O
Annealed. Softest condition for cold heading, bending or swaging before brazing.
Heat-treatable brazing-compatible alloy
6951 Aluminium Bar and Rod
6951 is a lean Al-Mg-Si-Cu alloy with a high melting range, good thermal conductivity and a useful T6 strength of about 270 MPa. It is best known as the core and fin alloy of vacuum-brazed heat exchangers; as bar and rod it is used for fittings, headers and machined parts that must be brazed into those assemblies. Metline supplies 6951 bar to order, extruded or drawn, with mill certificates, worldwide.
- Alloy
- 6951 (Al-Mg-Si-Cu)
- Tempers
- O, T4, T6
- T6 tensile
- About 270 MPa typical
- Key trait
- Brazes and heat-treats
What is 6951 aluminium?
6951 was developed for brazed assemblies. Its silicon and magnesium contents are deliberately lower than in 6061, which keeps the solidus temperature well above the 577 – 600 °C range at which aluminium-silicon filler metals melt. That margin lets the part survive the brazing cycle without local melting, and because 6951 is heat-treatable it can then be aged to recover strength.
This combination is why 6951 is the standard core material of vacuum brazing sheet (typically clad with 4004 or 4104) and a common fin alloy in plate-fin heat exchangers. Bar and rod in the same alloy are used when a solid component, such as a port fitting, manifold block, header bar or spacer, has to be brazed into a 6951 assembly and match its post-braze heat treatment.
6951 is not a structural bar alloy in the way 6061 or 6082 are. Its T6 strength is lower, and it is ordered in modest quantities, usually as extruded or drawn rod made to a specific size. If your part is not brazed, 6061 or 6063 bar will normally be cheaper and easier to source.
6951 chemical composition (wt %)
Limits are the registered Aluminum Association values for 6951. Silicon in particular is far lower than in 6061 (0.40 – 0.80 %), which is what raises the melting range.
| Element | Minimum | Maximum | Role |
|---|---|---|---|
| Silicon (Si) | 0.20 | 0.50 | Kept low so the solidus stays above brazing temperature |
| Iron (Fe) | — | 0.80 | Impurity |
| Copper (Cu) | 0.15 | 0.40 | Adds strength; makes the core electrochemically more noble than the filler |
| Manganese (Mn) | — | 0.10 | Impurity |
| Magnesium (Mg) | 0.40 | 0.80 | Forms Mg2Si for age hardening |
| Zinc (Zn) | — | 0.20 | Impurity |
| Others, each / total | — | 0.05 / 0.15 | |
| Aluminium (Al) | Remainder |
Mechanical and physical properties of 6951
Typical values from handbook data for wrought 6951. They are useful for comparison; certified values for a lot appear on the mill certificate.
| Temper | Tensile strength | Yield strength (0.2 %) | Elongation | Shear strength | Hardness |
|---|---|---|---|---|---|
| O (annealed) | 110 MPa / 16 ksi | 40 MPa / 6 ksi | 30 % | 75 MPa | 28 HB |
| T6 | 270 MPa / 39 ksi | 230 MPa / 33 ksi | 13 % | 180 MPa | 82 HB |
Typical physical properties
- Density
- 2.70 g/cm³ (0.0975 lb/in³)
- Modulus of elasticity
- About 69 GPa
- Thermal conductivity
- About 200 – 215 W/m·K (higher in O than in T6)
- Coefficient of thermal expansion
- About 23.4 µm/m·°C
- Specific heat
- About 890 J/kg·K
- Approximate melting range
- About 615 – 655 °C
Typical heat-treatment temperatures
- Annealing
- About 415 °C, slow cool
- Solution treatment
- About 530 °C, then rapid quench
- Artificial ageing
- About 160 °C to T6
After furnace brazing, the assembly is effectively solution treated; fast cooling from the brazing temperature followed by ageing restores much of the T6 strength.
6951 tempers for bar and rod
T4
Solution treated and naturally aged. A practical delivery condition when the part will be brazed and aged afterwards.
T6
Solution treated and artificially aged for full strength. Used for parts machined before assembly; brazing will reset the temper.
H112 / F
As-extruded condition for bar that will be machined and then brazed, where incoming strength is not critical.
6951 bar sizes and weights
Supply range (made to order)
- Cold-drawn round bar
- Approx. 5 – 100 mm
- Extruded round bar
- Approx. 5 – 300 mm, larger on request
- Square, hexagonal and flat bar
- To drawing
- Lengths
- Mill lengths or cut to length
- Surface
- Mill finish, bright drawn or turned
Because 6951 bar is produced to order rather than held as general stock, quantities, sizes and lead time are confirmed with each quotation.
Weight of 6951 round bar is about 0.00212 × d² kg per metre (d in mm). Common inch sizes are converted below.
| Diameter | mm | kg per metre |
|---|---|---|
| 3/8 in | 9.53 | 0.192 |
| 1/2 in | 12.70 | 0.342 |
| 5/8 in | 15.88 | 0.534 |
| 3/4 in | 19.05 | 0.770 |
| 1 in | 25.40 | 1.368 |
| 1-1/4 in | 31.75 | 2.138 |
| 1-1/2 in | 38.10 | 3.078 |
| 2 in | 50.80 | 5.472 |
| 2-1/2 in | 63.50 | 8.551 |
| 3 in | 76.20 | 12.313 |
| 4 in | 101.60 | 21.890 |
| 5 in | 127.00 | 34.203 |
| 6 in | 152.40 | 49.252 |
Tolerances and quality checks
Drawn bar is supplied to ASTM B211 or EN 754-3 style tolerance tables and extruded bar to ASTM B221 or EN 755-3, unless the drawing specifies tighter limits. As a guide, drawn rod holds noticeably tighter diameter tolerances than extruded rod, and turned or ground bar tighter still.
- Surface free of cracks, blisters, laps and corrosion; scratches and dents within the governing standard
- Each bar or bundle marked with alloy, temper and lot for traceability to the certificate
- Chemistry checked against the 6951 limits, with special attention to Si and Mg because they control the melting margin
- Mechanical test per lot in the delivered temper
- EN 10204 3.1 mill test certificate; certificate of origin and other export documents on request
Brazing, machining and joining 6951
Vacuum brazing
The main route. Magnesium in 6951 and in 4004/4104 filler helps disrupt the oxide film in vacuum, so no flux is needed. Typical peak temperatures are around 590 – 605 °C.
Flux (CAB) brazing
Possible, but the magnesium content reacts with standard potassium fluoroaluminate flux and impairs wetting. CAB lines usually prefer low-Mg core alloys or caesium-modified flux.
Post-braze ageing
Cool quickly from the braze temperature, then age around 160 °C to recover strength. Slow furnace cooling leaves the part much softer.
Machining
Machines well in T4 and T6. In the O temper it is gummy; use sharp tools with high rake.
Welding
TIG and MIG weldable with 4043 filler. Weld zones lose temper like other 6xxx alloys.
Corrosion
Good general resistance. In heat exchangers, the copper content makes the core slightly noble to the filler and to sacrificial 7072 layers, which helps protect the core.
Where 6951 bar and rod are used
- Plate-fin heat exchangers: header bars, side bars, spacer bars and port fittings brazed into 6951 cores
- Oil and fuel coolers: machined bosses and connectors brazed to clad plates
- Aerospace and defence thermal systems: environmental-control and electronics cooling assemblies, built to the customer specification
- Industrial cold plates: vacuum-brazed liquid cooling plates for power electronics
- Cryogenic equipment: brazed aluminium exchangers in gas processing, where 6951 parts are combined with 3003 and 5083
6951 compared with 3003 and 6061
| Property | 6951-T6 | 3003-H14 | 6061-T6 |
|---|---|---|---|
| Typical tensile strength | 270 MPa | 150 MPa | 310 MPa |
| Heat-treatable | Yes | No | Yes |
| Strength after brazing + ageing | Largely recovered | Annealed (soft) | Not brazeable with Al-Si filler without risk |
| Approx. solidus | About 615 °C | About 640 °C | About 580 °C |
| Typical use | Brazed structures needing strength | General brazed exchangers | Structural, machined, welded parts |
6061 has a solidus close to the melting range of Al-Si filler metals, so it is generally not furnace-brazed. 3003 brazes easily but cannot be heat-treated, so it ends up annealed after brazing. 6951 sits between the two.
How to order 6951 bar
- SpecifyAlloy and temper, diameter or section, length, brazing method, quantity, and the governing standard (ASTM B211, ASTM B221 or EN 754 / 755). 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
- The Aluminum Association – International Alloy Designations and Chemical Composition Limits (Teal Sheets)
- ASM International – Alloy Digest Al-195: Aluminum 6951 Brazing Sheet and Plate
- ASTM B211 – Aluminum and Aluminum-Alloy Rolled or Cold-Finished Bar, Rod and Wire
- ASTM B221 – Aluminum and Aluminum-Alloy Extruded Bars, Rods, Wire, Profiles and Tubes
- AWS C3.7 – Specification for Aluminum Brazing
6951 aluminium (aluminum) bar: frequently asked questions
Why is 6951 used for brazed parts instead of 6061?
6951 has much lower silicon, so its melting range starts around 615 °C, comfortably above the 577 – 600 °C range of Al-Si brazing fillers. 6061 starts melting close to that range and is at risk of local melting in the furnace.
What strength does 6951 have after brazing?
If the assembly is cooled quickly from the braze temperature and then artificially aged, it recovers much of its T6 strength (typical T6: about 270 MPa tensile, 230 MPa yield). Slow cooling leaves it closer to the annealed values.
Can 6951 be CAB (flux) brazed?
It can, but its 0.4 – 0.8 % magnesium interferes with standard fluoride fluxes. 6951 is mainly a vacuum-brazing alloy; CAB lines normally use low-magnesium cores or special fluxes.
Is 6951 bar a stock item?
It is usually made to order, because most 6951 is sold as brazing sheet and fin stock. We confirm the size range and production route for each enquiry.
What is the UNS number for 6951?
UNS A96951.
Do you supply 6951 sheet as well as bar?
Yes. Clad and bare 6951 sheet, coil, strip and foil for heat exchangers are covered on our 6951 brazing core page.
Building a brazed assembly in 6951?
Send the bar size, temper, quantity and your brazing route. We will confirm supply and certification.
