Filler Metal Selection Chart by Base Metal

How to Read an AWS Filler Designation

Every filler decision starts with reading the AWS classification correctly. The letters and numbers are not arbitrary — they encode tensile strength, product form, position, polarity, and chemistry. Once you can decode the string, most of the chart becomes self-explanatory.

Take a solid steel wire like ER70S-6 (classified under AWS A5.18). 'ER' means electrode/rod (usable as both a GMAW electrode and a GTAW filler rod), '70' means 70,000 psi minimum tensile, 'S' means solid, and '6' identifies the deoxidizer chemistry — in this case high manganese and silicon that wet out well and tolerate light mill scale. Compare that to a covered stick electrode like E7018 (AWS A5.1): 'E' is electrode, '70' is 70 ksi tensile, '1' means all-position, and '18' means an iron-powder low-hydrogen coating run on DCEP or AC.

Low-alloy and stainless fillers carry a suffix that tells you the alloy family. E8018-B2 is an 80 ksi low-hydrogen stick with a B2 (1.25% Cr – 0.5% Mo) chemistry for chrome-moly service; E9018-B3 steps up to 90 ksi and B3 (2.25% Cr – 1% Mo). On the stainless side, ER308L, ER316L, and ER309L (all AWS A5.9) name the alloy directly, with the 'L' denoting a low-carbon grade that resists carbide precipitation (sensitization) in the heat-affected zone. Learn the standard the filler falls under — A5.1 and A5.5 for stick, A5.18 and A5.28 for solid wire, A5.20 and A5.29 for flux-cored, A5.9 and A5.4 for stainless, A5.10 for aluminum, A5.15 for cast iron, A5.14 for nickel — and cross-referencing at the supplier counter becomes trivial.

• Tensile figure: The two- or three-digit number (60, 70, 80, 90) is the minimum tensile strength in ksi of the deposited weld metal — the anchor for matching decisions.
• Product form: ER = solid rod/electrode, E = covered stick electrode, EXXT = tubular (flux-cored/metal-cored), ERXXX-X = alloy solid wire.
• Position & polarity digits: On stick electrodes the last two digits encode coating and current: -10 (DCEP cellulosic), -18 (low-hydrogen), -24 (high-deposition flat/horizontal).
• Alloy suffix: -A1, -B2, -B3, -C1, -C3, -Ni1, -D2 identify Mo, Cr-Mo, Ni, and Mn-Mo chemistries for low-alloy service.

Matching vs. Over-Matching Strength (and When to Under-Match)

The governing rule for structural steel is that weld metal strength should meet or slightly exceed the base metal's specified minimum tensile — this is 'matching.' A 36 ksi yield / 58–80 ksi tensile A36 plate is welded with a 70-class filler (E70XX, ER70S-6, E71T-1), whose 70 ksi deposit comfortably matches. A572 Grade 50 also pairs with 70-class fillers because the weld metal still over-matches the 65 ksi tensile floor. AWS D1.1 Table 3.1 formalizes these 'matching filler metal requirements' for prequalified joints.

Over-matching — deliberately using a filler stronger than the base — is used sparingly. It buys nothing on a fillet weld sized by leg length rather than strength, and it can actually hurt: a much harder, higher-strength weld deposit on a softer base concentrates strain at the toe and raises hydrogen-cracking sensitivity. Reserve over-matching for specific engineering calls, not as a default 'stronger is safer' habit.

Under-matching is the counterintuitive but correct choice on some high-strength quenched-and-tempered steels (for example certain T-1 / ASTM A514 plate) and on many joints where fatigue and hydrogen cracking dominate over static strength. A slightly lower-strength, more ductile weld metal tolerates residual stress and hydrogen better. This is always an engineered decision documented on a WPS — never something you infer from a chart. The takeaway: match tensile for ordinary carbon and HSLA steel, and treat any deviation as a signal that a welding engineer, not a lookup table, owns the call.

For stainless and nickel alloys, 'matching' shifts from strength to chemistry and corrosion. You size the filler to preserve or exceed the base metal's alloy content — molybdenum for pitting resistance on 316, ferrite balance on duplex — because a mechanically strong but under-alloyed weld will pit or crack in service long before it fails on load.

Carbon, Low-Alloy, and Chrome-Moly Steel Fillers

Plain carbon steel (A36, A572, 1018, HSLA structural) is the easy case: 70-class fillers cover the vast majority of work. For GMAW, ER70S-6 is the default solid wire — high silicon and manganese let it flow over light mill scale, run on C25 (75% Ar / 25% CO2) or 100% CO2 at roughly 200–250 A on .035" in spray transfer, with gas flow around 35–45 CFH. ER70S-2 (triple-deoxidized) is the better pick over rust and contamination, and it doubles as the standard GTAW rod for steel. For stick, E6010 (DCEP, deep penetration, cellulosic) handles root passes and dirty steel; E7018 is the low-hydrogen workhorse for structural and code work.

Chrome-moly is where the suffix matters. The two dominant grades are P11 (1.25Cr-0.5Mo) and P22 (2.25Cr-1Mo), common in power-plant piping, boilers, and pressure work. Match P11 with B2 fillers — ER80S-B2 (GTAW/GMAW, A5.28) or E8018-B2 (SMAW, A5.5) — and P22 with B3 fillers, ER90S-B3 or E9018-B3. These alloys almost always require preheat (often 300–450°F) and post-weld heat treatment (PWHT) to control hardness in the heat-affected zone; the filler choice is inseparable from the thermal procedure, which lives on the WPS.

4130 chromoly — the thin-wall tubing used in race chassis, aircraft, and roll cages — is a special case that trips up a lot of fabricators. On thin, un-heat-treated 4130 tube, most builders deliberately do NOT use a matching B-series filler. ER70S-2 gives a softer, more ductile, crack-resistant weld that survives vibration and impact without cracking, while ER80S-D2 (a Mn-Mo wire, A5.28) is chosen when higher as-welded strength is needed. A full-strength B2/B3 deposit on thin 4130 without PWHT can be brittle — another reminder that 'matching the alloy' and 'matching the strength' are different goals.

• A36 / A572-50 (mild & HSLA): ER70S-6 (GMAW), E7018 or E6010/E7018 combo (SMAW), E71T-1 (FCAW). C25 or CO2 gas.
• P11 (1.25Cr-0.5Mo): ER80S-B2 / E8018-B2. Preheat + PWHT per WPS.
• P22 (2.25Cr-1Mo): ER90S-B3 / E9018-B3. Higher preheat, mandatory PWHT.
• 4130 thin-wall tube (no PWHT): ER70S-2 for ductility, ER80S-D2 for strength — not a full B-series filler.
• Weathering steel (A588 / Cor-Ten): For exposed, unpainted corrosion-matching, use a Ni-Cu-Cr weathering filler such as E8018-W2 / ER80S-Ni1-type wire.

Stainless Steel: 304, 316, and Duplex

Austenitic stainless follows a simple 'one number up' habit: weld 304/304L with ER308L, and 316/316L with ER316L. The 308 alloy is intentionally over-alloyed relative to 304 so that, after dilution from the base metal, the weld deposit still lands in the 304 corrosion range. Always favor the 'L' (low-carbon) grades — ER308L, ER316L — unless the service is above roughly 800°F, where the stabilized or higher-carbon 'H' grades resist creep better. For 316's pitting and chloride resistance in marine, chemical, and food-processing service, do not substitute 308 to save money; the missing 2–3% molybdenum is the entire point of the alloy.

Stabilized grades have dedicated fillers: 321 and 347 base metals are welded with ER347, which carries niobium to tie up carbon and prevent knife-line attack. For GTAW on all stainless, run 100% argon at 15–20 CFH on the torch and — critically — back-purge the root with argon (a trailing or dam purge) to prevent the sugary, oxidized 'crystalline' root that destroys corrosion resistance. Typical GTAW current on 1/8" 304 with a 3/32" ER308L rod is about 90–130 A DCEN.

Duplex stainless (2205, UNS S31803/S32205) is not welded with 308 or 316 — doing so wrecks the carefully balanced 50/50 ferrite-austenite microstructure and its stress-corrosion and strength advantages. Use ER2209 (A5.9) filler, which is deliberately enriched with nickel and nitrogen to restore austenite in the weld as it cools fast. Super duplex (2507, S32750) steps up to ER2594. Duplex welding is heat-input sensitive — too cold and the weld stays over-ferritic and brittle; too hot and you precipitate embrittling intermetallics. That balance is why duplex almost always runs on a qualified procedure with interpass temperature limits.

Aluminum: 6061, 5052, and the 4043-vs-5356 Decision

Nearly all aluminum filler questions come down to choosing between ER4043 (Al-5%Si) and ER5356 (Al-5%Mg), both under AWS A5.10. They are not interchangeable, and picking wrong causes cracking, weak welds, or ugly anodizing. ER4043 has a lower melting point, flows beautifully, and is far less crack-sensitive — it is the standard for the 6xxx family (6061, 6063 extrusion and plate) and for castings. ER5356 is stronger and more ductile, matches the 5xxx family (5052, 5083, 5086), color-matches when anodized, and is the choice whenever weld strength or a bright anodized finish matters.

6061-T6 is the classic trap. You can weld it with either rod, but the reasoning differs: ER4043 gives the most crack-free, forgiving weld and is preferred for thick sections and complex joints, while ER5356 gives higher as-welded shear strength and anodizes to match the base. The one hard rule — do not use ER4043 to weld high-magnesium 5xxx alloys (5083, 5086, 5456); the silicon in 4043 reacts with the magnesium to form brittle Mg2Si and the joint cracks. Conversely, avoid ER5356 on parts that will see sustained service above about 150°F, where high-Mg welds become susceptible to stress-corrosion cracking.

5052 sheet (marine, tanks, trailers) is welded with ER5356 — the magnesium filler matches the base and preserves corrosion resistance. Pure 1xxx aluminum uses ER1100. A newer option, ER4943, is an improved 4043 with added magnesium that delivers noticeably higher strength while keeping 4043's easy flow and low crack sensitivity; many shops now stock it as a stronger drop-in for 6061 work. Aluminum GTAW runs on AC (to break up the oxide) with 100% argon at roughly 20–35 CFH, using zirconiated or ceriated/lanthanated tungsten; GMAW runs spray transfer on 100% argon (or Ar-He blends for thick plate) with a push-pull or spool gun to feed the soft wire without birdnesting.

• 6061 / 6063 (6xxx): ER4043 for crack resistance and flow; ER5356 for strength and anodize match; ER4943 as a stronger 4043 upgrade.
• 5052 (5xxx, low-Mg): ER5356 — matches base, marine-grade corrosion resistance.
• 5083 / 5086 / 5456 (high-Mg): ER5356 or ER5183 only — NEVER ER4043 (brittle Mg2Si cracking).
• 1100 / 3003 (pure & Mn): ER1100 or ER4043; highly ductile, low strength.
• Elevated-temp service (>150°F): Prefer ER4043-family over high-Mg 5356 to avoid stress-corrosion cracking.

Cast Iron and Dissimilar-Metal Joints

Cast iron repair is dominated by nickel fillers under AWS A5.15, chosen because nickel weld metal stays soft and machinable despite the high carbon pickup from the iron. ENi-CI (roughly 99% nickel) gives the most machinable deposit and is preferred for small single-pass repairs on gray iron where you'll re-machine the surface, but it is the most expensive rod. ENiFe-CI (55% nickel, balance iron) is stronger, more crack-resistant, tolerates the higher dilution and sulfur/phosphorus of ductile and higher-strength irons, and costs noticeably less — it's the better general-purpose choice for structural cast-iron cracks. Technique matters as much as filler: either preheat gray iron to 500–1200°F for a hot procedure, or use short 1-inch stringer beads with immediate peening and strict interpass cooling for the cold method, to manage the brittle heat-affected zone.

Dissimilar-metal joints are where the chart earns its keep, because the correct filler is often neither of the two base metals. The classic example — joining stainless steel to carbon steel — uses ER309L / E309L-16, not 308. The extra chromium and nickel in 309 survives the dilution from the carbon-steel side and still solidifies as crack-resistant austenite; 308 would dilute into a martensitic, crack-prone deposit. 309L is also the standard first (buttering) layer when overlaying stainless onto carbon steel.

For higher-consequence dissimilar welds — stainless or low-alloy steel to nickel alloys, high-temperature service, or joints that will see PWHT — nickel-based fillers take over. ERNiCrMo-3 (Inconel 625 equivalent, A5.14) and ERNiCr-3 (Alloy 82) tolerate wide dilution, resist hot cracking, and match the thermal expansion behavior needed in petrochemical and power applications. Silicon bronze (ERCuSi-A) is the go-to for joining or braze-welding dissimilar copper, brass, and galvanized or thin steel at low heat input. The golden rule for dissimilar joints: pick the filler by what the diluted weld pool becomes, not by either parent metal — and for anything structural or pressure-bearing, confirm it against a qualified procedure.

Master Lookup Chart and When to Consult a WPS

The chart below consolidates the most common base-metal-to-filler pairings for quick reference at the bench or the supplier counter. It covers the 90% of everyday work; the remaining 10% — code fabrication, pressure vessels, high-strength Q&T steels, cyclically loaded structures, and anything requiring PWHT — is exactly where a lookup table must yield to a qualified Welding Procedure Specification.

A WPS (and its supporting Procedure Qualification Record, PQR) is a controlled document that specifies not just the filler class but the exact brand/AWS classification, diameter, shielding gas and flow, amperage/voltage/travel ranges, preheat and interpass temperatures, PWHT, joint geometry, and position — all proven by destructively tested coupons. Codes make it mandatory: AWS D1.1 governs structural steel, ASME Section IX and the BPVC govern pressure vessels and power piping (B31.1/B31.3), API 1104 governs pipelines, and AWS D1.2 covers structural aluminum. If your work falls under any of these, the WPS — not this chart — is the legal and technical authority.

Practical rule of thumb: use the chart to buy the right spool or box of rod and to sanity-check a repair, but consult (or write) a WPS the moment the joint is load-bearing on a permitted structure, holds pressure, sees fatigue or impact, involves a high-strength or heat-treated alloy, requires documented corrosion performance, or will be inspected to a code. When you're unsure which side of that line you're on, you're on the WPS side. Suppliers across the US can cross a mill certificate or base-metal spec to the correct AWS filler class, but they cannot qualify your procedure — that responsibility stays with the fabricator and the governing code.

Frequently Asked Questions