Interplay between Cu and Fe in the phase formation of recycled aluminium cast alloys

In recent years, ensuring the quality of recycled cast aluminium parts has become increasingly important in the transportation industry. Compared to primary alloys, secondary AlSi10Mg cast alloys made from recycled combustion engine parts (AlSi7MgCu0.5) have higher copper and iron contents and are not ideal for e-engine housings due to the decrease in corrosion resistance. Copper increases the hardness and strength of alloys by forming metastable phases from the Q-AlCuMgSi and θ-Al 2 Cu families, while iron forms the α-AlFeMnSi. Although these phases are well described in the literature on their own, it remains unclear what the interplay of increased copper and iron contents has on the occurrence of primary phases and their chemical composition. Therefore, we correlated the copper content with the primary phases formed in four different AlSi10MgCuX alloys (0.1, 0.8, 1.2, and 2.0 wt.%). Then, we combined experimental methods with numerical Scheil and precipitation calculations within the MatCalc© software to predict the phase fraction and chemical composition of the intermetallic phases beyond the presented chemical compositions in terms of iron and copper. We found that the critical copper value to form the Q-AlCuMgSi primary phase is 0.8 wt.% and 1.3 wt.% for the θ-Al 2 Cu phase. Finally, not all Cu is free to form phases and precipitates around and in the α-AlFeMnSi. Increased copper promotes the formation of the α-AlFeMnSi and suppresses the β-AlFeSi at high iron contents. These results are relevant for designing cast aluminium products using recycled alloys with high iron and copper contents.