How Copper Materials Are Grouped
Copper products are grouped into four families that behave quite differently in service. Pure copper, also called red copper, has a copper content above about 99.7 % with all other elements treated as impurities. Brass is a copper-zinc alloy, with H62 and H65 as the common Chinese designations and C27200 and C27000 as the UNS equivalents. Bronze is a copper alloy in which the principal addition is neither zinc nor nickel, covering tin bronze, aluminium bronze and phosphor bronze. Cupronickel uses nickel as the principal addition and appears as BFe10-1-1 or BFe30-1-1 in GB/T 5231 and as C70600 or C71500 in UNS. The pure grades are further divided by deoxidation route: ordinary copper T1, T2 and T3, oxygen-free copper TU1 and TU2, phosphorus-deoxidised copper TUP and TP2, and special grades such as arsenic, tellurium and silver copper. GB/T 5231 fixes the designations and composition limits, GB/T 2059 covers strip, ASTM B152/B152M covers plate, sheet and strip, ASTM B170 and ASTM F68 cover oxygen-free grades, and EN 13601 and EN 13602 cover rod, bar and wire for electrical use.
Grade Chemistry and Conductivity Benchmarks
| Grade | Typical composition | Conductivity | Typical use |
|---|---|---|---|
| T1 / T2 | Cu+Ag 99.95 % min / 99.90 % min | 100 % IACS and above | wire, cable, busbar |
| T3 | Cu+Ag 99.70 % min | slightly below T2 | general fabricated parts |
| TU1 / TU2 | Cu+Ag 99.97 % / 99.95 % min, oxygen 0.002 % / 0.003 % max | 101-102 % IACS | vacuum devices, electron tubes |
| TUP / TP2 | phosphorus-deoxidised, P 0.015-0.040 % | about 85-95 % IACS | tube, air-conditioning coils |
| C11000 | Cu 99.90 % min, oxygen 0.02-0.04 % | 100-101 % IACS | general electrical and sheet |
| C10100 | Cu 99.99 % min, oxygen 0.0005 % max | 101-102 % IACS | high-vacuum, microwave, accelerator parts |
Pure copper has a density of 8.96 g/cm3 and a melting point of 1083 C, and its thermal conductivity falls in the 385-401 W/(m.K) band depending on grade and temper. The international annealed copper standard used across the industry is 58.0 MS/m at 20 C, which is the reference point for the 100 % IACS figure quoted in every mill certificate.
Impurity Effects and Hydrogen Embrittlement
Trace elements affect the two properties that matter most, conductivity and hot workability. Phosphorus, titanium, iron and silicon reduce electrical and thermal conductivity sharply, which is why deoxidised copper is never specified for conductor duty. Cadmium and zinc have only a minor effect. Oxygen, sulphur, selenium and tellurium have very low solid solubility and form brittle compounds; they barely disturb conductivity but reduce processing ductility. The classic failure is hydrogen embrittlement, also called hydrogen disease: when ordinary copper containing cuprous oxide is heated in a reducing atmosphere such as hydrogen or carbon monoxide, the gas reacts with the oxide at grain boundaries to form high-pressure steam, and the metal cracks. Furnace brazing, bright annealing and welding of oxygen-bearing copper therefore require either a controlled atmosphere or the selection of oxygen-free or phosphorus-deoxidised grades. Bismuth and lead form low-melting eutectics with copper and cause hot shortness, while controlled additions of lead, tellurium or sulphur are used deliberately to improve machinability.
Supply Forms and Temper Selection
Copper is supplied as cathode for remelting, as wire rod for drawing, as bar and busbar for machining and fabrication, as strip for stamping, and as seamless tube for plumbing, refrigeration and heat exchange. Temper determines formability: soft O60 material is used for deep drawing and bending, H02 half-hard for general fabrication, and H04 or harder for busbars and parts that must hold shape under load. Bend radius, grain size and springback all change with temper, so a drawing that calls out a bend radius should also call out the delivery temper. Strip is typically supplied from 0.1 mm to 3 mm thick with the edge condition stated, bar from about 3 mm to 200 mm, and tube to the relevant product standard such as ASTM B88 for water tube, ASTM B280 for air-conditioning and refrigeration tube, or GB/T 1527 for drawn tube.
Quality Control and Common Misunderstandings
Receiving inspection should confirm grade, temper and conductivity rather than copper content alone. Practical checks are chemical analysis to GB/T 5121 or ASTM E478, tensile testing to ASTM E8, hardness to ASTM E18, grain size to ASTM E112, and electrical conductivity by the eddy-current method of ASTM E1004 or by resistivity measurement to ASTM B193. Three misunderstandings recur. The first is that red copper is always pure copper, when the term covers alloys with deliberate deoxidising additions. The second is that T2 and C11000 are interchangeable in every application, which is not true when oxygen content and hydrogen exposure interact. The third is that conductivity figures can be compared between certificates without checking test method and temperature, since conductivity varies with temperature and with the method used to measure it.
Frequently Asked Questions
Q: What is the difference between ordinary copper and oxygen-free copper?
A: Ordinary copper such as T2 or C11000 contains 0.02-0.04 % oxygen, while oxygen-free grades such as TU1, C10200 and C10100 keep oxygen at 0.003 % or below, which prevents hydrogen embrittlement during reducing-atmosphere processing.
Q: Why does TP2 copper dominate air-conditioning tube?
A: Phosphorus deoxidation produces a fine, weldable tube with good creep behaviour at the brazing temperatures used in coil manufacture; the conductivity penalty, at roughly 85-95 % IACS, is irrelevant for heat-exchanger duty.
Q: How is conductivity verified on incoming copper?
A: By the eddy-current conductivity method of ASTM E1004 or by resistivity measurement to ASTM B193, with the result reported in MS/m or in percentage IACS at the reference temperature of 20 C.
Q: Can phosphor bronze be substituted for copper in a conductor?
A: No; phosphor bronze conducts only about 15 % of what electrolytic copper does, so it is a spring and wear material rather than a conductor.
Q: What causes a copper part to crack after brazing?
A: Hydrogen embrittlement, in which reducing furnace gases react with cuprous oxide at grain boundaries and generate high-pressure steam; the remedy is to specify oxygen-free or phosphorus-deoxidised copper for that process route.
