High Copper Silicon Bronze Alloy for Corrosive Environments

Columbia Metals hold Coldur-A stocks in the half hard condition providing high mechanical strength and toughness. With tensile strength levels being comparable with those of high tin bronzes and stainless steels, Coldur-A is used for several mechanical applications such as fixings, fasteners and shafts. It has a low magnetic permeability, is also non-sparking, and offers a very good wear and galling resistance, making it suitable for bushes, bearings, washers, bolts and spark-resistant tooling.

Coldur-A is a high copper alloy, which is well-known for its combination of corrosion resistance, strength and formability and its attractive color. Small additions of manganese and silicon to the copper improve the overall corrosion resistance and the alloy’s mechanical properties without any impact on material workability. Coldur-A is also known as high silicon bronze and has built its reputation on being one of the easiest copper based materials to work with. It offers good forming characteristics combined with an impressive reddish old gold colouration that makes Coldur-A very desirable for a number of decorative and architectural applications. Coldur-A is known for being the best copper alloy for forming and offers an excellent hot and cold workability combined with a good machinability rating. A strong favorite with worldwide blacksmiths, Coldur-A is recognised for its hot working properties as the material flows readily in all hot forming and pressing operations. It can also be cold formed readily with up to 75% cold work that can be achieved in between anneals. It is possible for Coldur-A to work-harden rapidly through some forms of cold work and must not be subject to the highly severe deformation operations such as cold heading unless it is stress relief annealed to avoid the possibility of stress corrosion cracking.

Along with the above properties, Coldur-A can be easily joined and is readily brazed and soldered. It can be welded by all kinds of resistance welding, gas shielded arc welding and spot welding and by oxyacetylene methods.


The composition of Coldur-A is given in the table below:

Element Percentage
Silicon, Si 2.8 – 3.8
Manganese, Mn 0.5 – 1.3
Zinc, Zn 1.5 max
Iron, Fe 0.8 max
Copper, Cu Remaining

Key Features

The main features of Coldur A alloy are:

  • Excellent hot and cold formability
  • Attractive reddish old gold coloration
  • High strength properties
  • Low magnetic permeability
  • Excellent general corrosion resistance

Mechanical Properties (Specification Minima)

The mechanical properties of Coldur-A are:

  Up to 2" dia
Ultimate Tensile Strength (N/mm2) 485
0.2% Proof Strength (N/mm2) 260
Elongation (%) 20
Hardness (HRB) 75-95

Typical Physical Properties

The physical properties of Coldur-A are:

Density (gm/cm3) 8.53
Modulus of Elasticity (N/mm) 105000
Thermal conductivity (20°C - W/m°K) 36

Fabrication Properties

The fabrication properties of Coldur-A are:

Melting Range (°C) 970 - 1025
Annealing Temperature (°C) 480 700
Stress Relieving Temperature (°C) 320 380
Hot Working Temperature (°C) 710 870

Applications of Coldur-A

The corrosion resistance and strength properties also ensure it is suitable for many other applications from architectural metal work and marine hardware to electrical components and chemical engineering.

Coldur-A has a very attractive corrosion resistance and is superior to that of brasses and has a very good resistance to a number of corrosive environments. It offers good resistance to most kinds of fresh water, stagnant or slow moving sea water, fog and saline spray making it an ideal choice for boat building and marine hardware. It also features a resistance to a number of corrosive alkalis, acids, salts and organic chemicals including dilute hydrochloric acid, sulphuric acid, chlorides, sulphates and organic acids enabling applications in the food, chemical and brewing industry. It is also free from dezincification and strongly resists stress corrosion cracking. However, it cannot be used with certain sulphides, nitric acid, acid chromates, or oxidizing salts such as ferric chloride.

The innovative combination of excellent fabrication properties, high mechanical performance, high corrosion resistance and attractive gold bronze color make it a great favorite with sculptors, designers, fabricators and metal smiths.

The applications of Coldur-A are listed below:

  • Offshore and marine: Fasteners, propellor shafts, hull and deck fittings, fuel and water tanks, non-magnetic instrumentation, subsea electromechanical equipment and other hardware.
  • Chemical Processing: Autoclaves, chemical apparatus, drains, explosives plant, fans and ducts for corrosive vapours, fasteners, heat exchanger tube plates, filters, pickling and recovery plant, pressure vessels, pump rods and shafts, screen plates, stirrers, valve stems, vats and washers.
  • Others: Furniture, fire place surrounds, nameplates, sculptures, signs, bolts, cladding, door and window frames, hinge pins, latches, masonry fixings, slate and tile nails, panels, spring brackets, screws, step irons, tension bolts and wall ties. Bearing plates, bolts, busbar clamps, bushes, clutch discs, cotter pins, electrical conduit, fasteners, locking washers, piston rings, thrust washers and u-bolts.
  • Electrical: current-carrying electrical components such as slip rings, squirrel cages, springs, rotary switch contacts, contact blades, short-circuit rings, heavy duty switchgear.
  • Automotive: valve guides, bushes, valve seats.

This information has been sourced, reviewed and adapted from materials provided by Columbia Metals.

For more information on this source, please visit Columbia Metals.


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