Alloys

Metallic materials made from two or more elements, and what the additions achieve.

• 5000 series aluminium alloy

  Aluminium with magnesium in it — the marine alloy, and the one that welds properly.

• 6000 series aluminium alloy

  The aluminium everything is extruded from — window frames, bike frames, heat sinks and structural profile.

• 7000 series aluminium alloy

  The strongest aluminium there is — as strong as many steels, at a third the weight, and it does not like being welded or left in salt.

• Amalgam

  An alloy of mercury with another metal, liquid or pasty when fresh — how gold was extracted for two thousand years, and what most fillings were made of.

• Babbitt metal

  A soft metal that lets a shaft embed grit rather than be scored by it — bearing alloy, designed to be the part that wears.

• Brass

  Copper and zinc — the alloy that machines beautifully, resists seawater badly, and sounds better than either metal alone.

• Bronze

  Copper alloyed with tin — harder than either constituent, and the first engineered material to define an age.

• Cast iron

  Iron with enough carbon to pour but not to forge — brittle, cheap, superb at damping vibration, and the material the industrial revolution was built from.

• Cobalt-chromium alloy

  Harder and stiffer than titanium, and it does not wear — the bearing surface of a joint replacement, and the hot end of a turbine.

• Cupronickel

  Copper and nickel, which mix in any proportion — the metal of modern coins, condenser tubing and anything that has to sit in seawater.

• Duralumin

  Aluminium alloyed with copper and left to harden by itself — the discovery that made metal aircraft possible.

• Electrical steel

  Iron with three per cent silicon, rolled into a sheet whose crystals all point the same way — the material every transformer and every motor is built around.

• Electrum

  A natural alloy of gold and silver — what the world's first coins were struck from, and the reason coinage needed an assay from the very beginning.

• High-speed steel

  Tool steel that stays hard when it is red hot — which is what let machine tools run fast enough to change manufacturing.

• Invar

  An alloy that barely changes size with temperature — a coincidence of magnetism that turned out to be worth a Nobel Prize.

• Mischmetal

  The light rare earths alloyed together without being separated — the cheapest form rare earths come in, and the spark in every lighter flint.

• Neodymium magnet

  Neodymium, iron and boron in a structure that holds a magnetic field better than anything else known — and the reason a hard drive, an earbud and an electric motor can be small.

• Nichrome

  Nickel and chromium, which glows red hot for years without oxidising away — the wire in every electric heater, toaster and kiln.

• Nickel superalloy

  A nickel alloy that keeps its strength at four fifths of its own melting point — the reason a jet engine works, and the only large use of rhenium there is.

• Nitinol

  Bend it and it remembers — a metal that returns to a shape it was taught, and the reason a stent can be threaded through an artery.

• Osmiridium

  A natural alloy of osmium and iridium, denser than anything else that occurs in nature — and once the tip of every good fountain pen.

• Pewter

  Tin with a little antimony and copper — the tableware of ordinary households for five centuries, before pottery and then porcelain displaced it.

• Samarium–cobalt magnet

  Weaker than a neodymium magnet and untroubled by heat — the permanent magnet used where temperature rather than strength is the constraint.

• Solder

  A metal that melts low enough to join others without melting them — and the material every electronic device is held together with.

• Stainless steel

  Steel with enough chromium to repair its own oxide film — the material that made corrosion a design choice rather than a certainty.

• Steel

  Iron with a controlled, small proportion of carbon — the most-used engineered material in the world.

• Sterling silver

  Silver with 7.5 per cent copper, because pure silver is too soft to make anything from — and the copper is what makes it tarnish.

• Ti-6Al-4V

  One alloy is over half of all titanium used — the aerospace workhorse, and the metal a hip replacement is made of.

• Tool steel

  Steel that cuts, forms or shapes other materials — hard enough to hold an edge and tough enough not to shatter, which are opposing requirements.

• Weathering steel

  Steel that rusts on purpose, and then stops — the material of unpainted bridges and rust-coloured sculpture.

• Wootz steel

  The crucible steel of southern India, traded across the medieval world, and the material behind the patterned blades Europe could not reproduce.

• Zinc die-casting alloy

  The alloy behind almost every small metal part in a consumer product — cast to shape in seconds, and rarely noticed.