Alloys in Metallurgy

In metallurgy, an alloy is a macroscopically homogeneous metallic material consisting of at least two components. Of these two components, at least one is a metal. Together with the other component, it exhibits the properties of a metallic bond.

An alloy can be homogeneous or heterogeneous at the microscopic level. This depends on the type of alloy formation. Alloys that consist exclusively of mixed crystals or intermetallic compounds are homogeneous, such as copper-gold or copper-silver. All other alloys, which are composed of multiple phases, are heterogeneous. An example of a heterogeneous alloy is a mixture of tin and lead.

Thus, alloys are always mixtures of two or more metals that exhibit properties different from those of the pure metals from which they are formed. They are created by melting different metals together. The goal of an alloy is to combine the beneficial properties of the individual elements. This is intended to produce an even better metal. Certain alloys can also improve their mechanical properties as castings—whether cold-worked or heat-treated. They can thus become more fracture-resistant, harder, or more ductile.

Alloys have shiny surfaces, good mechanical properties, and high thermal and electrical conductivity.

Along with steel, iron is the most important metallic material. This is because it is tough, strong, readily available, and inexpensive. Iron-carbon alloys are particularly relevant. They occur in the form of steel and cast iron:

• Steel is a collective term for plastically deformable iron-carbon alloys that contain between 0.2% and a maximum of 2.06% carbon. Steel is malleable and can be rolled, pressed, and drawn. Steel can be hardened through heat treatment.
• Cast iron is a collective term for iron-carbon alloys that are not plastically deformable and contain at least 2.06% carbon (usually around 4%). It is hard, brittle, and castable. It is not malleable. Common products made of cast iron include pipes, heating systems, and machine components.

Iron is primarily used in the automotive, shipbuilding, construction, and mechanical engineering industries. It is also found in households in the form of cooking pots and cutlery.

A complete list of all alloys, including their properties and uses, can be found on Wikipedia.

Depending on how many components an alloy has, it is classified as a binary, ternary, quaternary, or polinary alloy. Experts refer to these as binary, ternary, quaternary, or polinary alloys. However, only those components that determine the alloy’s characteristic properties are counted.

Generally, alloys are divided into ferrous and non-ferrous alloys. Further classifications depend on how the alloys are formed or what special properties they possess. The following alloys exist today:

• Natural alloys are formed by the application of heat or the melting of elements. This occurs, for example, inside celestial bodies. However, they have different compositions and properties than man-made alloys.
• Ferrous alloys include cast iron and steel. The distinction is based on carbon content. Steel contains no more than 2.06% carbon, while cast iron contains at least 2.06% carbon.
• Non-ferrous alloys are alloys based on non-ferrous metals, such as bronze, brass, white gold, rose gold, or amalgams.
• Diffusion alloys form when atoms are distributed throughout the crystal lattice of the base metals. This type of alloy occurs, for example, during the carburizing of workpieces to harden them.
• Heusler alloys are special ferromagnetic alloys. They contain no iron, cobalt, or nickel.
• Shape-memory alloys are metals that return to their original shape when heated after being deformed.
• Cast alloys are used for direct shaping.
• Forged alloys are an intermediate product that is further adapted for its intended purpose through forming.
• Pseudoalloys are workpieces produced by sintering—the process of compressing various mixed metal powders together under heat.

Alloys are produced by:

• Melting the components together
• Sintering powdered components
• Annealing (diffusion of an element, e.g., carbon, into the surface of a workpiece)
• Co-electrolysis of metal salts
• Joint reduction of metal oxides
• Amalgamation

To identify an alloy, the base metal is listed first. This is followed by the most important component(s), indicated by the metal’s abbreviation followed by a number that denotes its percentage. Accordingly, the alloy CuZn37 consists of copper to which 37 percent zinc has been added. The formula for the iron-carbon alloy steel is an exception to this rule. In this case, iron is not specified. For example, steel C37 contains 0.37 percent carbon. The remainder is iron. Formally, DIN 1310, “Composition of Mixed Phases (Gas Mixtures, Solutions, Mixed Crystals); Basic Concepts,” governs the specification of the individual components of an alloy.