Filler Metal — What It Is and Why It Matters
Filler metal is the general term for any metal added to a weld joint to fill the gap and create the weld deposit. Filler metal comes in many forms depending on the welding process: solid wire (MIG), flux-cored wire (FCAW), coated electrodes (stick), bare rods (TIG), and brazing alloys.
Filler metal selection is one of the most critical decisions in welding — the filler must be metallurgically compatible with the base metal, provide adequate mechanical properties (strength, ductility, toughness), and perform well with the chosen welding process. Using the wrong filler metal can result in cracked, weak, or corrosion-prone joints.
Filler metals are classified by AWS (American Welding Society) specifications. The designation system encodes the filler type, tensile strength, usable positions, flux type, and chemical composition. Understanding these designations — like ER70S-6, E7018, and E71T-1 — is essential knowledge for any welder.
Frequently Asked Questions
How do I choose the right filler metal?
Match the filler metal to the base metal and welding process. For mild steel MIG, use ER70S-6 wire. For mild steel stick, E7018 for structural work or E6013 for general purpose. For stainless TIG, use the matching L-grade filler (ER308L for 304, ER316L for 316). Consult the filler metal manufacturer's guide for specific base metal combinations.
What does the ER in ER70S-6 stand for?
E = Electrode (it conducts welding current). R = Rod (it can also be used as a TIG filler rod). The 70 = 70,000 PSI tensile strength. S = Solid wire. 6 = higher silicon and manganese content for better wetting and deoxidation.