C21000 brass, a copper-zinc alloy with a nominal copper content of 60-63%, stands as a cornerstone material in precision engineering and CNC machining. Its unique combination of mechanical strength, excellent corrosion resistance, and superior machinability makes it a preferred choice for components requiring both durability and intricate geometries. At Dongguan Stirling Metal Products Co., Ltd., we leverage decades of experience to deliver C21000 parts that meet the most demanding specifications. This alloy, often referred to as “yellow brass” due to its characteristic golden hue, offers a remarkable balance of cost-effectiveness and performance, making it indispensable across industries from electrical connectors to marine hardware. With a density of 8.4 g/cm³ and a melting range of 900-940°C, C21000 is engineered for high-volume production, where consistent material properties are critical for maintaining tight tolerances and repeatable outcomes in CNC machining operations.
1. C21000 Basic Information
C21000, commonly known as brass, is a widely utilized copper alloy in the alpha-beta phase family. It exhibits a face-centered cubic (FCC) crystal structure, which contributes to its excellent ductility and formability. The alloy’s density of 8.4 g/cm³ and melting point of approximately 900-940°C make it suitable for a broad range of manufacturing processes, including hot forging, cold heading, and precision CNC machining. Its electrical conductivity, typically around 28% IACS, and thermal conductivity of 120 W/m·K ensure efficient heat dissipation in electrical and mechanical applications. The alpha-beta microstructure, with approximately 60-70% alpha phase and 30-40% beta phase at room temperature, provides a unique combination of strength and machinability. The beta phase, being harder and more brittle than the alpha phase, contributes to the formation of short, broken chips during machining, which is a key advantage for high-speed CNC operations. This alloy is also known for its excellent resistance to dezincification, a common corrosion issue in high-zinc brasses, thanks to controlled impurity levels and heat treatment processes.
2. Chemical Composition
The precise chemical composition of C21000 is critical to its performance. The following table outlines the standard composition ranges as per ASTM B36/B36M specifications:
| Element | Content (%) | Role in Alloy |
|---|---|---|
| Copper (Cu) | 60.0 – 63.0 | Primary element; provides strength and corrosion resistance |
| Zinc (Zn) | Balance | Enhances hardness and machinability |
| Iron (Fe) | ≤ 0.15 | Refines grain structure; improves strength |
| Lead (Pb) | ≤ 0.08 | Trace impurity; limited to maintain ductility |
| Tin (Sn) | ≤ 0.05 | Improves corrosion resistance in seawater |
| Nickel (Ni) | ≤ 0.05 | Enhances strength and toughness |
| Aluminum (Al) | ≤ 0.02 | Trace element; affects grain boundary properties |
| Other Elements (Total) | ≤ 0.15 | Includes manganese, silicon, and phosphorus as residuals |
The zinc content, ranging from 37-40%, places C21000 in the duplex alpha-beta region, offering a balance of strength and formability. Strict control of impurities ensures consistent mechanical properties and corrosion behavior. The iron content, typically maintained below 0.10% in premium grades, acts as a grain refiner, reducing the average grain size from 50-100 µm to 20-40 µm, which improves tensile strength by up to 10% without sacrificing ductility. Lead is kept below 0.08% to prevent hot shortness during forging and to maintain the alloy’s excellent cold-forming characteristics. Tin, even at trace levels, significantly enhances resistance to pitting corrosion in chloride-rich environments, making C21000 suitable for marine applications.
3. Mechanical & Physical Properties
C21000 exhibits a robust set of mechanical properties, making it suitable for structural and functional components. The following tables provide comprehensive data for both annealed and cold-worked conditions:
Mechanical Properties
| Property | Annealed Condition | Cold-Worked (H02) | Unit |
|---|---|---|---|
| Tensile Strength | 330 – 380 | 450 – 550 | MPa |
| Yield Strength (0.2% offset) | 160 – 200 | 310 – 380 | MPa |
| Elongation in 50 mm | 35 – 45 | 10 – 20 | % |
| Hardness (Rockwell B) | 60 – 75 | 80 – 95 | HRB |
| Hardness (Vickers) | 110 – 140 | 150 – 190 | HV |
| Modulus of Elasticity | 105 | 105 | GPa |
| Shear Strength | 200 – 240 | 280 – 340 | MPa |
| Fatigue Strength (10^7 cycles) | 100 – 120 | 150 – 180 | MPa |
Physical Properties
| Property | Value | Unit |
|---|---|---|
| Density | 8.4 | g/cm³ |
| Melting Point (Liquidus) | 940 | °C |
| Melting Point (Solidus) | 900 | °C |
| Thermal Conductivity (at 20°C) | 120 | W/m·K |
| Electrical Conductivity | 28 | %IACS |
| Specific Heat Capacity | 380 | J/kg·K |
| Thermal Expansion Coefficient (20-300°C) | 20.0 | ×10⁻⁶ /°C |
| Magnetic Permeability | < 1.01 | µ |
| Electrical Resistivity (at 20°C) | 6.2 | µΩ·cm |
These properties ensure that C21000 maintains dimensional stability under thermal loads and provides reliable electrical performance in connectors and terminals. The fatigue strength of 150-180 MPa in the cold-worked condition makes it suitable for cyclic loading applications, such as spring contacts and vibration-dampening components. The low magnetic permeability (< 1.01 µ) is critical for applications in sensitive electronic equipment, where magnetic interference must be minimized.
4. CNC Machining Characteristics
C21000 is classified as having excellent machinability, with a machinability rating of 80-90% relative to free-cutting brass (C36000). Its short chip formation and low cutting forces reduce tool wear and enable high-speed operations. Below are recommended CNC machining parameters for optimal results:
| Parameter | Recommendation | Notes |
|---|---|---|
| Cutting Speed (Turning) | 150 – 250 m/min | Use higher speeds for finishing passes; reduce to 120-180 m/min for interrupted cuts |
| Feed Rate | 0.05 – 0.15 mm/rev | Lower feed for fine surface finish; increase to 0.2 mm/rev for roughing |
| Depth of Cut | 0.5 – 3.0 mm | Roughing: 2-3 mm; Finishing: 0.5-1 mm; maximum 4 mm for heavy stock removal |
| Tool Material | Carbide (ISO K10-K20) | Coated carbide (TiN, TiAlN) for extended tool life; CBN for high-volume production |
| Coolant | Water-soluble emulsion (5-8% concentration) | Improves chip evacuation and surface quality; flood coolant recommended for deep holes |
| Surface Finish (Ra) | 0.4 – 1.6 µm | Achievable with proper parameters; mirror finish (Ra < 0.2 µm) possible with diamond tools |
| Tool Geometry | Rake angle: 5-10°, Relief angle: 6-8° | Positive rake reduces cutting forces; negative rake for high-speed roughing |
| Spindle Speed (Milling) | 3000 – 8000 rpm | Adjust based on tool diameter; use 0.02-0.05 mm/tooth feed for finishing |
Key machining considerations include:
- Chip Control: C21000 produces short, broken chips that are easily evacuated, reducing the risk of chip entanglement. Chip breakers are generally not required, but for deep hole drilling (L/D > 5), pecking cycles with 0.5-1 mm retracts are recommended.
- Heat Dissipation: High thermal conductivity (120 W/m·K) prevents heat buildup at the cutting edge, minimizing thermal distortion. This allows for cutting speeds up to 300 m/min in finishing operations without significant tool wear.
- Tool Wear: Carbide tools with TiN or TiAlN coatings are recommended for high-volume production to maintain edge sharpness. Typical tool life is 30-60 minutes at 200 m/min cutting speed, with flank wear limited to 0.3 mm.
- Threading and Tapping: Use spiral-flute taps with a 3-5% oversize to accommodate material springback. For M6 threads, a tap drill size of 5.0 mm is recommended, with a cutting speed of 10-15 m/min.
- Surface Finish Optimization: For Ra < 0.8 µm, use a wiper insert geometry with a nose radius of 0.8-1.2 mm and a feed rate of 0.05-0.08 mm/rev. Diamond turning can achieve Ra < 0.1 µm for optical applications.
5. Corrosion Resistance
C21000 demonstrates excellent corrosion resistance in a variety of environments due to the formation of a protective patina layer. Performance data is summarized below:
- Atmospheric Environment: Excellent resistance to urban, industrial, and marine atmospheres; corrosion rate < 0.5 µm/year in rural settings, and < 2 µm/year in industrial environments with SO₂ concentrations up to 10 ppm.
- Fresh Water: Suitable for potable water systems; corrosion rate < 2.5 µm/year at pH 6-8 and temperatures up to 60°C. Avoid stagnant water with high chloride content (> 200 ppm).
- Seawater: Good resistance in static conditions; avoid high-velocity flow (>1.5 m/s) to prevent erosion-corrosion. In tidal zones, corrosion rate is typically 5-10 µm/year, with pitting depth < 0.1 mm after 5 years.
- Acids and Alkalis: General resistance to dilute acids (e.g., acetic, citric) and alkalis; not recommended for strong mineral acids (e.g., HCl, H₂SO₄) at concentrations > 5%. In 10% sulfuric acid at 25°C, corrosion rate is 0.5 mm/year.
- Stress Corrosion Cracking: Susceptible in ammonia-containing environments; avoid exposure to NH₃ concentrations > 10 ppm. For applications in agricultural or chemical settings, stress relief annealing at 250-300°C for 1 hour is recommended to reduce residual stresses.
- Galvanic Corrosion: When coupled with stainless steel or titanium, C21000 acts as the anode and may corrode at rates up to 0.1 mm/year in seawater. Use insulating gaskets or coatings to prevent galvanic effects.
6. Typical Applications
C21000’s balanced properties make it ideal for a wide range of industries. Key applications include:
- Electrical Industry: Connectors, terminals, switchgear components, and busbars requiring 28% IACS conductivity. Used in automotive fuse holders and battery terminals where current ratings up to 100 A are common.
- Shipbuilding: Propellers, valve stems, pump impellers, and heat exchanger tubes for seawater systems. Propellers up to 2 meters in diameter are cast and machined from C21000 for corrosion resistance.
- Watch Parts: Precision gears, pinions, and decorative bezels requiring fine surface finishes (Ra < 0.8 µm). The alloy's non-magnetic properties are critical for mechanical watch movements.
- Lock Hardware: Lock cylinders, keys, and latch mechanisms demanding wear resistance and dimensional accuracy. C21000’s hardness of 80-95 HRB ensures long life in high-use applications.
- CNC Machined Parts: Automotive fuel system components, pneumatic fittings, and decorative trim pieces. Typical tolerances of ±0.02 mm are achieved in high-volume production.
- Architectural Hardware: Door handles, hinges, and railings exposed to indoor and outdoor environments. The alloy’s natural patina develops over time, providing a distinctive aesthetic.
- Musical Instruments: Brass instruments such as trumpets and saxophones use C21000 for its acoustic properties and workability. The alloy’s density and stiffness contribute to tonal quality.
7. Why Choose Dongguan Stirling Metal Products Co., Ltd.
Dongguan Stirling Metal Products Co., Ltd. combines material science expertise with advanced CNC machining capabilities to deliver C21000 components that exceed industry standards. Our commitment to quality is reflected in every aspect of our service:
- Material Procurement: We source C21000 from ISO 9001-certified mills, providing full material certificates (EN 10204 3.1) with traceability to heat numbers. Our inventory includes rod (6-100 mm diameter), bar (up to 6 meters), and custom extrusions.
- CNC Machining: Our 5-axis and multi-tasking machines achieve tolerances of ±0.01 mm, with surface finishes down to Ra 0.2 µm. We use in-process probing and statistical process control (SPC) to maintain Cpk > 1.33 for critical dimensions.
- Sample Production: Rapid prototyping in 3-5 days, including first-article inspection reports (FAIR) with dimensional data. We offer free DFM analysis to optimize part geometry for cost and performance.
- Batch Production: Scalable from 100 to 100,000+ units, with delivery in 7-15 days and 100% quality checks. Our lean manufacturing system reduces lead times by 20% compared to industry averages.
- Surface Treatment: In-house capabilities for polishing (mirror finish to Ra < 0.1 µm), electroplating (Ni, Cr, Sn, Ag), and passivation per ASTM B117. We also offer black oxide and antique finishes for decorative applications.
- Technical Support: Our engineering team provides DFM (Design for Manufacturability) feedback to optimize part geometry for cost and performance. We assist with material selection, tolerance analysis, and assembly design.
With over 15 years of experience in precision machining, Dongguan Stirling Metal Products Co., Ltd. is your trusted partner for C21000 components. Contact us for a free quote and consultation on your next project. Our team is available 24/7 to discuss your requirements and provide technical solutions.
