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Wednesday, 3 February 2016

ALUMINIUM ALLOYS

            Aluminium as such is a soft metal of relatively low strength. Most of the alloys of aluminium are made by alloying it with various percentage of magnesium; these are harder and stronger. It prevents the formation of a coarse crystalline structure during heat treatment. These alloys known as L-M series alloys can be extruded and are used extensively for structural work.
  • Copper s the main hardening element added while the addition of a small percentage of magnesium to an aluminium copper alloy still further improves the hardness and strength after heat treatment. Strength may also be improved by addition of small quantities of manganese and nickel to a copper-aluminium alloy.
  • Silicon, is next in importance to copper as a main alloying element, since in combination with magnesium it forms a hard compound known as magnesium silicate which is largely responsible for the hardness obtained on the treatment.
  • Manganese acts as a strengthening agent and prevents the formation of a coarse crystalline structure during heat treatment.
Some of the important aluminium alloys are discussed below: 
(i) DURALUMIN:

          A famous alloy of Aluminium containing 4% copper, 0,5% magnesium, 0.5% manganese, a trace of iron and rest aluminium is called DURALUMIN.
          It can be forged, cast and stamped. It has high strength and a low specific gravity (2.8). However, its corrosion resistance is much lower as compared to pure aluminium. Sometimes, duralumin is covered or clad by thin aluminium layer on all side, such material is called "ALCLAD". If 5-15% silicon is alloyed with aluminium, we get alloys which are temperature resistant. The alloy is soft enough for a workable period after it has been quenched. Its melting point = 650°C .
  1. It is widely used for sheets, tubes, forgings, rivets, nuts, bolts and similar parts.
  2. It is used in making cables.
  3. Casting made of Al-Si alloys are used for manufacture of pistons of two wheeler on a large scale.
  4. Alclad is extensively used in air planes and other machines where weight is a deciding factor.
  5. It is also used in surgical and orthopaedic work and non-magnetic and other instrument parts.
(ii) HINDALIUM:
          Hindalium is an alloy of aluminium, magnesium, manganese, chromium and silicon etc., and is the trade name of the aluminium alloy produced by Hindustan Aluminium corporation Ltd. Mirzapur (U.P).
       It is manufactured as a rolled product mainly for anodized utensil manufature (cost of hindalium is 1/3 of stainless steel). during this special care is taken to maintain the necessary mechanical and surface characteristics.
Hindalium utensils possess the following advantages: 
  1. Strong and hard.
  2. Non reactive with food acids.
  3. They cannot be easily scratched.
  4. Good surface finish.
  5. They can be easily cleaned.
(iii) MAGNELIUM:
It is alloy of aluminium, magnesium, copper and tin etc.,
It has the following properties:
  1. It is a light weight alloy.
  2. Brittle and poor castability.
  3. Percentage of elongation is 7% for cold worked state and 30% for annealed state.
  4. Good mechinability.
  5. It can be welded.
          It is mostly used in the aircraft and automobile industries like gear box housings, vehicle door handles, Tyre rim of racing cars, skeletel body of aeroplanes. Coffee-grinder parts, fixtures and racks, phone body etc.,



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