Why Brass Is Not One Material
Brass is a copper-zinc alloy, but the copper content changes the crystal structure, and the structure changes everything else: strength, ductility, whether the alloy can be cold formed or must be hot worked, how it machines, and how it behaves in water. Any discussion of the types of brass therefore starts with the phase diagram rather than with a product name.
Two practical facts follow from the diagram. First, the higher the copper content, the more ductile and corrosion resistant the alloy, and the more expensive it is. Second, as zinc increases, the alloy becomes stronger and harder, easier to hot work and to machine, and more susceptible to dezincification in chloride-bearing water. Almost every decision between brass grades is a trade between those two directions, moderated by small additions such as tin, aluminium, arsenic, lead or silicon.
The Three Structural Families
| Family | Copper content | Structure | Behaviour |
|---|---|---|---|
| Alpha brass | Above about 64 % | Single phase, face-centred cubic | Excellent cold workability; moderate strength; can be hardened only by cold work |
| Alpha-beta brass | About 55-63 % | Two phases, alpha plus beta | Good hot workability and machinability; stronger than alpha brass; less cold formable |
| Beta brass | Below about 55 % | Largely body-centred cubic beta phase | Hard and strong when ordered; limited ductility; used where hot working dominates |
Alpha brasses are the deep drawing and tube-drawing grades. They harden rapidly when cold worked, so they are supplied in a range of tempers and are annealed between forming operations. Alpha-beta brasses are the forging, extrusion and machining grades, and they cover most valve, fitting and fastener production. Beta brasses are a narrower group, used where hot working and high strength outweigh ductility.
Composition of the Commercial Types
The table groups the grades most often quoted in export trade by family, with the designations that appear on drawings and purchase orders. Composition limits are those of the applicable wrought copper alloy standard, such as the GB/T 5231 series or the corresponding UNS designations.
| Type | Typical designation | Nominal composition | Main characteristic |
|---|---|---|---|
| Cartridge brass | C26000, CuZn30 | 70 % Cu, 30 % Zn | Best combination of ductility and strength for cold forming |
| Yellow brass | H62 family, CuZn37 | About 62 % Cu | General purpose, good cold formability |
| Muntz metal type | H59 family, CuZn40 | About 59 % Cu | Hot forging and machining grade; lower cost |
| Naval brass | C46400, CuZn39Sn1 | About 60 % Cu with 0.5-1.0 % Sn | Better seawater and erosion resistance than plain brass |
| Admiralty brass | C44300, CuZn28Sn1 | About 71 % Cu with Sn and As | Condenser tube; resists impingement and dezincification |
| Aluminium brass | C68700, CuZn20Al2As | About 77 % Cu with 2 % Al and As | Seawater condenser tube; protective oxide film |
| Free cutting brass | C36000, CuZn36Pb3 | About 61.5 % Cu, 3 % Pb | Highest machining rate of the brass family |
| Lead-free machining brass | CuZn40Bi or CuZn38As types | Bismuth or silicon substituted for lead | Machinable grade for drinking water applications |
| Manganese bronze type | C86300 | High-strength cast or forged manganese brass | Heavy duty bearing and gear blanks |
The families overlap, and the addition elements are what separate grades that would otherwise be similar. Tin raises resistance to seawater and erosion, aluminium forms a protective film, arsenic suppresses dezincification, and lead improves machinability while reducing ductility and corrosion resistance.
Workability and Processing
Cold forming: alpha brasses such as C26000 and the H62 family are rolled, drawn, stamped and deep drawn to substantial reductions. Ductility falls rapidly with cold work, so intermediate anneals are scheduled into the process.
Hot forming: alpha-beta grades forge and extrude well. The beta phase is ductile at high temperature, which is why valve bodies and fittings are hot forged from these grades.
Machining: the leaded free-cutting grades machine at the highest rate in the family. Where lead is restricted, bismuth or silicon bearing grades are used instead, with a modest penalty in machining speed.
Joining: brasses braze and solder readily. Fusion welding is difficult because zinc volatilises, so welded brass fabrications are normally avoided in favour of brazed or mechanical joints.
Stress relief: any brass that has been heavily cold worked, and any brass part destined for damp or ammoniacal service, should be stress relieved to remove the residual stress that drives season cracking.
Corrosion Behaviour by Type
Copper content sets the baseline of corrosion resistance, and the minor additions decide the specific failure modes that have to be designed against.
Dezincification: the characteristic attack on high-zinc brasses in chloride-bearing water, in which zinc is selectively removed and the alloy becomes porous. Arsenic, antimony or phosphorus additions inhibit it in the alpha brasses used for tube.
Stress corrosion cracking: promoted by residual stress and by ammonia or amines. Stress relief after forming is the standard countermeasure.
Impingement and erosion: accelerated by high water velocity and entrained air. Tin in naval and admiralty grades, and aluminium in aluminium brass, improve resistance.
Selective attack in aggressive water: low-copper, high-zinc grades are unsuitable for long service; the higher copper types or a copper-nickel alloy should be selected.
For drinking water and food contact service, the choice of grade also has to satisfy the applicable national requirements, which in practice means a lead-free or low-lead alloy rather than a conventional leaded free-cutting grade.
Applications by Type
| Application | Usual type |
|---|---|
| Deep drawn components, cartridges, radiator cores | Cartridge brass C26000 |
| Tube, sheet, architectural and decorative work | Yellow brass, H62 family |
| Hot forged valves, fittings, pump bodies | Alpha-beta brass, H59 family and forging brasses |
| Marine hardware and seawater fittings | Naval brass C46400 |
| Condenser and heat exchanger tube | Admiralty brass C44300, aluminium brass C68700 |
| Turned parts, connectors, small fasteners | Free cutting brass C36000 |
| Heavy duty bushings, worm gears, wear parts | Manganese bronze type C86300 |
How to Select a Brass Type
Start with the process, not the product name: cold forming points to an alpha grade, hot forging to an alpha-beta grade, and heavy machining to a leaded or lead-free machining grade.
Then define the environment: fresh water, seawater, ammonia, food contact or dry indoor service each rule out a different group of alloys.
Then fix the delivery temper, because all mechanical requirements of a brass are quoted per temper rather than per grade alone.
Finally confirm the standard designation on the certificate, since trade names such as brass 58 or brass 62 do not define composition.
FAQ
Q: What is the difference between alpha and alpha-beta brass?
Alpha brass is a single phase alloy with more than about 64 % copper and has excellent cold working properties, which suits drawing, stamping and deep forming. Alpha-beta brass has about 55-63 % copper and a two phase structure, which makes it stronger and better for hot forging and machining but less suitable for severe cold forming.
Q: Which type of brass has the best corrosion resistance?
Corrosion resistance generally rises with copper content, so the alpha brasses used for tube are the most resistant of the plain brasses. Where seawater is involved, the tin bearing naval brass and the arsenic bearing admiralty and aluminium brasses are selected, and in severe conditions a copper-nickel alloy replaces brass altogether.
Q: Why is lead added to some brasses?
Lead acts as a chip breaker and lubricant, so it substantially increases machining speed and improves surface finish. It also reduces ductility and corrosion resistance, and its use is restricted in drinking water and food contact applications, which is why lead-free machining brasses containing bismuth or silicon have been developed.
Q: What is naval brass used for?
Naval brass contains about 60 % copper with a tin addition of roughly 0.5-1.0 %. The tin improves resistance to seawater and to erosion, so the grade is used for marine hardware, propeller shaft components, condenser tube plates and other parts exposed to flowing seawater.
Q: Can brass be welded?
Brasses are difficult to fusion weld because zinc volatilises from the weld pool and causes porosity. Brazing and soldering are the standard joining methods, and where welding is essential a silicon or aluminium bearing brass with better weldability is chosen instead of a plain alpha-beta grade.
Q: How do I specify brass correctly on a purchase order?
Quote the alloy designation together with the standard, the delivery temper, the dimensions and the form. Where corrosion or food contact is involved, add the service environment, so that the correct grade family is supplied rather than a cheaper grade that happens to be in stock.
