A characteristic of metals is that they always give off negatively charged electrons and thus form positively charged ions. Due to the electrostatic forces between the metal ions and the free electrons, metals are good conductors of electricity. In addition, this bond also results in a special structure. In the solid state, metals are crystals – the metal ions are densely packed and arranged geometrically evenly. When liquefied, they lose this crystalline structure and become amorphous substances whose atoms are still bound to one another but are disordered. How the crystal lattices are arranged is important for the other material properties: density, melting temperature, strength, yield point, elongation at break and hardness, to name just the most important ones.
Some metals such as aluminium, copper or zinc are often used in their pure form, usually 99.5 percent purity. However, in order to improve certain properties or to get new properties, some metals are mixed with other metals or non-metals. These alloys are usually compounds at the crystalline level: the atoms of the added substance accumulate in the interstices of the crystal lattice or replace individual metal atoms. Alloys of metals with other metals are, for example, brass, which consists of copper and zinc, bronze – made of copper and tin – and aluminum modified with copper and magnesium to form duralumin.
The best-known representative of the non-metal alloys is steel, which contains iron and carbon. Although steel is an alloy in itself, this is referred to as unalloyed steel. Low-alloy steel is only obtained when other metals are added, between one and five percent alloying elements. If the admixture is more than five percent, we are talking about high-alloy steel. Alloyed steels have different properties and are often subjected to a heat treatment for further optimization. We give an insight into the hardening process in the bag of tricks.
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