Some master alloys may contain more than 50 % of the main alloy element. Due to their high melting point, their high vapor pressure in the liquid state or their oxidation propensity, certain metals are not or only partly suitable for alloying. In this case, instead of using the pure metal, so-called master alloys are used which comprise the desired additional component and a base metal.
The base metal is usually identical with the main component of the melt to be alloyed. For example, the preferred alloying agents for molten iron and steel are ferro-alloys, i.e. master alloys containing iron as the base metal. Similarly, master alloys with copper as the base metal are used for the production of copper alloys and pure aluminum is used as the base metal for aluminum casting (see Aluminum mater alloy).