What Are C28000 and C22000?
C28000 and C22000 are two well-known copper-zinc alloys with very different zinc levels. C28000, called Muntz metal, contains about 59.0–63.0% copper with the balance zinc, and is one of the strongest, most machinable brasses. C22000, called commercial bronze or 90-10 bronze, contains 89.0–91.0% copper with the balance zinc; the name bronze is historical, since the alloy is actually a copper-zinc brass. The composition gap drives every other difference: C22000 is more ductile, corrosion resistant, and conductive, while C28000 is stronger, harder, and easier to machine. Both alloys are specified in ASTM B36 for sheet, strip, and plate and in ASTM B111 for condenser tubes.
Composition and Mechanical Properties
| Property (annealed, typical) | C28000 (Muntz Metal) | C22000 (Commercial Bronze) |
| Copper | 59.0–63.0% | 89.0–91.0% |
| Zinc | Balance | Balance |
| Tensile strength | 345–415 MPa | 275–345 MPa |
| Yield strength (0.2%) | 125–170 MPa | 95–130 MPa |
| Elongation | 30–45% | 40–55% |
| Hardness (HB) | 80–100 | 60–80 |
| Density | 8.39 g/cm³ | 8.80 g/cm³ |
| Melting range | 899–940 °C | 1020–1045 °C |
C28000 is roughly 20–30% stronger than C22000 in the annealed condition because the higher zinc content strengthens the alpha-beta microstructure. C22000, with more copper, is more malleable and easier to bend, stamp, and draw into complex shapes.
Corrosion Resistance Compared
In atmospheric exposure, C22000 forms a protective patina and resists tarnishing better than C28000, making it the choice for outdoor fixtures and architectural hardware. In fresh and salt water, C28000 is prone to dezincification, the selective leaching of zinc that leaves porous, weakened copper, especially in warm oxygenated water; C22000 resists dezincification far better and is used in marine hardware. C22000 also tolerates mild acids and alkalis better, suiting food processing and chemical tanks, while C28000 is attacked by strong acids and carries a higher risk of stress corrosion cracking in ammonia or chloride-rich coastal environments. Where severe corrosion is expected, C22000 or a tin bronze is preferred over C28000.
Machinability and Fabrication
C28000 is significantly easier to machine than C22000: its higher zinc content produces short, brittle chips and lower tool wear. On the CDA machinability scale where free-cutting brass C36000 equals 100, both C28000 and C22000 are rated about 40, but shop experience still favors the higher-zinc alloy for drilling and turning. C22000 welds better by TIG or MIG because less zinc vaporizes during welding; C28000 needs care, preheat, and flux to avoid porosity. C22000 offers excellent cold formability, while C28000 is preferred for hot forging and casting because of its lower melting point and good fluidity.
Applications and Cost
C28000 Muntz metal is used for industrial valves, fittings, and piping; structural brackets and fasteners; architectural trim; and historically for ship hull sheathing and fasteners. C22000 commercial bronze is used for electrical connectors and terminals, marine hardware such as cleats and bolts, decorative items and plaques, musical instruments, and food processing equipment. Cost follows copper content: C28000 is cheaper and widely available in sheet, bar, and castings, while C22000 costs more because it contains over 90% copper, and custom sizes may have longer lead times.
FAQ
Is C22000 a bronze or a brass?
Despite the name commercial bronze, C22000 is technically a copper-zinc alloy, which makes it a brass. The bronze name is historical, based on its copper-rich golden appearance. True bronzes use tin or other elements as the main alloying addition.
Which is stronger, C28000 or C22000?
C28000 (Muntz metal) is stronger and harder because of its higher zinc content, with annealed tensile strength of about 345–415 MPa versus 275–345 MPa for C22000. C22000 compensates with better ductility, corrosion resistance, and conductivity.
Which alloy resists corrosion better?
C22000 resists atmospheric, fresh-water, and mild chemical corrosion much better and is far less prone to dezincification in water service. C28000 needs protective coatings or inhibitors in aggressive or marine environments.
Can C28000 be welded?
Yes, but with difficulty. High zinc content vaporizes during welding, causing porosity; preheating, flux, and low heat input help, and brazing is often preferred. C22000 welds more readily with standard TIG or MIG procedures.
What is Muntz metal used for?
Muntz metal (C28000) is used for valves, fittings, fasteners, structural brackets, and architectural trim, and historically for ship hull sheathing. Its strength, machinability, and lower cost make it a practical structural brass.
Why is C22000 more expensive than C28000?
C22000 contains over 90% copper while C28000 contains about 60%, and copper is far more expensive than zinc. The higher raw-material cost makes C22000 roughly a third more expensive for equivalent shapes.
