Abstract: Surface aluminizing on magnesium was successfully farbricated by multi-pass friction stir processing (MP-FSP). The interface microstructure, mechanical properties, fractured surface and components were investigated by using optical microscopy (OM), electron probe microanalysis (EPMA), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy disperse spectroscopy (EDS) and electromechanical testing machine. In addition, the effect of different welding speed on the overlapping area (OA) interface microstructre and properites were also analyzed. The results showed that the interfacial macrostructure was consisted of N pass, OA and N+1 pass. A conversion zone containing Al+Al3Mg2 and Mg+Al12Mg17 was formed in the interfacial macrostructure. The thickness of OA conversion zone was increased with the welding speed decreased. Shear tensile test results showed that the shear force of the OA interface was increased with the welding speed decreased. The fracture mode was plastic fracture.