This study investigates the influence of various in-process cooling techniques on the microstructural characteristics and mechanical properties of the friction stir-welded AA-2219-T6 alloy. The in-process cooling methods used include normal air, dry fan, an oil-water mixture (20:80), and water. The primary objective is to determine the optimal cooling strategy for enhancing the quality of the weldment. The characterization included light microscopy, tensile testing, X-ray diffraction (XRD), microhardness testing, and scanning electron microscopy (SEM) analysis of fractured surfaces to evaluate the microstructure and mechanical properties. It was seen that in-process cooling methods significantly affect the microstructural features and mechanical properties of AA 2219-T6 alloy weldments. Findings indicated that the water-cooled method at 55 °C resulted in the highest density of Al2Cu particles, leading to superior hardness and mechanical properties compared to other in-process cooling methods. Specifically, the water-cooled samples exhibited a ~ 17% increase in hardness compared to air-cooled samples and achieved an ultimate tensile strength equivalent to 65.4% of the base metal. Furthermore, a notable volume of second-phase particles was observed on the fractured surfaces in the water-cooled condition, attributed to the lower in-process temperatures, thus underscoring the effectiveness of water cooling in friction stir welding.