The present study investigated the metallographic characteristics and distribution of precipitated phases within the weld nugget of 10 mm thick 2219–C10S aluminum alloy medium-thickness plate under different welding speeds using Bobbin tool friction stir welding (BT–FSW)

providing significant reference value for improving the quality and performance of BT–FSW joints of 2219–C10S aluminum alloy. The results indicate that the inhomogeneity of heat input in the thickness direction of the plate leads to the formation of a clustered structure in center region of the weld nugget. There is a notable disparity in the content

size

and distribution of the Al

2

Cu

precipitates across various regions of the weld. In the center of weld nugget zone

the area proportion and average size of the precipitates are the smallest

with a particle-like dispersion and the highest number of particles. The shoulder-affected zone has the highest area proportion of precipitates

while the sizes of precipitates in the shoulder- and heat-affected zones are comparable. Periodic immersion corrosion tests revealed that the base material exhibits the poorest corrosion resistance

followed by the heat- and shoulder-affected zones

with the center of weld nugget zone demonstrating the optimal corrosion resistance.