- Alloys are mixtures of metals where the metals are not chemically combined.
- They can also be made from metals mixed with non-metals such as carbon.
- Alloys often have properties that can be very different from the metals they contain, for example they can have more strength, hardness or resistance to corrosion or extreme temperatures.
- Alloys contain atoms of different sizes, which distorts the regular arrangements of atoms.
- This makes it more difficult for the layers to slide over each other, so they are usually much harder and stronger than the pure metal.
The regular arrangement of a metal lattice structure is distorted in alloys
- Most of the metals that are in everyday use around us are alloys.
- Some common examples are discussed below.
- Bronze is an alloy made of copper and tin. It is harder than copper and is used to make ornaments and medals.
- Brass is a common example of an alloy which contains 70% copper and 30% zinc. It is decorative and corrosion resistant and is used for low friction ornamental purposes such as plumbing and carpentry fittings.
Brass is used extensively in modern kitchen and bathroom fittings
- Aluminium is mixed with copper, manganese and silicon for aircraft body production as aluminium alloys tend to be stronger and lighter than pure aluminium.
- Aluminium and magnesium (5%) make an interesting alloy called magnalium which is also used extensively in automobile and aircraft construction.
- As well as being lighter and stronger, it is also more corrosion resistant than aluminium.
- Magnalium with 50% magnesium is used in the production of fireworks as it is more stable than pure magnesium but still burns brightly.
- Gold alloys are used to make jewellery.
- Gold metal is relatively soft and malleable so other metals such as copper, zinc and silver are added to provide strength and toughness.
- Carats are used to express the purity of gold jewellery.
- Pure gold with nothing else added is said to be 24 carat.
- A 12 carat piece of gold jewellery therefore contains 50% gold.
- For example a 12 carat necklace that weighs 50g contains 50% gold, so 25 grams.
Rose, yellow and white gold are alloys of gold with varying proportions of Cu, Pd and Ag
- Molten iron is an alloy of 96% iron, with carbon, phosphorus, silicon and sulfur impurities.
- It is too brittle so most of it is converted into steel by removing some of the impurities.
- Not all of the carbon is removed as steel contains some carbon, the percentage of which depends on the use of the steel.
- Alloys of steel are made from adding other metals to steel such as chromium, manganese or nickel.
- By carefully controlling the amounts added, the particular type of alloy required can be produced.
- Steel alloys are used in construction, transport, manufacturing and other industries.
Diagram of a high carbon steel drill bit which are used for drilling through other metals