ER4043 Aluminum TIG Filler: Properties, Applications & Diameter Chart

ER4043 is the most widely used aluminum TIG filler rod. Its 5% silicon content produces a fluid weld pool that flows easily, resists cracking, and tolerates a wide range of base alloy chemistries. If you’re TIG welding 6061, 6063, or any aluminum casting alloy, ER4043 is the default choice. It runs with pure argon shielding on AC at 60-250 amps depending on material thickness and rod diameter.

The wire is classified under AWS A5.10/A5.10M. Silicon acts as both a deoxidizer and a flow agent, lowering the melting point of the filler to around 1065-1170F (573-632C) compared to pure aluminum’s 1220F (660C). That lower melting range means the filler melts before the base metal gets dangerously hot, giving you a wider working window on heat-sensitive parts.

AWS A5.10 Classification

• E = Electrode
• R = Rod (TIG filler)
• 4043 = Alloy designation (Al-5Si)

The 4043 alloy number corresponds to the Aluminum Association’s 4xxx series (aluminum-silicon alloys). The “4” prefix identifies silicon as the major alloying element. Other common fillers in this family include ER4047 (12% silicon, used for brazing and high-dilution joints) and ER4145 (used for welding 2xxx-series alloys).

Chemical Composition

That 4.5-6.0% silicon range is the key to everything ER4043 does well. Silicon lowers the solidification temperature range, which reduces the time the weld metal spends in the partially solidified, crack-susceptible state. Narrow solidification ranges mean fewer solidification cracks, which is why ER4043 handles a broad range of base alloy chemistries without cracking.

Mechanical Properties

These numbers are lower than ER5356, which is one reason some engineers specify 5356 for structural applications. In an as-welded condition, ER4043 is softer and more ductile. For most non-structural and semi-structural work on 6061-T6, the joint is heat-affected zone (HAZ) limited anyway, not weld metal limited. The HAZ softens to roughly the same strength regardless of filler choice.

Base Metal Compatibility

ER4043 covers a wide range of aluminum alloys, which is its biggest advantage over ER5356.

Preferred base metals for ER4043:

• 6061 (most common structural alloy)
• 6063 (architectural extrusions, tubing)
• 6005, 6082, 6351 (structural extrusions)
• 3003, 3004 (sheet, cookware)
• A356, A357, 319, 413 (casting alloys)
• 1100, 1350 (commercially pure aluminum)

Not recommended for:

• 5083, 5086, 5456 (marine-grade, high-magnesium alloys; use ER5356 or ER5183)
• 5052 in structural or anodized applications (works but ER5356 is stronger and anodizes better)
• 7075 and other 7xxx-series alloys (generally not fusion-weldable)
• 2024, 2219 (use ER4145 or ER2319)

The casting alloys are where ER4043 really separates itself from ER5356. Aluminum castings typically contain 6-12% silicon already, and adding magnesium-rich filler (5356) to a silicon-rich base metal creates a brittle Mg2Si phase that cracks. ER4043’s silicon chemistry is compatible with casting alloys, making it the only safe choice for most cast aluminum repair.

Crack Resistance

ER4043’s wide freezing range and silicon content give it superior crack resistance compared to most other aluminum fillers. Solidification cracking in aluminum welds happens when the partially solidified weld metal is pulled apart by thermal contraction stresses. Silicon widens the eutectic trough in the Al-Si system, which keeps liquid available to heal incipient cracks during the final stages of solidification.

In practical terms, this means ER4043 forgives:

• Fit-up gaps that create high restraint
• Thick-to-thin transitions
• High-dilution joints where the base metal chemistry is uncertain
• Multi-pass welds on castings with variable composition

If you’re getting cracks with another filler, try ER4043 before changing your technique. The filler chemistry often fixes what amperage and travel speed adjustments can’t.

Diameter Selection

Aluminum TIG welding runs on AC (alternating current) for the cleaning action on the electrode-positive half cycle. This means your TIG machine needs AC output with adjustable balance control. Inverter machines with advanced AC waveform settings (adjustable frequency and balance) give the most control over puddle behavior and cleaning width.

Rod diameter for aluminum tends to run one size larger than you’d use on steel of the same thickness. Aluminum’s high thermal conductivity pulls heat away from the joint rapidly, so you need more filler volume and higher amperage to maintain the puddle. Don’t try to TIG aluminum with a rod so thin you can’t feed it fast enough.

The Anodizing Problem

ER4043’s biggest limitation is cosmetic. When a weldment is anodized (an electrochemical process that creates a hard, colored oxide layer), the silicon in the ER4043 deposit reacts differently than the base metal. The result is a dark gray or black weld zone that stands out visually against the lighter anodized base aluminum.

This color mismatch is purely cosmetic and doesn’t affect structural integrity or corrosion resistance. But it’s a deal-breaker for architectural, furniture, and consumer product applications where appearance matters.

Solutions:

• Switch to ER5356 if the base metal is compatible (5xxx or 6xxx series, not castings)
• Mechanical finishing before anodizing can minimize contrast but won’t eliminate it
• Paint or powder coat instead of anodizing eliminates the issue entirely
• Clear anodizing shows the most contrast; colored anodizing (especially darker colors) hides it somewhat

Shielding Gas and Setup

Gas: Pure argon, 99.99% purity minimum. Flow rate of 20-30 CFH for standard #6 or #7 cups. Using a gas lens allows lower flow rates (15-20 CFH) with better coverage.

Helium additions: For thick aluminum (over 1/4 inch), a 75% argon / 25% helium blend increases heat input without raising amperage. This is useful on heat sinks like thick castings and extrusions where pure argon can’t maintain the puddle. The trade-off is a less stable arc and higher gas cost.

Torch setup: Use a gas lens collet body for aluminum work. The laminar gas flow from a gas lens protects a wider area and allows you to extend the tungsten farther from the cup for better visibility in tight joints.

Tungsten selection: 2% lanthanated (blue) tungsten handles AC welding well and forms a clean balled tip. Size the tungsten to handle the amperage: 3/32" for up to 150A, 1/8" for up to 250A on AC.

Preheat and Technique

Aluminum’s thermal conductivity is roughly four times that of steel. On thick sections, the base metal wicks heat away faster than the arc can replace it, making it hard to establish and maintain the puddle.

Preheat guidelines:

• Under 1/8" thick: No preheat needed
• 1/8" to 1/4": Optional, 150-200F (65-93C) helps
• Over 1/4": Preheat to 200-300F (93-150C) recommended
• Castings: Always preheat, 300-400F (150-200C) for heavy castings

Caution on 6061-T6: Don’t exceed 350F (175C) preheat or you start over-aging the T6 temper in the base metal. The HAZ already loses T6 properties from welding heat; excessive preheat makes it worse.

Filler rod technique: Feed the rod at a shallow angle (15-20 degrees from horizontal) into the leading edge of the puddle. Don’t dip the rod into the center of the puddle, which cools it and creates discontinuities. Keep the rod tip within the argon envelope at all times to prevent oxidation.

Cleaning: Brush aluminum with a stainless steel wire brush dedicated to aluminum only (no carbon steel cross-contamination) immediately before welding. Aluminum oxide forms in minutes, so clean and weld without delay. Acetone or lacquer thinner removes oils and grease before brushing.

Storage

ER4043 TIG rod ships in sealed tubes or boxes of 36-inch cut lengths. Aluminum filler rod doesn’t rust, but it oxidizes. Heavy oxide buildup on the rod surface creates inclusions in the weld.

Store in a clean, dry location. Don’t let rods sit exposed to shop air for extended periods. If rods look dull gray or feel rough, they’ve picked up heavy oxide. Light surface oxide is normal and burns off in the arc. Wipe rods with acetone before use on critical applications.

Common Brands

ER4043 is widely stocked by all major welding supply companies:

• Lincoln Electric: SuperGlaze 4043
• ESAB: OK Autrod 4043
• Alcotec: ER4043 (Alcotec specializes in aluminum filler)
• Hobart: ER4043 (retail packaging)
• Blue Demon: ER4043

Price at time of writing runs $12-20 per pound for 36-inch cut lengths. Aluminum filler rod costs less per pound than stainless but more than carbon steel. Buy the largest pack size you’ll use within a year to get the best per-pound pricing.

For a comparison with the other primary aluminum filler, see the ER5356 aluminum TIG filler guide. For general filler rod selection across all base metals, check the TIG filler rod selection guide.