What C61400 Copper Alloy Is
UNS C61400 is an aluminum bronze - a copper alloy in which aluminium is the principal alloying addition, at about 7%, with iron at around 2% controlling grain structure and strengthening the matrix. It is known in European practice as CuAl7Fe3 and appears in ASTM B171 for plate, sheet, strip and rolled bar and in ASTM B111 for seamless condenser and heat exchanger tube.
It is worth being precise about the family, because the alloy is sometimes described loosely as a brass. It is not. Its distinctive properties - high strength, resistance to cavitation and erosion, and strong performance in seawater - come from the aluminium-rich phase and the iron addition, not from zinc. The zinc content is limited to a residual level, and the lead content is held to a very low maximum, which is an advantage in applications where lead-bearing alloys are restricted.
Chemical Composition
| Element | Requirement % | Effect |
|---|---|---|
| Cu | 88.0 min | matrix |
| Al | 6.0-8.0 | principal strengthener; builds the protective surface film |
| Fe | 1.5-3.5 | refines grain structure; raises strength and wear resistance |
| Mn | 1.0 max | residual; contributes to strength |
| Zn | 1.0 max | residual impurity |
| Pb | 0.01 max | residual; alloy is effectively lead-free |
The low lead limit has two consequences. First, the alloy is suitable for services where lead content is regulated. Second, and often overlooked, it means the material does not have the free-machining behaviour of leaded brasses, so it must be machined with tooling and parameters chosen for a work-hardening aluminum bronze rather than for a free-cutting brass.
Mechanical Properties
| Property | Behaviour |
|---|---|
| Tensile strength | high for a copper alloy; tube and bar are released against the minimum values tabulated in ASTM B111 and ASTM B171 for the ordered temper, and commercial C61400 product is commonly quoted with minimum tensile strength of about 550 MPa |
| Yield strength | commonly quoted around 275 MPa minimum, giving useful load-carrying capacity in pump, valve and wear parts |
| Elongation | typically at least 30% in the annealed condition, so the alloy retains ductility despite its strength |
| Hardness and wear | good resistance to sliding wear, galling and abrasive attack compared with brasses and pure copper |
| Electrical conductivity | low, on the order of 13% IACS; the alloy is selected for strength and corrosion resistance, not for conductivity |
Because aluminium bronzes work-harden strongly, the temper and the amount of cold reduction applied to the finished part have a large influence on the delivered properties. Purchase specifications should therefore state the temper rather than only the alloy, and should ask for tensile and yield results on the finished product.
Corrosion and Wear Behaviour
C61400 develops a protective aluminium oxide film on its surface, and that film is the source of its reputation in aggressive environments. It resists seawater, brackish water, many neutral salt solutions, dilute acids and a range of industrial chemicals, and it performs particularly well where flow is turbulent and where cavitation or impingement attack would damage softer copper alloys.
In wear service the alloy behaves well where loads are moderate to high and lubrication is imperfect. It resists galling against steel and stainless steel better than most copper alloys, which is why it is found in bushes, bearings, wear plates and pump components. Where loads are heavy, a nickel-aluminium bronze grade is often the next step up; where the environment is benign and cost is critical, a brass or tin bronze may be sufficient.
Typical Applications
Pump bodies, impellers, wear rings and diffusers for seawater and process pumps.
Valve bodies, seats, stems and trim for marine and chemical service.
Heat exchanger tube sheets, water boxes and condenser components.
Bearings, bushes and thrust washers in marine and industrial machinery.
Worm gears and heavily loaded gear components.
Propeller shaft liners, marine hardware and offshore structural fittings.
Fabrication, Machining and Joining Guidance
Hot working is carried out in the temperature range usual for aluminum bronzes, followed by a suitable anneal; the alloy is not intended for extensive cold forming because it work-hardens quickly. Annealing softens a cold-worked part and restores ductility for further forming or bending.
Machining requires positive rake tooling, rigid setups and cutting parameters that keep the tool engaged; the material work-hardens under the tool, so dwelling and repeated light passes produce a hard skin that accelerates wear. Sharp tools, adequate coolant and firm feeds give the best surface finish and tool life.
Welding is practical with gas tungsten arc and gas metal arc processes using a matching aluminum bronze filler metal. Joint preparation must be clean, preheat is normally minimal, and low heat input with stringer beads limits cracking and dilution. Brazing and soldering are more difficult than on brasses because of the tenacious surface oxide, and they require appropriate flux and surface preparation.
Inspection Points and Common Pitfalls
Verify the aluminium and iron contents on the certificate; both control strength and corrosion performance.
Check that the lead limit of the governing standard is respected, especially where the application restricts lead-bearing alloys.
Confirm the temper, and require mechanical test results from the finished product rather than from the ingot.
Do not specify free-machining parameters; the alloy is effectively lead-free and behaves accordingly.
Where the part will be welded after machining, allow for the strength lost in the weld zone and design the joint accordingly.
FAQ
Q: Is C61400 a brass or a bronze?
It is an aluminum bronze, not a brass. The main alloying element is about 7% aluminium with around 2% iron, and the zinc content is only a residual impurity. Its strength, wear resistance and seawater performance come from the aluminium-rich structure.
Q: What are the mechanical properties of C61400?
It is a high-strength copper alloy with commercial product commonly quoted at a minimum tensile strength of about 550 MPa, minimum yield strength around 275 MPa and elongation of at least about 30%. The governing ASTM specifications tabulate the minimum values that apply to each product form and temper.
Q: Does C61400 contain lead?
The lead content is held to a very low residual maximum, effectively 0.01%, so the alloy is considered lead-free. That also means it does not machine like a leaded free-cutting brass; it must be machined as a work-hardening aluminum bronze.
Q: Where is C61400 used?
Typically in pump bodies and impellers, valve bodies and trim, heat exchanger tube sheets and water boxes, bearings and bushes, worm gears, propeller shaft liners and marine hardware - situations that combine load, wear and a corrosive medium.
Q: Can C61400 be welded?
Yes, with gas tungsten arc or gas metal arc welding and a matching aluminum bronze filler metal. Clean joint preparation and low heat input are essential, and brazing or soldering is considerably more difficult than on brass grades because of the surface oxide.
Q: Is C61400 a good electrical conductor?
No. Its electrical conductivity is low, on the order of 13% IACS, far below pure copper and below the brasses. The alloy should be specified for strength, wear resistance and corrosion performance, not for conductivity.
