Metallic materials with metallic characteristics are often formed by two or more metal elements or metal-based addition of other non-metal elements through alloying processes (melting, mechanical alloying, sintering, vapor deposition, etc.) are called alloys . But the alloy may only contain one metal element, such as steel. (Steel is the general term for ferroalloys with carbon content between 0.02% and 2.00% by mass)
Here we need to note that the alloy is not a general conceptual mixture, or even a pure substance, such as a single-phase intermetallic compound alloy. The added alloying elements can form solid solutions, compounds, and produce endothermic or exothermic reactions, thereby changing the metal. The nature of the matrix.
The formation of alloys often improves the properties of elemental elements. For example, the strength of steel is greater than that of its main constituent element, iron. The physical properties of the alloy, such as density, reactivity, Young's modulus, electrical conductivity 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. with large differences. This is because the arrangement of atoms in the alloy and the element is very different.
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 coexistence of solid and liquid. Therefore, it can be said that the melting point of the alloy is lower than that of the component metal. See eutectic mixture. Among the common alloys, brass is an alloy of copper and zinc; bronze is an alloy of tin and copper, used for statues, ornaments and church bells. Some currencies use alloys (such as nickel alloys).