Microstructure and bending properties of die-casting alloys at various chromium contents

Abstract

A study of the effects of chromium addition on AlSi9Cu3(Fe) alloy was carried out. Die cast EN AC-46000 alloy
plates for microstructural investigation and bend testing were produced using a multispecimen die in a high
pressure, cold chamber machine. The Cr ranged within the tolerance limits of the EN AC-46000 type alloys,
according to the EN 1706 standard. The investigations allowed evaluation of modifications to microstructural
and bending properties produced by Cr additions. In particular, the microstructural analysis revealed that the
morphology of primary sludge compounds was mainly cubic-type, such as polyhedral, star-like and blocky,
while proeutectic ?-Alx(Fe,Mn,Cr)ySiz intermetallics showed blocky or polyhedral morphology at any Cr level.
Increasing the Cr content, the whole area fraction of these particles increased and the primary intermetallic
compounds segregated in the central region of the cross section of the castings. This was associated to a
mechanism similar to that suggested for the ESCs entrapment. The increase of brittle Fe-rich particles affected
the fracture load and the displacement to fracture of the alloy at the highest Cr level.