The following requirements are imposed on materials of this type:
– the minimum value of the specific electrical resistance;
– good mechanical properties (mainly tensile strength and elongation at break);
– the ability to easily handle, which is necessary for the manufacture of wires of small and medium cross-sections;
– the ability to form contacts with a small transient resistance during soldering, welding and other methods of connecting wires;
– Corrosion resistance.
The main requirement is the maximum conductivity of the material. However, the electrical conductivity of the metal can be reduced due to contaminants, deformation of the metal that occurs during stamping or drawing, which leads to the destruction of individual grains of the metal. The influence of metal deformations on it conductivity is eliminated during annealing, during which the number of defects in the metal decreases and the average size of the metal crystals increases. In this regard, conductor materials are used mainly in the annealed (soft) state.
The most common modern materials of high conductivity used in radio electronics are non-ferrous metals (copper, aluminum, zinc, tin, magnesium, lead) and ferrous metals (iron), which are used in pure form. Alloys of these metals are used even more widely, since they have better properties and are cheaper than pure metals. However, non-ferrous metals and their alloys are economically expedient to use in those cases when the necessary properties of products can not be obtained by using ferrous metals, cast iron and steel.
To improve the properties of non-ferrous alloys are subjected to heat treatment – annealing, quenching and aging. Annealing affects the softness of the material and reduces the stresses in the castings. Hardening and aging enhance mechanical properties.
Copper is one of the most common materials of high conductivity. It possesses the following properties:
Low electrical resistivity (of all metals only silver has a specific electrical resistance of several percent less than that of copper);
High mechanical strength;
Satisfactory corrosion resistance (even under conditions of high air humidity, copper is oxidized much more slowly than, for example, iron, intensive oxidation of copper occurs only at elevated temperatures);
Good solderability and weldability;
Good machinability (copper is rolled into sheets and ribbons and stretched into a wire).
Aluminum refers to so-called light metals (density of cast aluminum is about 2600, rolled 2700 kg / m3).
Aluminum has the following features:
The specific electrical resistance of aluminum (with an impurity content of not more than 0.05%) is 1.63 times greater than that of copper, so copper replacement with aluminum is not always possible, especially in radio electronics;
Aluminum is about 3.5 times lighter than copper;
Because of the high specific heat and melting heat of aluminum, heating the aluminum wire before melting requires more energy than heating and melting the same amount of copper;