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Alloys

Metal and Non-metals of Class 8

ALLOYS

A homogeneous mixture of two or more molten metal ( or a non – metal) is called alloy.  Pure metals generally do not have all the properties of a good metal, such as malleability, ductility, tensile strength, hardness, resistance to corrosion, conduction of heat and electricity, etc.

However, one or more of these properties can be improved by melting two or more metals (or non – metal) in some fixed proportion and then allowing the molten product to cool at room temperature. Such a product is called an alloy.

OBJECTIVE OF ALLOY MAKING:

Alloys are generally prepared to have certain specific properties which are not possessed by the constituent metals.  The main objects of alloy-making are:

  • To increase chemical reactivity.

  • To modify chemical reactivity.

  • To increase the hardness. 

  • To increase tensile strength.

  • To produce good casting.

  • To lower the melting point.

Name of alloy

Principal Metal

Composition

Properties

Uses

Duralumin

Aluminium 

Al = 95%

Cu = 4% 

Mn = 0.5%, 

Mg = 0.5%

Light weight and as strong as steel. 

Aircraft frames, rockets, speed boats, automobiles. 

Magnalium 

Aluminium

Al = 95%

Mg = 5%

Light weight, strong resists corrosion.

Used for making aeroplanes, household appliances, mirrors and scientific instruments. 

Stainless

Steel

Iron 

Fe = 83%

C = 1%

Cr = 15%

Ni = 1%

Resists corrosion

For making utensils, cutlery, surgical instruments and ornamental pieces. 

Manganese

steel

Iron

Fe = 84%

Mn  = 15%

C = 1%

Very tough and hard. 

Used for making safes, amour rock cutters etc. 

Tungsten 

Steel 

Iron

Fe = 79-84%

W = 15-20%

C = 1%

Very-very hard.

Used for making high speed tools. 

Aluminum

Bronze

Copper

Cu = 90%

Al = 10%

Golden yellow in colour. Durable and resistant to corrosion. 

Used for making artificial jewellery, coins, picture frames etc. 

Brass

Copper

Zn = 20-40%

Cu = 60-80%

Lustrous, more malleable and ductile than copper. 

Used for making shells of ammunition rounds, utensils, electric switches, statues, etc. 

Bronze 

Copper

Cu = 80% 

Zn = 10% 

Sn = 10%

Hard but brittle, resistant to corrosion. Takes very high polish.

Used for making shells, statues, coins and utensils. 

Gun Metal 

Copper

Cu = 88%

Sn = 10%

Zn = 1%

Pb = 1%

Very hard, gives a very good cast.

Used for making barrels of guns, gears and bearings. 

German 

Silver

Copper

Cu = 60%

Zn = 30%

Ni = 10%

As white as silver, malleable and ductile. 

Used for making imitation silver jewellery, utensils, etc. 

Bell Metal

Copper

Cu = 80%

Sn = 20%

Hard and brittle, produces with sonorous sound. 

Used for making bells and gongs. 

Monel Metal

Nickel

Cu = 28% 

Ni = 67% 

Fe = 5%

Resistant to corrosion, malleable and ductile. 

Used for making sinks, doors and windows screws. 

AMALGAM:

Amalgams are homogeneous mixtures of a metal and mercury. Example:  Sodium amalgam contains sodium and mercury. Different amalgams are prepared according to their uses.  For example, Sodium amalgam is produced to decrease the chemical reactivity of sodium metal. It is also used as a good reducing agent. Tin amalgam is used for silvering cheap mirrors.

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