Copper combines electrical and thermal conductivity with very good strength and stiffness. As a result of its very useful balance of properties, it is one of the most consumed metals, behind only steel and aluminium. Adding alloy elements increases strength and stiffness, at the expense of conductivity.

Copper mining and smelting have a significant carbon footprint. The global average, according to the International Copper Association (ICA), is 2.3 kgCOe/kg, with production in some cases resulting in as much as 3.8 kgCO2e/kg. Low-carbon copper, produced using renewable energy by companies such as Aurubis and Boliden, has a reduced carbon footprint of 1.5 kgCO2e/kg.

Copper is a noble metal able to resist weathering for many decades. In the presence of moisture, salt and high sulphur pollution, copper quickly begins to oxidise and progress through the weathering cycle – colour changes depending on the alloy elements. For copper, it progresses from reddish-pink through reddish-brown and ultimately, depending on the local climate, it will take on the characteristic copper-green.

Brasses contain zinc as the principal alloying element, along with other ingredients that may include iron, aluminium, nickel and silicon. They are available as wrought or cast.

Wrought brasses contain up to around one-third zinc. Up to this point, brasses maintain a face-centred cubic (FCC) crystal structure. Known as single-phase, or alpha (α), brasses, they are suitable for cold forming processes, such as drawing, spinning and pressing. Alloys with more than one-third zinc are harder, stronger and tend to be more difficult to cold-work and so are available as cast. These brasses, which contain more than one-third zinc, form both FCC and body-centred cubic (BCC) crystal structures and so are known as alpha-beta (α-β) brasses.

Wrought alloys (rod, bar, sheet, strip, and so on) are made up of around one-third zinc and include copper-zinc (yellow brass), copper-zinc-lead (leaded brass) and copper-tin-zinc (tin brass). They are stronger than pure copper, with excellent formability and machinability. As the proportion of zinc increases, the colour shifts from copper-red to gold.

Also know as the ‘yellow brasses’, wrought copper zinc alloys are resistant to corrosion, moderately high strength, and reasonably ductile in some forms – making them highly formable. They are used in musical instruments, architectural façades, jewellery, door handles and packaging. As the zinc content increases, the mechanical properties improve and the cost reduces (zinc is less expensive than copper).

Cast alloys include copper-zinc-lead (leaded brass), copper-tin-zinc (tin brass and red brass), copper-zinc-silicone and copper-bismuth. Also, rather confusingly, the family of alloys known as ‘manganese bronze’, in which zinc is the principal alloy element, are also referred to as high-strength yellow brass. They have excellent mechanical properties combined with a very high resistance to corrosion.

Bronzes are copper alloys in which the major alloying element is not zinc or nickel. In the past, bronze was used to describe copper alloys that contained tin as the principal alloy element – these alloys have excellent casting properties.

Wrought bronze alloys include copper-tin-phosphorus (phosphor bronze), copper-tin-lead-phosphorus (leaded phosphor bronze), copper-aluminium (aluminium bronze) and copper-silicone (silicon bronze). Aluminium bronzes are the strongest of the copper alloys and have a distinctive bright golden colour that is very resistant to tarnishing due to the oxidisation of the aluminium.

Cast alloys include copper-tin (tin bronze), copper-tin-lead (leaded tin bronze), copper-tin-nickel (nickel-tin bronze) and copper-silicon (silicon bronze).

Copper-nickel contains nickel as the principal alloy. And nickel silvers, so-called because they are almost indistinguishable from silver in appearance, are alloys that contain zinc and nickel as the principal elements.

Leaded coppers contain 20% or more lead, and are cast. And there are other special alloys that do not fit into these designations.

There are several different standards used for identifying copper alloys, such as:
– ASTM (American Society for Testing and Materials) Standards in North America
– CEN standards in Europe
– ISO (International Standards Organisation) is based on the element symbols and the descending proportion of alloying elements