<p>Upward and downward directional solidification experiments were carried out on a Cu–10Sn–2Zn–1.5Fe alloy to investigate the influence of buoyancy-driven convection on solute redistribution and microstructural evolution. At the early stage of solidification, samples solidified either upward or downward exhibited high nucleation rates owing to the presence of abundant Fe-rich particles, resulting in the formation of equiaxed grains. As solidification progressed, Fe-rich particles were progressively consumed and partially transported away from the solid-liquid interface by convection, promoting the equiaxed-to-columnar grain transition in both samples. Distinct solute redistribution behavior was observed due to the different convection conditions. Sn was enriched at the solid-liquid interface in the downward-solidified sample, resulting in the formation of columnar dendrites at the late stage of solidification. Whereas Sn tended to migrate away from the solid-liquid interface in the upward-solidified sample, no columnar dendrite was observed. These results highlighted the critical role of buoyancy-driven convection in controlling the microstructure evolution during solidification.</p>