Phosphor Bronze is a high-performance copper alloy that contains tin (Sn) and a small amount of phosphorus (P). Known for its excellent strength, corrosion resistance, and superior fatigue properties, this alloy is widely used in applications requiring durability, precision, and long service life.
The addition of phosphorus improves wear resistance, stiffness, and resilience, making Phosphor Bronze suitable for electrical, mechanical, and marine environments.
Common grades include C51000, C51900, C52100, and PB1, PB2, PB4 for cast forms.
Composition
The base of phosphor bronze is copper (Cu) with alloying additions:
| Element | Typical Range | Effect |
|---|---|---|
| Copper (Cu) | ~89–99.5% | Base metal providing ductility, conductivity & corrosion resistance. |
| Tin (Sn) | ~0.5–11% | Increases strength, hardness & corrosion resistance. |
| Phosphorus (P) | ~0.01–0.35% | Refines grain, increases stiffness, wear resistance, and deoxidizes the melt. |
| Lead (Pb) (optional) | ~0–3% | Added in some grades for improved machinability. |
| Zinc (Zn), Iron (Fe) | small amounts | Minor adjustments (machining, strength) |
Key Mechanical Properties
Phosphor bronze alloys vary with grade and temper, but in general:
Mechanical Properties (Typical Ranges)
| Property | Typical Range |
|---|---|
| Tensile Strength | ~345–690 MPa (50–100 ksi) depending on alloy & temper. |
| Yield Strength | ~180–620 MPa (varies with temper). |
| Elongation | ~6–40% depending on temper & composition. |
| Hardness (Brinell) | ~80–180+ HB. |
| Modulus of Elasticity | ~100–130 GPa. |
| Fatigue Resistance | Excellent (due to phosphorus grain refining). |
Physical Properties
| Property | Typical Value |
|---|---|
| Density | ~8.7–8.9 g/cm³. |
| Electrical Conductivity | ~10–20% IACS (fair). |
| Thermal Conductivity | Moderate (e.g., ~52–84 W/m·K). |
| Coefficient of Thermal Expansion | ~17–18 µm/m·°C. |
| Melting Range | ~880–1025°C (varies by alloy). |
Phosphor bronze maintains good conductivity and thermal behavior compared with many other structural alloys, supporting thermal stability in service.
Strengthening & Metallurgical Behavior
The alloy’s microstructure is primarily a copper matrix with tin-rich phases and very fine phosphorus-rich compounds that refine grains.
Phosphorus helps deoxidize the alloy during melting, reducing porosity and enhancing fluidity and casting quality.
High tin grades (e.g., ~8–10%) provide increased hardness and fatigue strength, while lower tin (~4–6%) offers balanced ductility and springiness.
Strengthening Mechanisms
Solid solution strengthening: from tin in copper.
Grain refinement: phosphorus reduces grain size, improving toughness and fatigue life.
Cold working and tempering: further increase yield strength in wrought tempers.
Phosphor bronze is not usually heat-treatable in the sense of age hardening like aluminum or some steels, but mechanical processing (cold drawing/rolling) and tempering significantly improve strength and elasticity.
Key Characteristics
| Feature | Benefit |
|---|---|
| High strength & fatigue resistance | Ideal for dynamic or cyclic loading conditions. |
| Excellent wear resistance | Good for sliding contacts and bearings. |
| Low coefficient of friction | Better performance against hard counterfaces. |
| Corrosion resistance | Tin improves corrosion behavior, especially in marine environments. |
| Fine grain structure | Improves toughness and fatigue life |
| Good conductivity | Suitable for moderate electrical applications. |
| Good formability & spring qualities | Excellent for wire, springs, and bent parts. |
Refining & Processing Properties
Phosphor bronze casts well due to phosphorus lowering molten viscosity and reducing defects.
Excellent fluidity for intricate castings and conformal shapes.
Phosphor bronze can be forged, rolled, and wrought into shapes such as bars, wires, and sheets.
Grades with small lead additions (e.g., C54400) offer enhanced machinability.
Cold drawing/rolling significantly increases strength and yield for spring wires and fine parts.
Annealing improves ductility before forming.
Available Forms
Bars & billets – round, square, rectangular.
Sheets, plates & strips – for stamping, connectors, contacts.
Tubes & pipes – bearings, bushings.
Wires & coils – springs, fasteners, electronics.
Near-net castings – bespoke parts
Typical Applications
Mechanical
Bearings & bushings – wear resistance and low friction.
Springs & fasteners – excellent fatigue resistance.
Gears & worm wheels – wear-handling in mechanical systems.
Cam followers, pins, thrust washers – sliding wear applications.
Electrical & Electronics
Electrical contacts, connectors, switches – fair conductivity and durability.
Industrial & Marine
Pump components, valves, diaphragms – corrosion resistance in fluids.
Specialty
Precision instrument parts, cryogenic connectors – stable at low temperatures.
Advantages & Why Choose Phosphor Bronze
Superior Fatigue Resistance
Excellent for springs and cyclic loading conditions due to phosphorus grain refining.
Balanced Strength & Ductility
Offers high mechanical strength with good flexibility for forming and resilient parts.
Wear & Corrosion Resistance
Tin improves corrosion resistance; phosphorus enhances wear resistance — ideal in harsh environments.
Low Friction & Good Bearing Behavior
Low coefficient of friction results in cooler operation and longer wear life.
Good Processing Flexibility
Can be cast, worked, tempered, and machined to tight tolerances.
Limitations & Considerations
Lower electrical conductivity compared with pure copper — may be limiting for high-current applications.
Machinability varies by grade — free-cutting grades with lead are easier to machine than lead-free grades.
Cost higher than brass/standard tin bronzes due to alloy complexity.
Summary
Phosphor bronze is a versatile, high-performance copper alloy known for strength, fatigue resistance, wear resistance, low friction, and corrosion resistance. Its balanced properties, combined with excellent formability and processing flexibility, make it a top choice for bearings, springs, electrical connectors, and marine/industrial components where durability and longevity matter.