Leaded Copper, designated under UNS L51100–L51199, refers to copper-based alloys containing controlled additions of lead to dramatically improve machinability, anti-galling behavior, and bearing performance, while retaining copper’s excellent thermal and electrical conductivity.
These alloys are widely used in machined components, bearings, bushings, and electrical hardware where free-cutting characteristics are critical.
Role of Lead
✔ Insoluble in copper — exists as discrete globules
✔ Acts as a solid lubricant
✔ Promotes chip breaking and smooth machining
Microstructure & Metallurgical Behavior
| Feature | Description |
|---|---|
| Matrix | α-copper (FCC) |
| Lead Distribution | Fine Pb globules at grain boundaries |
| Strengthening | Solid solution (Sn, Zn, Ni if present) |
| Lead Contribution | No strengthening (machining aid only) |
| Heat Treatment | Not precipitation hardenable |
| Annealing | Used to restore ductility |
Metallurgical Insight:
Lead improves machinability without increasing strength because it remains soft and
insoluble, acting as an internal lubricant during cutting.
Machinability & Tribological Performance
✔ Machinability rating up to 90–100% (brass benchmark)
✔ Short, well-broken chips
✔ Excellent surface finish
✔ Low friction and anti-seizure behavior
✔ Excellent resistance to galling and adhesive wear
✔ Performs well under boundary lubrication
Corrosion Resistance
Good Resistance To:
Atmospheric corrosion, freshwater, mild industrial environments
Moderate Resistance:
Seawater (better than brasses, inferior to bronzes)
Limitations:
❌ Strong acids
❌ Ammoniacal environments
Fabrication & Processing Properties
| Process | Performance |
|---|---|
| Machining | Outstanding |
| Cold Forming | Limited |
| Hot Working | Preferred if required |
| Soldering | Excellent |
| Brazing | Good |
| Welding | Not recommended |
| Casting | Selected grades |
Available Forms
Bars & rods
Plates & sheets
Tubes
Forgings
Castings
Precision-machined blanks
Key Characteristics
✔ Exceptional machinability
✔ Excellent thermal & electrical conductivity
✔ Low friction coefficient
✔ Good wear resistance
✔ Dimensional stability
✔ Cost-effective for mass production
Applications
Machined Components
Screws, nuts, bolts, valve components, fittings, connectors
Bearings & Bushings
Plain bearings, sleeve bushings, thrust washers
Electrical
Terminals, switch components, grounding hardware
Industrial & Automotive
Pump components, instrumentation parts, hydraulic fittings
Advantages of Leaded Copper
✔ Superior machinability vs pure copper
✔ Reduced tool wear
✔ Excellent surface finish
✔ Good wear and anti-galling properties
✔ Retains high conductivity
✔ Ideal for high-volume machining
Why Choose Leaded Copper (L51100 – L51199)?
Choose leaded copper when machining efficiency is critical, tight tolerances are required, conductivity must be retained, and bearing or sliding performance matters.
Engineering Summary:
Leaded Copper alloys are performance-machining materials engineered to deliver precision,
productivity, and reliability in machined copper components.