What C61400 Copper-Aluminum Bronze Is
C61400, often described simply as aluminium bronze D, is a wrought copper alloy built around a copper-aluminium base with about 7% aluminium and an iron addition of roughly 2%. The aluminium forms a hard, tenacious oxide film on the surface that is the source of the alloy's reputation in seawater, while the iron refines the grain structure and raises strength. The result is a material that behaves far more like a high-strength engineering alloy than like conventional tin bronze.
The grade is covered by ASTM B171 for copper alloy plate and sheet for pressure vessels and by ASTM B171M for the metric version, with tube products for condenser and heat exchanger service addressed by the same family of specifications. Cast forms of a similar aluminium bronze composition are covered by ASTM B148, but the wrought product discussed here has finer structure and higher ductility than the cast equivalent.
Chemical Composition
The composition ranges below are those normally specified for wrought C61400. The remainder of the material is copper with minor residual elements kept within the specification limits.
| Element | Range | Function |
|---|---|---|
| Copper | 88.0-92.5% | Base metal |
| Aluminium | 6.0-8.0% | Strength, hard surface film, corrosion resistance |
| Iron | 1.5-3.5% | Grain refinement and strength increase |
| Manganese | 1.0% maximum | Deoxidation and strengthening |
| Nickel | 1.0% maximum | Residual limit, improves toughness at low levels |
| Lead | 0.01% maximum | Kept deliberately low for hot workability |
The tight lead limit is not incidental. Aluminium bronzes are sensitive to hot shortness, and even small lead contents impair hot rolling and forging, so the specification keeps the residual level extremely low.
Physical and Mechanical Properties
The table below summarises the properties most often requested in technical enquiries. Values are typical for wrought product; the minimum figures that must be met on test are those stated in the applicable specification for the ordered temper.
| Property | Typical value |
|---|---|
| Density | About 7.89 g/cm³ |
| Melting range | Approximately 1040-1060 degrees C |
| Tensile strength | Approximately 480-550 MPa depending on temper |
| Yield strength | Approximately 200-250 MPa depending on temper |
| Elongation | Approximately 25-35% |
| Modulus of elasticity | About 110-120 GPa |
| Electrical conductivity | About 14% IACS |
| Thermal conductivity | About 40 W/m.K |
Strength in service rises further through work hardening: cold rolled or drawn C61400 develops yield strength well above the annealed value, which is useful for components such as shafts and wear parts that cannot be heat treated.
Corrosion and Wear Performance
The alloy's reputation rests on its behaviour in seawater. The protective aluminium oxide film reforms rapidly when damaged, giving strong resistance to general corrosion, to impingement and erosion corrosion at higher flow velocities, and to cavitation in pump and valve service. It also resists stress corrosion cracking and shows good fatigue strength in marine environments.
Two limits should be understood. The alloy is not intended for strongly reducing or heavily sulphide-polluted waters, where the protective film becomes unstable, and it should not be exposed to ammonia or ammonium compounds, which attack copper alloys generally. In correct seawater and brackish water service the material regularly delivers very long component life. Where the process stream is polluted or the chemistry fluctuates, the application should be reviewed on a case-by-case basis.
Fabrication, Welding and Heat Treatment
C61400 is readily hot worked and, in the annealed condition, cold formed to moderate reductions with inter-pass annealing. Machining is comparable to a medium-strength bronze and calls for sharp, positive rake tooling. Two fabrication points deserve attention:
Welding. The alloy is welded by gas tungsten arc and gas metal arc processes with matching or suitable copper alloy filler metals, using direct current electrode negative for TIG work. Preheating is generally not required for thin sections, and inter-pass temperature should be controlled to avoid excessive grain growth. Joints should be cleaned thoroughly before welding and the heat-affected zone cleaned after welding to restore the oxide film.
Heat treatment. Solution annealing with controlled cooling is used where maximum softness and ductility are required. Stress relief is applied after heavy cold work, but the alloy should not be held in the temperature range that promotes embrittlement during slow cooling.
Typical Applications
Pump bodies, impellers, wear rings and casings; valve bodies, seats, stems and trim; condenser and heat exchanger tube; seawater piping, flanges and fittings; propeller shafts, rudder components and other marine hardware; and welded structures in desalination and offshore service. The combination of strength, seawater resistance and weldability is what makes C61400 a standard selection where the duty cycle is corrosive and mechanically demanding.
On receipt, material should be checked for chemical composition against the specification, for mechanical properties in the ordered temper, for dimensional tolerance and for surface condition. Welded fabrications should be inspected for freedom from porosity and for correct restoration of the protective film on the finished surface.
FAQ
Q: What is C61400 made of?
It is a wrought copper-aluminium bronze with 88.0-92.5% copper, 6.0-8.0% aluminium and 1.5-3.5% iron, with low residual limits on manganese, nickel and lead.
Q: Why is C61400 used in seawater?
Its aluminium content forms a hard, self-repairing oxide film, giving excellent resistance to general corrosion, impingement attack and cavitation in seawater and brackish water.
Q: How strong is C61400 compared with brass?
It develops appreciably higher yield strength than plain brasses, with typical tensile strength in the region of 480-550 MPa and yield strength around 200-250 MPa in the annealed and lightly worked conditions.
Q: Can C61400 be welded?
Yes. Gas tungsten arc and gas metal arc welding are both used with matching filler metals, and the heat-affected zone should be cleaned afterwards so that the protective oxide film can reform.
Q: Is C61400 the same as cast aluminium bronze?
No. The wrought grade discussed here has a finer, more uniform structure and higher ductility than cast aluminium bronze to ASTM B148, and the two are specified separately.
Q: What services should C61400 avoid?
Strongly reducing conditions, heavily sulphide-polluted waters and ammonia-bearing media, all of which destabilise the protective surface film or attack copper alloys directly.
