Developing Al–Fe–Si alloys with high thermal stability through tuning Fe, Si contents and cooling rates

The use of recycled aluminum alloys can greatly reduce energy consumption and carbon emissions, but the high iron content limits the scope of application of recycled aluminum alloys. The development of alloys with good performance under high Fe content can enable iron-rich recycled aluminum alloys to have a new application direction. The key is to control the type and morphology of the Fe-rich phase in the alloy. In this work, the microstructure evolution of Al–Fe–Si alloys with varying Fe, Si contents and cooling rates was studied. It is found that as the Si content decreases, the iron-rich phases transform from the β-Al9Fe2Si2 to the eutectic α-Al8Fe2Si. Within a certain composition range, increasing the cooling rate will not only refine the microstructure but also promote the transformation of β-Al9Fe2Si2 to α-Al8Fe2Si. In this study, a microstructure containing only one type of second phase, in the form of fine eutectic α-Al8Fe2Si, has been obtained by water cooling of Al–5Fe–3Si melt. The mechanical properties of the alloy are similar to those of the Al–Si alloy under the same conditions, while the thermal stability of the microstructure is significantly better than that of the Al–Si alloy. These findings not only provide new insights for avoiding β-Al9Fe2Si2 phase in aluminum alloys, but also provide guidance for the development heat-resistant alloys with Al - α-Al8Fe2Si eutectic structures.