Extruded bar is the starting point for most machined brass components. The extrusion route decides grain flow, straightness and surface quality, and the final cold finishing pass decides temper; understood together, they explain why C28000 brass extruded bar machines cleanly, resists wet service and still accepts threading and light forming.
The Extrusion Route for C28000 Bar
C28000 is a 60/40 copper-zinc alloy containing both alpha and beta phases. The beta phase is ductile at elevated temperature, which is exactly what makes the alloy extrudable: billets are heated into a range where the structure deforms smoothly, typically between about 650 °C and 780 °C, and are pushed through a die to produce the bar profile. Extrusion is followed by controlled cooling, straightening and, where a temper is required, cold drawing or cold finishing.
Because the alloy passes through a hot stage, the extruded bar has fine, axially aligned grain flow. That flow is the reason extruded and drawn bar is preferred over machined-from-plate stock for parts loaded in tension, such as valve stems and threaded rods.
Composition Control and Grade Equivalents
The composition window for the UNS grade is fixed by the ASTM standards for the product form: copper 59.0 – 63.0 %, zinc as the balance, with lead, iron and other impurities held to the low residual limits of the applicable standard. Buyers working to Chinese or Japanese drawings frequently meet the same alloy under other designations, and the correspondence is summarised below.
| System | Designation | Copper content |
|---|---|---|
| UNS | C28000 (Muntz metal) | 59.0 – 63.0 % |
| China, drawn bar | H62, GB/T 4423 | 60.5 – 63.5 % |
| Japan, rod and bar | C2800, JIS H3250 | 59.0 – 63.0 % |
| Older European designation | CuZn40 | about 60 % nominal |
The three specifications describe the same family of 60/40 brass, with small differences in the copper band and in residual element control. When a drawing cites a Chinese grade and the delivered certificate quotes the UNS equivalent, the copper range of the ordered grade always governs.
Mechanical Performance by Temper
Extruded and drawn bar is ordered by temper under the ASTM B601 designation system, and the governing standard states the minimum tensile strength and minimum elongation for each temper line. Performance trends that the designer works with are consistent:
| Condition | Strength | Ductility | Typical use |
|---|---|---|---|
| Hot extruded, annealed | Lower | Highest | Heavy machining, bending, forming |
| Light drawn | Moderate | Good | General machined parts |
| Hard drawn | Higher | Moderate | Threaded studs, spacers |
| Extra hard | Highest | Limited | Wear parts, stiff fittings |
Acceptance values must always be taken from the temper line ordered; the trend table above describes relative behaviour and is not a substitute for the standard.
Physical, Machining and Finishing Behaviour
Physical constants: density 8.39 g/cm³, melting range approximately 900 – 940 °C, electrical conductivity about 28 % IACS in the annealed condition, thermal conductivity about 120 W/(m·K), modulus of elasticity about 103 GPa.
Machining: the beta phase breaks chips short, so the alloy machines well with positive rake tooling, sharp edges and flood coolant; tool wear is moderate and surface finish is consistent on automatic lathes.
Cold working: the alloy work hardens rapidly, so cold forming is limited to bending, coining and light drawing, with annealing between operations when reduction accumulates.
Joining: soldering and brazing are straightforward; fusion welding needs controlled heat input to limit zinc loss.
Surface finishing: bar can be polished, lacquered, tinned or plated after standard cleaning, and the bright colour is often left exposed on decorative parts.
Inspection Points That Decide Acceptance
Certificate of analysis showing copper, zinc and residual elements inside the limits of the ordered grade.
Tensile test result and elongation matched to the temper line that was ordered.
Diameter, ovality, straightness and length measured against the agreed tolerances.
Surface condition checked for extrusion marks, laps, seams and handling damage.
Grain flow and internal soundness assessed where the part will be heavily loaded or machined with deep cuts.
FAQ
Q: Why is extruded bar used instead of cast bar?
Extrusion consolidates the metal and produces continuous axial grain flow, giving better strength and more consistent machining than a cast structure.
Q: What is the copper content of C28000 extruded bar?
The UNS grade is specified at 59.0 – 63.0 % copper with zinc as the balance; the Chinese H62 grade of GB/T 4423 is specified at 60.5 – 63.5 % copper.
Q: Can extruded C28000 bar be cold formed after delivery?
Light bending and coining are practical, but the alloy work hardens quickly, so heavy forming requires an annealing operation.
Q: What temper is best for automatic machining?
A lightly drawn or annealed condition gives the best combination of chip formation and tool life; the exact temper is confirmed against the standard for the ordered line.
Q: How is bar straightness controlled?
By straightening after extrusion and drawing, then inspecting against the straightness tolerance agreed on the order.
Q: Is extruded C28000 bar suitable for wet service?
Yes. The alloy resists fresh water, marine air and salt spray well, with water chemistry reviewed where continuous chlorides are present.
