Properties and Uses of Alloys

An alloy is a mixture of two or more elements, with at least one element being a metal. These elements are not chemically combined, but instead mixed to create a material that has more desirable characteristics.

Some potential desirable characteristics of alloys include:

  • Increased hardness
  • Lower melting point
  • Improved corrosion resistance
  • Resistance to extreme temperatures

The image below shows the arrangement of atoms in a pure metal.

Green circles in a regular fixed shape representing a solid structure.

When pressure is applied to a pure metal, the layers of atoms can easily slide over each other, making the metal relatively soft. However, the atomic structure of an alloy is different, as shown in the image below:

Small white circles and bigger green circles together representing the structure of an alloy.

In an alloy, the atoms are different sizes, which makes it more difficult for the layers of atoms to slide over each other. As a result, alloys tend to be significantly stronger than their pure metal counterparts.

Common Alloys

Alloys offer many benefits, which is why many of the metals we encounter in our daily lives are alloys. Let’s look at some examples.

Copper alloys

Bronze is an alloy of copper and tin. It is the oldest known alloy and is significantly harder than pure copper. Bronze is commonly used for:

  • Coins
  • Ornaments
  • Statues
  • Medals

Brass is also an alloy of copper, but it is made of copper and zinc. Due to the corrosion-resistant properties of brass, it is used to make a wide range of objects, such as:

  • Doorknobs
  • Locks
  • Hinges
  • Taps

Steel alloys

Steel is an alloy of iron, containing a small amount of carbon, and other elements. The table below shows the main types of steel alloys, their properties and uses.

Steel alloyElements in the alloyPropertiesUses
High carbon steelIron and carbonVery hard, but also brittle• Cutting tools
Low carbon steelIron and carbonSofter and more easily shaped• Building frames
• Cookware
• Car bodies

As steel is an alloy of iron, it can rust. To prevent this, we can add chromium and nickel to form stainless steel.

Steel alloyElements in the alloyPropertiesUses
Stainless steelIron, chromium and nickelHard and corrosion-resistant• Cookware
• Cutlery
• Car bodies

Gold alloys

Gold, in its pure form, is a soft, malleable, and corrosion-resistant metal. To increase its strength and reduce malleability for jewellery-making, gold is alloyed with other metals like copper, silver and zinc. The added metals must not diminish the appearance of gold, as it is an important property.

The proportion of gold is measured in carats:

  • 24-carat gold is the purest form, containing 100% gold
  • 18-carat gold contains 75% gold
  • 12-carat gold has 50% gold

Aluminium alloys

Aluminium is commonly alloyed with copper, magnesium, zinc, silicon and manganese. Magnalium is an alloy of aluminium and magnesium. This alloy is not only stronger and more corrosion-resistant than pure aluminium but also has a lower density. As a result, it is widely used in automobile and aircraft construction.