What is an Alloy? - Definition & Examples

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  • 0:04 Everyday Metals
  • 0:30 Advantages of Alloys
  • 1:09 Types of Alloys
  • 1:44 How to Make an Alloy
  • 2:20 Alloy Composition Calculations
  • 3:45 Lesson Summary
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Lesson Transcript
Instructor
Nick Rogers
Expert Contributor
Matthew Bergstresser

Matthew has a Master of Arts degree in Physics Education. He has taught high school chemistry and physics for 14 years.

Alloys are mixtures of metal with other metals or non-metals. This process gives the material more desirable properties, such as increased hardness and lower melting points.

Everyday Metals

You probably see metal every day, but you may not realize that 90% of the metal that you encounter is actually what we call an alloy. An alloy is a mixture of metal with a second metal or other non-metal material. Airplanes, bicycles, and cooking pots are all usually made of different types of alloys. Some popular alloys include brass, solder metal, pewter, and sterling silver.

Advantages of Alloys

Mixing metals together or with non-metals offers many advantages. These combination materials can have enhanced hardness, lower melting points, and better tensile strength. Since pure metals have a high melting point, they tend to be very soft. Pure gold tends to be very malleable and is easily bent with a small amount of heat applied. This is the reason why most gold jewelry is actually an alloy.

Metals tend to be very reactive and have high melting points. Iron, for example, is very strong but reacts with moisture in the air and can rust very easily. Casting iron as an alloy can help to increase its inertness and prevent this.

Types of Alloys

There are two main types of alloys. These are called substitution alloys and interstitial alloys.

In substitution alloys, the atoms of the original metal are literally replaced with atoms that have roughly the same size from another material. Brass, for example, is an example of a substitution alloy of copper and zinc.

Interstitial alloys, on the other hand, mix together atoms that have very different sizes. Atoms are added to the original metal that are much smaller. For example, steel is created by adding a small number of carbon atoms in between the larger atoms in iron.

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Additional Activities

Alloys in Everyday Life

We just learned that alloys are metal solutions. Different metals and other elements are melted together resulting in different properties. Let's research how alloys are involved in our daily lives.


Research

Research the following alloys and report on the percentages of each element in the alloy.

  1. 10k yellow gold
  2. 14k yellow gold
  3. Sterling silver
  4. Rose gold
  5. Stainless steel
  6. Mild steel
  7. Aluminum alloy


Follow Up Questions

  1. What is the different percentages of gold in 10k yellow gold and 14k yellow gold?
  2. What are the other elements in yellow gold alloys?
  3. What are the other elements in rose gold alloys?
  4. Why are different elements added to gold to make jewelry?
  5. What is added to iron to make stainless steel?
  6. What special properties are beneficial for stainless steel compared to mild steel?
  7. What is added to iron to make mild steel?
  8. The famous ship the Titanic was made from mild steel. What was the percentage of additive elements in the Titanic steel compared to modern-day mild steel?
  9. What famous statue/monument is made from a copper alloy?
  10. Why are aluminum alloys so beneficial when building structures?


Exploring and Looking for Alloys

Mild steel is magnetic, no other commonly used alloy is. Use a magnet and your visual observations (color, density) to locate as many metals in your residence or school and categorize them as mild steel, stainless steel, copper alloy, or aluminum alloy.

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