Shrinkage induced flow, thermo-solutal convection and equiaxed grain motion are the major transport mechanisms contributing to macrosegregation formation in aluminum alloys produced through Direct Chill casting. Experimental and numerical studies were conducted to provide insight on macrosegregation formation in AA5182 ingots. Previous numerical studies indicated that the weak thermo-solutal convection, both individually and in its interaction with grain motion, has an insignificant contribution to macrosegregation formation. These studies were, however, conducted using 2D simulations of sheet ingots. In this paper, we carry out 3D modelling of sheet ingots with the same alloy by employing a multiphase, multiscale solidification model based on volume averaging method accounting for thermo-solutal convection and globular grain motion. We show that the coupling between thermo-solutal convection and grain motion is important to provide a better description of macrosegregation formation during DC casting of AA5182 alloy. The numerical work is discussed considering experimental horizontal macrosegregation maps.