4008 Aerospace Aluminium Welding Wire
4008 is an aluminium-silicon-magnesium filler wire with the composition of the casting alloy A356, made to SAE AMS 4181. It is used to weld and repair aerospace castings in A356, A357 and similar alloys where the weld must respond to the same solution treatment and ageing as the casting. Metline supplies 4008 MIG wire and TIG rod with lot certificates, worldwide.
- Alloy
- 4008 (Al-7Si-0.38Mg-Ti)
- Aerospace spec
- AMS 4181
- Base metals
- A356, A357, 356 castings
- Forms
- MIG spools, TIG rod
What 4008 wire is for
AMS 4181 describes 4008 as 7.0Si-0.38Mg-0.10Ti welding wire. In plain terms it is A356 casting alloy drawn into wire, with iron held very low.
Aerospace castings in A356 and A357 (gearbox and accessory housings, pump and valve bodies, brackets, duct elbows and missile structures) are often welded during manufacture to repair casting defects, or welded into assemblies. Those castings are then solution heat-treated and aged to T6 or T61. If the weld metal has a different composition, it will not harden the same way, and the weld becomes the weak point.
4008 solves that by matching the casting. Its magnesium content forms Mg2Si on ageing, so a weld made with 4008 and then heat-treated with the casting reaches strength, ductility and corrosion behaviour close to the parent metal. The very low iron limit (0.09 % maximum) keeps brittle iron-rich particles out of the weld, which matters for fatigue-loaded aerospace parts.
4008 chemical composition (wt %)
| Element | Limit | Purpose |
|---|---|---|
| Silicon (Si) | 6.5 – 7.5 | Fluidity and low shrinkage; matches A356 |
| Magnesium (Mg) | 0.30 – 0.45 | Forms Mg2Si for age-hardening response |
| Titanium (Ti) | 0.04 – 0.15 | Grain refinement of the weld bead |
| Iron (Fe) | 0.09 max | Kept very low for ductility and fatigue strength |
| Copper (Cu) | 0.05 max | Impurity |
| Manganese (Mn) | 0.05 max | Impurity |
| Zinc (Zn) | 0.05 max | Impurity |
| Beryllium (Be) | 0.0003 max | Limited in all welding fillers for health reasons |
| Others, each / total | 0.05 / 0.15 | |
| Aluminium (Al) | Remainder |
Limits as registered with the Aluminum Association for 4008 filler. AMS 4181 is the controlling document for aerospace orders; confirm against the revision on your purchase order (AMS 4181D is current at the time of writing).
Physical properties and weld performance
Physical properties (typical)
- Density
- about 2.68 g/cm³
- Melting range
- about 555 – 615 °C
- Heat-treatable
- Yes, by solution treatment and ageing with the casting
- Weld colour after anodising
- Grey, as with other Al-Si fillers
Mechanical properties of a 4008 weld depend on what happens after welding. As welded, the deposit behaves like an unaged Al-Si-Mg casting: moderate strength and good ductility. After full solution treatment and artificial ageing with an A356 casting, the weld approaches the casting's own T6 properties. For that reason, aerospace repair procedures qualify the complete sequence (preparation, welding, heat treatment and inspection) rather than quoting a fixed wire strength.
The wire itself is not a structural product, so tensile figures for the drawn wire are of little use to the welder. What matters is chemistry, cleanliness and diameter control, which is what AMS 4181 governs.
Specifications and classifications
| Document | Covers | Comment |
|---|---|---|
| SAE AMS 4181 | 4008 welding wire, 7.0Si-0.38Mg-0.10Ti | Aerospace purchasing specification |
| UNS A94008 | Alloy identity | Used on certificates and drawings |
| AWS A5.10 | Aluminium welding wires and rods | Classifies Al-Si-Mg casting-composition fillers; check which class your procedure names |
| ISO 18273 | International filler classification | Use when the procedure is written to ISO |
| AWS D17.1 / customer repair specs | Fusion welding for aerospace applications | Procedure and welder qualification |
Some older product listings link 4008 wire to MIL-DTL-27500 and EN 3475. Those are electrical cable documents and have nothing to do with welding filler. Order 4008 to AMS 4181 or the filler document named in your qualified welding procedure.
Sizes and packing
4008 wire supply range
- MIG (GMAW) wire
- Layer-wound spools, typically 0.8, 1.0, 1.2 and 1.6 mm diameter; 100, 200 and 300 mm spools and larger drums
- TIG (GTAW) rod
- Straight cut lengths, typically 1.6, 2.0, 2.4, 3.2, 4.0 and 5.0 mm diameter, about 914 or 1000 mm long
- Condition
- Hard-drawn (H18 / H19-type) for feeding; softer tempers for other wire uses on request
- Surface
- Shaved or cleaned, free of drawing lubricant, oxide and moisture
- Packing
- Sealed bags or cans with desiccant, cartons on pallets; tube packs for TIG rod
- Documents
- EN 10204 3.1 certificate or certificate of conformity with chemical analysis per lot
Diameter tolerance, cast and helix of spooled wire follow AWS A5.10 or the AMS document named on the order.
Welding A356 and A357 castings with 4008
- Locate and remove the defectGrind or machine out porosity, shrinkage or cracks to sound metal, with a smooth, open groove. Confirm removal with dye penetrant.
- CleanDegrease, then brush with stainless steel. Castings that have absorbed oil or fluids in service may need baking out first.
- Preheat if requiredThick castings are often preheated moderately to reduce cracking and porosity; follow the qualified procedure, as excessive preheat can affect the temper.
- WeldTIG with AC is usual for repair; MIG for production joints. Keep heat input controlled and fill craters to avoid crater cracks.
- Heat-treatSolution treat and age the casting with the weld (for example to T6) where the procedure requires matching properties.
- InspectRadiography and penetrant inspection to the casting acceptance standard on the drawing.
- Storage: keep wire sealed in its original packing in a dry, heated store; aluminium oxide hydrates and causes weld porosity
- Open spools: return part-used spools to a sealed bag with desiccant, or to a wire cabinet
- Cleaning base metal: degrease, then remove the oxide with a dedicated stainless-steel brush shortly before welding
- Feeding: use U-groove drive rolls, a PTFE or nylon liner and contact tips sized for aluminium
- Traceability: record the lot number from the label on the weld record, so the certificate links to the joint
Where 4008 wire is used
- Casting repair: weld repair of foundry defects in A356 and A357 aerospace castings before heat treatment
- Housings: gearbox, accessory-drive and pump housings
- Fluid components: valve bodies, manifolds and duct elbows cast in A356
- Assemblies: joining A356 castings to each other, or to 6061 wrought parts, when the assembly is heat-treated afterwards
- Ground and defence equipment: cast structures and housings in Al-Si-Mg alloys
4008 is not a general-purpose filler for welding aircraft fuselages or wings; riveted 2xxx and 7xxx primary structure is not fusion welded. For wrought 6xxx assemblies that are heat-treated after welding, 4643 is normally the better choice, and for as-welded general work 4043.
4008 compared with 4043, 4643 and 4047
| Filler | Si % | Mg % | Heat-treat response | Typical use |
|---|---|---|---|---|
| 4008 | 6.5 – 7.5 | 0.30 – 0.45 | Yes, matches A356 | A356 / A357 castings, post-weld heat-treated |
| 4043 | 4.5 – 6.0 | 0.05 max | Little | General 6xxx, 3xxx and casting welds, as welded |
| 4643 | 3.6 – 4.6 | 0.10 – 0.30 | Yes | 6xxx wrought assemblies, post-weld heat-treated |
| 4047 | 11.0 – 13.0 | 0.10 max | Little | Low-shrinkage welds, brazing |
How to order 4008 wire
- SpecifyAlloy and temper, diameter, MIG spool size or TIG rod length, quantity and the governing specification with its revision (AMS 4181 or the filler named in your welding procedure).
- ConfirmWe confirm the specification can be met, the tolerance class, test requirements and delivery terms (EXW, FOB, CIF or DAP).
- InspectMaterial is checked for dimensions and surface condition; any extra tests named on the order are carried out or arranged.
- DocumentEach lot ships with a mill test certificate to EN 10204 3.1 showing chemistry and mechanical results, traceable to the cast or lot number.
- Pack and shipExport packing in sealed, moisture-protected cases or on pallets, shipped by sea or air to your port or door.
References and standards
- SAE AMS 4181 – Aluminum Alloy, Welding Wire, 7.0Si-0.38Mg-0.10Ti (4008)
- AWS A5.10/A5.10M – Welding Consumables: Wires and Rods for Aluminum and Aluminum-Alloys, Classification
- AWS D17.1 – Specification for Fusion Welding for Aerospace Applications
- The Aluminum Association – International Alloy Designations and Chemical Composition Limits (Teal Sheets)
- ASM Handbook, Vol. 2 – Properties and Selection: Nonferrous Alloys and Special-Purpose Materials
4008 aerospace aluminium (aluminum) welding wire: questions
What is 4008 welding wire used for?
Welding and repairing A356, A357 and 356-type castings, especially when the casting is solution heat-treated and aged after welding so the weld must harden like the parent metal.
What specification covers 4008 wire?
SAE AMS 4181, titled Aluminum Alloy, Welding Wire, 7.0Si-0.38Mg-0.10Ti (4008). The UNS number is A94008.
Why is the iron limit in 4008 so low?
Iron forms brittle needle-shaped intermetallics in Al-Si alloys. Holding it to 0.09 % maximum keeps weld ductility and fatigue strength close to premium-quality castings.
Can I use 4043 instead of 4008 on A356 castings?
4043 welds A356 well as welded, but it contains almost no magnesium, so the weld will not reach T6-level strength after heat treatment. Where matching properties are required, use 4008.
What sizes of 4008 wire are available?
MIG wire typically 0.8 – 1.6 mm on spools, and TIG rod typically 1.6 – 5.0 mm in straight lengths. Other diameters can be quoted on request.
Do you ship 4008 wire internationally?
Yes. Metline supplies 4008 wire worldwide from Mumbai with lot certificates and sealed, moisture-protected packing.
Need 4008 filler for casting repair?
Send diameter, form, quantity and the AMS 4181 revision. We will confirm availability and documentation.
