▎ 摘　　要

In the present work, microstructural evolution and mechanical properties of a frictionally stir processed magnesium alloy reinforced with micro and nanoparticles were comprehensively investigated. Microstructural characterizations after the first deformation pass for both composites just implied a limited grain refinement along with the agglomeration/clustering of particles, and the difference between two composites was ignorable. While, deformation up to three FSP passes astonishingly followed a different trend, relative to the first pass. Achievement of a fine and homogenous microstructure in conjunction with the evolution of well-distributed particles and almost no sign of clusters were the outcomes of the third pass. Particularly, for the nanocomposite, a fine grain size of 2.29 mu m is achieved. Additionally, better mechanical properties including higher values of Vickers microhardness and yield and also ultimate tensile strengths were attained after the third pass, compared to the first one. Better distribution of nanoparticles and their decisive role in improving tensile properties, compared to microparticles, led to the achievement of high hardness of 83 HV and ultimate tensile strength of 192 MPa for the graphene nanocomposite. Furthermore, the change from a brittle fracture to the brittle-ductile and ductile fracture is observed for micro and nanoparticles after the third FSP pass. (C) 2019 Elsevier B.V. All rights reserved.