T2 copper, designated as C11000 in the UNS system and electrolytic tough pitch (ETP) copper in common parlance, is the workhorse of the electrical and thermal management industries. Its reputation is built on an exceptional balance of high purity, excellent conductivity, and good formability. The central question—can its electrical conductivity truly reach 99.9% IACS (International Annealed Copper Standard)?—is a critical one for design engineers and procurement specialists. The answer is a definitive yes, but with critical engineering nuances. While the theoretical maximum for pure copper is 100% IACS at 20°C, T2 copper, with a minimum copper content of 99.90%, can achieve 99.9% IACS or higher under strictly controlled processing conditions. In practice, the measured conductivity of T2 copper typically ranges from 98% to 102% IACS, depending on the specific impurity profile, oxygen content, grain size, and thermal-mechanical history. Achieving the 99.9% threshold requires a combination of high-purity feedstock, optimized annealing in a reducing atmosphere, and minimal cold work. This article provides a comprehensive, data-driven technical analysis of T2 copper, covering its chemical composition, mechanical and physical properties, CNC machining characteristics, and practical applications, with a focus on delivering actionable insights for precision manufacturing.
1. T2 Basic Information
T2 copper is a high-purity copper alloy classified under the Chinese standard GB/T 5231-2012, equivalent to C11000 in the U.S. system (UNS designation). It is characterized by a minimum copper content of 99.90%, with controlled levels of oxygen (typically 0.02% to 0.05%) and trace impurities. This grade is produced through electrolytic refining followed by melting and casting, resulting in a material with excellent electrical conductivity, thermal conductivity, and ductility. T2 copper is particularly favored in applications requiring high electrical performance, such as busbars, connectors, and winding wires, as well as in thermal management systems like heat sinks and cooling plates. Its machinability is rated as fair to good, but careful parameter selection is essential for achieving optimal surface finish and dimensional accuracy in CNC machining operations.
2. Chemical Composition
The chemical composition of T2 copper is tightly controlled to ensure consistent performance. The following table provides the standard composition ranges as per GB/T 5231-2012:
| Element | Content (%) | Notes |
|---|---|---|
| Copper (Cu) | ≥99.90 | Including silver (Ag) content |
| Oxygen (O) | 0.02 – 0.05 | Controlled for conductivity |
| Iron (Fe) | ≤0.005 | Impurity limit |
| Lead (Pb) | ≤0.005 | Impurity limit |
| Bismuth (Bi) | ≤0.001 | Impurity limit |
| Antimony (Sb) | ≤0.002 | Impurity limit |
| Arsenic (As) | ≤0.002 | Impurity limit |
| Nickel (Ni) | ≤0.002 | Impurity limit |
| Tin (Sn) | ≤0.002 | Impurity limit |
| Sulfur (S) | ≤0.005 | Impurity limit |
| Zinc (Zn) | ≤0.005 | Impurity limit |
| Phosphorus (P) | ≤0.001 | Impurity limit |
Note: The total impurity content (excluding oxygen) must not exceed 0.10%. The oxygen content is deliberately maintained at low levels to minimize embrittlement during hot working and to preserve electrical conductivity. Higher oxygen levels can reduce conductivity by up to 2% IACS due to the formation of copper oxide inclusions. For achieving 99.9% IACS, the oxygen content should be kept below 0.03%, and all other impurities should be minimized to the lower end of their specified ranges.
3. Mechanical & Physical Properties
T2 copper exhibits a combination of high ductility, moderate strength, and excellent thermal and electrical properties. The following tables summarize the key mechanical and physical properties for typical wrought forms (e.g., rod, plate, tube) in the annealed condition:
Mechanical Properties
| Property | Value | Unit | Condition |
|---|---|---|---|
| Tensile Strength | 210 – 250 | MPa | Annealed (O) |
| Yield Strength (0.2% offset) | 70 – 100 | MPa | Annealed (O) |
| Elongation at Break | 45 – 60 | % | Annealed (O), 50 mm gauge |
| Hardness, Rockwell F | 45 – 55 | HRF | Annealed (O) |
| Hardness, Vickers | 80 – 110 | HV | Annealed (O) |
| Modulus of Elasticity | 115 – 130 | GPa | All conditions |
| Poisson’s Ratio | 0.34 | – | All conditions |
Physical Properties
| Property | Value | Unit | Notes |
|---|---|---|---|
| Density | 8.94 | g/cm³ | At 20°C |
| Electrical Conductivity | 98 – 102 | % IACS | Annealed, at 20°C |
| Electrical Resistivity | 1.72 × 10⁻⁸ | Ω·m | At 20°C, for 100% IACS |
| Thermal Conductivity | 385 – 401 | W/m·K | At 20°C |
| Specific Heat Capacity | 385 | J/kg·K | At 20°C |
| Linear Thermal Expansion Coefficient | 17.0 × 10⁻⁶ | K⁻¹ | 20°C to 100°C |
| Melting Point | 1083 | °C | Pure copper |
| Magnetic Permeability | 1.0 (non-magnetic) | µ | At 20°C |
The electrical conductivity of T2 copper can indeed reach 99.9% IACS under optimal annealing conditions (e.g., 400-500°C for 1-2 hours in a reducing atmosphere). However, in practice, values between 98% and 102% IACS are typical, with higher values achieved through careful control of oxygen content and grain size. Cold working reduces conductivity by 2-5% IACS due to increased dislocation density, but this can be restored through annealing. For applications requiring maximum conductivity, a final anneal at 450°C for 1.5 hours in a hydrogen or nitrogen atmosphere is recommended.
4. CNC Machining Characteristics
T2 copper is classified as having fair to good machinability, with a machinability rating of approximately 20% relative to free-cutting brass (C36000). Its high ductility and thermal conductivity present unique challenges in CNC machining, including chip control, built-up edge formation, and heat dissipation. The following table provides recommended machining parameters for common operations:
| Operation | Cutting Speed (m/min) | Feed Rate (mm/rev) | Depth of Cut (mm) | Tool Material | Coolant |
|---|---|---|---|---|---|
| Turning (roughing) | 150 – 250 | 0.10 – 0.30 | 2.0 – 5.0 | Carbide (K10/K20) | Water-soluble oil |
| Turning (finishing) | 200 – 350 | 0.05 – 0.15 | 0.2 – 1.0 | Carbide (K10) or PCD | Water-soluble oil |
| Milling (roughing) | 120 – 200 | 0.10 – 0.25 (mm/tooth) | 1.0 – 3.0 | Carbide (K20) | Water-soluble oil |
| Milling (finishing) | 180 – 300 | 0.05 – 0.12 (mm/tooth) | 0.2 – 0.5 | Carbide (K10) or PCD | Water-soluble oil |
| Drilling | 80 – 150 | 0.05 – 0.20 | N/A | HSS-Co or Carbide | Water-soluble oil |
| Threading | 50 – 100 | 0.05 – 0.10 | N/A | Carbide (K10) | Oil-based |
Key machining considerations for T2 copper include:
- Chip Control: Use chip breakers or high-pressure coolant to manage long, stringy chips that can entangle tools.
- Built-Up Edge (BUE): Maintain cutting speeds above 200 m/min to reduce adhesion; use sharp tools with positive rake angles (10°-15°).
- Heat Dissipation: T2’s high thermal conductivity (385 W/m·K) rapidly removes heat from the cutting zone, reducing tool wear but requiring adequate coolant flow to prevent thermal distortion.
- Surface Finish: Achievable Ra values of 0.4-0.8 µm with finishing passes; use PCD tools for mirror-like finishes (Ra < 0.2 µm).
- Tool Wear: Carbide tools typically last 30-60 minutes of cutting time; PCD tools can exceed 200 minutes.
5. Applications
T2 copper is utilized across a broad range of industries due to its combination of high conductivity, corrosion resistance, and formability. Common applications include:
- Electrical Industry: Busbars, connectors, terminals, switchgear components, and winding wires for transformers and motors.
- Electronics: Printed circuit board (PCB) traces, heat sinks, and lead frames for semiconductor packages.
- Automotive: Radiator cores, brake line fittings, and electrical harness components.
- Marine: Propeller shafts, heat exchanger tubes, and seawater piping systems.
- CNC Machined Parts: Precision components such as valve bodies, pump parts, and decorative hardware requiring high surface finish.
- Construction: Roofing sheets, flashing, and plumbing fittings.
6. Why Choose Dongguan Stirling Metal Products Co., Ltd.
Dongguan Stirling Metal Products Co., Ltd. is a leading provider of T2 copper materials and CNC machining services, offering a comprehensive one-stop solution for precision manufacturing. Our capabilities include:
- Material Sourcing: Direct procurement from certified mills with full MTC (Mill Test Certificate) traceability, ensuring Cu ≥ 99.90% and conductivity ≥ 98% IACS.
- CNC Machining: State-of-the-art 3-axis and 5-axis CNC machines with tolerances down to ±0.005 mm and surface finishes as low as Ra 0.2 µm.
- Rapid Prototyping: Sample delivery within 3-5 working days for design validation.
- Batch Production: Scalable from 100 to 100,000+ parts with consistent quality, delivered in 7-15 working days.
- Surface Treatments: In-house capabilities for polishing, electroplating (e.g., silver, nickel, tin), passivation, and anodizing.
- Quality Assurance: ISO 9001:2015 certified, with 100% dimensional inspection and material verification for every order.
Our team of senior materials engineers and CNC specialists ensures that every T2 copper component meets the highest standards of performance and reliability. Contact us today for a free quote and technical consultation.
