If you walk into any fabrication shop working with aluminum, you will find a box of ER4043. Often referred to simply as “43” or “AlSi5,” this filler metal is the industry workhorse for joining 6xxx series alloys (like the ubiquitous 6061) and various casting alloys.
ER4043 or AlSi5 (As per ISO 18273) is a Silicon-Aluminum base Solid TIG & MIG Aluminum Welding filler wire rod available in spool and straight rods. ER4043 is a versatile Aluminum filler wire electrode used for welding 1100, 3003, 6065, 6065, 6061, 6201 and many other aluminum grades.
Alloying with silicon provide high wetting during welding and reduce the weld cracking sensitivity. This makes ER4043 a good aluminum welding filler wire rod for General purpose welding applications.
What is ER4043? (The Metallurgy)
ER4043 is an aluminum filler alloy containing approximately 5% Silicon. This addition of silicon is not accidental—it significantly changes the behavior of the molten weld pool.
- Fluidity: Silicon reduces the surface tension of the liquid aluminum, making the puddle extremely fluid. It “wets out” into the toes of the weld easily, creating a smooth, flat bead profile with excellent fusion.
- Crack Resistance: Aluminum is notorious for “Hot Cracking” (solidification cracking). The 5% Silicon chemistry pushes the alloy close to the eutectic point, meaning it solidifies within a very narrow temperature range. This leaves little time for thermal stress to tear the grain structure apart as it cools, making ER4043 the most crack-resistant aluminum filler available.
ER4043 Welding Wire Specification-Classification
Before adding this to your WPS (Welding Procedure Specification), verify compliance with the following international standards:
| Standard | Classification |
| AWS A5.10 / ASME SFA 5.10 | ER4043 (Rod & Electrode) |
| ISO 18273 | Al 4043A (AlSi5) |
| UNS Number | A94043 |
| CWB / CSA W48 | ER4043 |
| AMS4190K | 5.2Si (4043) |
ER4043 TIG Welding and MIG Welding Filler wire rod specification is AWS A 5.10. ER4043 is the classification of this wire. The F-Number of ER4043 is 23.
ER4043 Welding Wire Chemical & Mechanical Properties
ER4043 (as per AWS A5.10/ ASME Section IIC-SFA 5.10) or AlSi5 (As per ISO 18273) chemical compositions are mainly Silicon (4.5- 6%), Iron (0.8%) and other alloying elements as minor alloying elements are given in the below table.
| Silicon (Si%) – 4.5% – 6% | Magnesium (Mg%) – 0.05% |
| Iron (Fe%) – 0.80% | Zirconium (Zn%) – 0.10% |
| Copper (Cu%) – 0.30% | Titanium (Ti%) – 0.20% max |
| Manganese (Mn%) – 0.05% | Aluminum (Al%) – Balance |
| Beryllium (Be%) – 0.0003% | Other elements – 0.05 each to 0.15 in total |
Note: There are no mechanical properties (Tensile strength, Yield strength & Elongation and Toughness) required for ER4043 as per AWS A5.10.
Typical mechanical properties offered by welding consumables manufacturers for ER4043 TIG-MIG Filler wire are given in the below table for reference purposes only.
The reason for not specifying the mechanical properties for ER4043 is because of changes in strength due to different welding processes and heat input.
| Tensile Strength | 21- 33 Ksi (145- 228 MPa) |
| Yield Strength | 10- 27.5 Ksi (70- 190 MPa) |
| Elongation | 5 to 12% |
ER4043 gives a minimum tensile strength of 14 ksi (95 MPa) and fair weld metal ductility.
The Great Debate: ER4043 vs. ER5356
The most common question in aluminum welding is: “Should I use 4043 or 5356?”
Here is the definitive breakdown:
| Feature | ER4043 (Al-Si) | ER5356 (Al-Mg) |
| Fluidity & Wetting | Excellent. Flows like water. | Good. Stiffer puddle, more “sluggish.” |
| Crack Sensitivity | Low. Best for constrained joints. | Higher. More prone to crater cracks. |
| Weld Smut | Low. Very clean, shiny bead. | High. Leaves black soot (Magnesium Oxide). |
| Anodizing Color | Poor. Turns dark Grey/Black. | Excellent. Matches base metal silver. |
| Shear Strength | Lower. | Higher (Almost 2x stronger). |
| Ductility | Lower. | Higher (Better for forming). |
| Service Temp | Safe above 65°C (150°F). | Unsafe above 65°C (Stress Corrosion Cracking). |
The Verdict: Use ER4043 for general fabrication, brackets, frames, and castings where aesthetics (smoothness) and ease of welding are priority. Use ER5356 if the part will be anodized silver or requires higher structural shear strength.
ER4043 Melting Point
Melting point of ER4043 wire is 1065°F – 1170°F. ER4043 has a lower melting point and higher fluidity compared to ER5356 welding wire.
Due to lower melting point and resultant higher molten pool fluidity, ER4043 is also used for aluminum brazing applications.
What does ER4043 stand for?
ER4043 is a TIG & MIG Aluminum Welding solid filler wire having low melting point and higher weld pool fluidity compared to ER5356 filler wire.
ER4043 has lower weld cracking sensitivity for 6XXX aluminum grades making it a better option for welding compared to ER5356 Filler wire. ER4043 weldments can be used for service temperatures up to 65°C (150°F).
The main chemical composition of ER4043 is silicon with other minor alloying elements listed above.
What is ER4043 welding Filler Wire Rod used for?
ER4043 welding filler wire rod is a Si-Al based alloy that is commonly used to weld automotive parts, trailers, and structures made from wrought/ extruded aluminum or Cast Aluminum.
It can also be used to weld bicycle frames. The alloy has good resistance to corrosion and cracking, making it a popular choice for these applications.
ER4043 Welding Positions & Polarity
ER4043 can be used in all position welding using TIG & MIG welding. in TIG welding usually AC with HF current is used. in MIG, DCEP Welding polarity is used for ER4043 welding wire.
ER4043 TIG & MIG Welding Shielding Gas
Pure Argon (100%) is used when performing TIG and MIG Welding with ER4043 Aluminum welding filler wire electrode.
Argon being an inert gas, provides clean welds with good weld penetration. Aluminum is having a high thermal conductivity and hence use of argon gives deep weld penetration.
ER4043 TIG-MIG Welding Parameters
The most important parameter for ER4043 in TIG or GTAW is the current & Voltage. The current affects the size and shape of the weld pool.
It also affects the heat input and penetration into the metal. Too much current can cause excessive heat input and melting of the base metal.
It can also cause excessive spatter and poor weld quality. Too little current will produce a weak weld that may not be able to withstand stress.
Recommended TIG (GTAW) and MIG (GMAW) welding parameters for ER4043 welding filler wire are given in the below table. Pure argon (100%) is used as a welding shielding gas when welding with ER4043.
What is the difference between ER4043 and ER5356?
ER4043 and ER5356 are aluminum welding wires that have different properties. ER4043 is a Silicon-Aluminum base wire while ER5356 is Magnesium-Aluminum base wire.
ER4043 has a low melting point but higher molten pool fluidity compared to ER5356 wire.
ER5356 welding wire is suitable for anodizing after welding however ER4043 does not suit after weld anodizing weld applications.
ER5356 is a magnesium-containing wire that has a higher weldability, higher welding strength and better ductility. It is best used for welding thicker sheets of aluminum.
🏗️ Typical Applications
1. Automotive Components
Because ER4043 is less sensitive to cracking, it is the standard for welding cast aluminum manifolds, oil pans, and transmission housings (which are often A356 or 356.0 alloys).
2. 6061-T6 Fabrication
This is the most common structural aluminum. While ER5356 is stronger, ER4043 is often preferred for 6061 pipe and tube welding because the heat of welding reduces the strength of the 6061 HAZ (Heat Affected Zone) anyway, negating the strength advantage of the 5356 filler in many designs.
3. Repair Work
For general repairs where the base metal alloy is unknown, ER4043 is the safer bet. Its high fluidity helps bridge gaps and its crack resistance handles the stress of rigid, dirty parts better than magnesium-based fillers.
⚠️ Critical Limitations (When NOT to use ER4043)
- The “Anodizing” Trap: If you weld a beautiful architectural railing with ER4043 and send it for clear anodizing, the silicon in the weld will turn charcoal black. The weld will stand out like a sore thumb.
- High-Magnesium Parent Metals: Do not use ER4043 to weld 5xxx series alloys with high magnesium (like 5083 or 5086). The Silicon from the rod will react with the Magnesium in the plate to form Magnesium Silicide (Mg2Si), which creates a brittle microstructure prone to failure.
📊 Mechanical Properties (Typical As-Welded)
- Tensile Strength: 186 MPa (27,000 psi)
- Yield Strength: 124 MPa (18,000 psi)
- Elongation: 8% (Relatively low ductility)
- Melting Range: 573°C – 632°C
💡 NDT & Inspection Tips for ER4043
As an inspector, here is what you should look for when examining ER4043 welds:
- Lack of Fusion (LOF): Because 4043 flows so smoothly, it can sometimes “wash” over the cold base metal without actually penetrating. This is called “cold lap.” Ensure the welder is using sufficient amperage.
- Porosity: Aluminum is a hydrogen sponge. ER4043 is slightly less prone to visible porosity than 5356, but surface cleaning (removing the oxide layer with a stainless steel brush) is still mandatory.
- Crater Cracks: While resistant to general cracking, the “crater” (end of the weld) is still vulnerable. Check for “star cracks” at the termination points.
