Alloy that is mainly based on aluminum and is only used as additive during melting for the following purpose:
Some master alloys may contain more than 50 % of the main alloy element.
Master alloys facilitate the addition of defined alloy components particularly those with a high melting point (e.g. grained additives like oxides or bromides). The use of master alloys enables exact dosing and quicker distribution of additives in the melt. Aluminum master alloys are standardized in EN 575 (for an except, refer to Table 1). Reduction alloys and alloy blends are not included in the standard. The delivery shapes of the master alloys could be as follows (Fig. 1):
The products have to be visually inspected by the manufacturer and must be free of dross, corrosion, slag or salt inclusions, greases or other foreign bodies to such an extent that the melt quality and/or yield is not compromised (except for color residues as a result of color coding). The products can have cracks or cavities which may contain moisture. Therefore, the master alloys must be carefully dried and preheated in a furnace prior to charging in order to prevent the risk of heavy explosions or melt ejection.
In order to comply with the permissible maximum contents of additives and impurities, the starting materials used for producing master alloys must be of high purity. Obtaining a structure with low segregation is possible using different casting-related and metallurgical measures; as an example, the maximum content of segregating additives must be reduced and master alloys are often also produced in small-sized pig molds to achieve high solidification rates and maximum solubility without any segregation effects.
DIN Taschenbuch 455, Gießereiwesen 2, Nichteisen-Metallguss, Beuth Verlag, Zurich
EN 575:1995, Aluminium and aluminium alloys – Master alloys produced by melting – Specifications, CEN, Brussels
Aluminium Taschenbuch, Band 1: Grundlagen und Werkstoffe, Aluminium-Verlag GmbH, Düsseldorf