O (annealed)
Soft condition for cold heading, coiling and forming. Parts are solution treated and aged after forming.
Aerospace · GB high-strength wire
7A04 and 7B04 Aerospace Aluminium Wire
7A04 (formerly LC4) and its high-purity variant 7B04 are high-strength Al-Zn-Mg-Cu alloys from the Chinese GB system, close in performance to 7075. As wire they are used for pins, fasteners and cold-headed parts in aircraft and defence equipment. Metline supplies 7A04 and 7B04 wire in O and T6 to GB/T 3190 chemistry, and can cross-reference orders to 7075 under ASTM or AMS specifications for customers worldwide.
- Alloys
- 7A04 (LC4), 7B04
- Tempers
- O, T6 (W for heading)
- Diameter
- About 1 – 12 mm
- Standard
- GB/T 3190 chemistry
What 7A04 and 7B04 wire are
7A04 is the long-established Chinese high-strength aluminium alloy, known for decades as LC4. It belongs to the same Al-Zn-Mg-Cu family as 7075 and reaches similar T6 strength. 7B04 keeps the same main alloying ranges but limits iron and silicon tightly, which improves toughness and fatigue behaviour, in the same way that 7475 improves on 7075.
Wire is drawn from extruded rod in several passes with intermediate anneals, and finished in the annealed O condition or heat-treated to T6. Typical products are rivets and pins, screws, cold-headed blanks, and small machined parts for aircraft, helicopters, missiles and precision equipment. Buyers outside China usually meet these grades on drawings for equipment designed to GB or GJB standards, or when sourcing a 7075-class wire against an existing Chinese specification.
Because the grades are not identical to 7075, a direct substitution should be checked against the drawing. Where a Western specification is required, Metline can supply 7075 wire to AMS 4122, AMS 4124 or ASTM B211 instead.
| Grade | Former Chinese name | Nearest international grade | Comment |
|---|---|---|---|
| 7A04 | LC4 | 7075 (close, not identical) | Higher Mn, wider Zn range; related to the Russian V95 family |
| 7B04 | — | 7475 concept (high purity) | Low Fe and Si for toughness, mainly sheet, plate and wire |
| 7A09 | LC9 | 7075 | Chemistry overlaps 7075 almost completely |
| 7A03 | LC3 | 7050-type rivet use | Rivet wire alloy |
7A04 and 7B04 chemical composition (wt %)
| Element | 7A04 min | 7A04 max | Role |
|---|---|---|---|
| Silicon (Si) | — | 0.50 | Impurity |
| Iron (Fe) | — | 0.50 | Impurity |
| Copper (Cu) | 1.4 | 2.0 | Strength and SCC resistance |
| Manganese (Mn) | 0.20 | 0.60 | Higher than 7075; grain control and strength |
| Magnesium (Mg) | 1.8 | 2.8 | Forms MgZn2 with zinc |
| Chromium (Cr) | 0.10 | 0.25 | Grain control |
| Zinc (Zn) | 5.0 | 7.0 | Main strengthening element |
| Titanium (Ti) | — | 0.10 | Grain refiner |
| Others, each / total | — | 0.05 / 0.10 | |
| Aluminium (Al) | Remainder |
7B04 shares the copper, manganese, magnesium and chromium ranges of 7A04 but with zinc at about 5.0 – 6.5 %, silicon at most 0.10 % and iron at about 0.05 – 0.25 %. The low silicon and iron are what give 7B04 its higher toughness.
Limits as published in GB/T 3190. Check the current revision named on your order; minor limits for impurities can differ between editions.
Some sales sheets show 7A04 with only 0.1 – 0.4 % copper and no manganese. That does not match the GB grade; check the certificate for copper of 1.4 – 2.0 % and manganese of 0.20 – 0.60 %.
Mechanical and physical properties
GB product standards set minimum properties by product form, temper and size. The approximate values below are typical for drawn wire and rod and are given for comparison with 7075; always design to the minimums stated in the governing standard or on the certificate.
| Condition (approx.) | Tensile strength | Yield strength | Elongation |
|---|---|---|---|
| 7A04 / 7B04-O | About 250 MPa maximum | About 140 MPa maximum | Over 10 % |
| 7A04-T6 | About 530 – 580 MPa | About 420 – 500 MPa | About 6 – 10 % |
| 7B04-T6 | About 520 – 570 MPa | About 420 – 490 MPa | About 8 – 12 % |
| 7075-T6 (typical, comparison) | 572 MPa | 503 MPa | 11 % |
Physical properties (7A04)
- Density
- About 2.80 – 2.85 g/cm³ (handbook values)
- Modulus of elasticity
- About 70 – 72 GPa
- Electrical conductivity
- About 30 – 33 % IACS in T6
- Melting range
- About 475 – 640 °C
Tempers: O, T6 and the "T4" question
T6
Solution treated and artificially aged for peak strength. Used for pins, screws and machined wire parts.
W / "T4"
Freshly quenched wire is soft enough to head for a short time. 7xxx alloys keep ageing at room temperature, so a stable T4 does not exist; orders that say T4 should be clarified.
Over-aged tempers
Where stress-corrosion resistance is critical, over-aged conditions (similar to T73) can be specified for 7B04 or replaced by 7075-T73 wire.
Wire sizes and weights
Supply range
- Diameter
- About 1 – 12 mm; larger sizes as drawn or extruded rod
- Form
- Coils, spools or straight lengths
- Surface
- Bright drawn; cleaned for heading
- Tolerance
- Per GB/T or ASTM B211 tables, or tighter per drawing
| Diameter (mm) | kg per metre (2.85 g/cm³) | metres per kg |
|---|---|---|
| 1 | 0.0022 | 447 |
| 1.6 | 0.0057 | 175 |
| 2 | 0.0090 | 112 |
| 2.5 | 0.0140 | 71 |
| 3 | 0.0201 | 50 |
| 3.5 | 0.0274 | 36 |
| 4 | 0.0358 | 28 |
| 5 | 0.0560 | 18 |
| 6 | 0.0806 | 12 |
| 8 | 0.1433 | 7 |
| 10 | 0.2238 | 4 |
| 12 | 0.3223 | 3 |
Heading, machining and protection
Cold heading
Head in O or freshly quenched condition, then age. Heading T6 wire risks cracked heads.
Machining
T6 wire machines cleanly, like 7075-T6.
Joining
Not fusion-welded; mechanical joints only.
Protection
Anodise or coat; avoid sustained tensile stress in humid environments with peak-aged parts.
Where 7A04 and 7B04 wire are used
- Aircraft fasteners: pins, screws and special rivets
- Helicopters and UAVs: small high-strength pins and shafts
- Defence equipment: fasteners and cold-headed parts made to GB or GJB drawings
- Precision equipment: lightweight shafts, spacers and clips
How to order 7A04 or 7B04 wire
- SpecifyAlloy and temper, diameter, coil or length, quantity and the governing specification with its revision letter (GB/T 3190 chemistry plus the GB, GJB, ASTM or customer product standard). Add any customer or prime-contractor material specification that sits on top of the AMS.
- ConfirmWe confirm the specification can be met, the tolerance class, any extra tests (ultrasonic class, conductivity, fracture toughness, grain flow) and the delivery terms (EXW, FOB, CIF or DAP).
- InspectMaterial is checked for dimensions, surface condition and marking; tests named on the order are carried out or arranged with an independent laboratory.
- DocumentEach lot ships with a mill test certificate to EN 10204 3.1 giving chemistry, mechanical results and heat-treatment lot, traceable to the cast number.
- Pack and shipExport packing in sealed, moisture-protected wooden cases or on pallets, shipped by sea or air to your port or door.
References and standards
- GB/T 3190 – Wrought aluminium and aluminium alloys: chemical composition
- GB/T 16475 – Temper designation system for wrought aluminium and aluminium alloys
- ASTM B211 – Rolled or Cold-Finished Bar, Rod and Wire
- The Aluminum Association – International Alloy Designations and Chemical Composition Limits (Teal Sheets)
7A04 / 7B04 aerospace aluminium (aluminum) wire: FAQ
Is 7A04 the same as 7075?
They are close but not identical. 7A04 has more manganese (0.20 – 0.60 %) and a wider zinc range (5.0 – 7.0 %). T6 strength is similar, but substitution should be checked against the drawing.
What is the difference between 7A04 and 7B04?
7B04 is a high-purity version with silicon at most 0.10 % and low iron, giving better toughness and fatigue behaviour, much as 7475 improves on 7075.
What was 7A04 called before?
LC4, under the older Chinese designation system.
Can 7A04 wire be cold headed?
Yes, in the annealed or freshly quenched condition, followed by ageing to T6.
Can you supply an AMS-certified alternative?
Yes. If your customer needs an AMS or ASTM certificate, we can supply 7075 wire to AMS 4122, AMS 4124 or ASTM B211.
Need 7A04 or 7B04 wire?
Send grade, temper, diameter and standard. We will confirm availability and a delivered price.
