Brass vs Bronze: Copper Alloy Showdown

## Defining the Families **Brass** = Copper + Zinc. Zinc is the primary alloying element, typically 5-40%. Lead (up to 3%) is often added for machinability. **Bronze** = Copper + Tin, Aluminum, Silicon, or other elements (not zinc). Modern usage extends to aluminum bronzes (Cu-Al), silicon bronzes (Cu-Si), and phosphor bronzes (Cu-Sn-P). ## Key Grades Compared | Property | C36000 (Free-Cutting Brass) | C95400 (Aluminum Bronze) | |----------|----------------------------|-------------------------| | Composition | 61.5Cu-35.5Zn-3Pb | 81Cu-11Al-4Fe-4Ni | | UTS | 338 MPa | 620 MPa | | Elongation | 25% | 12% | | Machinability Rating | 100 (reference) | 60 | ## Corrosion Resistance Bronzes generally outperform brasses in aggressive environments: - **Seawater**: Aluminum bronze and tin bronze resist seawater attack far better than brasses, which are susceptible to dezincification (selective leaching of zinc). Brasses with less than 15% Zn or those inhibited with arsenic resist dezincification. - **Ammonia**: Brasses are susceptible to stress corrosion cracking (season cracking) in ammonia-containing environments. Bronzes are generally immune. - **Acids**: Phosphor bronzes and aluminum bronzes resist dilute sulfuric acid and many organic acids better than brasses. ## Machinability Free-cutting brass C36000 is the machinability benchmark for all copper alloys (rated 100). The lead content forms tiny inclusions that break chips cleanly. Aluminum bronzes machine at approximately 60%, requiring carbide tooling due to abrasive aluminum oxide inclusions. ## Strength Aluminum bronzes offer the highest strength in the copper alloy family. C95400 reaches 620 MPa tensile strength in the heat-treated condition, approaching some low-alloy steels. For applications requiring both copper-alloy corrosion resistance and structural strength, aluminum bronze is the clear winner. ## Cost Brasses are generally less expensive than bronzes because zinc costs less than tin or aluminum (in alloy form). C36000 brass costs approximately 5-8 USD/kg. Aluminum bronze C95400 costs approximately 10-15 USD/kg. ## When to Choose Each **Choose brass when**: Machinability is paramount (fittings, valves, screws), the environment is non-marine, formability is needed (deep drawing, stamping), or electrical conductivity matters. Plumbing fittings, musical instruments, and decorative hardware are classic brass applications. **Choose bronze when**: The application involves seawater or corrosive chemicals, high strength is required, wear resistance matters (bearings, bushings, gears), or ammonia SCC is a concern. Marine propellers, pump impellers, and heavy-duty bearings are classic bronze applications.