Picking the wrong aluminum filler creates cracks, corrosion, or ugly welds. The right filler depends on four factors: the base alloy series, the required joint strength, the service environment (especially saltwater), and whether the part will be anodized. This chart covers every common base alloy combination with the recommended filler and the reasoning behind each selection.
The two fillers you’ll use 90% of the time are ER4043 (Al-5Si) and ER5356 (Al-5Mg). Understanding when to pick each one solves most filler selection problems.
Quick Decision: ER4043 vs ER5356
Before looking up the chart, run through this checklist:
- Saltwater or chemical exposure? ER5356 (magnesium content matches 5xxx base alloys, no galvanic mismatch).
- Anodized finish required? ER5356 (ER4043 turns dark gray/black).
- High restraint or crack-sensitive joint? ER4043 (silicon improves fluidity and reduces crack sensitivity).
- Welding 5xxx-series base metal? ER5356 or ER5183 only.
- Welding 6xxx-series for general fabrication? Either works; ER4043 is easier.
- Post-weld heat treatment planned? ER4043 (responds well to aging cycle).
- Casting alloy (3xx.x)? ER4043 or ER4047 (silicon content matches castings).
Master Filler Selection Chart
This chart lists the primary recommended filler for each base alloy when welded to itself. For dissimilar aluminum-to-aluminum joints, use the filler recommended for the more crack-sensitive alloy.
| Base Alloy | Series | Primary Filler | Alternate Filler | Notes |
|---|---|---|---|---|
| 1100 | 1xxx (pure Al) | ER1100 | ER4043 | ER1100 for best color match; ER4043 for easier welding |
| 1350 | 1xxx (EC grade) | ER1100 | ER4043 | Electrical conductor alloy; ER1100 maintains conductivity |
| 2024 | 2xxx (Al-Cu) | Not recommended | -- | Extremely crack-sensitive; mechanical fastening preferred |
| 2219 | 2xxx (Al-Cu) | ER2319 | ER4043 | Only 2xxx alloy that welds reliably; aerospace use |
| 3003 | 3xxx (Al-Mn) | ER4043 | ER5356 | ER4043 standard; ER5356 if higher strength needed |
| 3004 | 3xxx (Al-Mn) | ER5356 | ER4043 | Higher Mg content favors ER5356 match |
| 5005 | 5xxx (Al-Mg) | ER5356 | ER4043 | Low-Mg alloy; either filler works for non-marine use |
| 5052 | 5xxx (Al-Mg) | ER5356 | ER5554 | Do not use ER4043 in marine environments |
| 5083 | 5xxx (Al-Mg) | ER5356 | ER5183 | ER5183 for heavier plate; ER4043 prohibited |
| 5086 | 5xxx (Al-Mg) | ER5356 | ER5183 | Same rules as 5083; marine structural alloy |
| 5454 | 5xxx (Al-Mg) | ER5554 | ER5356 | Elevated temp service (pressure vessels, tanks) |
| 5456 | 5xxx (Al-Mg) | ER5556 | ER5356 | Highest-strength 5xxx; use ER5556 for strength match |
| 6005 | 6xxx (Al-Mg-Si) | ER4043 | ER5356 | Extrusion alloy; ER4043 resists cracking |
| 6061 | 6xxx (Al-Mg-Si) | ER4043 | ER5356 | ER4043 default; ER5356 for anodize or marine use |
| 6063 | 6xxx (Al-Mg-Si) | ER4043 | ER5356 | Architectural extrusion; ER4043 for clean bead appearance |
| 6082 | 6xxx (Al-Mg-Si) | ER4043 | ER5356 | European structural alloy, same rules as 6061 |
| 7003 | 7xxx (Al-Zn) | ER5356 | ER5183 | Weldable 7xxx alloy; bike frames, recreational equipment |
| 7005 | 7xxx (Al-Zn) | ER5356 | ER5183 | Weldable; naturally ages after welding (recovers some strength) |
| 7039 | 7xxx (Al-Zn) | ER5183 | ER5356 | Military armor alloy; ER5183 preferred for strength |
| 7075 | 7xxx (Al-Zn-Cu) | Not recommended | -- | Fusion welding produces severe cracking; use FSW or rivets |
| A356/A357 | Casting (Al-Si) | ER4043 | ER4047 | Silicon casting alloys; 4xxx fillers match chemistry |
| 535 (Almag 35) | Casting (Al-Mg) | ER5356 | ER5183 | Magnesium casting alloy; must match with 5xxx filler |
Selection Criteria Explained
Crack Sensitivity
Hot cracking is the most common weld defect in aluminum, and filler selection is your primary defense. Aluminum alloys are most crack-sensitive when the total alloy content falls in the “crack-sensitive range” for each alloying system.
For the Al-Si system, crack sensitivity peaks around 1-1.5% silicon and drops at higher levels. That’s why ER4043 (5% Si) is resistant to cracking, while a weld deposit diluted to only 1% Si from a lean base alloy might crack. The high silicon content of ER4043 moves the deposit well past the crack-sensitive zone.
For the Al-Mg system, crack sensitivity peaks around 1.5-2.5% magnesium. ER5356 (5% Mg) pushes the deposit past this range. Trouble comes when dilution brings the effective magnesium level back down into the critical zone.
Strength
As-welded joint strength depends on both the filler and the base alloy’s HAZ response. The filler contribution:
| Filler | As-Welded Tensile (ksi) | Shear Strength (ksi) |
|---|---|---|
| ER1100 | 11-13 | 7.5 |
| ER4043 | 24 | 15 |
| ER4047 | 23 | 14.5 |
| ER5183 | 40-43 | 25 |
| ER5356 | 38-40 | 24 |
| ER5554 | 31-33 | 20 |
| ER5556 | 42 | 26 |
ER5356 and ER5183 produce significantly stronger deposits than ER4043. For structural applications governed by AWS D1.2, the design values are based on the weaker of the filler deposit or the HAZ, so the filler strength only matters if it’s the limiting factor.
Corrosion Resistance
The critical rule: match filler chemistry to the base alloy family for corrosive environments. Silicon-based fillers (4043, 4047) are electrochemically different from magnesium-based alloys (5052, 5083, 5086). In saltwater, the galvanic mismatch between an ER4043 weld and a 5083 base metal causes accelerated corrosion at the fusion line.
For non-corrosive environments (indoor structural, dry applications), this mismatch doesn’t matter, and ER4043 can be used on 5xxx alloys if crack resistance is the priority.
Color Match After Anodizing
Anodizing reveals the filler chemistry. ER4043’s high silicon content produces a dark gray or near-black weld line on anodized parts, which is unacceptable for architectural and decorative applications. ER5356 anodizes to a lighter shade that blends with 5xxx and 6xxx base alloys.
If anodized appearance matters, always use ER5356 or ER5183 filler regardless of the base alloy.
Dissimilar Aluminum-to-Aluminum Joints
When joining two different aluminum alloys, use the chart below. Find both base alloys and select the filler at the intersection. The general rule: pick the filler that’s compatible with both alloys and avoids the crack-sensitive range for either.
| Base A / Base B | 1100 | 3003 | 5052 | 5083 | 6061 | 6063 |
|---|---|---|---|---|---|---|
| 1100 | ER1100/4043 | ER4043 | ER4043* | ER5356 | ER4043 | ER4043 |
| 3003 | -- | ER4043 | ER5356 | ER5356 | ER4043 | ER4043 |
| 5052 | -- | -- | ER5356 | ER5356 | ER5356* | ER5356* |
| 5083 | -- | -- | -- | ER5356/5183 | ER5356 | ER5356 |
| 6061 | -- | -- | -- | -- | ER4043/5356 | ER4043 |
| 6063 | -- | -- | -- | -- | -- | ER4043/5356 |
*Asterisk indicates ER4043 acceptable for non-corrosive environments only; use ER5356 for marine or chemical service.
Specialty Fillers
Beyond ER4043 and ER5356, a few specialty fillers handle specific situations:
ER4047 (Al-12Si): Higher silicon content than ER4043. Used for brazing-temperature applications and repair of high-silicon casting alloys (A356, 319). Extremely fluid puddle, excellent for filling gaps on castings. Not suitable for structural code work.
ER2319 (Al-6Cu): The only filler for 2219 aluminum. Used in aerospace and cryogenic applications (liquid oxygen tanks). Responds to post-weld heat treatment. Not compatible with 5xxx alloys.
ER5554 (Al-2.7Mg-0.8Mn): Specifically designed for 5454 base alloy in elevated-temperature service. ASME pressure vessel code limits magnesium content above 150F service temperature, and ER5554 meets this requirement while ER5356 does not.
ER5556 (Al-5Mg-0.8Mn-0.1Cr): High-strength filler for 5456 base alloy. Produces the strongest as-welded deposit of any standard aluminum filler. Reserved for heavy structural marine applications.
Common Filler Selection Mistakes
Using no filler (autogenous welding) on 6xxx alloys. Without added filler, the weld deposit composition equals the base metal, which falls squarely in the crack-sensitive range for the Al-Mg-Si system. Autogenous TIG welds on 6061 crack almost every time. Always add filler.
ER4043 on 5xxx marine alloys. The silicon in ER4043 creates a galvanic mismatch with the magnesium-rich 5083 or 5086 base metal. In saltwater, the weld line corrodes preferentially. Use ER5356 or ER5183 on any 5xxx alloy that sees moisture, chemicals, or marine exposure.
Buying unbranded bargain filler. Aluminum filler chemistry must be tightly controlled. Off-spec wire with slightly high iron, silicon, or copper causes porosity, cracking, and corrosion failures that don’t show up until the part is in service. Buy from reputable manufacturers (Lincoln, Hobart, Alcotec, ESAB) and check the mill test report for each lot.
One filler for everything. Shops that stock only ER4043 eventually hit a 5xxx base alloy job where it’s wrong. Shops that stock only ER5356 fight cracking on highly restrained 6061 joints. Keep both fillers in stock and train your welders on when to switch.
Wrong filler diameter. Oversized filler rod on thin aluminum creates cold puddles and lack of fusion. Undersized filler on thick sections requires excessive dipping frequency and slow travel speeds. Match filler diameter to the material thickness and amperage per the process tables.
Storage and Handling
Aluminum filler metal absorbs moisture, which causes porosity. Store rods and wire in sealed containers. Once opened, use within a few days in humid environments or store in a rod oven at 120-150F. Don’t handle filler rod with oily gloves or set it on the shop floor.
Spooled MIG wire picks up contamination from the feeder. Replace contact tips regularly (they wear fast on aluminum) and use U-groove or V-knurled drive rolls with light tension to avoid shaving the wire. Teflon or nylon liners in the MIG cable are required for aluminum wire; standard steel spring liners shave the soft wire and create feeding problems.
When switching between ER4043 and ER5356 on a spool gun, change the contact tip. A tip worn to 4043’s diameter won’t feed 5356 cleanly, and vice versa. Mark each contact tip for the wire size and alloy it’s dedicated to.
For alloy-specific welding procedures, see the detailed guides on 6061-T6 aluminum and 5083 marine aluminum. For defect prevention across all alloys, read the aluminum crack prevention guide.
Back to the main aluminum welding guide.