The thermo-mechanical characteristics of Friction Stir Processing (FSP) in the AZ91 Magnesium alloy were simulated using a numerical model that used the Smoothed Particle Hydrodynamics (SPH) approach. Meshfree SPH technique, a particle-based Lagrangian approach, excels in monitoring field variables, interfaces, and material deformations. Its adaptability proves beneficial in FSP, especially for challenging experimental variables. The model in this work was analyzed against experimental data and developed via Altair RADIOSS FEM-based software. This SPH model resolves issues traditional grid-based systems struggle with, precisely predicting temperature, material flow, and tool tilt flaws. Strong agreement between measured and simulated temperatures across FSP phases confirms the SPH model's accuracy with errors below �5 around the shoulder perimeter 10 mm from the center of the Stir Zone (SZ). The SZ core reached 83 of the material's melting point, peaking at 666.3 K. In a tilted tool arrangement, the SPH model revealed an extended, defect-free SZ with elevated temperatures attributed to increased friction, improved material flow, and intensified shear pressures from tool churning. Evidence of plastic strain and deformation near the shoulder highlights the model's ability to capture complex thermo-mechanical dynamics in FSP. © 2024 Elsevier Ltd