TIG Filler Rod — Selection Guide

TIG filler rod is bare wire you hand-feed into the puddle, and it has to match the base metal chemistry almost exactly. There’s no flux to compensate for mismatches. Pick the wrong rod and you get cracking, porosity, or a weld with mechanical properties that don’t meet the joint requirements.

For mild steel, ER70S-2 is the standard choice. Its triple-deoxidized chemistry (titanium, zirconium, aluminum) produces the cleanest welds in the GTAW process. ER70S-6 works too, especially if you want to stock one wire type for both MIG and TIG. On chromoly (4130), ER70S-2 handles non-critical and thin-wall tubing, while ER80S-D2 provides a closer strength match for structural applications.

Stainless steel filler follows the base alloy directly. ER308L welds 304 stainless, ER316L welds 316, and ER309L handles dissimilar joints or overlay work. The “L” means low carbon (0.03% max), which prevents sensitization and intergranular corrosion in the heat-affected zone.

Aluminum TIG rod splits into two main choices. ER4043 contains 5% silicon for good fluidity and crack resistance on 6xxx-series and casting alloys. ER5356 adds 5% magnesium for higher shear strength and better anodizing response on 5xxx-series structural aluminum. Specialty rods like ER4047 (12% silicon) handle brazing-type joints and high-silicon casting repairs.

Beyond the common alloys, TIG filler rod covers silicon bronze (ERCuSi-A) for joining dissimilar metals and galvanized steel without zinc burn-off, nickel alloys (ERNiCr-3, ERNiCrMo-3) for Inconel and high-temp service, and copper-nickel (ERCuNi) for marine applications.

Rod diameter affects puddle control. Thinner rods (1/16 and smaller) suit sheet metal and precision work. Thicker rods (3/32, 1/8) fill heavier joints faster but need more heat to melt. The guides below cover rod selection by base metal, diameter-to-thickness pairing, and brand comparisons.