Alloy is a mixture of two or more chemical substances (at least one of which is a metal) with metallic properties. It is generally obtained by fusing each component into a uniform liquid and then condensing it.
Alloys can be at least one of the following three types: a single-phase solid solution of elements, a mixture of many metal phases, or an intermetallic compound of metals. The microstructure of alloys in solid solution has a single phase, and some alloys in solution have two or more phases. The distribution may be uniform or not, depending on the temperature change during the cooling process of the material. Intermetallic compounds typically consist of an alloy or pure metal surrounded by another pure metal.
Alloys are used in certain applications because they have some properties that are better than those of pure metal elements. Examples of alloys include steel, solder, brass, pewter, phosphor bronze, amalgam, and the like.
The composition of the alloy is generally calculated by mass ratio. Alloys can be divided into substitution alloys or interstitial alloys according to their atomic composition, and can be further divided into homogeneous phases (only one phase), heterogeneous phases (more than one phase) and intermetallic compounds (there is no obvious difference between the two phases). boundaries). [2]
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The formation of alloys often changes the properties of elemental substances, for example, the strength of steel is greater than that of its main constituent element, iron. The physical properties of an alloy, such as density, reactivity, Young’s modulus, electrical and thermal conductivity, may be similar to the constituent elements of the alloy, but the tensile strength and shear strength of the alloy are usually related to the properties of the constituent elements. very different. This is due to the fact that the arrangement of atoms in an alloy is very different from that in a single substance. For example, the melting point of an alloy is lower than the melting point of the metals that make up the alloy because the atomic radii of various metals are different, and it is difficult to form a stable crystal lattice.
A small amount of a certain element may have a great influence on the properties of the alloy. For example, impurities in ferromagnetic alloys can change the properties of the alloy.
Unlike pure metals, most alloys do not have a fixed melting point. When the temperature is within the melting temperature range, the mixture is in a state of solid and liquid coexistence. Therefore, it can be said that the melting point of the alloy is lower than that of the constituent metals. See eutectic mixture.
Among the common alloys, brass is an alloy of copper and zinc; bronze is an alloy of tin and copper, and is often used in statues, ornaments, and church bells. Alloys (such as nickel alloys) are used in the currency of some countries.
Alloy is a solution, such as steel, iron is the solvent, carbon is the solute.