Views: 358 Author: Site Editor Publish Time: 2022-03-03 Origin: Site
We know that precious metal alloys are composed of two or more of the elements including silver, gold, platinum, palladium, iridium, osmium, rhodium, and ruthenium, which is often used as small electrical contacts. Sometimes non-precious metal alloying elements are also used as electrical contacts components. Both of them have very good electrical conductivity and good mechanical properties, and they have the features of highly corrosion-resistance, and are machinable, so they can be the useful materials of electrical contacts.
Why use precious metal alloys for electrical contacts?
Some materials with high electrical conductivity such as silver, gold and platinum group metals etc. are often used as electrical contacts. Of course, there are disadvantages for some materials, such as poor mechanical properties leading to poor wear resistance. For example, there are many advantages for silver plating contacts, it can enhance the current-carrying capacity of the terminal and it is cheap. So, the contacts with silver plating are used in electric power or electricity. But silver plated contacts are easy to corrode and blacken, and cannot resistant to plugging. Its feature of chemical degradation is prone to reduce its electrical conductivity.
In order to overcome the problems caused by using pure precious metals, they are often alloyed with other metals. In this way, it can enhance the mechanical properties and corrosion resistance of precious metals and solve the limitations of them. Therefore, metal alloys for electrical contacts can be widely used for many fields.
What properties for the precious metal alloys?
Generally speaking, alloy electrical contacts have high requirements for metal alloys such as high electrical conductivity and corrosion resistance etc. For moving contacts such as switches, brushes or slip rings, they need good mechanical properties and wear resistance. Of course, the properties of precious metal alloys are more attractive than non-alloyed precious metals as metal contacts since they have many advantages as below:
High wear resistance
High corrosion resistance
High electrical conductivity
Highly reproducible material properties
Low contact resistivity
Good machining properties
Long service life
In daily life, silver-based, gold-based and platinum group-based alloys are often used for electrical contacts. Among platinum group-based alloys, platinum-based and palladium-based alloys are most common used for electrical contacts. In order to understand conveniently, here we take silver-based alloy contacts for instance.
The features of silver-based alloy contacts
We know that silver is a good contact material since it has excellent electrical and thermal conductivity, and strong resistance to oxidation. But, its disadvantages are that it has the features of low wear resistance, low softening temperature and its strong affinity to sulfur, which will make the surface of the silver form silver sulfide layer to make its electrical resistance increase. If it is alloyed, its mechanical properties will be changed. For example, hardness and tensile strength can be improved to enhance wear resistance and erosion resistance. Generally, Cu is one of common used alloying elements, and Ni is another one. AgCu20 composed of 80 wt.% Ag and 20 wt.% Cu. is a good example of a silver-based alloy.