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Alloys – Definition, Composition, Properties and Uses

Last Updated : 12 Oct, 2021
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A substance created from the mixing of two or more metals is referred to as an alloy. Combinations of metals and other elements can also be used to create alloys. The properties of alloys are frequently dissimilar to the qualities of their constituent components. When compared to pure metals, alloys frequently have greater strength and hardness. Red gold, which is made by combining copper and gold, is an example of an alloy. White gold, which is made by combining silver and gold, is another major gold alloy. The several properties of metals like malleability, ductility, strength, etc., can be improved by mixing other metals with them. The mixture of various metals is called an alloy.

What are Alloys?

An alloy is a mixture of two or more metals or an alloy is a mixture of metal and small amounts of non-metals.

Pure metals are never used in industries for manufacturing purposes. A combination of metals is used to enhance the properties of a single metal and this combination of metals is known as an alloy. It may also contain metal and non-metal. In general, an alloy of metals is made by melting the various metals in the proper proportions and then cooling the mixture to room temperature. An alloy of a metal and a non-metal can be prepared by first melting the metal and then dissolving the non-metal in it, which is followed by cooling it to room temperature. In comparison to metals, alloys have more strength and last longer.

For example- 

  1. Aluminium metal is light but not strong, but an alloy of aluminium with copper, magnesium and manganese is light as well as strong.
  2. Aluminium metal is light but not hard, but an alloy of aluminium with magnesium is light as well as hard.
  3. Iron is the most widely used metal. But it is never used in the pure form because pure iron is very soft and stretches very easily when hot. When a small amount of carbon is mixed with iron, an alloy called steel is obtained. Also when the iron is mixed with chromium and nickel, we get an alloy called stainless steel, which is strong, tough and does not rust at all.

Various Composition of Alloys

Some of the common alloys are Brass, Steel, Stainless steel, Bronze, Solder, amalgam etc. The compositions of various alloys are given below:

  • Bronze was the first alloy to be discovered. It’s made up of copper and tin. It has a copper content of 90% and a tin content of 10 %. To improve the overall characteristics, very small amounts of zinc, nickel, or manganese may be added.
  • Copper and zinc are combined to make brass. It contains approximately 80 % copper and 20 % zinc. Other components can be added in smaller amounts. Brass is used to improving copper’s electrical characteristics.
  • Steel is made by mixing 90 % iron and 1% carbon. It’s more corrosion-resistant and long-lasting.
  • Stainless steel is made by mixing iron with chromium and nickel. It contains approximately 18 % chromium and 5 % nickel.
  • Alnico is a metal alloy made up of iron, nickel, cobalt, and aluminium.
  • Tin and lead alloys are used to make solder. It’s made up of 50 % lead and 50 % tin.
  • Cast iron is formed by mixing iron with carbon. It contains 96-98% of iron and 2-4% of carbon. Silicon traces may also be discovered.
  • Sterling silver is made by combining 92.5 % silver and 7.5 % other metals, most commonly copper. If the air contains sulphur compounds, silver will corrode and turn black. Copper or other metals can be blended with silver to make this alloy that reduces tarnishing.
  • Nickel, chromium, and iron are used to make nichrome. It has a high resistance, melting point, ductility, and other properties. It has a high resistance to electron flow and is difficult to oxidize.
  • Amalgam is a mercury alloy including one or more additional metals. A solution of sodium metal in liquid mercury metal is known as sodium amalgam.
  • Gold with a purity of 24 carats is regarded as the purest. Pure gold is very soft due to which it is not suitable for making jewelry. To make gold harder, it is mixed with a small amount of silver or copper. In India gold ornaments are made of 22 carats of gold, which means that 22 parts of pure gold is alloyed with 2 parts of either silver or copper.

Properties of Alloys

Each alloy has certain useful properties. An alloy’s properties are distinct from those of the individual metals from which it is produced. Some properties of alloys are given below.

  1. Alloys are harder than their constituent metals.
  2. Alloys are more resistant to corrosion than pure metals.
  3. Alloys are more durable than the metals they are made from.
  4. The electrical conductivity of alloys is lower than that of pure metals.
  5. Alloys have a lower melting point than the metals from which they are made.
  6. Alloys have greater ductility than their constituent metals.

Uses of Alloys

Alloys are used in a number of ways in our daily lives. Some of the most common uses of alloys are given below.

  • Brass is used for making cooking utensils, screws, locks, doorknobs, electrical appliances, zippers, musical instruments, decoration and gift items
  • Bronze is used to make statues, coins, medals, cooking utensils, and musical instruments, among other things.
  • Alnico is a ferromagnetic substance and is used in permanent magnets.
  • Solder is used to repair or join two pieces of metals, i.e., it is used to permanently join electrical components.
  • Surgical devices, musical instruments, cutlery, and jewellery are all made of sterling silver.
  • Stainless steel is used for the construction of railways, bridges, roads, airports etc. It is also used for making cooking utensils and other products.
  • Alloys of aluminium are lightweight, so they are used for making bodies of aircraft and their parts.
  • Because of their high-temperature strength and superplastic behaviour, titanium alloys are widely used in the aerospace industry.
  • Amalgam is a mercury alloy that is utilized in medicinal procedures. Dentists also use it to fix cavities in teeth.
  • Certain alloys of gold such as rose gold, are used for jewellery making purposes.

The Iron Pillar at Delhi

The Iron Pillar near Qutub Minar in Delhi is made up of wrought iron which is low carbon steel. It is 8 meters high and 6000 kg in weight. Indian iron craftsmen constructed this pillar in 400 BC. Though wrought iron rusts slowly with time, the ironworkers have developed a process that prevented the wrought iron pillar from rusting even after thousands of years. 

The formation of a thin film of magnetic oxide of iron Fe_{3}O_{4}  on the surface has prevented corrosion. This thin layer was formed on the surface of the pillar as a result of finishing treatment given to the pillar by painting it with a mixture of different salts, then heating and rapid cooling. This pillar stands in a good condition more than 2000 years after it was made. This pillar has not rusted at all. It suggests that ancient Indians were well-versed in metals and alloys.

Sample Questions

Question 1: What is meant by 22 carats of gold?


22 carats of gold, means that 22 parts of pure gold is alloyed with 2 parts of either silver or copper.

Question 2: How is an alloy made?


An alloy of metals is prepared by mixing the various metals in molten state in required proportions and then cooling their mixture to the room temperature.

Question 3: How are alloys used in the Aerospace industry?


Aluminum is a lightweight metal and its alloys are used in the aerospace industry. These alloys are used for making bodies of aircrafts and to form high strength parts for jet engines. These parts deal with the extremities of temperature, pressure and vibration. They provide high strength and the ability to function at very high temperatures.

Question 4: Which alloy is used by the dentists?


Amalgam is an alloy of mercury metal. An amalgam consisting of mercury, silver, tin and zinc is used by dentists for filling in teeth.

Question 5: Why is the Iron Pillar at Delhi still not rusted?


The formation of a thin film of magnetic oxide of iron Fe_{3}O_{4}  on the surface of the pillar has prevented the rusting of Iron Pillar, as a result of finishing treatment given to the pillar by painting it with a mixture of different salts, then heating and rapidly cooling. 

Question 6: What are the constituents of stainless steel?


Stainless steel is a mixture of iron with chromium and nickel. It is very strong and do not rust. It is commonly used for making cooking utensils.

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