Center line segregation in twin-roll cast AZ31 magnesium alloy

A three-dimensional approach to microstructural investigations was for the first time applied to a continuous cast material in order to understand solidification processes and liquid flow during casting. A twin-roll cast AZ31 magnesium alloy strip was subjected to observations by light optical microscopy, electron microscopy, and X-ray microtomography. The last one is found to be the only suitable for the 3D characteristic of the segregation channels containing Mn and Al-rich primary phases located in the central zone of the strip. It was shown that a reliable three-dimensional image of the volume containing central line segregation cannot be obtained using conventional metallographic methods, whereas X-ray microtomography allows the complete reconstruction of major features of the central segregation in the alloy.