Definition and Background
C28000 is a wrought copper-zinc alloy with a nominal composition of about 60% copper and 40% zinc, placing it in the two-phase alpha-beta region of the copper-zinc system. That structure is the key to its character: the alpha phase supplies ductility and corrosion resistance, while the beta phase makes the alloy hot workable and gives it tensile strength well above the single-phase 70/30 brasses. In older trade language the 60/40 composition was called Muntz metal, and it is still common to see the alloy described simply as 60/40 brass.
The grade is standardised in ASTM B135 for seamless brass tube, ASTM B36 for brass plate, sheet, strip and rolled bar, and ASTM B124 for forging rod and shapes. European equivalents are covered by designations in EN 12164, EN 12167 and EN 1652. Because the copper content is lower than in the 70/30 grades, C28000 is also less sensitive to raw material price movement, which keeps it attractive for large architectural and marine packages.
Chemical Composition and Physical Properties
The composition and physical data below reflect the ranges normally specified for wrought C28000 product. The balance of the composition is zinc in each case.
| Element or property | Value | Comment |
|---|---|---|
| Copper | 59.0-63.0% | Main alloying element |
| Zinc | Balance | Forms the beta phase with copper |
| Lead | 0.30% maximum | Residual element limit |
| Iron | 0.07% maximum | Residual element limit |
| Density | About 8.39 g/cm³ | Typical for 60/40 brass |
| Melting range | About 900-940 degrees C | Lower than pure copper |
| Electrical conductivity | About 28% IACS | Adequate for earthing and connector parts |
| Thermal conductivity | About 120 W/m.K | Useful in heat transfer hardware |
| Modulus of elasticity | About 100-110 GPa | Typical for alpha-beta brass |
Mechanical Properties and Tempers
C28000 is supplied in a range of tempers, and the mechanical properties required on test depend on the temper ordered. In the annealed condition the alloy is soft enough for hot forming and moderate cold bending; as cold reduction increases, tensile strength and hardness rise and elongation falls. The table below sets out the practical differences that matter when specifying.
| Temper | Condition | Relative strength | Suitable processes |
|---|---|---|---|
| O60 | Annealed | Lowest of the range | Hot forging, severe forming, machining |
| H02 | Half hard | Intermediate | General fabrication, moderate bending |
| H04 | Hard | Highest of the range | Structural and wear-resistant parts |
Where a project requires guaranteed minimum tensile and yield values, they are stated in the applicable product specification and verified on test coupons taken from the delivered lot. Annealing softens the material and restores ductility, so any heat treatment carried out after the final forming operation must be accounted for when properties are being relied upon.
Corrosion Behaviour
In clean fresh water and in ordinary atmospheric exposure C28000 performs well, and its warm golden colour makes it popular for external architectural metalwork. The alloy does not carry the tin or arsenic additions used in the inhibited grades, so it can suffer selective loss of zinc in aggressive waters, particularly where chloride levels, temperature and flow velocity are high. For seawater piping and for condenser service, a tin-bearing grade or an aluminium bronze is the safer choice.
Where the material is used in marine atmospheres, occasional washing to remove chloride deposits extends service life considerably. Contact with more noble metals such as stainless steel or graphite should be avoided in wet conditions, because galvanic attack will concentrate on the brass.
Forming, Joining and Machining
The two-phase structure makes C28000 an excellent hot working alloy: it forges, extrudes and hot stamps at temperatures well below the melting range and is the base material for many hot pressed valve bodies and fittings. Cold working is limited. The alloy can be bent and flanged in thin sections, but heavy cold deformation of annealed stock should be avoided because the beta phase tends to crack.
Machining. Free-cutting behaviour is only moderate, since the lead content is low; sharp tools, positive rake angles and generous chip clearance are needed.
Brazing and soldering. Both are straightforward with standard copper alloy filler metals; joints should be cleaned and fluxed according to the process used.
Welding. Fusion welding is possible but the zinc volatilises, producing fume and porosity, so filler metal selection, ventilation and controlled heat input matter.
Heat treatment. Stress relief annealing is used after heavy forming to reduce the risk of season cracking in service.
Applications and Inspection Points
Typical uses include hot forged and machined fittings and valve bodies, marine hardware, architectural sections and grilles, fastener stock, heat transfer hardware, and general industrial components where strength, appearance and cost are all considered. It is also used for blanking and coinage-type applications where a warm colour is wanted at lower cost than a 70/30 alloy.
Incoming inspection normally covers chemical composition, temper or hardness, dimensions and surface quality. For components intended for wet service, evidence that the alloy is not intended as a substitute for an inhibited grade should be part of the technical review, and stress relief should be confirmed for parts that were heavily formed before installation.
FAQ
Q: What is C28000 made of?
It is a copper-zinc alloy with about 59-63% copper, the balance zinc, and residual limits of 0.30% maximum lead and 0.07% maximum iron.
Q: Why is C28000 easier to hot work than 70/30 brass?
Its higher zinc content produces a two-phase alpha-beta structure, and the beta phase deforms readily at elevated temperature, which is why the alloy is a standard choice for hot forging and extrusion.
Q: Can C28000 be welded?
It can be welded with suitable processes and filler metals, but zinc volatilisation causes fume and porosity, so ventilation, controlled heat input and correct filler selection are essential.
Q: Is C28000 suitable for seawater service?
It offers moderate resistance and is used for marine hardware, but for continuous seawater contact or high-velocity flow a tin-bearing brass or an aluminium bronze such as C61400 gives better resistance to selective zinc loss.
Q: What is the difference between C28000 and C26000?
C26000 is a 70/30 single-phase brass that is more ductile and better for cold forming, while C28000 is a 60/40 two-phase brass that is stronger and better for hot working but less tolerant of heavy cold deformation.
Q: Which standards cover C28000?
ASTM B135 for seamless tube, ASTM B36 for plate, sheet, strip and rolled bar, and ASTM B124 for forging rod and shapes, with European equivalents in the EN 12164, EN 12167 and EN 1652 series.
