Non-Ferrous metals: Manufacture The bauxite is purified and then dissolved in fused cryolite (double fluoride of aluminium and sodium). The aluminium is then separated from this solution by electrolysis at about 910°C.
Properties: Pure aluminium has silvery color and lusture. It is ductile, malleable and very good conductor of heat and electricity. It has a very high resistance to corrosion than the ordinary steel. Its specific gravity is 2.7 and melting point is 658°C. Its tensile strength varies from 95 to 157 MN/m2. In proportion to its weight it is quite strong. In its pure state the metal would be weak and soft for most purposes, but when mixed with small amounts of other alloys, it becomes hard and rigid. It may be blanked, formed, drawn, turned, cast, forged and die cast. Its good electrical conductivity is an important property and is broadly used for overhead cables. It forms useful alloys with iron, copper, zinc and other metals.
Applications: It is mainly used in aircraft and automobile parts where saving of weight is an advantage. The high resistance to corrosion and its non-toxicity make it a useful metal for cooking utensils under ordinary conditions. Aluminium metal of high purity has got high reflecting power in the form of sheets and is, therefore, widely used for reflectors, mirrors and telescopes. It is used in making furniture, doors and window components, rail road, trolley cars, automobile bodies and pistons, electrical cables, rivets, kitchen utensils and collapsible tubes for pastes. Aluminium foil is used as silver paper for food packing etc. In a finely divided flake form, aluminium is employed as a pigment in paint. It is a cheap and very important non ferrous metal used for making cooking utensils.
Aluminium alloys: The aluminium may be easily alloyed with other elements like copper, magnesium, zinc, manganese, silicon and nickel to improve various properties. The addition of small quantities of alloying elements into other metals helps to converts the soft and weak metal into hard and strong metal, while still retaining its light weight. Various aluminium alloys are
- Magnalium and
- Hindalium , These alloys are discussed as below:
Duralumin: It is an important wrought alloy. Its composition contains following chemical contents.
Copper = 3.5-4.5%
Manganese = 0.4-0.7%
Magnesium = 0.4-0.7%
Aluminium = 94%
Properties: Duralumin can be very easily forged, casted and worked because it possesses low melting point. It has high tensile strength, comparable with mild steel combined with the characteristics lightness of Al. It however possesses low corrosion resistance and high electrical conductivity.
This alloy possesses higher strength after heat treatment and age hardening. After working, if this alloy is age hardened for 3 or 4 days. This phenomenon is known as age hardening. It hardens spontaneously when exposed to room temperature. This alloy is soft enough for a workable period after it has been quenched. It is light in weight as compared to its strength in comparison to other metals. It can be easily hot worked at a temperature of 500°C. However after forging and annealing, it can also be cold worked.
Applications: Duralumin is used in the wrought conditions for forging, stamping, bars, sheets, tubes, bolts, and rivets. Due to its higher strength and lighter weight, this alloy is widely used in automobile and aircraft components. To improve the strength of duralumin sheet, a thin film of Al is rolled along with this sheet. Such combined sheets are widely used in air-craft industries. It is also employed in surgical and orthopedic work, non-magnetic work and measuring instrument parts constructing work.
Y -alloy: Y-Alloy is also called copper-aluminium alloy. The addition of copper to pure aluminium increases its strength and machinability. Its composition contains following chemical contents.
Copper = 3.5-4.5%
Manganese = 1.2-1.7%
Nickel = 1.8-2.3%
Silicon, magnesium, iron = 0.6% each
Aluminium = 92.5%.
Properties: The addition of copper in aluminium increases its strength and machinability. Y-alloy can be easily cast and hot worked. Like duralumin, this alloy is heat treated and age hardened. The age-hardening process of Y-alloy is carried out at room temperature for about five days.
Applications: Y-Alloy is mainly used for cast purposes, but it can also be used for forged components like duralumin. Since Y -alloy has better strength than duralumin at high temperatures, therefore it is much used in aircraft engines for cylinder heads, pistons, cylinder heads, crank
cases of internal combustion engines die casting, pump rods etc.
Magnalium: Magnalium is an alloy of aluminium, magnesium, copper, nickel and tin etc. It contains
Al = 85 to 95%, Cu = 0 to 25%, Mg = 1 to 5%,
Ni = 0 to 1.2%, Sn = 0 to 3%, Fe = 0 to 0.9%,
Mn = 0 to 0.03%, Si = 0.2 to 0.6%.
It is made by melting the aluminium with 2-10% magnesium in a vacuum and then cooling it in a vacuum or under a pressure of 100 to 200 atmospheres.
Properties: Magnalium is light in weight and brittle. This alloy possesses poor castability and good machinability. It can be easily welded.
Applications Due to its light weight and good mechanical properties, it is mainly used for making aircraft and automobile components.
Hindalium: Hindalium is a common trade name of aluminium alloy. It is an alloy of aluminium, magnesium, manganese, chromium and silicon etc. In India, it is produced by Hindustan Aluminium Corporation Ltd., Renukoot (U.P.). Hindalium is commonly produced as a rolled product in 16 gauges. Utensils manufactured by this alloys are strong and hard, easily cleaned, low cost than stainless steels, having fine finish, having good scratch resistance, do not absorb much heat etc
Applications: Hindalium is mainly used for manufacturing anodized utensil. Utensils manufactured by this alloys are strong and hard, easily cleaned, low cost than stainless steels, having fine finish, having good scratch resistance, do not absorb much heat etc.