C28000 brass, also known as 60/40 brass or Muntz metal, stands as a cornerstone material in the engineering world, prized for its exceptional balance of strength, corrosion resistance, and machinability. As a senior materials engineer at Dongguan Stirling Metal Products Co., Ltd., I have overseen thousands of CNC machining projects utilizing this versatile copper-zinc alloy. Its unique microstructure, consisting of a dual-phase alpha-beta (α+β) structure, delivers mechanical properties that outperform single-phase brasses, making it the material of choice for demanding applications in marine hardware, electrical connectors, and precision mechanical components. In this comprehensive technical guide, we will dissect the chemical composition, mechanical and physical properties, CNC machining parameters, and real-world applications of C28000 brass, providing engineers and procurement specialists with the data needed to optimize their designs and manufacturing processes.
1. C28000 Basic Information
C28000, commonly referred to as Muntz metal or 60/40 brass, is a wrought copper-zinc alloy with a nominal composition of 60% copper and 40% zinc. It is classified under the UNS (Unified Numbering System) as C28000 and is recognized for its high strength, moderate ductility, and excellent resistance to dezincification in certain environments. The alloy’s dual-phase microstructure, with approximately 60-70% alpha phase and 30-40% beta phase, provides a unique combination of hot workability and cold formability. C28000 is typically supplied in the annealed (O) or half-hard (H02) temper, with tensile strengths ranging from 330 to 550 MPa depending on the processing history. Its density of 8.4 g/cm³ and thermal conductivity of approximately 120 W/m·K make it ideal for applications requiring efficient heat dissipation, such as heat exchanger components and electrical terminals. The alloy’s melting range of 890-905°C allows for hot working at temperatures between 750-850°C, while its cold formability is enhanced by the alpha phase’s ductility.
2. Chemical Composition
The chemical composition of C28000 brass is tightly controlled to ensure consistent mechanical and corrosion properties. The following table provides the standard composition ranges as per ASTM B36/B36M and ASME SB36 specifications:
| Element | Content (%) | Role in Alloy |
|---|---|---|
| Copper (Cu) | 60.0 – 63.0 | Primary alloying element; provides strength and corrosion resistance |
| Zinc (Zn) | Balance (approx. 37.0 – 40.0) | Strengthens the matrix; improves machinability |
| Iron (Fe) | ≤ 0.15 | Refines grain size; enhances strength |
| Lead (Pb) | ≤ 0.08 | Impurity; controlled to avoid embrittlement |
| Tin (Sn) | ≤ 0.05 | Minor addition; improves corrosion resistance |
| Nickel (Ni) | ≤ 0.05 | Stabilizes alpha phase; enhances toughness |
| Other Elements (Total) | ≤ 0.15 | Includes manganese, silicon, and aluminum; limited to maintain purity |
It is critical to note that the copper content must remain above 60% to maintain the desired alpha-beta phase balance. Lower copper levels can lead to excessive beta phase, reducing ductility and increasing susceptibility to stress corrosion cracking. At Dongguan Stirling Metal Products Co., Ltd., we verify all incoming material with optical emission spectroscopy (OES) to ensure compliance with these specifications. The zinc content is typically balanced to achieve a beta phase fraction of 30-40%, which optimizes machinability without compromising corrosion resistance.
3. Mechanical & Physical Properties
C28000 brass exhibits a robust set of mechanical and physical properties that make it suitable for high-stress applications. The data below is based on standard test methods (ASTM E8 for tensile, ASTM E18 for hardness) and typical values for the half-hard (H02) temper:
| Property | Value | Unit | Standard |
|---|---|---|---|
| Tensile Strength | 330 – 550 | MPa | ASTM E8 |
| Yield Strength (0.2% offset) | 160 – 350 | MPa | ASTM E8 |
| Elongation (in 50 mm) | 10 – 35 | % | ASTM E8 |
| Hardness (Brinell) | 80 – 140 | HB | ASTM E10 |
| Hardness (Rockwell B) | 50 – 85 | HRB | ASTM E18 |
| Hardness (Vickers) | 90 – 160 | HV | ASTM E92 |
| Density | 8.4 | g/cm³ | ASTM B328 |
| Thermal Conductivity (at 20°C) | 120 | W/m·K | ASTM E1225 |
| Electrical Conductivity (at 20°C) | 28 | %IACS | ASTM B193 |
| Modulus of Elasticity | 105 | GPa | ASTM E111 |
| Poisson’s Ratio | 0.33 | – | ASTM E132 |
| Melting Point (Liquidus) | 905 | °C | ASTM E794 |
| Melting Point (Solidus) | 890 | °C | ASTM E794 |
| Specific Heat Capacity | 380 | J/kg·K | ASTM E1269 |
| Thermal Expansion (20-300°C) | 19.0 | µm/m·°C | ASTM E831 |
These properties make C28000 particularly attractive for components that must withstand moderate mechanical loads while maintaining dimensional stability. The thermal conductivity of 120 W/m·K is approximately 70% that of pure copper, enabling efficient heat transfer in applications like valve bodies and heat exchanger tubes. The electrical conductivity of 28% IACS is sufficient for many electrical connector applications, though lower than high-copper alloys. The modulus of elasticity of 105 GPa provides good stiffness for structural components, while the Poisson’s ratio of 0.33 indicates typical metallic behavior under load.
4. Corrosion Resistance
C28000 brass demonstrates excellent corrosion resistance in a variety of environments, though its performance is highly dependent on the specific conditions. The dual-phase structure can be susceptible to dezincification in acidic or high-chloride environments if not properly alloyed. Below is a detailed breakdown of its corrosion behavior:
- Atmospheric Environment: Excellent resistance to general atmospheric corrosion, including industrial, rural, and marine atmospheres. In marine environments, a protective patina forms, reducing further attack. Typical corrosion rate: < 0.5 µm/year.
- Fresh Water: Suitable for fresh water applications, including potable water systems. Corrosion rates are typically < 2 µm/year in soft water and < 5 µm/year in hard water. However, avoid stagnant conditions to prevent pitting.
- Seawater: Good resistance in seawater, with corrosion rates of 10-20 µm/year in flowing seawater. However, in stagnant or low-flow conditions, dezincification can occur, leading to selective leaching of zinc. For marine propellers and valves, inhibitors like arsenic (0.02-0.06%) are often added to mitigate this.
- Acids and Alkalis: General resistance to dilute acids (e.g., sulfuric acid up to 10% concentration) and alkalis (e.g., sodium hydroxide up to 20%). Avoid concentrated acids and strong oxidizing agents like nitric acid, which cause rapid attack.
- Stress Corrosion Cracking (SCC): Susceptible to SCC in ammonia-containing environments and under high tensile stress. For critical applications, stress-relief annealing at 250-300°C for 1-2 hours is recommended.
- Galvanic Corrosion: When coupled with more noble metals (e.g., stainless steel, copper), C28000 may act as an anode, accelerating corrosion. Use insulating gaskets or coatings to prevent galvanic effects.
To enhance corrosion resistance, Dongguan Stirling Metal Products Co., Ltd. offers surface treatments such as passivation (chromate-free) and electroplating (nickel, tin, or silver) for components exposed to aggressive media. For dezincification-prone environments, we recommend using inhibited grades with trace arsenic additions.
5. CNC Machining Performance
C28000 brass is renowned for its excellent machinability, earning a machinability rating of 80-90% relative to free-cutting brass (C36000, rated at 100%). The beta phase in the microstructure contributes to chip breakage, while the alpha phase provides ductility for good surface finish. Below are the recommended CNC machining parameters based on our extensive experience at Dongguan Stirling Metal Products Co., Ltd.:
| Parameter | Recommended Value | Unit | Notes |
|---|---|---|---|
| Cutting Speed (Turning) | 150 – 300 | m/min | Use higher speeds for finishing; lower for roughing |
| Cutting Speed (Milling) | 100 – 250 | m/min | Adjust based on tool diameter and coating |
| Feed Rate (Turning) | 0.10 – 0.30 | mm/rev | Use lower feeds for fine surface finish |
| Feed Rate (Milling) | 0.05 – 0.20 | mm/tooth | Reduce for thin-walled sections |
| Depth of Cut (Roughing) | 2.0 – 5.0 | mm | Maximize material removal rate |
| Depth of Cut (Finishing) | 0.2 – 0.5 | mm | Ensure dimensional accuracy |
| Tool Material | Carbide (K10-K20) or CBN | – | Uncoated or TiN-coated for longer tool life |
| Tool Geometry | Positive rake angle (5-10°) | – | Reduces cutting forces and heat generation |
| Coolant | Water-soluble emulsion (5-8%) | – | Flood coolant recommended for heat dissipation |
| Surface Finish (Ra) | 0.4 – 1.6 | µm | Can achieve < 0.2 µm with fine finishing |
| Tool Life (Carbide) | 30 – 60 | minutes | At recommended cutting speeds |
Key machining considerations include:
- Chip Control: The beta phase promotes short, broken chips, reducing chip entanglement. Use chip breakers for high-speed operations.
- Tool Wear: Carbide tools with TiN or TiAlN coatings provide tool life of 30-60 minutes at recommended speeds. Avoid high-speed steel (HSS) due to rapid wear.
- Heat Generation: Due to high thermal conductivity, heat is quickly dissipated, reducing thermal distortion. However, use coolant to prevent work hardening in the beta phase.
- Dimensional Accuracy: C28000 has low thermal expansion (19.0 µm/m·°C), enabling tight tolerances of ±0.01 mm in CNC machining.
- Surface Integrity: Avoid excessive cutting speeds above 350 m/min to prevent surface tearing. Use sharp tools and light finishing passes for optimal surface quality.
For complex geometries, we recommend using 3-axis or 5-axis CNC machines with rigid setups to minimize vibration. At Dongguan Stirling Metal Products Co., Ltd., we achieve tolerances as tight as ±0.005 mm on critical features using advanced CMM inspection. Our machining centers are equipped with high-pressure coolant systems (up to 70 bar) to enhance chip evacuation and tool life.
6. Typical Applications
C28000 brass is utilized across diverse industries due to its combination of strength, corrosion resistance, and machinability. Key applications include:
- Electrical Industry: Conductive parts, connectors, terminals, and switch components. Its 28% IACS conductivity is adequate for low-to-medium current applications up to 100 A.
- Shipbuilding: Propellers, propeller shafts, valve bodies, and marine hardware. The alloy’s resistance to seawater corrosion makes it ideal for components exposed to saltwater, with service life exceeding 20 years in moderate environments.
- Watch Parts: Precision components such as gears, pinions, and decorative bezels. The fine surface finish achievable with CNC machining (Ra < 0.4 µm) meets horological standards for luxury timepieces.
- Lock Hardware: Lock cylinders, keys, and latch mechanisms. The alloy’s wear resistance and machinability allow for complex key profiles with high security features.
- CNC Machining Parts: Precision parts for automotive, aerospace, and industrial machinery, including bushings, bearings, and fittings. The material’s dimensional stability ensures consistent performance under cyclic loading.
- Heat Exchangers: Tubes and plates in heat exchangers for chemical processing and HVAC systems. Thermal conductivity of 120 W/m·K ensures efficient heat transfer, with operating temperatures up to 250°C.
- Architectural Hardware: Door handles, railings, and decorative trim. The alloy’s golden appearance and corrosion resistance make it suitable for both interior and exterior applications.
In our facility, we have produced C28000 components for marine propellers up to 500 mm in diameter and electrical connectors with tolerances of ±0.01 mm. The material’s versatility makes it a cost-effective alternative to bronze in many applications, offering similar performance at a lower material cost (approximately 30-40% less than C93200 bronze).
7. Why Choose Dongguan Stirling Metal Products Co., Ltd.
Dongguan Stirling Metal Products Co., Ltd. is a premier provider of C28000 brass materials and CNC machining services, with over 15 years of experience in the industry. Our commitment to quality and precision sets us apart:
- Material Sourcing: We partner with certified mills (e.g., KME, Wieland) to supply C28000 with full MTC (Mill Test Certificate) compliance to ASTM B36/B36M and EN 1652 standards. All material is traceable from melt to finished product.
- CNC Machining Capabilities: Our facility houses 50+ CNC machines (3-axis, 4-axis, and 5-axis) from brands like Mazak and Haas, capable of achieving tolerances of ±0.005 mm and surface finishes down to Ra 0.2 µm. We also offer Swiss-type turning for small-diameter components.
- Quality Control: We employ CMM (Coordinate Measuring Machine), optical profilometry, and hardness testing (Rockwell and Brinell) for 100% inspection on critical dimensions. Our ISO 9001:2015 certified quality management system ensures consistent output.
- Lead Times: Sample making in 3-5 days and batch production in 7-15 days, with rush options available for urgent orders. We maintain a 95% on-time delivery rate.
- Surface Treatments: In-house capabilities include polishing (mechanical and electrochemical), electroplating (nickel, tin, silver, gold), passivation, and powder coating. We also offer black oxide and chromate conversion coatings.
- Technical Support: Our engineering team provides DFM (Design for Manufacturing) feedback to optimize your designs for cost and performance. We offer free consultation on material selection and machining strategies.
We have successfully delivered over 10,000 C28000 components to clients in North America, Europe, and Asia, with a defect rate of less than 0.5%. For a free quote or technical consultation, contact us today. Let Dongguan Stirling Metal Products Co., Ltd. be your trusted partner for precision brass components.
