Three Material Families, One Confusing Set of Names
Purchasing conversations frequently mix up copper, brass and bronze, and the confusion is expensive. A part drawing that calls for copper may be satisfied perfectly well by brass, or it may fail in service if brass is substituted for copper on a conductivity requirement. The three families are defined by what is alloyed with the copper.
Red copper is unalloyed copper, typically 99.9 percent copper or higher. It offers the best electrical and thermal conductivity and the best ductility, but the lowest strength.
Brass is a copper-zinc alloy. Zinc raises strength and hardness while lowering conductivity and ductility.
Bronze is copper alloyed primarily with tin, or with aluminium in the case of aluminium bronze, and offers superior corrosion and wear resistance at a higher cost.
Red Copper: Highest Conductivity, Lowest Strength
Red copper, also called pure copper, contains more than 99.9 percent copper. Its face-centred cubic structure gives it outstanding ductility and excellent electrical and thermal conductivity, and the standard grades T1 and T2 map closely to UNS C11000 in American practice. The trade-off is mechanical: tensile strength is on the order of 200 MPa in the annealed condition, so a threaded fastener in red copper would strip long before it reached the design load. Red copper is therefore specified where conductivity is the governing requirement, such as busbar, cable conductor, electrical switchgear connections of large cross-section and heat exchanger tubing, and it is rarely the right answer for a structural fastener.
Brass: Zinc Content Drives Everything
Brass is the copper-zinc alloy family and the natural home of brass fasteners and fittings. Increasing zinc raises strength and hardness and reduces ductility and conductivity. Above roughly 45 percent zinc the alloy becomes brittle and difficult to process, which is why most commercial brass grades keep zinc below about 40 percent. The H series designations under GB/T 5231 indicate the nominal copper content, so a lower H number means more zinc, higher strength and lower cost.
| Grade | Copper content, % | Character | Typical use |
|---|---|---|---|
| H59 | 57.0 to 60.0 | Highest strength and hardness of the ordinary brasses, lowest cost, weakest dezincification resistance | Cost-sensitive hardware, nuts, washers, brackets, dry-service fasteners |
| H62 | 60.5 to 63.5 | The best all-round balance of strength, ductility, machinability and cost | Plumbing fittings, valves, connectors, stamped and drawn parts, terminals |
| H65 | 63.5 to 68.0 | Higher copper, better cold formability and corrosion resistance, lower strength than H62 | Deep-drawn parts, radiator cores, decorative trim, tube and strip for forming |
H62 is the workhorse grade and should be the default choice unless a specific requirement pushes the choice towards H59 for cost and strength, or towards H65 for formability and corrosion life.
Bronze: Tin and Aluminium Alloying for Tough Service
Bronze covers copper alloys in which tin, aluminium, silicon or beryllium is the principal alloying addition. Tin bronzes and phosphor bronzes provide substantially better resistance to seawater, steam and dilute acids than any ordinary brass, together with good wear resistance and useful bearing properties. Typical duty includes marine hardware, pump and valve components, worm gears, sleeve bearings, spring contacts and chemical plant fittings. Aluminium bronzes add high strength and excellent resistance to seawater and to many process chemicals, and are often selected for valve bodies, pump impellers and wear rings. The price of this performance is higher material cost and, in several grades, harder machining.
Lead in Brass and the Export Market
Free-cutting brasses contain a deliberate lead addition, in the range of roughly one to three percent, which dramatically improves machinability so that screw heads form cleanly and threads cut sharply. The leaded free-cutting grades remain the fastest and cheapest way to produce high-volume turned parts from the copper alloy family. However, lead is a restricted substance in many export markets, and for potable water contact and electrical and electronic equipment the market has shifted towards lead-free free-cutting brasses that replace lead with bismuth or silicon while retaining a machinability rating close to the leaded grades. For any export programme, the destination regulation, not the workshop habit, should determine whether a leaded grade is permissible.
Selection Guidance and Inspection Points
Conductivity is the governing requirement: use red copper in an appropriate temper, or a very low-zinc brass if a small strength increase justifies a modest conductivity loss.
Strength and cost dominate and the environment is dry: H59 is the economical answer.
Forming, machining, general fittings: H62 is the default.
Deep drawing and good general corrosion life: H65.
Seawater, steam, wear or bearing duty: a tin, phosphor or aluminium bronze, not any ordinary brass.
Fasteners for potable water contact: confirm the lead restriction of the destination market before ordering a leaded free-cutting grade.
FAQ
Q: Is brass the same as copper?
No. Copper is essentially unalloyed, at 99.9 percent purity or higher, while brass is a copper-zinc alloy. Brass is stronger and cheaper, copper conducts better and is more ductile.
Q: What is the difference between brass and bronze?
Brass is alloyed with zinc, bronze principally with tin or aluminium. Bronze normally gives better corrosion and wear resistance and costs more.
Q: Which brass grade should be the default choice?
H62. It offers the best balance of strength, ductility, machinability and cost, and it covers the majority of fittings, connectors and formed parts.
Q: When is H65 preferred over H62?
When cold formability and corrosion life matter more than strength, for example in deep-drawn parts, radiator components and decorative trim.
Q: Why is lead added to some brasses?
To improve machinability and chip formation so that high-volume turned parts can be produced quickly with a good surface finish. Lead content is restricted in several export markets, so lead-free alternatives may be required.
Q: Can brass be substituted for bronze in marine service?
Not safely. Ordinary brasses are prone to dezincification and to stress corrosion cracking in chloride environments, so marine hardware should use a bronze or another alloy designed for seawater duty.
