Study of the microstructure and mechanical properties of Al-Si-Fe with additions of chromium by suction casting

Abstract

The effect of Cr additions on the Al-20Si-5Fe alloy, produced by means of two different solidification methods is presented and discussed. The modification of iron intermetallics and the microstructural refinement through suction casting were also assessed. Several Al−20Si−5Fe−xCr (x = 1.0, 3.0 and 5.0 wt%) alloy ingots were prepared by arc melting furnace (AMF). Rods of each alloy were produced by copper mold suction casting under Ar atmosphere. The elemental chemical analysis was performed by X-ray fluorescence spectrometry (XRF). The microstructure of all samples was investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The microstructural analysis revealed the presence of α−Al, eutectic silicon (SiE), primary silicon (SiP), Al3FeSi2 and Al95Fe4Cr phases. The microhardness and compressive properties were measured in order to correlate the microstructural changes with Cr additions. The acicular Al3FeSi2 intermetallic compound (2D) obtained by conventional solidification was found to be a plate-like structure (3D). The highest microhardness value was found for the alloys with the 5 wt% Cr (220 HV) in conventional solidification. However, for suction casting, the highest microhardness was 192 HV for the 3 wt% Cr. Although the microhardness dropped with the suction casting, the compressive plasticity of the alloy did increase considerably (>300%), being the microstructural homogeneity the main contributor to the ductility behavior.