These are alloys of copper and tin and were the first to be developed about four thousand years ago. They were the first metallic alloys, gradually replacing stone and flint and were so important they led to a period in time being named the Bronze Age.
Tin bronze and phosphor bronze
Wrought alloys with 4–8% tin are harder, stronger and stiffer than the wrought brasses and, in strip and wire form, are produced with a combination of high yield strength and good corrosion resistance, which makes them ideal for use as springs.
The addition of small amounts (0.01–0.45) of phosphorus further increases the hardness, fatigue resistance and wear resistance, leading to applications such as springs, fasteners, masonry fixings, shafts, valve spindles, gears and bearings. Cast phosphor bronzes with up to 10% tin and 20% lead are widely used for heavy duty bearings.
This is an alloy of copper with 5–12% aluminium, with additions of iron, nickel, manganese and silicon, available in cast and wrought form. These alloys are stronger than the brasses or tin bronzes with better corrosion resistance due to a hard, adherent, protective alumina film (Al2O3). They have an attractive golden colour, with very little tarnishing with time. The major use for aluminium bronzes is in seawater applications, such as:
- Pumps and valve components
- Pipe fittings
- Heat exchangers
- Bearings, where they meet exacting specifications, and are widely used for defence applications.
These are alloys of copper with 3% silicon and 1% manganese. Silicon bronzes have a good combination of strength and ductility, good corrosion resistance and easy weldability. They are used in architectural product applications such as:
- Door fittings
- Church doors
- Window frames
- Wall ties
- Fastener material for marine applications.
This alloy is a firm favourite with sculptors and metalsmiths because of its workability, longevity and attractive golden bronze colour.
Manganese bronze and architectural bronze
There may be confusion when brasses are incorrectly called bronze. Manganese bronze CuZn40Mn1Pb1 (CW720R) is a brass used for architectural applications, where the manganese leads to the formation of an attractive chocolate brown colour.
The term ‘architectural bronze’ is sometimes applied to a leaded brass CuZn41Pb1Al which in service, due to the aluminium, develops an attractive golden lustre. Like all brasses these alloys combine longevity with an aesthetic appeal, which improves with time and gives a feeling of luxury and prestige to any building, both inside and out. They are available in all forms and are used for cladding, windows, doors and curtain walls. They are usually finished by waxing.