Dross formation during remelting of aluminum 5182 remelt secondary ingot (RSI)

This article reports, for the first time, a surprising result that in the center part of some commercial aluminum 5182 remelt secondary ingot (RSI), more than 50% of the alloy turns to dross during melting. The solidification microstructure of the RSI was characterized in order to understand where the dross comes from and how it forms. Optical microscopy showed that severe interdendritic porosities and hot tears exist in the RSI. These cavities provide continuous channels that expose the internal interdendritic surfaces to the atmosphere outside of RSI. SEM revealed that the dendrites in the center of RSI are covered by magnesium and aluminum oxides. It is the oxidation of the surfaces of the interdendritic pores that results in a large amount of dross formation during the remelting of aluminum 5182 RSI.