Alloys of Aluminium

The alloying elements are added to aluminium to improve the mechanical and chemical properties. The tensile strength, hardness, rigidity, machinability and casting properties are improved. The alloys of aluminium are used in cast and wrought conditions. The mechanical properties of aluminium alloys can be improved by precipitation hardening. The major hardening elements are copper, manganese, zinc, silicon, titanium and magnesium. Problems of porosity are observed in some aluminium alloys. Porosity develops due to presence of gases in the alloys during the time of melting process. Molten aluminium also dissolves considerable amount of hydrogen. The defect of gas porosity can be removed by treating the molten metal with a suitable flux. Bubbling of nitrogen and chlorine gas through the molten metal also removes these gaseous impurities. Use of hexachloroethane tablets in the metal bath helped to eliminate these gaseous impurities. Aluminium is a lighter metal. It is one and half times heavier than magnesium. Due to its light, aluminium has wide range applications in the production of components and structures. It is used in aircraft, satellite, rockets and auto mobile sector due to its light weight and high strength. Development of metal fatigue is also negligible. A number of aluminium alloys are developed with specific standard to meet the varieties of requirements of different industries. The aluminium alloys can be easily used as a foundry material and forging material. It can be also used in rolling and extrusion sector. High resistance to atmospheric corrosion also makes aluminium alloys applicable in chemical industries. Good conductivity of electricity, a non magnetic nature made it possible for use in electrical wires and electrical instruments.

Both cold and hot working of aluminium made it more popular. Demand for its alloys increased in the foundries, forging and fabrication industries. Copper is added up to 5.5% to improve the metal fatigue, elastic properties and hardness. Silicon is added up to 1% along with copper and magnesium to enhance the hardness and heat resistant characters. Similarly manganese is added up to 1.5% to improve hardness, strength and machinability character. Magnesium is added up to 3% to increase strength, hardness and corrosion resistance. Elements like zinc, nickel and chromium are also added to improve the properties of aluminium.

The alloys of aluminium may be divided into two groups as wrought alloys and cast alloys. Further the alloys may be divided as heat treated and without heat treated alloys. The wrought alloys may show properties which are rigid, hard, tough and corrosion resistant. The cast alloys are mainly hard and corrosion resistant. The cast alloys are widely used in sand casting and dye casting. The aluminium silicon alloys that are caste alloys have large scale applications in various industries. The addition of small quantities of alloying elements converts aluminium into hard and strong substance. But the alloys retain the light weight of aluminium. Copper alloys with aluminium give rise to aluminium bronze alloys. Duralumin is an important wrought alloy of aluminium, copper, manganese and magnesium. Duralumin is used for production of sheets, bars, tubes and rivets. Another aluminium alloy with zinc, magnesium, copper and nickel is used in the construction materials for its high strength, corrosion resistance and light weight. This type of alloy is also used for parts of aero engine and auto mobile engine. It has also uses in heat treatment operations.

Aluminium-Silicon alloys are important casting alloys. The properties of alloys depend upon the amount of silicon present. Addition of copper increases the response to precipitation hardening. Aluminium-Silicon-Magnesium alloys provide higher strength and machinability character. These alloys find application in carburettor and pump castings. Aluminium-Silicon-Magnesium alloys have good casting properties. These alloys are used for machine parts. With the addition of nickel, the alloy get stable strength and retain hardness up to 250'C. These alloys are used for diesel engine pistons and air cooled cylinder heads for automobile and aircraft engines. Addition of chromium and manganese increases the heat resistant properties of these alloys. Aluminium-Magnesium alloys are used in casting. Theses alloys have high resistance to corrosion. Addition of zinc helps in decreasing the metal fatigue of the alloys. These alloys are used in the machines that work under high stress and strain conditions