Phosphor bronze
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Phosphor bronze is an alloy of copper with 3.5 to 10% of tin and a significant phosphorus content of up to 1%. 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 also improves the fluidity of the molten metal and thereby improves the castability, and improves mechanical properties by cleaning up the grain boundaries.
Further increasing of phosphorus content leads to formation of a very hard compound Cu3P (copper phosphide), resulting in a brittle bronze with only special uses.
Phosphor bronze is used for springs and other applications where resistance to fatigue, wear and chemical corrosion is required. It is also used in acoustic instrument strings (for acoustic guitars, mandolins, etc...).