Filler Material in TIG Welding: A Practical Selection Guide

Two TIG rods sit on the workbench, the same diameter, the same silvery color — and one of them is about to cost a shop a failed pressure test. Choosing filler material in TIG welding is quiet, invisible work: the arc still looks good, the bead still looks pretty, and the failure only shows up later at a dye-penetrant test, a pressure test, or a customer complaint. Getting it right starts with knowing exactly what the rod is doing in that puddle.

Filler Material in TIG Welding: What It Is and Why It Decides the Weld

Two TIG rods sit on the workbench. Same diameter, same manufacturer. One gets loaded into the torch, the other goes back in the drawer. That difference is enough for one job to fail a dye-penetrant inspection weeks later, or to bleed out from a weld that should have held pressure. Nothing about that weld looked wrong. The failure was hiding in the chemistry, and the chemistry came from the rod.

So here is the direct answer. Filler material in TIG welding is the consumable you add separately from the torch. It is not the tungsten, which is non-consumable: it makes the arc and does not become part of the weld. Everything in the finished joint comes from two places only, melted base metal and melted filler. That is why the filler’s chemistry, not just the base metal’s, governs the strength, corrosion resistance, hardness and appearance of what you deposit.

GTAW and TIG: Two Names for One Process

The formal name is Gas Tungsten Arc Welding, abbreviated GTAW, and it is the term the American Welding Society uses. TIG is the trade name for the same process, coined when it was introduced as “tungsten inert gas.” Specifications and code books say GTAW; the shop floor says TIG. Nothing changes between the two words: same torch, same tungsten, same shielding gas, same puddle. Many shops use both words on the same job.

Autogenous vs Filler-Added

Not every TIG weld has filler in it. Autogenous GTAW means no filler is added and the joint comes entirely from melted base metal. It is used daily: thin-gauge sheet and tube, closure welds on cylinders and vessels, tube-to-tube joints already butted and waiting to be sealed, and repairs where added metal would change the geometry.

With no filler you get no dilution from a second alloy, no extra heat, and a finished weld chemically identical to the base metal. That is a virtue when the base metal suits the service and heat input must stay low. The price is that you cannot add strength, adjust composition, compensate for a chemistry mismatch or fill a gap. When the base metal is wrong, filler is the only option.

What Counts as “Filler Metal”

In AWS and ASME usage, filler metal covers more than the rod in your hand. It includes solid filler rods in standard lengths and diameters, cut rod lengths cut for a specific joint, and, less commonly, solid wire fed by hand into the puddle. A stick electrode and a MIG wire are filler metal too. What it always means is a consumable that is melted and becomes part of the weld. For a primer, see our guide to all-position welding rods.

Four Inputs Behind Every Filler Decision

Every filler decision comes down to four inputs:

• Base metal specification. Not “mild steel,” but the actual grade, condition and chemistry. A36, 304L, 6061-T6 and 4130 each point to a different filler family.
• Service environment. Corrosion, pressure, elevated temperature, sour service, a code inspection regime, or a cosmetic finish nobody wants to look at twice.
• Governing code. AWS D1.1, D1.2, D1.6, ASME Section IX, or a client specification, which sets minimum mechanical properties and sometimes the filler itself.
• Joint configuration and process. Joint design, thickness, welding position, root pass or fillet, and whether the part sees a heat treatment afterward.

The Filler Is a Chemistry Bridge

Hold those four inputs in your head and the filler’s purpose becomes obvious: a deliberate bridge between base metal and service. In a simple case it matches the base metal closely enough to act like a continuation of it. In a harder case it bridges two alloys and compensates for dilution, the mixing of melted base metal into the pool that drags the deposit off its intended chemistry. Weld 316L stainless to a carbon steel flange and the pool is mostly carbon steel however good the rod, so the filler is over-alloyed to land back on stainless.

That is not a minor detail. The AWS has authored more than 350 standards for welding practices and procedures, and a classification like ER70S-2 is not a casual label a distributor invented. It is a chemistry-and-properties specification with defined mechanical requirements, which is why it carries contractual weight on an inspected job. For the technique side, our TIG fundamentals overview covers the arc, the puddle and machine setup. Knowing what the filler must do inside that puddle separates a passing weld from one that merely looks good.

How Filler Metal Is Classified: Reading AWS and ISO Numbers

Filler metal arrives in a wall of cardboard boxes, each carrying a code that looks like the operator’s license for a jet. ER70S-2. ER308L. ER4045. Read those strings and you can pick the right rod, check a supplier’s quote, and catch a rep who shipped the wrong classification.

The AWS system is not random soup. Break a code into four pieces, form then strength then family then variant, and the code stops being a mystery.

The Anatomy of a Classification

Take ER70S-2 apart:

• ER: electrode or rod, a solid bare consumable fed through a torch. Plain E marks stick electrodes like E7018.
• 70: nominal tensile strength in thousands of psi. 70 ksi is about 483 MPa, the number that tells you whether the deposit carries load.
• S: the stainless and carbon/low-alloy steel family. An A in that slot means aluminum or magnesium alloy.
• -2: the dash number identifying the type within the family, describing fill or operating characteristics rather than strength.

The Carbon Steel Family

Every ER70S member carries the same 70 ksi rating, so the choice is about behavior in the puddle, not strength.

• ER70S-2: general-purpose workhorse. Good out of position, clean on fillets and root passes, the mild steel default.
• ER70S-3: general-purpose rod for a range of applications, rare on the TIG shelf today.
• ER70S-4: higher deposition rates flat and downhand, so common on production fillet work.
• ER70S-5: higher strength and silicon, used where higher deposition and mechanical properties are needed.
• ER70S-6: the pipe and structural tube favorite. Higher silicon means better wetting and fluid puddle behavior, the standard pick for root passes.
• ER70S-7: a higher-strength classification for specific applications, often in code-driven structural work.

What the Letter Suffix Does for Stainless

Stainless classifications add an L for low carbon, roughly 0.03% maximum. That letter matters: at moderate carbon levels in the heat-affected zone, stainless can form chromium carbide precipitates along grain boundaries. That is sensitization, and it is where corrosion later attacks.

• ER308L: 19 to 21% chromium, 9 to 11% nickel. Your 304 and 304L filler.
• ER309L: 23 to 25% chromium, 12 to 14% nickel. Over-alloyed filler for stainless to carbon steel, or stainless to stainless.
• ER312: 29 to 31% chromium, about 9% nickel. Highest-chromium filler for severe dissimilar metal welding.

The family also runs ER308LMo and ER309LMo for molybdenum service, ER316L for 316, ER321 for titanium-stabilized 321, ER347 for niobium-stabilized 347, ER385 for high-nickel alloys and ER2209 for duplex stainless. Our guide to Alloy 20 welding procedures and filler metals shows the same chemistry logic in a real corrosion service.

A Quick Decoding Table

Classification	Family	Typical use
ER308L / ER316L	Stainless	304, 316 stainless
ER4043 / ER4045 / ER5356	Aluminum	Most aluminum GTAW work
ER7068 / ER7155	Aluminum	7000-series high strength
ERNiCrMo-3 / ERNiCrMo-4	Nickel alloy	625, C-276, superalloys
ER CuSi-A / ER CuAl-A	Copper alloy	Copper, aluminum bronze

• Aluminum: ER4043, ER4045, ER4047, ER5356, ER5556, ER7068, ER7155
• Nickel: ERNi-3, ERNiCr-3, ERNiCrFe-2, ERNiCrMo-3, ERNiCrMo-4, ERNiFeCr-1, ERNiCu-7
• Copper: ER CuSi-A, ER CuSn-A, ER CuAl-A, ER CuNi

Aluminum work rewards clean prep and the right filler, which is why we wrote up how to prep aluminum right before we talk about the rod.

Where to Look: The AWS A5.x Specifications

AWS A5.18 covers electrodes and rods for tungsten arc welding, the carbon and low-alloy steel parent. A5.9 covers stainless steel welding electrodes and rods, A5.14 nickel and nickel alloy, A5.28 aluminum and magnesium alloy, and A5.13 copper and copper alloy electrodes and rods.

These standards give classifications contractual weight. AWS lists more than 350 welding standards, and a spec calling for “A5.18 Class ER70S-2” points at defined chemistry and certified properties.

A Classification Is a Contract, Not a Recipe

A classification defines what the rod is: its chemistry and its minimum mechanical properties. It says nothing about how to weld with it. The A5.x tables give tensile strength, yield strength, elongation and, for some classifications, Charpy impact values at temperature, so read them rather than guess from the code.

Fit-up, cleaning, amperage, gas, travel speed and heat input live in the welding procedure specification, which sits on top of the classification. ASME and AWS publish the qualification frameworks, and TWI’s technical knowledge library is free reference material.

The ISO and European View

Outside North America the numbering differs but the logic matches. ISO 9606 covers welder qualification by material family: part 1 steels, part 2 aluminium, part 3 copper and copper alloys, part 4 nickel and nickel alloys. ISO 15614 covers procedure qualification and welding procedure specification format. EN 10204 defines inspection document types, with 3.1 and 3.2 certificates providing the traceability European fabrication requires.

A European drawing calling for ISO 9606-1 qualification and EN 10204 3.2 certification wants what the AWS equivalent wants: a qualified welder, a qualified procedure, documented material identity. Different labels, same discipline. Learn the number, confirm the details against the current standard and the product data sheet, and the shop buys with confidence.

Choosing Filler Metal by Base Material and Service Condition

Base metal tells you where to start. Service condition tells you where to finish. A filler that works on a dry indoor carbon steel bracket can fail quietly on the same steel in a marine splash zone, and the difference is chemistry no base metal spec tells you.

Carbon and Low-Alloy Steels

Three carbon steel rods cover most of what a GTAW shop touches:

• ER70S-2 — the general-purpose workhorse, handling out-of-position work, fillet welds and root passes better than most.
• ER70S-6 — higher strength and higher silicon, which feeds the puddle faster. Common for pipe and higher-strength carbon steel.
• ER70S-4 — built for deposition rate on flat and downhand fillets, where the arc can push a bigger puddle.

The governing rule comes from AWS D1.1, Structural Welding Code: for matching filler metal, the filler metal strength must be at least equal to the base metal minimum specified tensile strength. A lower-strength filler needs approval through a qualified procedure, not a shop-floor shortcut.

Chromoly is less exotic than it sounds. 4130 and 4340 usually run ER70S-2 or ER70S-6, with higher-strength classifications reserved for specific post-weld heat treatment or code requirements. For the stick-process comparison, see alloy steel welding electrodes.

Stainless Steel: Where Dilution Changes Everything

Stainless filler selection is where “match the base metal” stops being good enough, and understanding why will save you failed joints.

The standard stainless pairings:

Base Metal(s)	Typical GTAW Filler	Why
304 / 304L	ER308L	Nominal chemistry match, low carbon for corrosion
316 / 316L	ER316L	Adds molybdenum for pitting resistance
304 to 316	ER309L	Over-alloyed filler tolerates the mix
Stainless to carbon steel	ER309L, ER309LMo, ER312	Extra chromium and nickel offset dilution
347	ER347	Stabilized with niobium
321	ER321	Stabilized with titanium
Duplex 2205	ER2209	Duplex chemistry with a ferrite buffer

The “over-alloyed” fillers do two jobs: extra chromium and nickel so the diluted deposit lands close to the required chemistry, and a little delta ferrite, the ferrite number the procedure specifies. A fully austenitic weld can be prone to hot cracking, and a few percent of ferrite breaks up that crack-prone continuous path. OSHA’s welding standard and AWS D1.6 both treat the procedure as the controlling document.

Aluminum: Match the Series, Watch the Silicon

Aluminum filler choice is mostly a series question:

• 3003, 5052, 6061 — ER4045 or ER5356. ER4045 flows well and is easy to work with; ER5356 is the more forgiving, higher-strength choice for many jobs.
• 5000- and 6000-series, including marine work — ER5356 or ER5556.
• 7000-series — ER7155 or ER7068.

ER4045 carries noticeably higher silicon than ER5356, and silicon is what makes it flow so nicely. That is also why ER4045 is avoided on 7000-series aluminum: those alloys are already hot-cracking sensitive, and extra silicon pushes them toward the brittle eutectic range. Keep silicon down and heat input controlled on high-strength aluminum.

Aluminum prep deserves attention because filler cannot fix a dirty joint. Our guides on cleaning aluminum for welding and aluminum MIG welding cover surface preparation and oxide removal, much of it applying under the TIG torch.

Nickel Alloys and Copper Alloys

Each nickel or copper alloy gets its own classification, matched to the exact alloy rather than a generic rod. Our Alloy 20 welding procedures guide shows the pattern, matching one alloy family to a specific filler set and procedure.

Service Conditions Change the Answer

Now the part base metal specs never mention:

• Corrosion — take the more corrosion-resistant option, such as ER316L over ER308L, and check the chloride content and temperature range the service sees.
• Elevated temperature and creep — austenitic stainless and nickel alloys hold up far better than ferritic or martensitic grades, so high-temperature code work usually specifies a specific qualified filler.
• Sour service — H2S environments demand hardness limits and often hardness-based filler requirements, not just a chemistry match.
• Galvanized steel — grind the zinc coating back from the weld zone and keep amperage low to limit zinc vapor. Use a clean rod such as ER70S-2 or ER70S-6; wire that touched galvanized steel will contaminate the weld.

Quick Selection Table

Stainless rows are in the table above. The other common choices:

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Choosing Filler Metal by Base Material and Service Condition

Base metal tells you where to start. Service condition tells you where to finish. A filler that works on a dry indoor carbon steel bracket can fail quietly on the same steel in a marine splash zone, and the difference is chemistry no base metal spec tells you.

Carbon and Low-Alloy Steels

Three carbon steel rods cover most of what a GTAW shop touches:

• ER70S-2 — the general-purpose workhorse, handling out-of-position work, fillet welds and root passes better than most.
• ER70S-6 — higher strength and higher silicon, which feeds the puddle faster. Common for pipe and higher-strength carbon steel.
• ER70S-4 — built for deposition rate on flat and downhand fillets, where the arc can push a bigger puddle.

The governing rule comes from AWS D1.1, Structural Welding Code: for matching filler metal, the filler metal strength must be at least equal to the base metal minimum specified tensile strength. A lower-strength filler needs approval through a qualified procedure, not a shop-floor shortcut.

Chromoly is less exotic than it sounds. 4130 and 4340 usually run ER70S-2 or ER70S-6, with higher-strength classifications reserved for specific post-weld heat treatment or code requirements. For the stick-process comparison, see alloy steel welding electrodes.

Stainless Steel: Where Dilution Changes Everything

Stainless filler selection is where “match the base metal” stops being good enough, and understanding why will save you failed joints.

The standard stainless pairings:

Base Metal	Typical GTAW Filler
Carbon steel	ER70S-2, ER70S-6, ER70S-4
4130 / 4340 alloy steel	ER70S-2, ER70S-6
3003 / 5052 / 6061 aluminum	ER4045, ER5356
5000 / 6000 series aluminum	ER5356, ER5556
7000-series aluminum	ER7155, ER7068
Inconel 625	ERNiCrMo-3
C-276	ERNiCrMo-4
Alloy 825	ERNiFeCr-1
Pure nickel

Base Metal(s)	Typical GTAW Filler	Why
304 / 304L	ER308L	Nominal chemistry match, low carbon for corrosion
316 / 316L	ER316L	Adds molybdenum for pitting resistance
304 to 316	ER309L	Over-alloyed filler tolerates the mix
Stainless to carbon steel	ER309L, ER309LMo, ER312	Extra chromium and nickel offset dilution
347	ER347	Stabilized with niobium
321	ER321	Stabilized with titanium
Duplex 2205	ER2209	Duplex chemistry with a ferrite buffer

The “over-alloyed” fillers do two jobs: extra chromium and nickel so the diluted deposit lands close to the required chemistry, and a little delta ferrite, the ferrite number the procedure specifies. A fully austenitic weld can be prone to hot cracking, and a few percent of ferrite breaks up that crack-prone continuous path. OSHA’s welding standard and AWS D1.6 both treat the procedure as the controlling document.

Aluminum: Match the Series, Watch the Silicon

Aluminum filler choice is mostly a series question:

• 3003, 5052, 6061 — ER4045 or ER5356. ER4045 flows well and is easy to work with; ER5356 is the more forgiving, higher-strength choice for many jobs.
• 5000- and 6000-series, including marine work — ER5356 or ER5556.
• 7000-series — ER7155 or ER7068.

ER4045 carries noticeably higher silicon than ER5356, and silicon is what makes it flow so nicely. That is also why ER4045 is avoided on 7000-series aluminum: those alloys are already hot-cracking sensitive, and extra silicon pushes them toward the brittle eutectic range. Keep silicon down and heat input controlled on high-strength aluminum.

Aluminum prep deserves attention because filler cannot fix a dirty joint. Our guides on cleaning aluminum for welding and aluminum MIG welding cover surface preparation and oxide removal, much of it applying under the TIG torch.

Nickel Alloys and Copper Alloys

Each nickel or copper alloy gets its own classification, matched to the exact alloy rather than a generic rod. Our Alloy 20 welding procedures guide shows the pattern, matching one alloy family to a specific filler set and procedure.

Service Conditions Change the Answer

Now the part base metal specs never mention:

• Corrosion — take the more corrosion-resistant option, such as ER316L over ER308L, and check the chloride content and temperature range the service sees.
• Elevated temperature and creep — austenitic stainless and nickel alloys hold up far better than ferritic or martensitic grades, so high-temperature code work usually specifies a specific qualified filler.
• Sour service — H2S environments demand hardness limits and often hardness-based filler requirements, not just a chemistry match.
• Galvanized steel — grind the zinc coating back from the weld zone and keep amperage low to limit zinc vapor. Use a clean rod such as ER70S-2 or ER70S-6; wire that touched galvanized steel will contaminate the weld.

Quick Selection Table

Stainless rows are in the table above. The other common choices:

Base Metal	Typical GTAW Filler
Carbon steel	ER70S-2, ER70S-6, ER70S-4
4130 / 4340 alloy steel	ER70S-2, ER70S-6
3003 / 5052 / 6061 aluminum	ER4045, ER5356
5000 / 6000 series aluminum	ER5356, ER5556
7000-series aluminum	ER7155, ER7068
Inconel 625	ERNiCrMo-3
C-276	ERNiCrMo-4
Alloy 825	ERNiFeCr-1
Pure nickel	ERNi-3
70/30 copper-nickel	ERNiCu-7
90/10 copper-nickel	ERNiCr-3
Copper and silver alloys	ER CuSi-A
Copper-nickel	ER CuNi
Aluminum bronze	ER CuAl
Phosphor bronze	ER CuSn

For code context, the AWS codes and standards page lists AWS D1.1/D1.1M:2025-AMD1 for steel, AWS D1.2/D1.2M:2026 for aluminum, AASHTO/AWS D1.5M/D1.5:2025 for bridges and AWS A3.0M/A3.0:2025 for process inspection, while AWS D1.6 covers stainless steel. Confirm against the current edition and the project WPS.

Rod Diameter, Amperage, Polarity, and Shielding Gas

Choosing the right filler classification is not enough to weld anything. The rod chemistry has to reach the puddle at the right speed, the right heat, and under the right shield. Diameter, amperage, polarity, and shielding gas control all three, and a weld can look acceptable while any one of them is wrong.

Start with diameter, because it sets the ceiling on everything else. Standard TIG rod diameters are 1/16 in (1.6 mm), 3/32 in (2.4 mm), 1/8 in (3.2 mm), 5/32 in (4.0 mm), 3/16 in (4.8 mm), and 1/4 in (6.4 mm).

Matching Rod Diameter to Joint Thickness

The shop rule of thumb: match rod diameter roughly to joint thickness up to about 6 mm (1/4 in), then step up for heavier sections. Below that, you are choosing control; above it, deposition rate.

• 3/32 in (2.4 mm) for thin material and out-of-position work, where the puddle must stay where you put it.
• 1/8 in (3.2 mm) as the general-purpose choice for 3/16 in to 1/2 in plate.
• 5/32 in (4.0 mm) to 3/16 in (4.8 mm) for heavier joints where you want to fill the puddle faster.
• 1/4 in (6.4 mm) for thick sections and high-deposition work, where a smaller rod means endless drips.

The reasoning is simple physics. A smaller rod melts faster, needs less heat, and gives finer puddle control. A larger rod deposits faster but dumps more heat in less time, and it becomes hard to control vertically or overhead because the molten metal wants to run. If a weld is out-of-position and you are fighting the puddle, drop a diameter rather than dropping the amperage.

Amperage: The Number You Qualify, Not the Number You Guess

The working shop rule is roughly 1 amp per 0.001 in of base metal thickness, about 40 A per mm. A 1/4 in (6 mm) plate commonly lands in the 90–120 A range. On the consumable side, a 1/8 in rod typically covers roughly 60–130 A DCEN, while a 3/32 in rod sits lower because it is a thinner stick that melts sooner.

Rod diameter	Typical base metal thickness	Typical DCEN amperage band
1/16 in (1.6 mm)	Sheet metal, up to 1/16 in	20–80 A
3/32 in (2.4 mm)	Thin material, out-of-position work	40–100 A
1/8 in (3.2 mm)	3/16 in to 1/2 in plate	60–130 A
5/32 in (4.0 mm)	3/8 in to 3/4 in plate	90–150 A
3/16 in (4.8 mm)	Heavy plate, 3/4 in and up	120–200 A
1/4 in (6.4 mm)	Thick sections, high deposition	150–250 A

Polarity: DCEN, DCEP, and AC

DCEN (direct current electrode negative) is the default for GTAW and should stay that way for most work. A commonly cited rule of thumb puts roughly two-thirds of the arc heat into the work piece and one-third into the electrode. That is why DCEN gives deep penetration while protecting the tungsten from melting down as fast as the work.

DCEP (direct current electrode positive) does the opposite. It adds penetration and provides cathodic cleaning, the oxide-scouring action that used to be vital on aluminum welding. But it also drives most of the heat into the tungsten, so it is a special-purpose tool. Modern square-wave inverters largely replaced DCEP for aluminum by delivering AC with a controllable balance.

Aluminum and magnesium welding is done on AC, and on a modern square-wave machine the operator sets the electrode-negative balance around 70–80% EN. Higher EN favors penetration; lower EN favors cleaning. Too far toward EN and you break through the oxide and get porosity; too far the other way and you lose penetration. If you are new to aluminum TIG, the cleaning and prep steps in how to prep aluminum for welding are worth reading alongside the machine settings, because no balance setting rescues dirty metal.

Choosing the Tungsten by Color

• Green (pure tungsten) for AC aluminum and magnesium. Lowest current capacity, so keep amperage modest.
• Red (thoriated, 1–2% thorium) for DCEN. Excellent DC life and easy to start; thorium affects handling and disposal in some jurisdictions.
• Gold (lanthanated) for DCEN and AC. Strong all-around electrode, good AC performance, sharp point that holds well.
• Gray (ceriated) for DC and AC. Good arc start and AC balance, a solid choice when you switch between materials.

Sharpen the tungsten on a dedicated wheel before you start. A dirty, blunt, or wandering tungsten is one of the fastest ways to raise porosity and tungsten contamination in the puddle. If you are adding a machine to the shop, our airgas welding equipment guide covers the supporting gear, and aerospace TIG welding shows how much setup discipline a demanding job demands.

Shielding Gas

Pure argon at 99.99% purity or better is the standard for carbon steel, stainless, and aluminum in GTAW. For aluminum, use the highest purity you can get: hydrogen contamination from lower-purity gas is a leading cause of porosity in aluminum welds, and no amount of technique fixes it.

Typical shielding gas flow is 15–25 cubic feet per hour, adjusted for nozzle size and whether you are welding indoors or in a draft. Too little flow lets air in and oxidizes the puddle. Too much swirls the shielding gas and can suck in air from the wrong direction.

Do not use argon/CO2 blends in TIG. The CO2 fraction attacks the tungsten electrode and shortens its life badly. For high-heat GTAW of copper, where you need more thermal conductivity than argon can give you, helium blends are the standard answer. Gas selection and handling details are covered in the AllGas welding supply and safety guide.

Put the pieces together: diameter sets the heat and control, amperage sets how fast the base metal melts, polarity decides where heat and cleaning go, and gas protects the puddle from the air. When a TIG weld goes wrong, work through those four in order before blaming the filler metal.

TIG Rod vs MIG Wire vs Stick Electrode: Picking the Right Consumable

Most people choose a consumable out of habit, not by the job. The stick machine was already set up, so the shop orders E7018 by the case. The torch is already lit, so the joint gets ER70S-2. Line the three up side by side and the choice stops being mysterious.

What each consumable actually is

A TIG rod is a solid, bare wire with no flux coating, supplied in cut lengths and fed by hand into the puddle. In practice it runs from roughly 0.035 in to 0.125 in diameter, so the same classification comes in noticeably thicker stock than welding wire. With no sheath around it, the rod has to be clean before it goes into the puddle.

MIG wire is continuous, spooled and pushed through the gun. Common diameters are 0.030 in, 0.035 in and 0.045 in. Stick electrodes are the odd one out: a filler core wrapped in a flux coating that melts, boils and leaves a slag blanket over the bead, and that slag must be chipped or ground off before inspection.

Feature	TIG rod (GTAW)	MIG wire (GMAW)	Stick electrode (SMAW)
Form	Solid, bare, cut lengths	Solid, spooled	Flux-coated core
Typical sizes	0.035 to 0.125 in	0.030, 0.035, 0.045 in	Common stick diameters
Deoxidizers	Not added the same way	Si and Mn added	Provided by the flux
Slag	None	None	Yes, must be removed
Spatter	Minimal	Low to moderate	Moderate
Deposition rate	Lowest	High	High
Surface tolerance	Clean metal only	Fair	Handles rust and dirt
Bead appearance	Cosmetic, repeatable	Good	Rougher, coated

The chemistry detail that explains why MIG feels easier

Here is the part most shops skip. A TIG ER308L rod and a MIG ER308L wire come out of the same family, sitting in the same 19 to 21 percent chromium, 9 to 11 percent nickel window set by theAWS A5.9 classification. The difference is what gets added on top.

MIG wires are deliberately deoxidized with silicon and manganese so the puddle stays fluid and the arc stays stable when the plate carries mill scale or light rust. Bare GTAW rods are not deoxidized that way, which is a genuine chemical reason MIG runs smoothly while bare TIG rod is more prone to electrode freezing, seen as a stuttering arc and a tip that keeps balling up. The same story plays out on carbon steel, where an ER70S-6 wire and an ER70S-2 rod share the 70 ksi family but differ in silicon, manganese and deposited strength.

The practical tradeoffs

TIG is the slowest and most expensive of the three per hour, but it gives the welder precise puddle control, no slag, minimal spatter and a clean cosmetic bead that is easy to inspect and pass. MIG is faster and cheaper with higher deposition and still makes a good weld on production steel. Stick is the most forgiving and works in awkward field conditions where the metal is rusty, dirty or outside a booth, which is why it remains a mainstay on structural and repair work. Advantages of stick welding covers that case in more depth.

Where each one wins

• TIG: thin stainless, aluminum of any thickness, small components, pipe root passes, and stainless repairs where the existing metal must stay intact.
• MIG: high-production carbon steel, structural fillet welds, and aluminum work where volume matters more than a cosmetic finish, as covered in the aluminum MIG welding guide.
• Stick: heavy structural fillets, outdoor and field fabrication, dirty or rusty steel, and positions where a machine would be more trouble than it is worth. A primer on electrode selection sits in the all-position welding rod guide.

A cut length of solid MIG wire can physically be dipped into a TIG puddle. What it gives up is the reason to bother: it forfeits the classified GTAW chemistry, the certified mechanical properties, and the controlled diameter a proper rod carries on its data sheet.

Finally, do not forget the option that costs nothing: some joints genuinely need no filler at all. Autogenous TIG is the answer for thin-gauge stainless where the joint closes by melting the edges together, for sealing tube ends, and for adding a bead without changing the assembly’s chemistry. TWI’s technical knowledge library covers where autogenous welds behave best and where they do not.

Match the consumable to the joint, not to the machine in the corner, and half of your filler selection problems disappear before they reach the workbench.

Codes, Qualification, and What a Filler Classification Does Not Promise

Pick the wrong filler and the weld fails on the bench, where it is cheap to fix. Pick the right filler, weld it with an unqualified procedure, and the job fails anyway, this time in front of an inspector who is checking paperwork instead of metal. That second failure is what this chapter is about.

Every filler decision in TIG welding eventually meets a rulebook. Some rulebooks are laws and contracts (ASME pressure vessel work is both), some are consensus standards written by AWS and AASHTO, and some are customer specifications that borrow heavily from the first two. None of them care how pretty the bead looks. They care about chemistry, strength, traceability and proof. If you understand that layer early, filler selection stops being guesswork and starts being engineering.

The Code Landscape

These are the standards most TIG shops encounter in North America, with the current editions shown on the AWS codes and standards page:

Standard	What it governs
AWS D1.1/D1.1M:2025-AMD1	Structural Welding Code, Steel. The default reference for structural work and for filler strength matching rules.
AWS D1.2/D1.2M:2026	Structural Welding Code, Aluminum.
AWS D1.6	Structural Welding Code, Stainless Steel.
AASHTO/AWS D1.5M/D1.5:2025	Bridge and highway structures.
AWS A3.0M/A3.0:2025	Welding Process Inspection, including visual inspection acceptance criteria.
ASME BPVC Section IX	Qualification of welders, operators and welding procedures.
ASME BPVC Sections I and VIII	Power boilers and pressure vessels.
ASME B31.1 and B31.3	Power piping and process piping.
ISO 9606-1, -2, -3, -4	Welder qualification for steel, aluminium, copper, and nickel and nickel alloy.
ISO 15614	Procedure qualification and the format of the WPS.

The ASME family is searchable through the ASME codes and standards finder, and practical interpretation of the ISO system is well covered in TWI’s technical knowledge library.

The Hierarchy: Rod to Record

Think of the paperwork stack as a chain, where each link only holds if the one below it does.

1. Classification. What the rod is: its chemistry and minimum mechanical properties.
2. Welding Procedure Specification (WPS). How it will be welded: filler designation and diameter, amperage, shielding gas, technique, preheat and interpass temperature, cleaning requirements.
3. Procedure Qualification Record (PQR). The test coupon results that prove the procedure works within the ranges it covers.
4. Welder Performance Qualification (WPQ). Proof that the individual welder can deposit sound welds inside that procedure’s limits.
5. Inspection. Visual and nondestructive examination confirming the actual part matches the procedure.

A filler classification sits at the top of that chain, and no higher. It tells you what the metal is. It cannot tell you whether your joint was fit up properly, whether your edges were clean, whether your heat input stayed in range, or whether the welder on the torch is qualified. A classification is never a substitute for a qualified procedure. Welding specifications in aerospace work make the same point loudly: aerospace TIG welding standards lean on documentation, not rod choice alone.

Matching Rules and Other Limits

• Strength matching. Under AWS D1.1, the filler metal’s tensile strength must be at least equal to the base metal’s minimum specified tensile strength.
• Lower-strength filler. Codes can permit it when it is qualified and documented. The paperwork is the permission.
• Impact testing. Where toughness matters, the filler must meet Charpy impact requirements at the service temperature, not just a tensile number.
• Heat input and interpass. Excess heat on quenched and tempered steels, stainless, or aluminum creates problems no filler classification addresses.

Traceability and Proof

Prove what you used, after the rod is gone and the job is closed.

• AWS product certification for A5.x filler metals, which lets the classification carry a certified-properties mark.
• The manufacturer’s certificate of conformity shipped with the product.
• EN 10204 3.1 and 3.2 certificates for international work and material traceability.
• Lot or heat number records retained with the job record, so a questionable weld can be traced back to a specific rod.

AWS also sells the credentials that prove the human side of this work, including Certified Welding Inspector (CWI), Certified Welding Supervisor (CWS) and Certified Welding Engineer (CWEng), plus welder performance qualification and welding procedure qualification credentials. Details are on the AWS education page.

In short, the classification tells you what you are holding. The procedure, the qualification records and the inspection tell you whether anyone will accept it.

Common Filler Metal Mistakes and How to Fix Them

Most filler metal problems are quiet. The arc behaves, the bead comes out, and the defect surfaces later at a dye-penetrant test or under a microscope. In practice, though, a short list causes the majority of TIG filler problems: wrong filler for the job, a dirty rod, wrong amperage, and wrong travel speed. Here is how to recognize each one and what to change.

Electrode Freezing and Stubbing

“Freezing” means the filler stops melting and the puddle cools around it. The causes are consistent: too much filler offered at once, not enough current to melt it, an arc stretched too long, an oxidized or dirty rod, the rod touching the tungsten, or travel speed so slow the heat sinks into the puddle instead of the rod.

• Step down to a smaller diameter so the rod melts before the puddle does.
• Shorten the arc and keep the filler in the hottest part of the arc zone.
• Dip the rod into the leading edge of the puddle and let it flow in. Do not stir.
• Keep rods in their sealed tube, and wipe off the blackened end between welds.

Sticking to the tungsten usually means the rod wandered to the wrong side of the arc. Reset your hand position and the technique fundamentals in our guide to TIG technique and filler control will save you a lot of trial and error.

Lack of Fusion and Excess Penetration

Lack of fusion means the bead sat on the base metal instead of melting into it. Usual reasons: not enough heat, travel too fast, dirty or oxide-covered base metal, the wrong filler for the parent metal, and poor bead placement. More heat, a slower speed, clean metal and a correct classification solve most of it.

Excess penetration is the mirror problem. The drivers are excessive amperage, insufficient filler addition, and slow travel speed on thin material. On thin plate the control is heat: drop the amperage, add filler sooner, keep the travel speed up and use a smaller rod. On stainless, back the heat off before you burn through.

Hot Cracking in Stainless Steel

Stainless hot cracks open in the heat-affected zone. The drivers are high heat input, high restraint, inadequate ferrite in the deposit, sulfur contamination and unclean edges. The fixes map one for one: a low-carbon filler such as ER308L, controlled heat input, interpass temperature held to the procedure, and joint edges ground clean before fitting. TWI’s technical knowledge library is a reliable free reference for joint preparation and filler selection questions.

Porosity

On aluminum, look for moisture on the rod or the base metal, hydrogen pickup, contaminated shielding gas or a leaking gas line, and inadequate oxide cleaning. On carbon steel, add dirty or rusty surfaces and weak shielding. Check the gas delivery first: a leaking fitting, or a cylinder left open long enough to admit air, will contaminate the argon and the whole weld.

Undercut, Crater Cracks and Sword Shapes

Undercut shows up when the work angle or filler angle pulls the arc off the toe of the bead, when travel speed drags too slow, and when the welder does not dwell at the toes to fill them. Correct the torch angle, add a brief dwell at each toe, and keep the speed steady.

Crater cracks and the tapered “sword” shape at the end of a bead happen when the arc is broken before the puddle is filled. Pour the crater full, then taper up and down as you break the arc, or add a run-off tab where the joint allows it.

Dirty Aluminum Welds and Contaminated Tungsten

Aluminum TIG requires AC at roughly 70–80% electrode-negative balance plus mechanical cleaning with a dedicated stainless brush and solvent. If the bead looks grey and sooty, check the balance setting, change the rod and redo the joint prep. Our step-by-step guide to prepping aluminum for welding covers the cleaning sequence in detail.

Tungsten contamination shows as a wandering arc, a discoloured tip and a spattered nozzle. The causes are the filler rod touching the tungsten, an arc length that is too long, or the wrong tungsten type. A dirty tungsten will arc badly no matter which rod you feed.

Distortion and Misalignment

Excess heat input, poor sequence and a lack of fixturing cause most distortion and mismatch. Back-stepping, tacking, deliberate fixture design and planning the sequence ahead of time pull the heat and the shrinkage where you want them.

When the Weld Is Already Suspect

Stop. Cut it out completely, clean, re-fit and re-qualify. Never weld over a suspect joint and hope the second pass hides it.

Handling, Storage, and Safety Around Filler Metal

Filler metal is the consumable most shops never put away, and the one most likely to pick up moisture, rust, or shop grease. It looks harmless until it becomes porosity, contamination, or an arc that will not behave.

Aluminum First: Dry, Sealed, and at Room Temperature

Aluminum filler is the most demanding material to store, because aluminum GTAW welds are extremely sensitive to hydrogen. Moisture pickup is the leading cause of porosity in aluminum GTAW, and a rod can absorb enough moisture to blow holes through a fillet weld.

Keep aluminum rods sealed, ideally with desiccant inside, and open them only when you are ready to weld. If the container has sat in a cold truck or shed overnight, let it reach room temperature before cracking the seal: warm humid air condensing on cold rod is a free shot at porosity. Keep it closed between welds. For cleaning rules that pair with storage, see our guide to preparing aluminum for welding.

Stainless Hygiene: Keep Iron Away

Stainless filler needs different discipline. Carbon steel dust on a stainless rod, or a brush that touched mild steel, leaves free iron on the surface. It rusts, streaks, and undermines the corrosion performance the alloy was chosen for, so keep stainless brushes, tools, and files separate from anything used on carbon steel.

Filler type	Storage rule	Warning sign
Aluminum (ER4045, ER5356)	Sealed with desiccant, room temp before opening	White powdery bloom, pitted rod
Stainless (ER308L, ER316L)	Original packaging or sealed tube, dedicated tools	Rust spotting on the rod
Carbon steel (ER70S-2, ER70S-6)	Dry tube or rod holder, off the floor	Surface rust, flaking scale, kinked rod
Nickel alloys	Sealed and dry, separate from stainless	Discoloration, surface tarnish

Labeling, Traceability, and Rod Handling

Label every container with the classification, the diameter, and the lot or heat number, which is how you connect a finished weld to the material in it. For pressure equipment, aerospace, or any job with an inspection hold point, lot traceability is not optional, and shops at that level can learn more from our aerospace TIG welding standards and training overview.

On the bench, cut rods to consistent lengths and keep them on a holder or in a tube, not loose in a drawer, so you can grab the right length without touching the surface. Wipe oil and grease off rods and hands before handling filler or gas equipment. 29 CFR 1910.253 requires cylinders and apparatus to be kept free of oily or greasy substances and cylinders stored at least 20 feet from highly combustible materials. Never touch an oxygen regulator with greasy hands. Our welding gas supply and cylinder safety guide covers the storage side.

Personal Protection: Helmet, Lens Shade, and Clothing

A welding helmet with the correct lens shade is not a comfort item, because TIG arc light can cause permanent arc eye in a fraction of a second. 29 CFR 1910.252(b)(2)(ii)(H) sets the minimum shade guide: shade 12 for gas-shielded arc welding of ferrous metals, shade 11 for nonferrous. Wear leather gloves, flame-resistant clothing, and sleeves that cover the skin, and keep synthetics away from the arc.

Ventilation, Fumes, and Respirators

Fume control starts with the room, not the mask. 29 CFR 1910.252(c)(1)(iii) requires local exhaust or general ventilating systems to keep toxic fumes, gases, and dusts below the maximum allowable concentrations in 1910.1000. And 1910.1000(e) sets the order of operations: engineering and administrative controls come first, and respirators are used only where those controls are not feasible.

When respiratory protection is needed, 29 CFR 1910.134 requires a written program, medical evaluation before fit testing, fit testing, and NIOSH-certified equipment. Assigned protection factors are 10 for an air-purifying half mask, 50 for a full facepiece, and 1000 for a powered air-purifying full facepiece, and 1910.134(d)(3)(iv)(B) calls for an air-purifying respirator with a NIOSH-certified HEPA or other particulate filter.

Hazard Communication and Hot Work

Under 1910.252(c)(1)(iv), filler metals, fluxes, coatings, and coverings must be in the employer’s Hazard Communication program, with SDS access and training for handlers. Keep safety data sheets accessible: 29 CFR 1910.1200 governs that program, including container labels and SDS availability. Two labeling rules catch people out. 1910.252(c)(1)(v)(B) requires filler metal containers to carry the notice about adequate ventilation and ANSI Z49.1, and 1910.252(c)(1)(v)(C) requires brazing filler metals with cadmium in significant amounts to be labeled for cancer, lung and kidney effects, and acute toxicity.

Hot work needs a fire watch as well as a helmet. 29 CFR 1910.252(a)(1)(1) incorporates NFPA Standard 51B for fire prevention in cutting and welding, the reference behind standard fire watch practice: a trained watch with an extinguisher, checking nearby areas and decks for smoldering material after the work is finished.

A Practical Workflow: From Base Metal to a Qualified Weld

Everything so far collapses into one repeatable routine, and that routine keeps filler decisions from turning into coin flips. Most filler failures are not exotic metallurgy gone wrong. They come from a shortcut: an unidentified base metal, a rod pulled from an unlabeled bin, a procedure assumed rather than qualified.

The Seven-Step Decision Process

1. Identify every base metal and get the paperwork. Ask for the material test report or material specification. A magnet, a color and a guess are not a chemistry report.
2. Define the service environment. Corrosion, temperature, pressure, governing code and cleanliness. Sour service, food-grade stainless and galvanizing each change the answer.
3. Choose the classification, then the product. Pick ER308L over ER308, then select a rod that actually carries that classification with certification.
4. Pick the diameter and check access. The rod has to reach the joint. A 3/32 in rod that cannot enter the groove on a backup bar forces a bad compromise.
5. Set polarity, tungsten and gas. DCEN for most work, AC at 70 to 80 percent electrode-negative balance for aluminum, and a tungsten type and gas purity matched to the metal.
6. Qualify the procedure and the welder. A WPS proven by a PQR and a welder performance qualification make the choice defensible, and AWS offers qualification and certification programs to help you get there.
7. Control handling and traceability. Dry storage, clean rods, lot numbers on the job record, and SDS access kept current.

Five Worked Scenarios

Joint	Classification	Rod	Process notes
304L nozzle to 316L pipe	ER308L	3/32 in	DCEN, 99.99% argon, purged and vented
5052-H32 aluminum bracket	ER5356	3/32 in	AC at 70 to 80 percent EN, dedicated brush, dry rod storage
1/4 in A36 structural gusset	ER70S-2	1/8 in	D1.1 strength match met; WPS sets amperage, preheat, interpass
316L flange to A36 steel	ER309LMo	3/32 in	Over-alloyed deposit offsets dilution from carbon steel
4130 chromoly tube	ER70S-6	1/8 in	WPS governs, including any post-weld heat treatment

In the tank nozzle job, 304L matched to 316L stays inside the 308 family, so ER308L handles it cleanly, but the purge decides success: back-purge with argon, vent the far end, and confirm with a purge meter rather than by feel. OSHA’s welding standard at 29 CFR 1910.252(a)(3) expects used containers to be cleaned of flammable materials and greases and hollow spaces vented, with inert gas purging recommended. A stainless weld that looks perfect and then rusts from behind is a purge problem, not a rod problem.

Aluminum is the most demanding case here. 5052-H32 wants ER5356, an AC arc at 70 to 80 percent electrode-negative balance, and argon of very high purity, because hydrogen pickup drives porosity in aluminum GTAW. Cleaning matters as much as chemistry, so keep a dedicated stainless brush; our guide to prepping aluminum for welding covers the details worth building into a work instruction. Store the rod dry, sealed and at room temperature.

For the gusset, AWS D1.1 requires filler metal tensile strength to at least equal the base metal’s minimum specified tensile strength. A36 has a minimum of 58 ksi and ER70S-2 is nominally 70 ksi, so the match is satisfied. Welding 316L to A36 changes the answer: ER309LMo, because extra chromium and nickel offset dilution from carbon steel melting into the puddle. The 4130 chromoly tube runs ER70S-6 under a WPS that governs heat input and post-weld heat treatment; pair it with our alloy steel welding electrode selection guide.

Three Questions to Ask Any Supplier

• What is the exact classification? Get the full AWS designation, not just the family name.
• What are the certified mechanical properties for the diameter in my hand? Property tables are published per size, and the rod you receive should match the one in your hand.
• What certification and lot traceability come with the product? Look for AWS product certification, a manufacturer’s certificate of conformity, or EN 10204 3.1/3.2 certification with a heat or lot number you can record.

Those three answers separate a classified product from a spool of unidentified metal in a plastic bin, and they let you trace a weld back to a heat number months later. The all-position welding rod guide helps when you compare what is on the shelf against what the job actually needs.

Cost, Stocking and the Bottom Line

Filler metal is one of the smallest lines on a welding invoice. Labor, gas, power, fixturing and rework run the total, and a rejected weld adds a cut-out, a re-fit, a re-test and a scrapped part. Buying the correct rod the first time is the cheapest quality decision in the job.

On stocking, keep the diameters you actually consume, buy small quantities of the sizes that spoil, never mix lots without recording the change, and store every product properly. If you run high volume on aluminum or steel, compare TIG against our aluminum MIG welding guide to know when the faster process is right. Work the seven steps in order and the filler decision stops being a judgment call and starts being a documented one.

Key Takeaways and Where to Go Next

Filler material in TIG welding looks like a small decision: pick up a rod, feed it into the torch, strike an arc. But that rod’s chemistry ends up inside your weld, long after the machine is sold and the shop has moved on. Here is everything above, condensed so it can be printed and stuck on the wall.

Eleven things worth remembering

1. Filler is the weld, not an accessory. The tungsten electrode is non-consumable, so deposited metal comes only from the base metal plus the filler you feed. Whatever chemistry is on the rod goes into the bead.
2. Read the classification like a chemistry contract. ER means electrode or rod, solid and torch-usable. The two digits are nominal tensile in ksi (70 equals 70,000 psi, roughly 483 MPa); the family letter and dash number identify the type within the family.
3. Match filler strength to base metal. AWS D1.1 requires filler tensile strength to at least match the base metal’s minimum specified tensile strength, unless the code and the engineer’s procedure allow otherwise.
4. Dissimilar joints need over-alloyed fillers. Stainless to carbon steel gets ER309L, ER309LMo or ER312, whose extra chromium and nickel offset dilution and buffer the deposit against cracking.
5. Low carbon protects stainless. The “L” suffix means roughly 0.03% maximum carbon, limiting sensitization in grades like ER308L, ER309L and ER316L.
6. Aluminum follows its own map. ER4045 and ER5356 cover most work, ER5356 or ER5556 handle 5000-series marine, and 7000-series moves to ER7155 or ER7068, since ER4045 is hot-crack sensitive there.
7. Choose the smallest rod that still gives you control. 3/32 in for thin material and out-of-position work, 1/8 in for 3/16 to 1/2 in plate. A smaller rod melts faster, needs less heat and behaves far better vertically and overhead.
8. Keep the rod clean and dry. Moisture drives porosity in aluminum, and iron contamination on stainless rods causes rust and can compromise corrosion performance.
9. Rod diameter cannot rescue a bad setup. Electrode freezing, lack of fusion, undercut and crater cracks trace back to amperage, travel speed and technique far more often than to the rod’s brand.
10. A classification is not a procedure. The WPS and the qualified welder make the weld, not the label on the can.
11. Let the code make the final call. AWS D1.1/D1.1M:2025-AMD1, AWS D1.2/D1.2M:2026, AASHTO/AWS D1.5M/D1.5:2025 and AWS A3.0M/A3.0:2025 are the current editions for steel, aluminum, bridge work and inspection.

Choose your next step

For the hobbyist and small shop, start narrow and build outward: ER70S-2 in 3/32 in for mild steel, ER308L in 3/32 in for 304 and 316, ER5356 in 3/32 in for aluminum, paired with a high-purity argon regulator you trust. Learn those three, then add the odd alloy. Get aluminum surface preparation right first; our guide to prepping aluminum for welding covers that step in detail.

For the professional fabricator, build a filler matrix tied to the base metals your shop actually runs, qualify procedures properly, keep WPS, PQR and welder qualification records together, and treat the manufacturer’s data sheet and the current code edition as the source of truth. ESAB publishes solid TIG welding technical resources on rod selection, and our look at aerospace TIG welding standards and training shows how much documentation rides along with a critical weld.

Where to go from here depends on what you weld. Our all-position welding rod guide breaks down the common classifications, and if you are still choosing a process rather than a rod, why stick welding still holds up is worth reading alongside it.

Everything here comes back to one idea: filler material in TIG welding is a chemistry decision first and a technique decision second. Match the classification to the base metal and the service it must survive, pick the smallest rod that still gives you control of the puddle, keep it clean and dry, then let the qualified procedure and the current code make the final call. Pick the right rod and go make something good.

Frequently Asked Questions

What is the best filler rod for TIG welding mild steel?

ER70S-2 is the general-purpose workhorse for carbon steel, handling most fillet work, out-of-position welds and pipe root passes. ER70S-6 is the usual pick for higher-strength carbon steel and pipe because of its higher strength and silicon content. Whichever you choose, the filler’s tensile strength should meet or exceed the base metal’s minimum specified strength per AWS D1.1.

What size TIG rod should I use for a given plate thickness?

A good starting point is a rod diameter roughly equal to the joint thickness up to about 6 mm (1/4 in), stepping up for heavier sections. In practice, 3/32 in suits thin material and out-of-position work, 1/8 in handles 3/16 to 1/2 in plate, and 5/32 to 3/16 in for heavier joints. Always confirm against your WPS rather than the rule of thumb.

Is ER308L the right filler for both 304 and 316 stainless steel?

ER308L is the standard choice for 304 and 304L, while 316 and 316L take ER316L. If you need a single rod for both 304 and 316, ER309L is the usual answer because its higher chromium and nickel tolerate the mix and reduce cracking risk. For stainless-to-mild-steel joints, ER309LMo or ER312 is standard.

What is the difference between ER70S-2 and ER70S-6?

Both are carbon steel GTAW rods in the 70 ksi family, but ER70S-6 has higher strength and higher silicon and manganese content, which gives better mechanical properties and a more forgiving puddle. ER70S-2 is the easier all-round rod for out-of-position and fillet work. Note that the MIG wire of the same name is deliberately deoxidized, which is part of why it runs more smoothly than bare TIG rod.

Can I use MIG wire as TIG filler metal?

You can feed a cut length of solid MIG wire into a TIG puddle, but you give up the classified chemistry, certified mechanical properties and controlled diameter that a proper GTAW rod provides. On code work, use filler metal classified for the process under AWS A5.18 and named explicitly in the WPS.

Can you TIG weld aluminum, and which rod should I use?

Yes, with AC (or a DC machine with a cleaning pulse), a clean torch and properly dry filler. Use ER4045 for most aluminum, ER5356 or ER5556 for 5000 and 6000 series including marine work, and ER7155 or ER7068 for 7000 series. Keeping aluminum rod dry is critical, since moisture pickup is the leading cause of porosity.

Why does my TIG filler rod keep freezing or sticking to the puddle?

That usually means too much filler, too little current, or too long an arc. Try a smaller rod, dip the rod into the leading edge of the puddle and let it flow in rather than stirring, keep the arc short, and clean the rod before use. If the rod is touching the tungsten, stop immediately, because tungsten contamination wrecks the arc and the nozzle.

Do I need certified filler metal for code work?

Yes. Code work requires filler metal that matches the classification named in the WPS and that is traceable. AWS publishes product certification for A5.x filler metals, and manufacturers supply a certificate of conformity plus, where required, EN 10204 3.1 or 3.2 certification. Keep the lot and heat numbers with the job records.

Is it safe to TIG weld galvanized steel?

It can be, with the right controls. Grind the zinc coating back from the weld zone, use a clean bare rod such as ER70S-2 or ER70S-6, keep the amperage on the low side to limit zinc vapor, and make sure the shop has fume extraction in place. Zinc oxide fume causes metal fume fever, so ventilation is not optional here.

Can I TIG weld with no filler metal at all?

Yes, that is autogenous GTAW, where the base metal melts and no filler is added, and it is used for thin sheet, tube-to-tube and closure welds where the joint design allows it. For most structural and pressure-retaining joints, filler is required to meet the specified strength, corrosion resistance and finished section thickness.