Formation of Intermetallic Sludge Phases in Al‐Mg‐Si Alloys with High Concentrations of Alloying Elements: A Drawback for Increasing Sustainability

The need for sustainable aluminum alloys requires a critical review of given alloy specifications to facilitate higher tolerances for contaminating alloying elements and consequently a broader usage of scrap material for fabrication. In this regard, Al‐Mg‐Si alloys are particularly of high interest, as they are widely used for engineering applications due to their excellent properties. However, their specifications usually only allow rather small concentrations of the alloying elements which is a serious drawback for increasing the sustainability of these alloys. In order to figure out the metallurgical limitations, the concentrations of Si, Cu, Fe, Zr, Ni, and Mo are systematically varied, using the Al‐Mg‐Si alloy 6082 with a maximum content of such constituents according to the standard as the starting point. Surprisingly, this 6082‐maximum condition already shows the formation of sludge phase particles. Depending on the Si concentration of the alloy, the formation of different types of sludge phases is apparent. While the cubic α ‐Al 12 (Fe,Mn,Cr) 3 Si 2 phase forms at high Si concentrations, the monoclinic Al 45 (Fe,Mn,Cr) 7 sludge phase is detected in the case of a moderate Si concentration. Moreover, an increase in the quantity of sludge phases is observed in the presence of Mo due to the incorporation of Mo into both types of phases.