The Four Branches of the Copper Family
Copper is not a single material but a family of pure metals and alloys that share one base element while differing widely in composition, strength, conductivity and corrosion behaviour. In commercial purchasing the word copper may refer to electrolytic tough pitch copper, to a copper-zinc brass, to a tin bronze or to a copper-nickel alloy, and each branch is governed by its own standard, temper range and price level. Grouping the family into four branches - pure copper, brass, bronze and cupronickel - gives buyers, designers and inspectors a practical basis for reading grade designations and matching a material to a duty.
Chinese industry describes the family through the wrought copper and copper alloy composition standard GB/T 5231, while export orders usually cite ASTM or EN designations for the same materials. Being able to move between the two systems prevents the most common ordering error in this market: buying a copper alloy where pure copper is required, or paying for conductor-grade purity that the application does not need.
Pure Copper: Grades, Conductivity and the Hydrogen Disease Risk
Pure copper is a rose-red metal that develops a purple-brown oxide film in air, which is why Chinese trade usage often calls it purple copper. Its density is about 8.96 g/cm³ and its melting point about 1084 °C. In the annealed condition its electrical conductivity approaches 100 % IACS, second only to silver among commercial metals, and its thermal conductivity reaches roughly 400 W/(m·K). Pure copper also has excellent hot and cold workability and useful resistance to the atmosphere, to seawater and to a number of non-oxidising acids, alkalis and salt solutions.
The designation system becomes simple once the prefixes are known:
Ordinary copper: T1 to T4, with T1 the highest purity and progressively lower copper content as the number rises.
Oxygen-free copper: TU1 and TU2, produced without residual deoxidants, used where reducing atmospheres or maximum conductivity are involved.
Deoxidised copper: TUP and TUMn, with controlled phosphorus or manganese additions.
Special coppers: small additions of silver, tellurium or arsenic to obtain creep resistance, machinability or specific corrosion service.
Impurities matter more in pure copper than in any other branch. Titanium, phosphorus, iron and silicon depress conductivity sharply, while bismuth and lead form low-melting eutectics that cause hot brittleness. The best known failure mode is hydrogen disease: when ordinary copper that contains grain-boundary cuprous oxide is heated in a reducing atmosphere, hydrogen or carbon monoxide reacts with the oxide to form high-pressure water vapour or carbon dioxide at the grain boundaries and the metal cracks. Oxygen-free grades are therefore specified for brazing and for any high-temperature operation in a reducing atmosphere.
Brass: Copper-Zinc Alloys and the Alpha / Alpha-Beta Boundary
Brass is a copper-zinc alloy. In the binary system, increasing zinc raises strength and lowers plasticity, and industrial practice keeps zinc below roughly 45 %, above which brittleness degrades performance. Two structural zones dominate selection:
Single-phase alpha brass below about 39 % zinc: zinc dissolves in the copper lattice and the alloy retains good plasticity in both cold and hot working. H68 is the typical example.
Two-phase alpha plus beta brass above about 39 % zinc: a harder beta phase appears, so plasticity falls while tensile strength rises and hot working dominates. H59 is the common example.
The Chinese designation rule is the letter H followed by the copper mass fraction, so H96 contains nominally 96 % copper and H59 about 59 %. Cast grades take a Z prefix, for example ZH62. Where a third element is added, its symbol and content follow, as in HPb59-1 with about 1 % lead for machinability, or HSn70-1 and HAl77-2 with tin and aluminium additions for condenser and marine service. High-copper grades such as H90 and H96 are single-phase and golden-yellow with excellent workability; lower-copper grades are chosen for structural parts such as bolts, nuts, washers and springs.
Bronze: Tin Bronze and the Special Bronzes
Bronze originally meant a copper-tin alloy, named for the grey-green colour of its patina. Modern usage covers tin bronze as well as a group of tin-free special bronzes that are generally cheaper or better suited to particular duties:
Tin bronze such as QSn4-3: good corrosion resistance and wear behaviour, used for bearings and pump components.
Aluminium bronze such as QAl7: higher strength and strong resistance to seawater and chloride attack.
Silicon bronze such as QSi3-1: good weldability together with useful electrical properties.
Beryllium bronze such as QBe2: very high strength and hardness after precipitation hardening, used for springs and non-sparking tooling.
Lead bronze and cast tin bronze such as ZCuSn10P1: bearing and bushing materials cast close to shape.
Chinese designations use Q plus the main alloying element symbol and its mass fraction, with a Z prefix for cast products, so ZCuSn10P1 is a cast tin bronze containing about 10 % tin and 1 % phosphorus.
Cupronickel: Copper-Nickel Alloys for Marine and Thermal Service
Copper-nickel alloys are silver-white, which is why the family is called white copper in Chinese usage. Nickel raises strength, adds strong resistance to seawater and chloride environments and improves thermoelectric behaviour. Simple cupronickel is a binary copper-nickel alloy, while complex grades add manganese, iron, zinc or aluminium to refine corrosion performance. Commercial cupronickel splits into structural grades and electrochemical grades, and the two marine workhorses are 90-10 cupronickel, designated BFe10-1-1 and corresponding to UNS C70600, and 70-30 cupronickel, designated BFe30-1-1 or C71500. Both are supplied mainly as seamless condenser, evaporator and heat exchanger tube to ASTM B111 or its ASME equivalent, and both depend on controlled iron and manganese additions to keep the protective surface film intact in fast-flowing seawater.
Designations, Supply Forms and Selection Notes
| Group | Naming rule | Typical grades | Distinguishing behaviour |
|---|---|---|---|
| Pure copper | T plus purity number; TU for oxygen-free | T1-T4, TU1, TU2, TUP | Conductivity near 100 % IACS; soft; hydrogen disease risk if oxygen-bearing |
| Brass | H plus copper content | H96, H90, H68, H59, HPb59-1 | Strength rises and conductivity falls as zinc increases; workability set by phase structure |
| Bronze | Q plus main element | QSn4-3, QAl7, QSi3-1, QBe2 | Wear and seawater resistance; beryllium grades hardenable to high strength |
| Cupronickel | B plus nickel content | BFe10-1-1, BFe30-1-1 | Silver-white; best seawater corrosion resistance in the family; used for condenser tube |
All four groups are supplied as rod, wire, plate, strip, tube, foil and profiled sections. Plate and strip are hot or cold rolled, tube and bar are extruded or drawn, and wire is drawn down from rod. A purchase order therefore has to state more than the grade: the standard, the temper or condition, the dimensions and tolerances and the required inspection certificate all have to be defined, because the same designation delivered in a different temper behaves differently in strength and formability.
FAQ
Q: How can I tell pure copper from brass and bronze by grade designation?
Chinese designations encode the family in the first letter: T for pure copper, H for brass, Q for bronze and B for cupronickel, with a following number giving the main element content, as in H68 for 68 % copper brass or BFe10-1-1 for 90-10 cupronickel. International orders use the same logic through UNS numbers such as C11000 for electrolytic tough pitch copper, C26000 for cartridge brass and C70600 for 90-10 cupronickel.
Q: Which copper material has the highest electrical conductivity?
Pure oxygen-free and electrolytic copper grades such as C10100, C10200 and C11000 reach or slightly exceed 100 % IACS in the annealed condition. Alloying always reduces conductivity, so brass, bronze and cupronickel are selected for strength and corrosion resistance rather than for conductor duty.
Q: What is hydrogen disease and which grades avoid it?
Hydrogen disease is the cracking of copper that contains dispersed cuprous oxide when it is heated in a hydrogen or carbon monoxide bearing atmosphere, because the gas reacts with the oxide to create high-pressure steam or carbon dioxide at the grain boundaries. Oxygen-free grades such as TU1 and TU2 are specified for brazing and high-temperature reducing service.
Q: When should I choose bronze instead of brass?
Choose bronze for bearing, bushing and heavy-duty wear applications and for seawater or chloride service, where tin, aluminium or silicon additions give better load capacity and corrosion resistance than the equivalent brass. Brass remains the more economical and more workable choice for fasteners, fittings, decorative parts and general cold-formed components.
Q: Why do condenser tubes use cupronickel rather than brass?
Copper-nickel alloys form a stable, iron and manganese supported surface film that resists flowing seawater and inhibits pitting and impingement attack. This gives 90-10 and 70-30 cupronickel a longer service life than the brasses in seawater cooled condensers, which is why they are the standard choice for power station, desalination and marine heat exchanger tube.
Q: Are the same temper and dimension tolerances available in every group?
No. Tempers, dimensional ranges and permissible tolerances are defined separately for each product form and standard, so a pure copper strip order and a cupronickel tube order cannot share a single specification line. The grade, standard, temper, dimensions, tolerance class and test requirements should be listed separately for each item on the enquiry.
