A chemical element is considered a light metal if it fulfils two conditions:
1. metallic properties
2. density up to 4.99 g/cm³.
Metals that have a density of more than 5.0 g/cm³ are considered heavy metals.
Light metals and their properties
The limit of 5 g/cm³ restricts the choice of available light metals to the following elements:
With the exception of aluminium, magnesium and titanium, all light metals are of secondary technical importance. They are used as additives for alloys or are important in technical chemistry and electrical engineering. The chemical-physical properties of the light metals differ greatly from each other. Lithium, potassium and sodium, for example, burn on contact with water, while caesium, francium and strontium are radioactive.
Light metals in mechanical and plant engineering
For mechanical engineering, magnesium, aluminium and titanium are particularly important as light metals. They offer everything that is expected of a metallic material. These include the following properties:
- arbitrary melt formability
- defined elasticity, yield strength and tensile strength
- electrically conductive
- easily machinable
In the case of the elements mentioned, chemical inertness is also a welcome technical property. They behave uncritically under normal circumstances. Furthermore, they can easily be mixed with other elements to form alloys with defined properties.
Specific properties of magnesium
With a density of 1.74 g/cm³ h, magnesium is a particularly light metal. It is particularly suitable for casting applications. Precision die-casting can be used to produce components with thin walls from magnesium. It is combustible, producing a flame that is almost impossible to extinguish, with a temperature of up to 3000 °C.
Specific properties of aluminium
Aluminium can be technically shaped in any way. The toughness and hardness of this light metal can be considerably increased by a special heat treatment. For a long time, the so-called "dural" (dur = hard) was the most important material in aircraft construction. Aluminium is comparatively inert chemically and does not burn as easily as magnesium. It is also very inexpensive.
Specific properties of titanium
Titanium is the hardest, technically usable light metal. For its part, it is already very strong. As an additive for structural steels, it can considerably increase their technical properties. It is easy to form, but its high toughness makes it much more difficult to form than aluminium.