Skip to main content

What is aluminum ? and What are its Alloys ?

ALUMINUM :

Aluminum is a white metal produced by electrical processes from the oxide ( alumina ) , which is prepared from a clayey mineral called bauxite. In India they are chiefly available in Bihar, Madhya Pradesh, Karnataka, Maharashtra and Tamil Nadu.

It is silvery - white in color and extensively used where a light non corrosive metal is desired as in aircraft and automobile components where the saving of weight is an advantage. In its pure state the metal would be weak and soft for most purposes, but when mixed with small amounts of other metals it becomes hard and rigid. So it may be blanked, formed, drawn, turned, cast, forged, and die-cast. Its good electrical conductivity is an important property and aluminum is used for over head cables. The high resistance to corrosion and its non-toxicity make it a useful metal for cooking utensils ; under ordinary conditions, water and air have practically no effect on it. Since pure aluminum is more corrosion resistant than any alloy of aluminum ,a thin layer of pure aluminum is generally cladded on the sheets of aluminum alloy to elimination corrosion. Again pure aluminum is not heat treatable. Aluminum alloy cladded by thin layer of aluminum can be heat treated. In this composite, the core containing aluminum alloy can be hardened. Aluminum has the property of being beaten into foil and this aluminum foil is now widely used as silver foil. Aluminum metal of high purity have got high reflecting power and is Therefore, widely used for reflectors, mirror and telescopes. The melting point of aluminum is 658*C and is having a specific gravity of 2.65.




ALUMINUM ALLOYS : 

Aluminum finds its widest uses when alloyed with small amounts of other metals. The addition of small quantities of other alloying elements converts this soft, weak metal into a hard and strong metal, while still retaining its light weight. Alloys can be classified as cast or wrought , both groups containing alloys that are age-hardened. The alloys in each of these two classes are further classified according to whether they respond to heat treatment of  the strengthening type.




For the casting of general engineering use, aluminum is alloyed with small amounts of copper and zinc in the proportion of 12.5 to 14.5 per cent zinc and 2.5 to 3.0 per cent copper. An Important series of casting and forging alloys having high strength have recently been developed for use in aeroplane construction. One example of such alloys is : zinc 5 per cent, magnesium 5 per cent , copper 2.2 per cent, nickel up to 1 per cent , aluminum the remainder.

An important and interesting wrought alloy is known as duralumin. This is composed of 3.5 to 4.5 per cent copper, 0.4 to 0.7 per cent manganese , 0.4 to 0.7 per cent magnesium, and aluminum the remainder. It is widely used in wrought condition for forging, stampings, bars, sheets, tubes and rivets. It is interesting because of its age-hardening property. After working if the metal is allowed to age for 3 to 4 days, it will be hardened. This phenomenon is called age - hardening. In the heat - treated and aged condition duralumin may have a tensile strength up to 4 kgf per mm2 (400 Newton per mm2).

Another alloy known as Y- alloy contains 3.5 to 4.5 per cent copper, 1.8 to 2.3 per cent nickel, and 1.2 to 1.7 per cent magnesium. This alloy has the characteristic of retaining good strength at high temperatures. Y-alloy is therefore, useful for piston and other components of aero- engines. It is also largely used in the form of sheets and strips, and after proper heat treatment this may brought to minimum tensile strength of about 35 kg-f per mm2. (350 Newton per mm2).

Beryllium copper are solution heat treated and precipitation hardened. Aging time is 2 to 3 hours at around 325*C. Aluminum bronzes containing more than 10 per cent aluminum are quenched from 650*C and subsequently tempered at a low temperature.

 


Labels:

Comments

Post a Comment

Popular posts from this blog

Advantages And Disadvantages Of Air Refrigeration System :

 Advantages Of  Air Refrigeration : 1. The refrigerant used namely air is cheap and easily available. 2. There is no danger of fire or toxic effects due to leakages. 3. The weight to ton of refrigeration ratio is less as compared to other systems. Disadvantages Of Air Refrigeration : 1. The quantity of  Refrigerant used per ton of refrigeration is high as compared to other systems. 2. The COP of the system is very low. Therefore running cost is high. 3. The danger of frosting at the expander valves is more as the air contains moisture content. 
Post a Comment
Read more

ELECTRICAL COMPARATORS AND ITS WORKING

Electrical Comparators are used as a means of  detecting and amplifying small movements of a work contacting elements. An electrical comparator consists essentially of  a pick-up head or transducer for converting a displacement into a corresponding change in current and a meter or recorder connected in the circuit to indicate the electrical change, calibrated to show in terms of displacement. Generally, an amplifier is needed to provide the requisite sensitivity and to match the characteristics of different parts of  the circuit. Electrical comparators can be classified according to the electrical principle used in the pick-up head. Most of the comparators use either a differential transformer, an inductance bridge, a strain gauge or a capacitor as a means of detecting movement of the gauging element. There are different types of  electrical comparators. One kind called an electrolimit gauge is used to check or measure the outside diameter of a  roll. The objec...
Post a Comment
Read more

THROTTLE GOVERNING OF STEAM TURBINES

Steam Pressure at inlet to a steam turbine is reduced by throttling process to maintain the speed of the  turbine constant at part load and hence this method of governing is called "Throttle Governing".  Construction : Throttle governing system consists of  a centrifugal governor, a lever , an oil pump , a pilot piston , control valve , a relay piston and a throttle valve. The throttle valve is moved by a relay piston. The relay piston is actuated by pilot piston control valve. There are two piston valves covering ports in the pilot piston control valve without any overlap. These piston valves are operated by lubricating oil supplied by a gear pump at 2 to 4 bar. The oil returns to the drain from this chamber.  Working : When the turbine works on full rated load, the throttle valve will remain open. When the load is decreased, the energy output of the turbine becomes in excess and the turbine shaft speed increases. Hence, governor sleeve will lift. The upward movemen...
Post a Comment
Read more