Conventional Aluminum designations differentiate between heat treatable and non-heat treatable alloys, depending on their main alloying element. By introducing the AlMgZn(Cu) crossover alloy concept a step forward has been taken by escaping the conventional alloying system. The 5/7-crossover alloy overcomes the long-standing trade-off between the excellent formability of 5xxx-series alloys and the high strength of 7xxx-series alloys. However, the respective tolerance intervals of the composition, in particular of the impurity elements must be closely examined for these new alloy classes.
This study is investigating the primary intermetallic phases formed upon casting of AlMgZn(Cu) alloys with different content of impurity elements (Fe and Si). Microstructure analysis was done via electron microscopy. Different cooling methods were applied to evaluate the influence of cooling rate on the formation of the primary intermetallic phases. Results indicate a strong dependency of primary phases on the cooling rate as well as the Fe/Si ratio.