The influence of Fe, Mn and Cr addittions on the formation of iron-rich intermetallic phases in an Al-Si die-casting alloy

The microstructure evolution of a high-pressure die-cast AlSi9Cu3(Fe) alloy is studied over different Fe, Mn and Cr content. Fe-rich intermetallic phases were characterized by using optical microscope, image analysis, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS). The results revealed that the amount of Fe-rich phases as well their size increase by increasing the elemental content. Needle-like particles appear in the alloy with higher Fe:Mn ratio, while coarse α-phases assume polygonal, stark-like or Chinese script morphology according to the Fe:Mn:Cr balance as revealed by EDS analysis. The 3D-SEM investigation suggests that both the polygonal and stark-like morphology can be associated to a rhombic dodecahedron structure. The morphology evolution of the Fe-bearing particles as a function of the chemical composition and casting process is proposed and discussed.