Overview
Bronze is a copper-tin alloy (typically 5-12% tin) with small additions of phosphorus (0.01-0.35%) for deoxidation and strength. Phosphor bronze offers superior strength, wear resistance, fatigue resistance, and corrosion resistance compared to brass, making it the preferred material for bearings, springs, gears, and marine components.
ρ = 8800 kg/m³ (typical for CuSn8 phosphor bronze)
Mechanical Properties
| Property | Value (Phosphor Bronze, spring temper) |
|---|---|
| Density | 8,800 kg/m³ |
| Young's Modulus | 110 GPa |
| Yield Strength | 150 MPa (annealed) / 550 MPa (spring temper) |
| Ultimate Tensile | 350 MPa (annealed) / 700 MPa (spring temper) |
| Elongation | 65% (annealed) / 5% (hard) |
| Fatigue Limit | 250 MPa (spring temper) |
| Hardness | 80-200 BHN |
| Melting Range | 950-1050°C |
Key Properties
- Wear resistance: Excellent for bearings and bushings; tin forms hard Cu₃Sn intermetallics
- Fatigue resistance: Outstanding — the material of choice for springs and electrical contacts
- Corrosion resistance: Superior to brass in marine and chloride environments
- Low friction: Good against steel shafts; often used as bearing surface
- Spring properties: Can be work-hardened to high spring temper
- Anti-galling: Resists welding and seizure in metal-to-metal contact
Common Bronze Alloys
| Alloy | Sn% | Key Alloy | Use |
|---|---|---|---|
| C51000 | 5% | Phosphor bronze | Springs, fasteners, contacts |
| C52100 | 8% | Phosphor bronze | Heavy-duty springs, bearings |
| C54400 | 4% + Pb | Free-cutting phosphor bronze | Bearings, bushings, machined parts |
| C93200 | 7% | SAE 660 bearing bronze | Sleeve bearings, bushings (most common) |
| C95400 | — | Aluminum bronze | High-strength, marine, heavy load |
| C90500 | 10% | Tin bronze (gunmetal) | Gears, valves, high-pressure fittings |
Applications
- Bearings & bushings: Sleeve bearings, flange bearings, thrust washers (SAE 660 standard)
- Springs: Electrical contacts, relay springs, instrument bellows, connector clips
- Gears: Worm wheels, gear wheels, sprockets (high load, low speed)
- Marine hardware: Propellers, shafts, underwater fittings, pump components
- Fasteners: High-strength bolts, nuts in corrosive environments
- Electrical: Switch contacts, fuse clips, terminal blocks
- Musical instruments: Cymbals, bells, guitar strings, saxophone mouthpieces
- Sculpture & art: Cast bronze statues, plaques, architectural elements
Bearing Design Notes
Phosphor bronze bearings (SAE 660 / C93200):
- Maximum PV value: ~1.75 MPa·m/s (50,000 psi·ft/min)
- Good with grease or oil lubrication
- Run well against steel shafts (HRC ≥30 recommended)
- Embeddability: tolerates minor dirt contamination better than harder materials
- Allow 0.025-0.100 mm clearance depending on shaft size
Summary
Phosphor bronze (density 8800 kg/m³) is the premium copper-tin alloy for wear, fatigue, and corrosion-critical applications. It is the standard for sleeve bearings and high-performance springs. More expensive than brass but its performance in demanding mechanical and marine service justifies the cost.