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Silicon Bronze and Copper-Nickel

This group collects the copper alloys chosen for weldability and seawater: silicon bronze (C65500, 3 % Si, 1 % Mn) is the one copper alloy that TIG-welds as easily as steel, and copper-nickel (C70600 with 10 % Ni, C71500 with 30 %) is the standard for seawater piping and condenser tube because it neither corrodes nor fouls. The nickel silvers (C75200, C77000 — copper, nickel and zinc, no silver) sit here too, along with the high-performance Cu-Ni-Si and Cu-Ni-Sn connector alloys. Strengths are modest, 100–400 MPa yield by temper, except the age-hardening C70250 and C72900 at 550–900 MPa.

Popular silicon bronze and copper-nickel grades

Compare in the explorer
GradeYield, MPaTensile, MPaDensity, g/cm³MachinabilityWeldabilityBest for
C655001654008.53PoorExcellentWeldable silicon bronze, marine fasteners
C651003804558.75PoorExcellentLow-silicon bronze for cold-headed screws
C706001203108.94PoorExcellent90/10 copper-nickel seawater pipe and tube
C715001403808.94PoorExcellent70/30 copper-nickel for fast or hot seawater
C752004275178.73PoorFairNickel silver springs, optical and musical parts
C702506407008.82FairFairHigh-strength conductive connector strip
C693002905508.3Very goodFairLead-free machinable silicon brass

All 68 silicon bronze and copper-nickel grades

Choose silicon bronze and copper-nickel for

Welded copper-alloy assemblies, marine and architectural fasteners, seawater piping, condenser and evaporator tube, heat-exchanger tube sheets, coinage and nickel-silver hardware, high-performance connector strip, and lead-free machined plumbing parts.

Look elsewhere when

The part is a plain machined fitting (C36000 brass at three times the cutting speed), a shaft or bushing under load (C63000 aluminum bronze), a conductor (C11000), a spring at high stress (C17200 or C51000), or a large seawater pump body where cast C95800 or C86500 is the economical form.

Yield strength against electrical conductivity, Silicon bronze & copper-nickel among every copper alloy grade

No materials in view have both of these properties.

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Silicon bronze and copper-nickel by application

Welded assemblies and fasteners
C65500 bar, plate and wire for welded frames, tank fittings and marine bolts; C65100 for cold-headed screws and rivets. Both weld with ERCuSi-A filler and resist salt spray and stress cracking.
Seawater piping and heat exchangers
C70600 tube for condensers, coolers and ship piping up to about 3 m/s flow; C71500 above that or in polluted harbour water; C44300 admiralty brass only in clean fresh cooling water.
Connectors and beryllium-free springs
C70250 strip for high-current connectors; C72900 and C72500 for springs, bearings and bushings where beryllium copper is not allowed.
Silver-coloured hardware
C75200 and C74500 nickel silver for keys, zippers, instrument parts, optical frames and plated flatware; C77000 for the spring parts of the same products.

Working with silicon bronze and copper-nickel

Welding
C65500 is the easiest copper alloy to weld: TIG or MIG with ERCuSi-A, no preheat, good colour match, minimal fume. Copper-nickel welds with ERCuNi (70/30) filler for both grades and needs a clean joint free of sulfur and lead. Nickel silver is soft-soldered or silver-brazed rather than welded.
Machining
Silicon bronze and copper-nickel machine at about 20–30 % of C36000 with gummy, stringy chips; sharp tools, positive rake and good chip control are essential. C69300 is the exception at about 75 % with short chips. Nickel silver machines like a stiff brass.
Forming
Copper-nickel tube bends and expands into tube sheets easily; annealed C65500 and nickel silver deep-draw and spin well. Strength is set by cold work, from about 100 MPa annealed to 400 MPa hard. C70250 and C72900 are supplied mill-hardened and formed in that condition within their bend limits.
Finishing
Copper-nickel and silicon bronze are used bare in seawater; the film that forms in the first weeks is the protection, so avoid stagnant start-up water and never pickle it off. Nickel silver polishes, plates and holds a lacquer well.

Other copper alloy series

Silicon Bronze and Copper-Nickel — frequently asked

What is silicon bronze and copper-nickel?

This group collects the copper alloys chosen for weldability and seawater: silicon bronze (C65500, 3 % Si, 1 % Mn) is the one copper alloy that TIG-welds as easily as steel, and copper-nickel (C70600 with 10 % Ni, C71500 with 30 %) is the standard for seawater piping and condenser tube because it neither corrodes nor fouls. The nickel silvers (C75200, C77000 — copper, nickel and zinc, no silver) sit here too, along with the high-performance Cu-Ni-Si and Cu-Ni-Sn connector alloys. Strengths are modest, 100–400 MPa yield by temper, except the age-hardening C70250 and C72900 at 550–900 MPa.

Which grade of silicon bronze and copper-nickel should I use?

C65500 for anything welded or hot-headed — marine bolts and nuts, architectural fabrications, tank fittings, TIG filler for brass repairs; C65100 (1.5 % Si) for cold-headed screws, rivets and wire. C70600 90/10 copper-nickel for seawater piping, condenser and heat-exchanger tube and desalination hardware; C71500 70/30 when the water is faster, hotter or more polluted, or the tube must be stronger. C75200 nickel silver for springs, optical and musical hardware and anything that must look silver after plating wears; C77000 is the strongest spring nickel silver. C70250 for high-performance connector strip that needs 40 % IACS with 550–700 MPa yield, and C72900 (spinodal Cu-Ni-Sn) as the beryllium-free alternative to C17200 for bearings and springs. C69300 is the lead-free silicon brass that replaces C36000 in potable water.

Which grade of silicon bronze and copper-nickel is the strongest?

C72900 has the highest yield strength in the series at 1,000 MPa; C72800 follows at 800 MPa. Values are for each grade's default condition.

Which grade of silicon bronze and copper-nickel is easiest to machine?

C69300 (machinability very good, 80/100), then C69710 (80/100).

Is silicon bronze and copper-nickel heat-treatable?

No. These grades are strengthened by cold work and softened by annealing, not by heat treatment; the conditions are listed on each grade page.

90/10 or 70/30 copper-nickel for seawater?

C70600 90/10 for most piping, condenser and cooler tube: it is the cheaper alloy, forms and welds more easily, and resists pitting and biofouling in clean seawater up to about 3 m/s. C71500 70/30 for higher flow velocities, hotter or sulfide-polluted water, submarine and offshore systems, and where higher strength lets the wall be thinner — about 140 MPa yield against 105 for 90/10 in the annealed temper.

Is nickel silver a silver alloy?

No — it is copper with 10–18 % nickel and 15–30 % zinc, named for its colour. C75200 (65 Cu, 18 Ni, 17 Zn) is the common grade for keys, optical frames, instrument parts and the base under silver plate; C77000 has more zinc and is the spring grade. It tarnishes much more slowly than brass, machines and forms like a stiff brass, and contains no lead unless a leaded grade such as C79200 is specified.