High-Copper Alloys, Coldur A

Coldur-A® is considered to be a high copper alloy that is well-known for its combination of strength, formability and corrosion resistance and also for its attractive color. Small additions of manganese and silicon to the copper enhance the overall mechanical properties and corrosion resistance of the alloy without any detrimental effect on the workability of the material. Coldur-A® is also called a high silicon bronze and has built its reputation by being one of the easiest copper based materials to work with.

It provides exceptional forming characteristics along with an attractive reddish old gold coloration that makes Coldur-A® highly desirable for a number of decorative and architectural applications. Its corrosion resistance and strength guarantee it is also ideal for several other applications from electrical components and marine hardware to chemical engineering.

Columbia Metals hold stocks of the Coldur-A® in the half hard condition which provides high mechanical strength and toughness. With tensile strength levels that are comparable to those of many high tin bronzes and stainless steels, Coldur-A® is used for a number of mechanical applications such as fixings, shafts and fasteners. It has a low magnetic permeability, is also non-sparking, and offers an extremely good wear and galling resistance, which makes it ideal for bushes, washers, bolts, bearings and spark-resistant tooling.

The corrosion resistance of Coldur-A® is also extremely impressive and is considered to be superior to that of brass with an excellent resistance to a number of corrosive environments. It offers a superb resistance to most types of fresh water, stagnant sea water or slow moving, saline spray and fog, enabling it to be a classic choice for boat building and marine hardware. It also has a resistance to a number of potentially corrosive acids, salts, alkalis and organic chemicals including sulfuric acid, organic acids, chlorides, diluted hydrochloric acid and sulfates, enabling its use in the food, chemical and brewing industries.

It strongly resists stress corrosion cracking and is also free from the issues of dezincification. However, it is not ideal for use with some sulfides, acid chromates, nitric acid, or oxidizing salts such as ferric chloride.

  • High strength properties
  • Attractive coloration
  • Excellent hot and cold formability
  • Low magnetic permeability
  • Readily weldable
  • Extremely good corrosion resistance
  • Non-sparking
  • High anti-galling properties
  • High wear resistance

Coldur-A® is perhaps most renowned for being the best copper alloy for forming and offers an exceptional hot and cold workability along with a good machinability rating. A firm favorite with blacksmiths all over the world, Coldur-A® is known for its hot working properties as the material readily flows in all hot forming and pressing operations.

It can also be readily cold formed, with up to 75% cold work that can be attained in between anneals. Coldur-A® can work-harden rapidly via a few forms of cold work and should not be subjected to the extremely severe deformation operations such as cold heading unless it is stress relief annealed in order to avoid the possibility of stress corrosion cracking.

Besides the properties mentioned above, Coldur-A® is known to be one of the easiest copper alloys to join and is readily soldered and then brazed. It is suitable for different types of resistance welding, spot welding and gas shielded arc welding and for oxyacetylene methods. The unique combination of exceptional fabrication properties, attractive golden bronze color, high mechanical performance and its high corrosion resistance enable it to be a firm favorite with designers, metal smiths, sculptors and fabricators alike.

Technical Data

Nominal Composition (%)

Cu Si Fe Zn Mn
Rem 2.8-3.8 0.5-1.3 1.5 max 0.8 max


Mechanical Properties (specification minima)

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


Typical Physical Properties

Density (g/cm3) 8.53
Modulus of Elasticity (N/mm) 105,000
Thermal conductivity (20 °C; W/m °K) 36


Fabrication Properties

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


Round Bar Weight and Stock Sizes

Diameter Weight Diameter Weight Diameter Weight
ins kg/ft kg/m ins kg/ft kg/m ins kg/ft kg/m
0.250 0.08 0.26 0.625 0.52 1.76 1.125 1.71 5.62
0.313 0.12 0.38 0.688 0.63 2.13 1.250 2.08 6.82
0.375 0.18 0.60 0.750 0.75 2.50 1.500 2.99 9.81
0.500 0.33 1.07 0.875 1.02 3.39 1.750 4.03 13.22
0.563 0.42 1.41 1.000 1.34 4.44 2.000 5.32 17.45


21g - 1/4” thick in a comprehensive range


1/2” square available from stock


NB Weight data for guidance only.

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