What Are the Three Types of Brass?
Brass is a copper-zinc alloy family rather than a single material. The decisive variable is how much zinc is taken into solid solution in the copper lattice, because the copper-zinc equilibrium diagram divides commercial brasses into three structural classes: alpha brass, alpha-beta (duplex) brass and beta brass. Each class has its own crystal structure, and that structure controls how the metal responds to cold working, hot working, machining, brazing and corrosion in service.
Reading a designation such as C26000, C23000 or CuZn37 with these three classes in mind allows a designer or purchasing engineer to predict formability, strength and joining behaviour before any trial order is placed.
Phase Structure and the Copper-Zinc Ratio
The classification follows the phases present at room temperature, which in turn follow the composition. The ranges in the table below are the ones used throughout the industry.
| Class | Copper (wt.%) | Zinc (wt.%) | Structure | Preferred forming route |
|---|---|---|---|---|
| Alpha brass | above 65 | below 35 | Single phase, face-centred cubic | Cold working, deep drawing, pressing |
| Alpha-beta brass | 55-65 | 35-45 | Alpha plus ordered body-centred cubic beta prime | Hot working, extrusion, forging |
| Beta brass | 50-55 | 45-50 | Body-centred cubic, ordered at low temperature | Hot working only, rarely used alone |
The alpha phase is a substitutional solid solution of zinc in copper. It is tough and ductile, behaves much like copper itself and is comparatively difficult to machine because the chips do not break cleanly. Beta prime is harder and stronger than alpha, is readily deformed at elevated temperature and is brittle when cold. Duplex brasses therefore combine a soft, corrosion-tolerant matrix with a stronger second phase.
Two composition notes are worth remembering. First, the optimum cold formability of alpha brass occurs near 32 percent zinc; above that figure the ductility falls away quickly. Second, alpha-beta structures reach their maximum strength near 45 percent zinc. Both facts follow directly from the phase diagram rather than from any proprietary treatment.
Alpha Brass: Properties and Applications
Alpha brasses are the most widely used group. They contain only the face-centred cubic phase, which gives them excellent cold ductility, a warm golden colour that becomes redder as copper rises, and good resistance to atmospheric and fresh-water corrosion. Red brasses containing roughly 15 percent zinc or less, for example C23000 or the CuZn15 family, belong here and are chosen where colour, thermal conductivity and resistance to dezincification all matter.
Typical alpha grades and their uses include:
CuZn15 and CuZn20 type red brasses for architectural strip, roofing and condenser work.
CuZn30 cartridge brass for deep-drawn cases, radiator cores and complex pressed parts.
CuZn37 for general-purpose sheet, strip and tube where moderate strength is sufficient.
Because alpha brasses strain-harden rapidly, intermediate annealing is normally required between heavy drawing passes. They are also readily brazed and soldered, which is why they dominate plumbing and heat-transfer hardware.
Alpha-Beta (Duplex) Brass
Adding zinc beyond about 35 percent introduces the beta prime phase and creates the duplex structure. The material becomes significantly stronger and harder, loses much of its room-temperature ductility and gains excellent hot workability, which is why duplex brasses are supplied as extrusions, forgings and hot-rolled rod rather than as deep-drawn sheet.
The classic duplex compositions are CuZn40 and the 60/40 family, including naval brass types that add about 0.75 percent tin to improve resistance to seawater. These grades are the workhorses of valve bodies, pump components, shafts, fasteners and marine hardware. They machine far better than alpha brasses because the harder beta particles help the chip to break, and free-machining versions add a controlled amount of lead for even better chip control.
The trade-off is dezincification. In aggressive water or chloride service, selective loss of zinc can leave a porous copper-rich residue. Alloying with small additions of arsenic, antimony or phosphorus, as specified for admiralty and inhibited brasses, suppresses this mechanism effectively.
Beta Brass and Why It Is Rarely Used Alone
Beta brasses contain roughly 45 to 50 percent zinc and consist of the body-centred cubic beta phase. They offer high strength and hardness and are hot worked with ease, but they are brittle at room temperature and have limited corrosion resistance. In practice the fully beta structure appears only in special compositions; most commercial materials described loosely as beta brass are actually duplex brasses with a beta-rich structure.
Where the beta phase is used, it is usually as a minor constituent that improves hot formability or machinability of an otherwise alpha-beta alloy. Designers should treat a fully beta material as a hot-working grade only and not specify it for components that must absorb impact or be cold formed.
How to Specify the Right Class
Selection normally runs through four questions. What forming route will be used, cold or hot? What strength level is required? What is the service environment, particularly with respect to chlorides and ammonia? And what surface finish or colour is expected? Alpha brasses answer the first question when cold forming dominates; duplex brasses answer it when hot forming, machining or higher strength dominate.
Where a standard designation is needed, the relevant documents are ASTM B111 for copper-alloy tube, ASTM B36 for plate, sheet, strip and rolled bar, ASTM B16 for free-cutting rod and bar, ASTM B124 for forging rod and bar, and EN 12164 or EN 12167 for European rod and profile products. Each of these specifications states the composition limits and the temper designations, so the three-class framework should be used to choose the family first and the exact standard second.
FAQ
Q: What are the three types of brass?
The three types are alpha brass with a single face-centred cubic phase, alpha-beta or duplex brass containing both alpha and beta prime phases, and beta brass with a body-centred cubic structure. They are distinguished by copper and zinc content.
Q: How do I tell alpha brass from duplex brass?
Alpha brass typically contains more than 65 percent copper and cold forms well, while duplex brass contains 55 to 65 percent copper, is stronger and harder, and is normally hot worked. A microstructural examination or a supplier specification will confirm the class.
Q: Which brass type is best for cold deep drawing?
Alpha brass. CuZn30 and CuZn37 offer the best combination of ductility and strength for deep drawing, with intermediate anneals between heavy reductions.
Q: Why is beta brass not used for structural parts?
Beta brass is brittle at room temperature and has modest corrosion resistance. It is chosen for hot forming operations rather than for components that must resist impact loading.
Q: Is naval brass a duplex brass?
Yes. Naval brass is a 60/40 copper-zinc duplex brass with about 0.75 percent tin added for marine corrosion resistance, placing it in the alpha-beta class.
Q: Does the three-class system replace standard grade designations?
No. It is a structural framework. Final ordering still uses UNS numbers or EN designations together with the applicable ASTM or EN product specification and temper.
