An Overview on the Identification and Characterization of Cu-Rich Second Phases in Casting Al Alloys

This work presents an overview on the identification and characterization of the Cu-rich second phases obtained from the liquid state during the solidification of casting Al alloys. Among them, Al 2 Cu, Al 2 CuMg and Q (Al 5 Mg 8 Cu 2 Si 6 ) dominate, representing an important part of the microstructures of these alloys. They mainly present fibrillar eutectic and block-like shapes, their amounts and morphologies depending on variables such as chemical composition of the alloy, the manufacturing process, the differences in local cooling rates, and the heat treatment cycles. It was found that morphological and gray scale similarities between Cu-rich and other second phases pose a challenge for their identification, making necessary the use of a combination of imaging techniques such as optical microscopy and scanning electron microscopy, including energy-dispersive spectroscopy. Besides, a validation study using XRD is indispensable. Examples of their identification and characterization using these tools are presented in this work, including their morphological analysis through shape descriptors, and microstructural modifications depending on the manufacturing variables. The contribution of the Cu-rich phases and their morphologies to the mechanical properties of the Al alloys is also assessed.