9.3 Alloys and their properties

2026 Syllabus Objectives

Core:

  1. Describe an alloy as a mixture of a metal with other elements, including:
    • (a) brass as a mixture of copper and zinc
    • (b) stainless steel as a mixture of iron and other elements such as chromium, nickel and carbon
  2. State that alloys can be harder and stronger than the pure metals and are more useful
  3. Describe the uses of alloys in terms of their physical properties, including stainless steel in cutlery because of its hardness and resistance to rusting
  4. Identify representations of alloys from diagrams of structure

Supplement: 5. Explain in terms of structure how alloys can be harder and stronger than the pure metals because the different sized atoms in alloys mean the layers can no longer slide over each other


What are Alloys? 🔑

Alloys are mixtures of elements (usually metals) designed to have properties that are useful for a particular purpose. They are not pure elements and therefore do not appear in the Periodic Table.

💡 Key Point: Substances such as steel, bronze, and brass share the properties of metals but are actually alloys, not pure elements.

Formation of Alloys

Alloys are formed by:

  1. Mixing the molten metals together thoroughly
  2. Allowing them to cool and form a solid

The resulting alloy is not simply a mixture of different crystal regions. Instead, the atoms of the second element form part of the overall crystal lattice.


Pure metals are not always the most useful for practical purposes:

  • Iron is quite soft and rusts easily
  • Copper is not very strong

Alloying can modify the properties of a metal to make it:

  • Stronger
  • Harder
  • More resistant to corrosion

Advantages of Alloys

Alloys are generally harder, stronger, and more corrosion resistant than the original individual metals.

Important: Strength is not the only property to consider when designing an alloy. Different alloys are designed for different purposes.


Important Alloys and Their Compositions 📌

1. Brass

Brass is an alloy of copper and zinc.

ComponentTypical Percentage
Copper70%
Zinc30%

Properties:

  • Harder than pure copper
  • 'Gold' coloured

Uses:

  • Musical instruments
  • Ornaments
  • Electrical connections

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