▎ 摘　　要

In the present research, multi-pass friction stir processing (FSP) was employed for the first time to disperse graphene in the form of graphene nano-platelets (GNPs) into an AA5052 aluminum-magnesium alloy to fabricate a new Al-Mg/3 vol% GNPs nanocomposite. After five cumulative FSP passes, the GNPs were distributed within the metal-matrix. Field emission-scanning (FE-SEM) and transmission electron microscopy (TEM) analyses were used to examine the dispersion of GNPs, and suggested negligible deterioration of the graphene planar structure following FSP. Some clusters of graphene originating from the initial powder remained due to the high surface energy of these GNPs, while grain orientations were evaluated in the nanocomposite using electron back scattering diffraction (EBSD). A fine equiaxed recrystallized grain structure with an average size of 2.1 pm was formed in the stir zone (SZ) after FSP while dispersing GNPs. Indentation revealed the hardness of the nano composite increased by 53% compared to the processed Al-Mg alloy. Yield strength also was improved by more than three times while preserving ductility which achieved 20% strain before fracture. Fractographic studies of tensile test specimens revealed a mixed ductile-brittle fracture behavior. Based on the micromechanics theory, three models considering the microstructural parameters (Le., aspect ratio, mean size, and volume fraction of GNPs, grain size, and clustering during process) were developed to predict the strengthening effects of GNPs in the terms of elastic modulus, yield strength, and indentation hardness. Correlation between these predicted values and experimental data are discussed in detail.