Pure aluminium is very soft. If you want to make something stronger but still lightweight, hard-wearing, and able to survive the high temperatures in an airplane or car engine, you mix aluminium and copper. For food packaging, you don’t need anything like the same strength, but you do need a material that’s easy to shape and seal. You get those qualities by alloying aluminium with magnesium. Suppose you want to carry electricity over long distances from power plants to homes and factories. You could use copper, which is generally the best conductor (carrier) of electricity, but it’s heavy and expensive. Aluminium might be an option, but it doesn’t carry electricity so readily. One solution is to make power cables from aluminium alloyed with boron, which conducts electricity almost as well as copper but is a great deal lighter and less droopy on hot days. Typically, aluminium alloys contain 90–99 per cent aluminium
What’s Aluminium like?
Aluminium is soft, lightweight, fire-proof and heat-resistant, easy to work into new shapes, and able to conduct electricity. It reflects light and heat very effectively and it doesn’t rust. It reacts easily with other chemical elements, especially oxygen, and readily forms an outer layer of aluminum oxide if you leave it in the air. We call these things aluminium’s physical and chemical properties.
Aluminium really comes into its own when you combine it with other metals to make aluminium alloys (an alloy is a metal mixed together with other elements to make a new material with improved properties—it might be stronger or it might melt at a higher temperature). A few of the metals commonly used to make aluminum alloys include boron, copper, lithium, magnesium, manganese, silicon, tin, and zinc. You mix aluminium with one or more of these depending on the job you’re trying to do.
Aluminium can be combined with other materials in a quite different way in composites (hybrid materials made from two or more materials that retain their separate identity without chemically combining, mixing, or dissolving). So, for example, aluminium can act as the “background material” (matrix) in what’s called a metal matrix composite (MMC), reinforced with particles of silicon carbide, to make a strong, stiff, lightweight material suitable for a wide variety of aerospace, electronic, and automobile uses—and (crucially) better than aluminium alone.