<p>To obtain high-quality joints of Mg–9Al–Zn alloy in engineering manufacturing, and reveal the optimization mechanism of weld quality. This study fabricated Mg–9Al–Zn alloy friction stir welded joints. A flow field model was established using the Coupled Euler–Lagrange method. Optimal parameters for maximum tensile strength were determined via range analysis, and the flow field reasonably explained the texture orientation evolution. By characterizing the grain size, texture evolution and recrystallization characteristics in different areas of the optimal joint, the toughening and strengthening mechanism of the joint is revealed. Electrochemical corrosion and tribological analysis of weld samples were carried out. This study provides vital theoretical support for research on regulating the mechanical properties, corrosion resistance, and wear resistance of Mg–9Al–Zn alloy weld joints. Results show that friction stir welded reduced the joint texture’s preferred orientation, with textures in different welding regions deflecting towards the plastic deformation and material flow directions. From the base metal to the nugget zone, the proportion of recrystallized grains increased, grains were significantly refined, the Schmid factor decreased, the energy required for grain slip initiation increased, and the joint strength was enhanced. During electrochemical corrosion, the Al–Mn precipitate phase in the 400-70-0.15 joint dissolved, and grain refinement facilitated passive film formation. Its corrosion rate was 47.29% lower than the 500-75-0.15 joint, and the strength and corrosion resistance of the optimized weld joint were improved simultaneously. Moreover, the uniform discontinuous distribution of Al–Mn precipitates reduced adhesion and plowing effects, maintaining good friction and wear properties in the 400-70-0.15 joint.</p>