Phosphor bronze is an alloy of copper with 3.5–10% of tin and up to 1%phosphorus. The phosphorus is added as deoxidizing agent during melting.
These alloys are notable for their toughness, strength, low coefficient of friction, and fine grain. The phosphorus reduces the viscosity of the molten alloy, which makes it easier and cleaner to cast and reduces grain boundaries between crystallites.
Further increasing the phosphorus content leads to formation of a very hard compound Cu3P (copper phosphate), resulting in a brittle form of phosphor bronze, which has a narrow range of applications.
Around 2001, the Olin Corporation developed another phosphor bronze alloy comprising:
• Zinc – 9.9%
• Tin – 2.2%
• Iron – 1.9%
• Phosphorus – 0.03%
• Copper – 85.97%
Olin developed this new alloy for use in electrical and electronic connectors. When assessed in strictly metallurgical terms it is not true phosphor bronze, but a form of iron-modified tin brass.