<p>This study investigates the effects of potassium modification on the microstructure and mechanical properties of the A319 aluminum alloy. Potassium was added in varying amounts (0, 0.03, 0.06, and 0.09 wt.%) to the A319 melt, and the resulting microstructures were analyzed using optical and scanning electron microscopy. Also, tensile properties were evaluated according to the ASTM B557-10 standard. The results showed that potassium significantly refined the microstructure, transforming coarse, elongated silicon particles and needle-like β phases into finer, more rounded shapes. This refinement led to improved tensile strength and elongation, with the optimal modification observed at 0.06 wt.% potassium, yielding a tensile strength of ~ 310 MPa and an elongation of ~ 8%. However, increased potassium content also resulted in higher porosity. The study concludes that potassium is an effective modifier for enhancing the ductility of A319 alloy, with 0.06 wt.% being the optimal concentration.</p>