Summary
Engineering alloys can conveniently be subdivided into two types : ferrous and non-ferrous. Ferrous alloys have iron as their principal base metal, whereas non-ferrous alloys have a principal metal other than iron. The steels, that are ferrous alloys, are by far the most significant metal alloys mainly because of their relatively low cost and wide range of mechanical properties. The mechanical properties of carbon steels might be varied considerably by cold working and annealing. While the carbon content of steels is increased to about 0.3%, they can be heat-treated by quenching and tempering to produce high strength with reasonable ductility. Alloying elements such like chromium, nickel and molybdenum are added to plain-carbon steels to produce low-alloy steels. Low-alloy steels have good combination of high strength and toughness and are used extensively in the automotive industry for uses such as shafts, gears & axles.
Aluminium alloys are the most important of the non-ferrous alloys mainly because of their lightness, workability, corrosion resistance, and relatively low cost. Unalloyed copper is used extensively because of its high electrical conductivity, workability, corrosion resistance, and relatively low cost. Copper is alloyed with zinc to from a series of brass alloys which have higher strength than unalloyed copper. Bronzes are other series of alloys when Cu is alloyed with tin or aluminium.
Stainless steels are important ferrous alloys because of their corrosion resistance in oxidising environments. To make a stainless steel “stainless”, it must contain at least 12% Cr.
Cast irons are other industrially important family of ferrous alloys. They are low in cost and have special properties such as good castability, wear resistance, and durability. Grey cast iron has high machinability and vibration damping capacity due to the graphite flakes in its structure. White and iron, yet another variety having carbon in cementite form and is harder.
Other non-ferrous alloys briefly discussed in this unit are magnesium, titanium, and nickel alloys. Magnesium alloys are exceptionally light and have aerospace applications and are used in radio and instrument industry. Titanium alloys are expensive but have a combination of strength and lightness not available from any other metal alloy system and so are used extensively for aircraft structural parts. Nickel alloys have high corrosion and oxidation resistance and are therefore commonly used in the oil and chemical process industries. Nickel when alloyed having chromium & cobalt forms the basis for the nickel- base superalloys which are necessary for gas turbines in jet aircraft and some electric- power generating equipment.
In this unit, we have discussed to a limited extent the structure, properties, & applications of some of the significant engineering alloys.