Constrained Friction Processing (CFP) is a novel solid-state technique suitable to produce rods especially from lightweight materials. The technology is particularly interesting to overcome the processing challenges associated with Mg due to its hexagonal close-packed (hcp) structure. The process is a variation of the refill friction stir spot welding (refill FSSW) technique, and is performed by plunging the rotating shoulder into the base material, which causes the material to be extruded into the cavity crated by the retraction of the rotating probe and, at the same time, being constrained by it. The complex shear and the heat generated during the process causes metallurgical transformations in the material, such as dynamic recrystallization, allowing for substantial grain refinement to micro-or even submicro-scale. In this study, real time data – torque, axial force and temperature – acquired from the process are analyzed in order to present, for the first time, a description of the CFP technique. Furthermore, the resultant features of the microstructure of a refined rod is explored.