Effect of Fe and Mn Content on the Microstructures and Tensile Behaviour of AlSi7Cu3 Alloy: Thermal Analysis and Tensile Tests

Abstract

The present study was performed on two AlSi7Cu3 alloys with different Fe and Mn contents (standard alloy and high-Fe/Mn alloy). The evolution of microstructures during solidification of the standard AlSi7Cu3 alloy was investigated by thermal analysis and interrupted quenching test. The effect of Fe and Mn content on the solidification reaction and sequence were studied. The results show that increasing the Fe and Mn content changes the precipitation sequence of the iron-intermetallic α-Al15 (Fe,Mn)3Si2 and β-Al5FeSi, leading to the precipitation of α + β phases at a higher temperature. Microstructural characterizations were also performed on the fully solidified alloys to study the effect of Fe and Mn content on the microstructure of AlSi7Cu3 alloy. Fe and Mn were found to promote the formation of Fe-intermetallics. With the increase of Fe/Mn content, Fe-intermetallics increased in both size and amount, while more small pores (Feret diameter < 200 µm) were also introduced. 3D networks of α-Al15(Fe,Mn)3Si2 and β-Al5FeSi phases were revealed by Lab X-ray Computed Tomography, however, it is difficult to perform a quantitative analysis of the respective volume fraction of α-Al15(Fe,Mn)3Si2 and β-Al5FeSi phase from their 3D morphology. Monotonic tensile tests on both alloys show the mechanical properties of the studied alloys were not sensitive to the Fe/Mn content, while the fractography analysis reveals that cracks growth and final fracture under monotonic load are more prone to occur through the eutectic Si, Al2Cu phases and iron-intermetallics than through aluminium matrix.