Alloys and types of alloys

Generally speaking, metals are the most useful in the form of alloys. Around 30 metallic elements serve modern needs, but over five thousand alloys are known and hundreds of them are in common uses. Sizable amounts of certain metals are convertible into compounds of a great importance. Brass, bronze, pewter and stainless steel are examples of alloys. In general, alloys are formed when two or more metals are melted together and the mixture is allowed to cool and solidify. Alloys may also contain certain nonmetals such as carbon, sulphur, arsenic, phosphorous and silicon.

The main reason why so many different alloys are prepared is that modern industry requires metals with certain properties or certain combinations of properties which no metallic element in the pure state can provide. Metallurgists attempt to regulate both physical and chemical properties of metals through the preparation of alloys. Various kinds of stainless steel illustrate alloys whose chemical properties help them to resist the action of acids and the corroding agents of the atmosphere. Some of the metals used in automobile and aircraft engines, particularly in valves, should be able to withstand extremely high temperatures. Even now, improvements in the gas turbine or jet engine may well depend on the development of new improved heat-resisting alloys.

The aircraft industry needs metals that combine great strength with light weight. Many other industries have their own particular needs for metals with certain chemical and physical properties. All this should give you a pretty good idea of why alloys have been described as «metals made to order». Alloys may be classified in several ways. They can be classified according to composition, uses or notable properties. According to composition, we have ferrous alloys (those which contain iron) and nonferrous alloys (those which do not contain iron). The former group includes all the various kinds of steel - ordinary steels as well as alloy or special steels.

The nonferrous alloys are further subdivided according to the predominant or base metal. Thus we have alloys in which aluminium, lead, copper, gold, silver, or any other metal except iron makes up the largest per cent of any constituent. In the terms of uses, there are antifriction alloys and solders. Groups of alloys based upon distinctive properties include the lightweight alloys and low melting point alloys.

Speculum is an alloy of copper and tin formerly used in reflecting telescopes to make the main mirror as it could be cast, ground, and polished to make a highly reflective surface. It has now been largely replaced by silvered glass for this purpose.

steel Any of a number of alloys consisting predominantly of iron with varying proportions of carbon (up to 1.7%) and, in some cases, small quantities of other elements (alloy steels), such as manganese, silicon, chromium, molybdenum and nickel. Steels containing over 11-12% of chromium are known as stainless steels.

Solder is an alloy used to join metal surfaces. A soft soldermelts at a temperature in the range 200-300°C and consists of a tin-lead alloy. The tin content varies between 80% for the lower end of the melting range and 31% for the higher end. Hard solderscontain substantial quantities of silver in the alloy. Brazing soldersare usually alloys of copper and zinc, which melt at over 800°C.

Phosphor bronze is an alloy of copper containing 4% to 10% of tin and 0.05% to 1% of phosphorus as a deoxidizing agent. It is used particularly for marine purposes and where it is exposed to heavy wear, as in gear wheels.

German silver is an alloy of copper, zinc, and nickel, often in the proportions 5:2:2. It resembles silver in appearance and is used in cheap jewellery and cutlery and as a base for silver-plated wire.

Babbitt metal is any of a group of related alloys used for making bearings. They consist of tin containing antimony (about 10%) and copper (1-2 %), and often lead. The original alloy was invented in 1839 by the US inventor Isaac Babbit (1799-1862).

Brass is a group of alloys consisting of copper and zinc. A typical yellow brass might contain about 67 % of copper and 33 % of zinc.

Bronze is any of a group of alloys of copper and tin, sometimes with lead and zinc present. The amount of tin varies from 1 % to 30 %. The alloy is hard and easily cast, and extensively used in bearings, valves and other machine parts. Various improved bronzes are produced by adding other elements; for instance phosphor bronze contain up to 1% of phosphorous. In addition certain alloys of copper and metals other than tin are called bronzes - aluminium bronze is a mixture of copper and aluminium. Other special bronzes include bell metal, gun metal, beryllium bronze. Beryllium bronze is a hard, strong type of bronze containing about 2%of beryllium, in addition to copper and tin.

Cast iron is a group of alloys containing 1.8 to 4.5% of carbon. It is usually cast into specific shapes ready for machining, heat treatment or assembly. It is sometimes produced direct from the blast furnace or it may be made by from remelted pig iron.

Pewter is an alloy of lead and tin. It usually contains 63% of tin. Pewter tankards and food containers should have less than 35% of lead so that the lead remains in solid solution with tin in the presence of weak acids in the food and drink . Copper is sometimes added to increase ductility and antimony is added if a hard alloy is required.

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