Formation of iron-rich intermetallic phases during solidification of aluminium casting alloys

Iron is the most common and detrimental impurity in aluminium casting alloys and has long been associated with impaired properties and often an increase in casting defects. While the negative effects of iron are clear, the mechanism involved is not fully understood. It has generally been associated with the formation of iron-rich intermetallic phases. However, the conditions that control the formation of these phases are not well understood. Many factors, including solute elements, melt treatment, iron level and cooling rate, could play a role. The interactions between iron and other common alloying elements in aluminium casting alloys are investigated in the present study. The iron-rich intermetallic phases were characterized using the electron microanalysis technique (EPMA) and compared with the results predicted from Thermocalc(R).