<p>This study systematically investigates the effects of repeated gravity casting on the microstructure and mechanical properties of 6061 aluminum alloy. With an increasing number of casting cycles from one to ten, grain coarsening and a decrease in dislocation density were observed, mainly due to the significant depletion of magnesium from 1.03 to 0.01% and titanium from 0.009 to 0.005%. These microstructural changes led to a decrease in solid-solution strengthening and grain-boundary strengthening, resulting in a 30% reduction in tensile strength, while ductility increased by about three times. Moreover, work hardening decreased with increasing the casting cycle, which can be attributed not only to the microstructural changes but also to the increase in stacking fault energy (SFE) associated with compositional evolution. From the transmission electron microscopy (TEM) observations, in the 1-cycle sample, Mg₂Si precipitates were finely dispersed and a high amount of Mg element in the matrix, resulting in significant dislocation accumulation, whereas the 10-cycle sample exhibited weaker dislocation tangling. These microstructural evolutions provide insight into the degradation of mechanical performance in aluminum alloys subjected to multiple casting processes.</p>