Machining
Machines well in T6 with short chips and a good finish. Avoid machining in the annealed state, where it is gummy. Leave allowance for distortion on long slender parts.
Ultra-high-strength 7xxx bar
7A04 T6 Aluminium Rod and Bar
7A04 is the Chinese GB designation for an Al-Zn-Mg-Cu "super-hard" alloy, formerly called LC4 and closely related to the Russian alloy V95. In the T6 condition, extruded 7A04 bar reaches strengths at or above 7075-T6, which makes it the standard high-strength bar on drawings that follow GB or GOST practice. Metline supplies 7A04 round, square and hexagonal bar in T6 to GB/T 3191, worldwide.
- Alloy
- 7A04 (Al-Zn-Mg-Cu)
- Temper
- T6 (O on request)
- Diameter
- Approx. 10 – 400 mm
- Standards
- GB/T 3190 · GB/T 3191
What is 7A04 aluminium?
7A04 is a 7xxx-series alloy that combines 5 – 7 % zinc with magnesium and copper. Ageing produces a dense population of fine MgZn2-type precipitates, which gives it some of the highest strengths available in wrought aluminium. In Chinese and former-Soviet engineering practice it fills the role 7075 plays elsewhere: highly loaded aircraft structure, landing-gear parts, fittings and high-strength machined components.
Compared with 7075, 7A04 allows a wider zinc range, adds manganese (0.20 – 0.60 %) and uses a lower chromium range. In practice the two are close in strength and behaviour, but they are separate alloys under separate standards. If a drawing specifies 7A04 under GB/T 3191, substituting 7075 to ASTM B221 (or the reverse) needs the approval of the design authority.
Like other peak-aged 7xxx alloys, 7A04-T6 has limited ductility, is notch-sensitive and is susceptible to stress-corrosion cracking when loaded in the short-transverse direction in a moist environment. Good detail design, generous radii and protective finishing are part of using it well.
7A04 chemical composition (wt %)
Limits per GB/T 3190. Each lot is certified with its actual analysis.
| Element | Minimum | Maximum | Role |
|---|---|---|---|
| Zinc (Zn) | 5.0 | 7.0 | Main strengthening element with Mg |
| Magnesium (Mg) | 1.8 | 2.8 | Forms MgZn2 precipitates |
| Copper (Cu) | 1.4 | 2.0 | Adds strength; moderates stress-corrosion behaviour |
| Manganese (Mn) | 0.20 | 0.60 | Grain and recrystallisation control |
| Chromium (Cr) | 0.10 | 0.25 | Grain control |
| Silicon (Si) | — | 0.50 | Impurity |
| Iron (Fe) | — | 0.50 | Impurity |
| Titanium (Ti) | — | 0.10 | Grain refiner |
| Others, each / total | — | 0.05 / 0.10 | |
| Aluminium (Al) | Remainder |
Mechanical properties of 7A04-T6 bar
GB/T 3191 sets minimum longitudinal properties for extruded 7A04-T6 bar that depend on diameter. The figures below are the values commonly quoted for the main size range; very small and very large diameters have different limits, and the certificate states the test result for your lot.
| Property | 7A04-T6 extruded bar | Basis |
|---|---|---|
| Tensile strength | ≥ 530 MPa | Specified minimum, common size range |
| Yield strength (0.2 %) | ≥ 400 MPa | Specified minimum, common size range |
| Elongation | ≥ 5 % | Specified minimum |
| Modulus of elasticity | About 71 – 72 GPa | Typical |
| Density | About 2.85 g/cm³ | Typical |
| Hardness | About 150 HB | Typical, T6 |
Typical tensile values in T6 are often somewhat above the minimum. Design to the minimum, and allow for lower elongation and toughness than in 6xxx or 2xxx alloys.
Standards and equivalent grades
| System | Designation | Comment |
|---|---|---|
| China (GB) | 7A04 | GB/T 3190 composition; GB/T 3191 extruded bar; GB/T 3880 sheet |
| China (former) | LC4 | Older designation still seen on drawings |
| Russia (GOST) | V95 (В95), 1950 | Close relative; V95pch / V95och are higher-purity versions |
| Aluminum Association | 7075 (nearest) | Similar strength; different Mn and Cr limits |
| Aerospace (China) | 7A04 / 7B04 | 7B04 is a higher-purity variant with better toughness |
7A04 bar is often bought alongside 7A04 / 7B04 wire for rivets and with 7A09 bar, which has better stress-corrosion resistance and is widely used for forgings.
7A04 bar sizes and weights
Supply range
- Round bar
- Approx. 10 – 400 mm diameter (about 0.39 – 15.6 in)
- Square and hexagonal bar
- To order
- Length
- Typically 1 – 6 m, or cut to length
- Temper
- T6; O for later heat treatment
- Surface
- Mill finish, peeled or turned
A 7A04 round bar weighs about 0.00224 × d² kg per metre (d in mm).
| Diameter (mm) | kg per metre | kg per 3 m bar |
|---|---|---|
| 10 | 0.224 | 0.67 |
| 16 | 0.573 | 1.72 |
| 20 | 0.895 | 2.69 |
| 25 | 1.399 | 4.20 |
| 30 | 2.015 | 6.04 |
| 40 | 3.581 | 10.74 |
| 50 | 5.596 | 16.79 |
| 60 | 8.058 | 24.17 |
| 80 | 14.33 | 42.98 |
| 100 | 22.38 | 67.15 |
| 120 | 32.23 | 96.70 |
| 150 | 50.36 | 151.09 |
| 200 | 89.54 | 268.61 |
| 250 | 139.90 | 419.70 |
| 300 | 201.45 | 604.36 |
Machining, heat treatment and finishing
Heat treatment
Solution treat at about 465 – 475 °C, quench rapidly in water, then age artificially (for example around 120 – 140 °C). Follow the governing standard for exact cycles.
Joining
Spot welding is practical; fusion welding is not recommended because of hot cracking and strength loss. Use riveting, bolting or bonding.
Corrosion protection
Sulphuric or chromic anodising and primer are standard for aircraft parts. Avoid sustained short-transverse tensile stress in moist environments.
Notch sensitivity
Use generous radii, avoid sharp re-entrant corners and keep surface finish fine on fatigue-loaded parts.
Inspection
Ultrasonic testing of larger bars and conductivity or hardness checks are common acceptance tests.
Where 7A04 bar is used
- Aircraft structure: frames, stringers, spar caps and heavily loaded fittings
- Landing gear and actuators: machined brackets, links and housings
- Fasteners and rivets: bar and wire for high-strength fasteners
- Propeller and rotor components: hub parts and fittings
- Heavy vehicles: wheel hubs and high-load brackets
- Defence and tooling: high-strength mounts, jigs and dies
7A04 compared with 7075, 7A09 and 2A12
| Property | 7A04-T6 | 7075-T6 | 7A09-T6 | 2A12-T4 |
|---|---|---|---|---|
| Typical strength level | Very high | Very high | High | High |
| Stress-corrosion resistance | Low | Low (T6) | Better | Moderate |
| Fatigue behaviour | Fair | Good | Good | Very good |
| Weldability | Poor | Poor | Poor | Poor |
| Typical standard | GB/T 3191 | ASTM B211 / B221 | GB/T 3191 | GB/T 3191 |
For new designs outside GB/GOST practice, 7075 is easier to source and certify internationally. Where stress-corrosion risk is high, consider 7A09 or an over-aged 7075-T73 temper instead of 7A04-T6.
How to order 7A04 bar
- SpecifyAlloy and temper, diameter or section, length, quantity, and the governing standard (GB/T 3191 or the specification on your drawing). Attach a drawing if the material will be cut or machined to shape.
- QuoteWe confirm availability, tolerances, certification and delivery terms (EXW, FOB, CIF or DAP) for your destination.
- ProcessMaterial is cut to length or size on request, marked for traceability and inspected for dimensions and surface.
- DocumentEach lot ships with a mill test certificate to EN 10204 3.1 showing chemistry and mechanical results; third-party inspection can be arranged.
- ShipExport packing in seaworthy wooden cases or on pallets with moisture protection, by sea or air to your port or door.
References and standards
- GB/T 3190 – Wrought aluminium and aluminium alloys: chemical composition
- GB/T 3191 – Aluminium and aluminium alloy extruded bars
- GOST 4784 – Aluminium and wrought aluminium alloys: grades
- The Aluminum Association – International Alloy Designations and Chemical Composition Limits
7A04 aluminium (aluminum) bar: frequently asked questions
What is the equivalent of 7A04?
Its closest relatives are the Russian alloy V95 (В95) and, internationally, 7075. They are similar in strength but have different composition limits, so substitution needs approval.
What strength does 7A04-T6 bar have?
GB/T 3191 commonly specifies at least about 530 MPa tensile, 400 MPa yield and 5 % elongation for extruded T6 bar in the main size range. Limits vary with diameter.
Can 7A04 be welded?
Spot welding works; gas and arc welding are not recommended because the alloy cracks and loses strength in the weld zone.
What does "super-hard aluminium" mean?
It is a Chinese term for the high-zinc 7xxx alloys such as 7A04 and 7A09, which reach the highest strengths among wrought aluminium alloys.
Which shapes can you supply?
Round bar is most common; square and hexagonal bar and other sections can be supplied to order.
Do you ship 7A04 bar outside India?
Yes. Metline supplies 7A04 bar worldwide with EN 10204 3.1 certificates and export packing.
Need 7A04 bar?
Send the diameter, length, quantity and specification. We will confirm availability and a delivered price.
