Non-Ferrous Alloys

Due to poor physical and mechanical properties and high costs the nonferrous metals are seldom used in their pure state. But their alloys carry very good physical and mechanical properties and are widely used. In general they have lower strength, hardness and modulus of elasticity than irons and steels. However, they carry their own importance due to some exceptional properties they possess, like lightness, ease in fabrication, good machinability, high resistance to corrosion, attractive appearance and good castability etc. Some commonly used nonferrous alloys are described in the following articles.

BRASSES All brasses are basically alloys of copper and zinc. There are two main varieties of brasses :

1. Alpha brass (upto 37% Zn) - for cold working.

2. Alpha Beta brass (33% to 46% Zn) - for hot working.

Alpha brasses are very ductile and can be reality cold worked without any chances of fracture. They can be cold rolled into sheets, drawn into wires, deep drawn and drawn into tubes. In these brasses, as the proportion of zinc increases, their strength increases but ductility decreases.

They are work hardened when subjected to intensive cold working, but ductility can be regained by annealing them at 6000 C. Slow cooling provides maximum ductility, but for common uses they may be water quenched. Deep drawing of this brass requires periodical annealing during the process.

An alpha-beta brass loses strength at high temperatures but becomes very plastic. It, therefore, responds very well to hot rolling, hot extrusion, hot stamping and casting, etc. When cold worked, fractures are always likely to develop.

Common types of brasses in engineering use are the following :

Cartridge brass

It has 70% Cu and 30% Zn. It is very strong and ductile. It is used for a wide range of drawn components like cartridge cases, head lamp reflectors, radiator shells and drawn tubes.

Muntz metal

It contains 60% Cu and 40% Zn and can be cast, rolled, extruded and stamped. It is a sort of general purpose alloy having good resistance to corrosion. It is used for casting pump parts, valves, tapes and other similar items.

Naval brass

It contains 60% Cu, 39% Zn 1% tin. It is more or less similar in composition to Muntz metal except that 1% Zn is replaced by 1% tin. As a result of this change the resistance to sea water corrosion is vastly improved. This alloy is, therefore, widely used for cast and forged fittings for ships.

Admiralty brass

It contains 70% Cu, 29% Zn and 1% tin. It is similar to cartridge brass in composition except that 1% Zn is replaced by 1% tin. It can be cold worked and has good resistance to sea water corrosion. It is cold drawn into tubes and rolled into sheets and bars. It is widely used in ship fittings, bolts, nuts, washers and the other items subjected to sea-water corrosion. It is also used in condenser plant.

Gilding brass

It contains upto 15% Zn and the rest Cu. It is a very good cold working alloy and is used for jewellery, decorative and ornamental work. It is commercially available as cold rolled strip, wire or sheet. Its colour, according to the percentage of Zn. Varies from red to bright yellow. It is also called Gilding metal.

Delta brass

Also known as Delta metal, it consists of 60% Cu, 37% Zn and 3% iron. It can be easily hot worked, forged, rolled extruded and cast. It has a fairly good tensile strength after hot working and casting. It also has a good corrosion resistance. It can suitably replace steel castings.

Free cutting brass It contains 60% Cu, 37% Zn and 3% Pb. It is specially used in machining work, such as producing components from bar stock on turret and automatic lathes. It is also used for making cast, forged or stamped blanks to be used for further machining. With this metal very high speeds and feeds can be employed in machining.

Beta brass

It contains 50% Cu and 50% Zn. Higher percentage of zinc renders it hard and brittle, but it softens quickly when heated and melts at 8700 C. Its main application is as a brazing solder (spelter).

Colouring brass

Various brass components can be imparted different colours by chemical treatment. A few examples are giving of golden colour and black colour, the former being used in decorative and ornamental work and the latter in optical instruments parts. For golden colour the finished brass components are boiled in a solution consisting of water 24 parts, saltpeter 2 parts, alum 1 part and HCI 1 part, all by weight. Similarly the solution for boiling the parts for giving black colour, consists of 4.5 litre water, 0.16 kg potassium cyanide and 0.06 kg white arsenic.

Silicon brass

It contains 80% Cu, 16% Zn and 4% Si. It responds well to welding and is widely used for refrigerators and fire extinguisher shells. It can also be easily sand or gravity die cast, hot stamped and extruded. It can be used as a cheaper substitute for phosphor bronze.

Clock brass

It contains 65% Cu, 34% Zn and 1% Pb. The lead content improves its bearing qualities and machinability. It is mostly available in strip form and is widely used in making small gears and pinions for clock work.

High tensile brass

It is similar to Naval brass but carries small additions of A1, Mn, iron, Ni and Pb. Its tensile strength is 69 tonnes/mm² . It is used where high tensile strength and toughness along with good resistance to corrosion are required. It may be sand or die cast and forged. It is mainly used for large marine components, such as pump bodies and ship propellers.

It contains about 70% Cu, 30% Zn and small additions of Ni and A1. It can be hardened by usual heat treatment. It can be annealed by quenching from 850⁰ C and can be hardened by reheating to 500⁰ C. It is widely used for gears, pinions, formed and pressed parts where ability to harden after working is an advantage.