What H90 Brass Is and How It Is Designated
H90 is a copper zinc alloy of the single phase alpha type, containing nominally 90% copper and 10% zinc. Because the zinc content stays below the room temperature solubility limit of zinc in copper, the microstructure remains a single face centred cubic alpha phase, which is the reason for the excellent cold working behaviour, the warm golden colour and the good resistance of the alloy to general corrosion in ordinary atmospheres.
The same material appears under several designation systems, and cross referring them avoids confusion in purchase documents. It is listed as H90 in GB/T 5231, as CuZn10 in ISO and EN nomenclature with the material number CW501L, as UNS C22000 in the American system, and as C2200 in JIS. All of these describe a wrought copper zinc alloy with a copper content between 88% and 91%, so a specification that quotes grade plus temper plus dimensions is unambiguous in any of them.
Chemical Composition Limits
The composition of H90 is controlled by maximum limits on the impurity elements rather than by narrow ranges, because it is the copper content that governs the phase structure and the working behaviour. Typical limits for the wrought grade are given below.
| Element | Content |
|---|---|
| Cu | 88.0 - 91.0% |
| Ni | 0.5% max |
| Fe | 0.10% max |
| Pb | 0.03% max |
| Total impurities | 0.20% max |
| Zn | Remainder |
Iron and nickel are the elements that most affect performance at these levels. Both refine the grain and raise strength, but they also raise electrical resistivity, so a heat or strip order for conductive duty usually specifies the lower end of the permitted range. Lead is deliberately held very low, which is what allows H90 to be used in potable water and in decorative parts that come into contact with skin. Zinc makes up the balance and, at about 10%, keeps the alloy in the single phase field where ductility is highest.
Mechanical and Physical Properties
H90 combines moderate strength with high ductility, and the balance between the two is set by temper rather than by composition. Annealed strip and tube show a minimum tensile strength of approximately 390 MPa with a minimum elongation of about 3% in the standard minimum requirements, and cold worked tempers trade elongation for strength. A density of roughly 8.8 g/cm³, consistent with a 90% copper, 10% zinc mixture, makes the alloy lighter than pure copper while retaining the metallic conductivity and the reflective colour that decorative and electrical users value.
Strength and ductility: tensile strength from about 390 MPa in the annealed condition upward with cold reduction, with elongation falling as strength rises.
Cold formability: very good, allowing deep drawing, cold heading, bending, coining and high reduction rolling without intermediate annealing in many sequences.
Hot formability: good within the recommended hot working window, but the window is narrower than for lower copper brasses and is best respected in forging and extrusion schedules.
Conductivity: electrical and thermal conductivity are lower than those of pure copper because dissolved zinc scatters electrons and phonons, but remain sufficient for contacts, terminals and heat transfer strip.
Surface finishing: accepts tin plating, metallising, enamelling and lacquering readily, which supports decorative and radiator applications.
Processing and Heat Treatment
Two temperature windows dominate shop practice for H90. Hot working, such as forging, extrusion or hot rolling, is carried out between about 775 °C and 850 °C, where the alloy is soft enough to deform without cracking. Annealing of cold worked material is performed between about 540 °C and 600 °C to restore ductility and relieve internal stress before further reduction or before a part enters service.
Stress relief is worth separate attention. Cold formed H90 parts retain residual tensile stress that makes them sensitive to stress corrosion cracking in ammoniacal or mercury bearing environments, so a low temperature stress relief anneal is common practice for parts that will be stored, shipped or installed in humid industrial atmospheres. Where parts are to be soldered or brazed, the sequence of forming, annealing and joining is planned so that the final anneal does not destroy dimensional accuracy or surface finish.
Corrosion Behaviour and Service Limits
In the atmosphere, in fresh water and in neutral aqueous solutions H90 develops a protective surface film and corrodes very slowly, which is why it has a long history in plumbing, radiator and decorative service. Two limits should be respected. First, in seawater the corrosion rate may reach the order of 0.1 mm per year and can rise further where flow is turbulent or where the protective film is damaged by suspended solids, so marine use is normally confined to hardware, fittings and low velocity waterway pipe rather than to high velocity heat transfer surfaces. Second, ammonia, ammonium salts and mercury compounds attack the alloy and, in stressed cold worked parts, can cause stress corrosion cracking; these media disqualify H90 irrespective of the temper selected.
Because the zinc content is only about 10%, H90 is far less prone to dezincification than the higher zinc brasses such as H62 or H59, and it therefore tolerates mildly aggressive water that would attack those grades. Where chlorides, elevated temperature and stagnant conditions combine, however, selective attack remains possible and a periodic inspection routine is the practical safeguard.
Typical Applications by Industry
Building services and hardware: water heater tanks, radiator hot and cold pipe material, radiator corrugated strip, zipper components, light bezels and general hardware.
Electrical and electronic equipment: contacts, conductive parts, terminals, shielding and insulation support components that need moderate strength with good conductivity.
Mechanical engineering: valves, pipe fittings, bolts and fasteners, machined parts and other components that need ductility plus resistance to fresh water corrosion.
Heat transfer: radiator belts, heat transfer strip and low velocity water circuits where the thermal conductivity of the alloy is sufficient for the duty.
Decorative and consumer goods: medals, ornaments, personal accessories, cosmetic packaging and architectural trim, where the golden colour and the finishing response of the alloy are the deciding factors.
Marine and ship equipment: shipboard fittings, rivets, waterway pipe and waveguide components that operate outside high velocity seawater service.
Frequently Asked Questions
Q: What does the designation H90 mean?
The H marks a copper zinc wrought alloy in the Chinese designation system and the number indicates a nominal copper content of about 90%, so H90 corresponds to CuZn10, CW501L, UNS C22000 and JIS C2200.
Q: Is H90 brass the same as C22000?
They describe the same family of 90% copper, 10% zinc wrought alloy. C22000 is the unified numbering system designation, so a purchase order quoting either grade with the required temper and dimensions will match the same product.
Q: Why is the lead limit in H90 so low?
Lead is held to 0.03% maximum so that the alloy can be used in potable water systems, in decorative parts contacting skin and in applications where residual lead would be a regulatory concern.
Q: Can H90 brass be used in seawater?
Only with care. The corrosion rate in seawater may reach the order of 0.1 mm per year and increases in turbulent flow, so the alloy is best kept to low velocity pipe, fittings and hardware rather than to high velocity heat transfer surfaces.
Q: What are the working and annealing temperatures for H90?
Hot working is carried out between about 775 °C and 850 °C and annealing of cold worked material between about 540 °C and 600 °C. Both windows apply to the standard wrought composition.
Q: Does H90 suffer from dezincification?
It is much less susceptible than higher zinc brasses because the zinc content is only about 10% and the alloy remains single phase alpha. Selective attack is still possible in stagnant chloride containing water, so inspection remains advisable.
