copper alloys

Copper has been humanity's working metal for thousands of years, and for good reason: it conducts electricity and heat better than almost anything affordable, resists corrosion, is easy to shape, and takes a warm reddish shine. Copper alloys are what you get when you add other elements to tune it, trading a little of copper's conductivity for more strength, hardness, castability, or a different color.

Pure copper is prized for wiring and heat exchangers because its electrical conductivity is second only to silver. But it is soft, so for hardware we alloy it. The two great families are brass (copper plus zinc) and bronze (copper plus tin, and by extension aluminum, silicon, or beryllium), each covered separately. Copper alloys strengthen mainly by solid-solution strengthening (dissolved atoms distort the lattice and impede dislocations) and by cold work; a few, like beryllium copper, are age-hardenable to spring tempers. A useful bonus: copper and many of its alloys are naturally antimicrobial, killing bacteria on contact, which is why hospital door handles are sometimes brass.

Copper alloys show up in electrical connectors, plumbing, marine fittings, musical instruments, coins, bearings, and springs. The honest trade-offs: copper is dense (about 8.9 g/cm^3, heavier than steel) and increasingly expensive, and every alloying addition that raises strength lowers electrical conductivity, so you cannot have maximum strength and maximum conductivity in the same alloy. Designers pick a copper alloy by which of those they need more.