels too small for the joint and 1/8 inch would add too much metal.
Rod diameter and starting settings
Match the filler diameter to the thickness of the material and the size of the joint, not simply to the welder’s maximum output. As a rough guide, 1/16-inch rod suits thin sheet and tubing, 3/32-inch suits common brackets and medium-gauge material, and 1/8-inch suits heavier joints requiring more deposited metal.
For TIG welding mild steel, use DCEN: direct current electrode negative. Start around 1 amp per 0.001 inch of material thickness as a rough estimate, then adjust for joint type, fit-up, and heat sinking. A 1/8-inch steel joint may need roughly 100 to 140 amps, while thin 16-gauge sheet may require closer to 50 to 90 amps. These are starting ranges, not fixed rules.
Use 100% argon, commonly at about 15 to 20 cubic feet per hour indoors with a standard gas lens or cup. Too little gas causes oxidation and porosity; too much can create turbulence and pull air into the shielding envelope. Keep the torch angle modest, maintain a short arc, and feed the rod at the front edge of the puddle.
Common failure modes
Porosity: Check contaminated steel, damp filler, loose gas fittings, drafts, and an excessive arc length. Store rods clean and dry.
Black or gray bead: This usually indicates poor shielding, a dirty surface, or excessive heat. Clean the tungsten and verify that post-flow continues long enough to protect the hot electrode.
Bead refuses to wet the joint: Increase cleaning, verify DCEN, shorten the arc, and check that you are not moving too quickly. ER70S-6 may improve wetting, but it will not fix an oil-coated joint.
Burn-through: Reduce amperage or travel faster, use a smaller rod, improve fit-up, and tack the joint more closely. ER70S-2 may feel easier to control on thin clean material, but technique matters more than the alloy designation.
Which one should you buy?
Buy ER70S-2 if your steel is clean and you prioritize controlled, attractive TIG beads. Buy ER70S-6 if you want a forgiving general-purpose rod for fabrication, repair work, and surfaces that may retain a little scale after preparation. If the price difference is small, keeping both diameters of both alloys on hand is useful. For a single budget purchase, ER70S-6 is fine for most mild-steel repairs; for thin, clean, appearance-critical work, ER70S-2 is worth choosing.