Everyone heard the word “alloy”, and some consider it to be synonymous with the term “metal”. But these concepts are different. Metals are a group of characteristic chemical elements, while alloy is the product of their combination. In their pure form, metals are practically not used, moreover, they are difficult to obtain in their pure form. Whereas alloys are ubiquitous.
What is alloy
Let's look at this issue in more detail. So, an alloy is a combination of several metals or one and various non-metallic additives. Such compounds are used universally. Alloy is a macroscopic homogeneous system obtained by melting. They have been known since ancient times, when mankind, using primitive technologies, learned to produce cast iron, bronze, and a little later - steel.
The production and use of these materials is due to the fact that it is possible to obtain an alloy with specified technological properties, while many characteristics (strength, hardness, corrosion resistance and others) are higher than those of its individual components.
Main types
How are alloys classified? This is done by the type of metal, which is the basis of the connection, namely:
- Black. The basis is iron. Ferrous alloys include all types of steels and cast irons.
- Colored. The base is one of non-ferrous metals. The most common non-ferrous alloys are based on copper and aluminum.
- Alloys of rare metals. Based on vanadium, niobium, tantalum, tungsten. They are mainly used in electrical engineering.
- Alloys of radioactive metals.
Other elements are added to the main component in the alloy - metals and non-metals, which improve its technological properties. These additives are called dopants. Also, harmful impurities are present in the alloys - when their permissible value is exceeded, the material decreases many characteristics. So now you know what alloy is.
Alloys are also classified into double, triple and others - according to the number of components. By the homogeneity of the structure, they are homogeneous and heterogeneous. By their distinctive properties - low-melting and refractory, high-strength, heat-resistant, antifriction, corrosion-resistant and materials with special properties.
Mechanical properties
The mechanical properties of the alloys determine the performance of the material when exposed to external forces. In order to find out the characteristics of the compound, the sample is subjected to various tests (stretched, scratched, loaded, pressed into it with a metal ball or diamond cone, examined under a microscope) to determine the strength, elasticity, plasticity.
Physical
The composition of the alloy determines its physical properties. These include specific gravity, electrical conductivity, melting point, specific heat, coefficient of volumetric and linear expansion. The physical properties of the alloys are also magnetic. They are characterized by residual induction and magnetic permeability.
Chemical
What are the chemical properties of an alloy? These are characteristics that determine how the material reacts to various active, including aggressive, agents. The chemical effect of the medium can be seen visually: iron “eats” rust, a green coating of oxides appears on bronze, steel dissolves in sulfuric acid.
In metallurgy and heavy engineering, many methods are used to combat the aggressive influence of the external environment: new, more resistant materials based on copper, titanium and nickel are developed, alloys are coated with protective layers - varnishes, paints, oxide films, and improve their structure. As a result of negative environmental factors, industry annually suffers damage in the millions of tons of steel and cast iron.
Technological
What is technological effectiveness? An alloy in industry is not needed on its own; any part is made from it. Therefore, the material will be heated, cut, deformed, subjected to heat treatment and other manipulations. Manufacturability is the ability of an alloy to undergo various methods of hot and cold processing, for example, to melt, easily spread and fill the mold, deform in hot or cold form (forging, hot and cold stamping), weld, and process with a metal cutting tool.
Technological properties can be divided into:
- Foundries. They are characterized by fluidity — the ability to fill the casting mold, shrinkage (percentage loss in volume after cooling, hardening) and segregation — a complex process in which an inhomogeneous material structure is formed in different parts of the casting.
- Ductility. This is the ability of the alloy to deform under shock and take the desired shape without loss of integrity. Some metals have good ductility only when hot, while others are cold and hot. For example, steel is forged in a red-hot form. Alloys of aluminum and brass take their proper shape at room temperature. Bronze does not lend itself well to impact deformation, and cast irons are not ductile and under the influence of a hammer are destroyed (with the exception of malleable cast iron).
- Weldability. Low-carbon steel has good weldability ; this characteristic is much worse for high-alloy steels and cast irons.