Alloys (Oxford AQA IGCSE Combined Science Double Award): Revision Note

What are Alloys?

• An alloy is a mixture of two or more metals or metal with a non-metal such as carbon

  • Steel is made from iron and carbon

• Alloys often have properties that can be very different from the metals they contain

  • They can be stronger and harder

  • They are resistant to corrosion or extreme temperatures

• These enhanced properties can make alloys more useful than pure metals

Structure of an alloy

• Brass is an alloy of copper and zinc and is much stronger than either metal

  • It is used in musical instruments, ornaments and doorknobs

• Different types of steel are made by varying the carbon content and by adding other metals

• For example, stainless steel is a mixture of iron and other elements such as chromium, nickel and carbon

  • It is used in cutlery because of its hardness and resistance to corrosion

• Alloys of iron with tungsten are extremely hard and resistant to high temperatures

• Alloys of iron mixed with chromium or nickel are resistant to corrosion

• Aluminium is mixed with copper, manganese and silicon for aircraft body production as the alloy is stronger but still has a low density

Why are the properties of an alloy different to a pure metal?

• Alloys contain atoms of different sizes, which distorts the normally regular arrangements of atoms in metals

• This makes it more difficult for the layers to slide over each other, so alloys are usually much harder than the pure metal