What ASTM B111 C61300 Aluminium Bronze Is
UNS C61300 is an aluminium bronze, one of the three aluminium bronze grades that ASTM B111/B111M lists for seamless condenser tube and ferrule stock, together with C60800 and C61400. Its composition centres on about 7 % aluminium with an iron addition in a copper matrix. Aluminium in solid solution and the iron-rich phases that form on cooling give the alloy a combination of strength and resistance to erosion-corrosion that no tin brass or aluminium brass can match.
That property profile explains where the grade is used. C61300 tube is selected for condensers and heat exchangers handling fast, aerated or solids-bearing water, and for components such as tube plates, valves and pump parts in marine service where a soft alloy would be washed away. It is not a substitute for the brasses in clean, slow-flowing cooling water, where its lower thermal conductivity and higher cost are not justified.
Chemical Composition
ASTM B111 controls C61300 within the limits below; values are in mass percent.
| Element | Requirement | Role |
|---|---|---|
| Copper (Cu) | Balance, approximately 88 % and above | Matrix |
| Aluminium (Al) | 6.0-7.5 % | Strength and protective film formation |
| Iron (Fe) | 2.0-3.0 % | Refines structure; raises strength |
| Manganese (Mn) | 0.20 % max | Residual element |
| Nickel (Ni) | 0.15 % max | Residual element |
| Zinc (Zn) | 0.30 % max | Residual element |
| Tin, silicon, lead | Individually capped residual levels | Kept low to protect ductility |
The residual limits matter more than they appear to. Iron must be high enough to refine the cast structure but not so high that coarse iron-rich particles act as corrosion initiation sites, and the residual elements are capped so that the alloy stays a single phase alpha-plus-kappa structure rather than developing the embrittling beta phase.
Physical and Mechanical Properties
Aluminium bronze is denser than the brasses at roughly 7.9 g/cm³ and solidifies in the region of 1025 C and above. Because aluminium in solid solution scatters both heat and current, thermal and electrical conductivity are only a few tens of watts per metre kelvin and well below those of the admiralty and aluminium brasses; the grade is therefore chosen for strength and erosion resistance rather than for maximum heat transfer. The material is non-magnetic and keeps its dimensions well at elevated temperature because of its low coefficient of thermal expansion.
| Condition | Tensile strength | Elongation | Typical use |
|---|---|---|---|
| Annealed (soft) | Order of 480 MPa minimum | 30 % and above | U-bending, tube sheet rolling |
| Hard drawn | Order of 620 MPa minimum | Around 12 % | Straight high pressure tubes |
ASTM B111 assigns minimum tensile and yield strengths to each UNS number and temper and requires expansion and flattening tests, so the temper must be stated on the order rather than left to the mill. Hard drawn tube is roughly a third stronger than annealed tube but has far less capacity to absorb bending, which is why U-bend condensers use the annealed condition.
Corrosion and Erosion Resistance
In flowing seawater the alloy builds an aluminium-rich oxide film that is continuously repaired as long as water keeps moving over the surface. This gives it excellent resistance to impingement attack and to erosion-corrosion, the two mechanisms that most often destroy condenser tube. It also performs well in chlorinated cooling water and in many dilute acids and alkalis.
The limits are equally well defined. Aluminium bronze is not recommended for stagnant, poorly aerated seawater, where the protective film does not repair itself and pitting or crevice attack starts. It is sensitive to stress corrosion cracking in ammonia-bearing environments, and polluted harbour water containing sulphides can cause selective phase attack, particularly if the tube was not correctly heat treated. Where water is slow, dirty and stagnant, a copper-nickel grade is the better choice; where it is fast and clean, C61300 is one of the strongest options among the copper alloys in ASTM B111.
Typical Applications
Condenser and heat exchanger tubes in high velocity seawater duty
Tube plates, water boxes and ferrules for marine heat transfer equipment
Valve bodies, seats and stems for seawater and process lines
Pump casings, impellers, wear rings and shaft sleeves
Gears, bearings, guides and bushings requiring high strength and wear resistance
Desalination and shipboard piping exposed to chlorides and sand
Fabrication, Welding and Inspection
Tube is produced by hot working the cast stock and then cold drawing with intermediate anneals, finishing with a controlled anneal that removes any retained beta phase. Hot working has to stay inside a relatively narrow temperature window, and overheating followed by slow cooling is the classic way to produce a brittle tube. Cold drawing raises strength and improves the surface finish; the finished tube is annealed when it must be bent or expanded into a tube sheet.
Welding is done by TIG or MIG with a matching aluminium bronze filler; no preheat is needed for thin sections, and the joint should be cleaned of copper smut afterwards because residual films promote corrosion. Machining calls for sharp, positive rake tooling, heavy feeds and no dwelling, since the alloy work hardens readily. Before dispatch, tube is checked by chemical analysis, tensile and hardness testing, dimensional and surface inspection, hydrostatic pressure test and eddy current examination, and the heat treatment record is reviewed because corrosion performance depends on it as much as on composition does.
FAQ
Q: What is the aluminium content of C61300?
The aluminium range specified for this grade is 6.0-7.5 %, supported by an iron addition of 2.0-3.0 %; the copper content is the balance of the composition.
Q: How does C61300 differ from C60800 and C61400?
C60800 is a lower aluminium bronze with about 5 % aluminium and an arsenic addition, C61300 and C61400 both contain about 7 % aluminium and differ mainly in their iron and residual element limits.
Q: Can C61300 tubes be used in stagnant seawater?
No, the alloy relies on continuous water movement to maintain its protective film; stagnant or poorly aerated seawater causes pitting and crevice attack, so a copper-nickel grade is preferred there.
Q: Why is the heat treatment of aluminium bronze so important?
Retained beta phase makes the material brittle and vulnerable to selective phase attack in service, so the final anneal and the cooling rate must be controlled and recorded.
Q: What filler is used to weld C61300?
A matching aluminium bronze filler is used with TIG or MIG processes, and the joint is cleaned afterwards to remove copper smut that would otherwise start corrosion.
Q: Is C61300 magnetic?
No, the alloy is non-magnetic, which is one reason it is found in marine and electrical equipment alongside its strength and wear resistance.
