Phosphor bronze is a member of the family of copper alloys. It is composed of copper that is alloyed with 0.5–11% of tin and 0.01–0.35% phosphorus, and may contain other elements to confer specific properties (e.g. lead at 0.5–3.0% to form free-machining phosphor bronze). Alloyed tin increases the corrosion resistance and strength of copper, while phosphorus increases its wear resistance and stiffness.
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. It was originally formulated by the Belgian Georges Montefiore-Levi.