Phosphor bronze (sometimes sold with the shorter name Phos 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.
Phosphor bronze is used for springs, bolts and various other items used in situations where resistance to fatigue, wear and chemical corrosion are required (e.g., a ship's propellers in a marine environment). The alloy is also used in some dental bridges.
Grades A, C and E – C51000, 52100, 50700 are commonly used nonferrous spring alloys. The combination of good physical properties, fair electrical conductivity and moderate cost make Phosphor Bronze round, square, flat and special shaped wire desirable for many springs and electrical contacts and a wide variety of wire forms where cost of properties does not prescribe Beryllium copper. 
Phosphor Bronze (94.8% copper, 5% tin, 0.2% phosphorus) is also used in cryogenics. In this case the combination of a fair electrical conductivity, and a low thermal conductivity allows to make electrical connection to devices at ultra low temperature without adding an excessive heat load.
Spent nuclear fuel overpack
Oxygen-free copper can be alloyed with phosphorus (CuOFP alloy) to better withstand oxidizing conditions. This alloy has application as thick corrosion-resistant overpack for spent nuclear fuel disposal in deep crystalline rocks.
Phosphor bronze is used in some metal wind instruments notably saxophones, and gives them a distinctive, reddish-orange hue, which can look different to the yellow-gold color of standard brass. It has been hotly debated that the bronze can give the instrument different acoustic properties to saxophones, though there is no scientific evidence that the material has any significant effect on the sound. Any such claims may be more marketing hyperbole rather than established fact. Additionally, phosphor bronze is sometimes used in brass instruments (e.g., Flugelhorns), plus percussion instruments such as cymbals and snare drums. Some acoustic instrument strings for acoustic guitars, mandolins and violins are wrapped with this metal. Some harmonica reeds are made of phosphor bronze, such as those by the Suzuki Musical Instrument Corporation.
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