The influence of Cr content on the Fe-rich phase formation and impact toughness of a die-cast AlSi9Cu3(Fe) alloy

The influence of chromium on the microstructure and impact toughness of high-pressure die-cast AlSi9Cu3(Fe) alloy was investigated systematically as the content of Cr was varied. The results indicate that, with the increase of Cr content, the area fraction of primary (sludge) and secondary (proeutectic) α-Alx(Fe,Mn,Cr)ySiz intermetallic compounds increase. Moreover, the sludge morphology evolves from polyhedral to branched or star-like shapes while the secondary Fe-rich particles seem to not be morphologically affected. The polyhedral sludge particles are associated to a regular rhombic dodecahedron, while the star-like and branched morphologies originate from hollowed rhombic dodecahedron. From the load–deflection curves, the impact toughness (Wt)and maximum load absorbed by the specimens (Fm) during impact testing were measured. The mechanical tests reveal that Wt and Fm values are almost constant up to 0.12wt.% Cr content achieving about 15.7 J and 9.3 kN, respectively, while a further addition of Cr ( 0.15 wt.%) leads a overall performance decrease higher than 9%.