What C60800 Aluminum Bronze Is
C60800 is a copper-based alloy in which aluminium replaces zinc and tin as the principal alloying addition. The aluminium content of the grade is held in the region of 5%, which places it among the lower-aluminium, higher-ductility members of the aluminium bronze family and makes it suitable for wrought tube as well as for castings. Aluminum bronze tube in this grade is specified for seamless condenser and heat exchanger service in ASTM B111, and the alloy also appears in plate and sheet specifications used for fabricated components.
The defining behaviour of the family is the formation of a thin, tenacious aluminium oxide film on the surface. The film is electrically insulating and chemically stable, and it re-forms immediately when damaged, which is the origin of the alloy's resistance to seawater, to many acids and alkalis, and to metal-to-metal wear.
Chemical Composition
| Element | Weight % | Function |
|---|---|---|
| Copper (Cu) | Balance, nominally 91-94 | Matrix; conductivity and ductility |
| Aluminium (Al) | 5.0-6.5 | Strength, hardness and wear resistance |
| Iron (Fe) | 0.50 max | Grain refinement; raises tensile and fatigue strength |
| Manganese, nickel, zinc, lead | Low residual levels | Processing behaviour and corrosion resistance |
The composition is deliberately economical in alloying terms: aluminium is inexpensive, and the strengthening effect it produces is far larger than its percentage suggests. Iron is restricted because above a low maximum it forms coarse intermetallic particles that reduce ductility and can act as initiation sites for corrosion, while manganese and nickel are allowed only at low residual levels.
Physical and Mechanical Properties
| Property | Value or behaviour |
|---|---|
| Tensile strength | 550-700 MPa in cold worked conditions |
| Hardness | Approximately 150-200 HB |
| Wear resistance | Excellent; oxide film provides anti-friction and anti-seizure behaviour |
| Corrosion resistance | Excellent in seawater, acids and alkalis; good stress corrosion resistance |
| Service temperature | Approximately -200 C to 400 C |
| Forming processes | Casting, forging, extrusion, rolling, drawing |
| Density | Approximately 8.2-8.5 g/cm³ |
Two practical points follow from this table. First, the strength and hardness quoted above are typical of cold worked product; annealed tube and soft strip are considerably softer and are supplied to the mechanical property limits of the applicable standard for the ordered temper. Second, the excellent wear behaviour of the alloy is a surface phenomenon driven by the oxide film, so machining and finishing operations should leave a sound surface rather than a heavily smeared one.
Corrosion and Wear Performance
In seawater the alloy resists general corrosion, impingement attack and stress corrosion cracking better than the high-zinc brasses, which makes it a candidate for condenser tube, pump and valve components and for components exposed to high-velocity flow. It also performs well in many organic and inorganic acids and in alkaline solutions, which extends its use to chemical plant equipment.
The principal corrosion risks are not general wastage but selective attack. Aluminium bronze can suffer selective phase attack if the microstructure is unsound, and it can be attacked in polluted or sulphide-bearing waters where the protective film is destabilised. Correct heat treatment, a fine and uniform structure, and control of cooling water quality are therefore part of the corrosion specification, not optional extras.
Applications
Marine engineering. Seawater pump bodies and impellers, valves, propellers and stern gear, and heat exchanger and condenser tube.
Mechanical engineering. Bearings, bushes, worm wheels, gears, wear plates and sliding components under high load and moderate speed.
Chemical and process plant. Reactor liners, agitators, pipework and heat transfer equipment resistant to acid and alkaline media.
Aerospace and defence. Bearing and structural components requiring high strength and stable performance across a wide temperature range.
Power and desalination. Condenser tube, valve trim and pump components in coastal and desalination plants.
Processing and Selection Guidance
Machining. The alloy machines cleanly but work hardens quickly, so cuts should be generous enough to stay below the hardened layer and tooling should be sharp. Avoid dwelling on the surface.
Cold forming. Ductility is lower than that of brass, so cold working should be carried out in stages with intermediate annealing, and sharp bend radii should be avoided.
Welding. The alloy can be welded, but the aluminium oxide film must be removed immediately before welding and an appropriate inert gas shield used. Matching filler metal and controlled heat input protect the corrosion resistance of the joint.
Heat treatment. Anneal in the 600-750 C range and cool according to section size and the required structure; excessive grain growth is the main risk and should be controlled.
Corrosion design. Keep seawater velocity inside the design range, avoid stagnant pockets and deposits, and do not couple the alloy to less noble metals in wet service without insulation.
Inspection. Confirm chemistry, mechanical properties and dimensions, verify structure where corrosion duty is critical, and apply eddy current or hydrostatic testing to tube supplied for heat exchanger service.
FAQ
Q: What is the difference between aluminum bronze and aluminum brass?
Aluminum bronze such as C60800 uses aluminium in a copper matrix without a large zinc addition, giving high strength and wear resistance. Aluminium brass is a copper-zinc alloy with a small aluminium addition and is used mainly for corrosion resistant tube.
Q: Why is C60800 used for seawater duty?
Its aluminium content produces a tough protective oxide film that resists seawater, impingement attack and stress corrosion cracking, and that re-forms immediately after mechanical damage.
Q: Is the alloy suitable for bearings?
Yes. The oxide film gives anti-friction and anti-seizure behaviour, so the alloy performs well in bearings, bushes, gears and sliding parts under high load and moderate speed.
Q: How does the alloy behave during cold working?
Ductility is lower than that of brass. Cold forming should be carried out in stages with intermediate annealing, and the material should not be bent to very tight radii without suitable tooling.
Q: What is the working temperature range?
The alloy performs across approximately -200 C to 400 C, maintaining stable mechanical properties at both low and elevated temperatures within that range.
Q: Which standards apply to the alloy?
Seamless heat exchanger tube is covered by ASTM B111, with plate and sheet grades covered by the corresponding plate specifications. The purchase order should name the UNS number, the product standard, the temper and the required tests.
