Role of grain refining in macrosegregation upon direct chill casting of AA 2024 round billet

The addition of grain refiners during industrial direct chill (DC) casting of aluminum billets promotes formation of smaller equiaxed grains with obvious advantages. However, the role of grain refining in the extent of macrosegregation in DC cast Al alloys is still unclear. This is particularly evident in the case of commercial aluminum alloys with various alloying elements. In this work, the structure and associated macrosegregation patterns in DC cast AA 2024 (Al-Cu-Mg) aluminum alloy billets were studied at different casting speeds. The concentration profiles of Cu and Mg, measured along the billet diameter, showed an expected negative segregation in the center and close to the surface. The severity of segregation increases at a higher casting speed. On the other hand, grain refining does not seem to have any dramatic effect on the macrosegregation patterns. The experimental results are correlated with microstructural observations such as grain size and morphology and the occurrence of "floating" grains across the cross-section of the billet.