Abstract
This study focuses on primary impurities, called intermetallics, in the microstructure of
Al-Si-X alloys, their formation, effects and treatments to eliminate or ameliorate their
deleterious effects. Intermetallic compounds are usually formed when alloying elements,
such as Fe, Cu, Mn, Mg and Sr. are added to Al-Si based alloys. These elements
are depicted by X in the alloys formation expression. The chapter noted that the most
common intermetallics are iron (Fe) based, and several of these Fe-phases, including the
most harmful Fe-phase, β-Al5SiFe, are listed and discussed. Fe-phase intermetallics are
deleterious to the mechanical properties of Al-alloys; however, addition of <0.7% Fe helps
prevent soldering in die casting mould. The effects of Fe-phase and other intermetallics
formed by Cu, Mg and Mn were examined. Further, some techniques of eliminating or
mitigating the negative influences of intermetallics were discussed.