Zhao Rongxia,Pei Jinxuan,Du Wenbo,Zhao Zhanyong,Zhang Lizheng,Gao Jianfeng,Bai Peikang,Tie Di
The surface of graphene (GNP) has been successfully coated with magnesium nano-metal to form composite structures in situ via the organic chemical reduction method. The results demonstrate that the organic chemistry plated was successfully used to synthesize 30–50 nm Mg nanoparticles (nano-Mg) smoothly occurred on the surface of graphene. The HRTEM results confirmed that heterogeneous nucleation of Mg promoted the tight bonding between the nano-Mg and the graphene interfaces. In addition, the wettability and dispersibility of magnesium-coated graphene within the AZ91 alloy matrix have been greatly improved, resulting in more β-Mg 17 Al 12 strengthening phase with a size of 100–300 nm dispersion and precipitation in the enhanced magnesium-matrix composite. These results reveal that the magnesium-coated graphene significantly affects the microstructure of the composite and exhibits an excellent reinforcement effect. Graphic Abstract
Rongxia Zhao,Zhanyong Zhao,Peikang Bai,Wenbo Du,Di Tie,Zhen Zhang,Liqing Wang,Yu Wang
Magnesium-coated graphene (GNPs) was successfully prepared by a novel organic chemical reduction method with significantly improved wettability and dispersion. The GNPs were uniformly distributed in the matrix, while a finer and more dispersed strengthening phase β-Mg 17 Al 12 was precipitated around it. Moreover, MgO nanoparticles were formed by in-situ reaction on the surface of GNPs, forming nano-scale contact and tight interfacial bonding with the substrate, thereby significantly improving the wear resistance of the composites. The wear mechanism has also changed from severe delamination and abrasive wear to mixed wear of slight delamination , adhesion, and oxidation . The increase in wear resistance is attributed to the combined effect of the lubrication and load transfer of GNPs, the enhanced effect of fine precipitates on the mechanical properties of the matrix, and the synergistic effect of in situ generated MgO nanoparticles against deformation.
A new organic chemical reduction method was successfully used to synthesize magnesium-coated graphene (GNPs), and xGNPs/AZ91 nanocomposites with different contents were fabricated by vacuum hot-pressing sintering. The microstructure of the composite was mainly composed of the matrix (α-Mg) and the precipitated phase (β-Mg 17 Al 12 ) with different morphologies such as rods, spindles, and granules. The coarse irregular β phases precipitated along the grain boundaries, while fine rod-like β phases were distributed inside the crystal grains. With the increase of GNPs content, the grain and structure are significantly refined under the action of two mechanisms of increasing the nucleation rate and hindering the growth of grains. The average grain size of the 2.5-wt% GNPs/AZ91 composite dropped from 40.78 µm to 25.39 µm, a reduction of 37.7%. In addition, the orientation relationship (OR) between β-Mg 17 Al 12 and α-Mg was shown as [—3 —1 —1] β-Mg17Al12 )∥[1 —1 0 —1] α-Mg . Further, finer β phases were further precipitated in the grain boundaries and matrix. Moreover, the β precipitated phase and the GNP, as well as the GNP and magnesium-matrix formed a nano-scale contact interface and a diffusion bonding interface, thereby greatly enhancing the interface bonding strength between GNP and the matrix. Compared with AZ91 alloy , the grain refinement and load transfer caused by GNPs increased the microhardness of the composite by 17.6% and the friction coefficient was decreased by 37.4%. The significant improvement in the wear resistance of the composites was due to the effect of the lubricating layer formed by GNPs on the wear surface, which changed from severe delamination wear to slight delamination and abrasive wear behavior.
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