Introduction to alloy classification
These alloys of copper and tin were the first metallic alloys to be developed by mankind, about four thousand years ago, and were used for coins, weapons, tools, jewellery and ornaments. They revolutionised the way man lived leading to archaeologists naming the period the Bronze Age.
In modern times wrought bronzes have been developed with 4-8% tin which are harder, stronger, and stiffer than wrought brasses and, in strip and wire form, are produced with a combination of high yield strength and good corrosion resistance. The addition of small amounts (0.01-0.45%) of phosphorus increases the hardness, fatigue resistance and wear resistance, leading to their use in applications such as springs, bellows, flexible tubing, fasteners, masonry fixings, shafts, valve spindles, gears and bearings.
Special alloy characteristics
Alloying elements with copper, in this case tin and phosphorus, can result in lower electrical conductivity compared to pure copper. The most widely used phosphor bronze for electrical purposes contains 0.2% phosphorus and 5% tin and has an electrical conductivity of 15% IACS (Copper is 100% IACS). However, the combination of high yield strength, which gives a good contact force, and good corrosion resistance make this bronze ideal for a wide range of small electrical connectors, switches, current carrying springs and rotor bars. These properties are retained at high operating temperatures.
Wrought leaded phosphor bronzes (3-4% lead) combine the above properties with outstanding machinability and significant self-lubrication, self-seating and alignment in bearing applications and excellent resistance to seizure. Applications include thrust washers, bearing bushes, cams, clutch plates, intricate machined fasteners and other turned parts, clock and instrument parts, gears, pinions, pump and valve spindles and engraved components.
Special alloy characteristics
Phosphor bronzes with higher tin contents are available in all the common cast forms. They have up to 13% tin and 2.5% lead (for machinability) and nickel (for strength and hardness) and are widely used for bearings and gears.
Equivalent Specifications
