Alloys

Alloys

An alloy is a mixture or metallic solid solution composed of two or more elements.

Learning Objectives

Define the term alloy.

Key Takeaways

Key Points

  • An alloy is a mixture or metallic solid solution composed of two or more elements.
  • An alloy’s properties are usually different from those of its component elements.
  • Alloy constituents are usually measured by mass.
  • Unlike pure metals, most alloys do not have a single melting point; rather, they have a melting range in which the substance is a mixture of solid and liquid.

Key Terms

  • amalgam: an alloy containing mercury
  • microstructure: the fine structure of a pure metal or alloy, as revealed by magnifications of 25x or greater
  • racemic mixture: a mixture that has equal amounts of left- and right-handed enantiomers of a chiral molecule
  • eutectic mixture: a mixture of substances having a melting point lower than that of any of its components

An alloy is a mixture or metallic-solid solution composed of two or more elements. Examples of alloys include materials such as brass, pewter, phosphor bronze, amalgam, and steel. Complete solid solution alloys give single solid phase microstructure. Partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history. An alloy’s properties are usually different from those of its component elements.

Examples of alloys include materials such as brass, pewter, phosphor bronze, amalgam, and steel. Complete solid solution alloys give single solid phase microstructure. Partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history. An alloy’s properties are usually different from those of its component elements.

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Steel: Steel is an alloy whose major component is iron.

Alloy constituents are usually measured by mass. An alloy is usually classified as either substitutional or interstitial, depending on its atomic arrangement. In a substitutional alloy, the atoms from each element can occupy the same sites as their counterpart. In interstitial alloys, the atoms do not occupy the same sites. Alloys can be further classified as homogeneous (consisting of a single phase), heterogeneous (consisting of two or more phases), or intermetallic (where there is no distinct boundary between phases).

Alloying a metal involves combining it with one or more other metals or non-metals, which often enhances its properties. For example, steel is stronger than iron, its primary element. Physical properties (density, reactivity, conductivity) of an alloy may not differ greatly from those of its constituent elements, but its engineering properties (tensile strength and shear strength) may be substantially different.

Unlike pure metals, most alloys do not have a single melting point; rather, they have a melting range in which the substance is a mixture of solid and liquid. However, for most alloys, there is one particular proportion of constituents, known as the “eutectic mixture,” at which the alloy has a unique melting point.