Abstract A new process of vacuum-free semi-solid stirring joining on SiCp/A356 composites was investigated. The experimental setup and mathematical model of fixed-point stirring experiment were developed to study the influence of stirrer rotating upon the distribution of flow field and mechanical effect during semi-solid stirring joining. Numerical simulation and experimental results showed that the stirrer rotates to drive semi-solid filler alloy convection, so that a greater alternating pressure and wall shear stress were generated at the brazing interface, which increased the extrusion effect and broken effect to the surface oxide film on the brazing side, and further, removed the oxide film and increased the bonding rate of the brazing interface.