As a new type of carbon material reinforcement, graphene nanoplatelets (GNPs) have excellent mechanical, electrical, thermal and optical properties. Adding GNPs with a large specific surface area to the magnesium matrix can significantly improve the mechanical properties, the thermal and electrical properties of the magnesium matrix. However, so far, few reports focused on GNPs reinforced magnesium matrix composites, especially for lack of feasible fabrication technologies. Thus, in the present work, a new method for fabricating GNPs reinforced magnesium matrix composites is presented. First, the GNPs were dispersed by ultrasonic dispersion. Subsequently, the AZ91D magnesium alloy particles and the uniformly dispersed GNPs were mixed in a V-type powder mixer. Finally, GNPs reinforced magnesium matrix composites were prepared by semi-solid thixomolding. The effects of GNPs contents (0.3%, 0.6%, 0.9%, mass fraction) on the microstructure and properties of magnesium matrix composites were studied. The results show that the GNPs were uniformly distributed in the matrix, which were well combined with the matrix, and the addition of GNPs could refine the grain size and reduce porosity. Compared with AZ91D magnesium alloy, the addition of GNPs improved the tensile strength and hardness of the material. When the content of GNPs was 0.6%, the mechanical properties of the composites were the best, and the hardness and tensile strength reach up to 92.3 HV and 245 MPa.
Fund: National Natural Science Foundation of China(51774254);National Natural Science Foundation of China(51774253);National Natural Science Foundation of China(51701187);National Natural Science Foundation of China(U1610123);National Natural Science Foundation of China(51674226);National Natural Science Foundation of China(51574207);National Natural Science Foundation of China(51574206);Science and Technology Major Project of Shanxi Province(MC2016-06)
Fig.2 Thixomolded composite mold and sampling locations for OM observation (position A), hardness measurement (position B) and density (position C)
Fig.3 TEM images (a, b) and XRD spectrum (c) of graphene nanoplatelets (GNPs)
Fig.4 Appearances of AZ91D magnesium alloy particles without (a) and with (b) GNPs
Fig.5 OM images of AZ91D (a) and AZ91D composites with 0.3%GNPs (b), 0.6%GNPs (c) and 0.9%GNPs (d) fabricated by thixomolding (Insets show the corresponding distributions of grain size)
Fig.6 SEM images (a, b) and EDS (c) of 0.6%GNPs/AZ91D composite fabricated by thixmolding
Fig.7 EDS map analyses of 0.6%GNPs/AZ91D composite fabricated by thixmoldingColor online(a) Mg (b) Al (c) O (d) C (e) EDS
Fig.8 TEM (a) and HRTEM (b) images of 0.6%GNPs/AZ91D composite fabricated by thixmolding
Fig.9 XRD spectra of AZ91D and GNPs/AZ91D composites fabricated by thixmolding
Table 2 Mechanical properties of AZ91D and GNPs/AZ91D composites fabricated by thixmolding
Fig.10 Tensile curves of AZ91D and GNPs/AZ91D composites fabricated by thixmolding
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