A unique grain refinement mechanism ‘dislocation containment sites (DCS)’ in mobilized shear bands (SBs) are observed though HR-TEM, which contributes to strengthening significantly for the Hybrid-SPD (HSPD) processed Mg alloy investigated in the present work. This DCS are evolved through inter-planar movement inside SBs due to extreme loading conditions in (0002) basal plane. The improvement in tensile and fracture properties observed has shown direct relationship with dislocation density (ρ) and found to be maximum in case of 70% hot rolled-16.6% uniaxially forged specimen (yield (236 MPa), tensile (259 MPa), and EP-PSFT (JQ, 18.57 kJ.√m)) compared to solutionized specimen. The precipitates such as globular (larger and finer) and needle (finer) shaped are also affecting microstructural evolution hugely for grain refinement as observed in HSPDed Mg alloy. These precipitates are characterized using HR-TEM/EDS and X-ray diffraction technique to explain the strengthening mechanisms contributing to HSPDed Mg alloy. © 2020 Elsevier B.V.