Preparation And Mechanical Properties Of Graphene-aluminum Matrix Nanolaminated Composites

In traditional metal matrix composites,the microstructure with reinforcements disorderly and uniformly distributed in the matrix,increases the strength of composites but substaintially sacrifices the ductility and toughness,leading to restricte its further development and application.During a long-term evolution,natural biological materials(bones,wood and shell,etc)have a fine architecture,which give rein to the double benefites of microstruture and composite,and achieve the excellent strengtheningtoughening matching.Insipired by the structure-function relationship between the laminated structure and the strengthening-toughening matching of nacre,the preparation of aluminum matrix composites reinforced by graphene(reduced graphene oxide,rGO)with a bioinspired nanolaminated structure is conducted.The lateral size effect of graphene on the mechanical properties of the composites is further analysed.The optimization conditions for the strength-ductility matching of the composites is discussed.The main conclusions of this thesis are as follows:1.Optimize and prepare graphene oxide with different lateral size.Single-layer dispersion of of graphene oxide with small lateral size is successfully conducted by ultrasonic processing.Graphite oxide with a large diameter was chosen as the starting material to prepare larger lateral size of graphene oxide by precisely controlling the time and temperature of chemical oxidation and the power of subsequent sonication.The lateral size of three kinds of graphene oxide ranges from submicrometer to more than ten microns,which covers the critical value estimated by the shear lag theory.The as-prepared graphene oxide are used as reinforcements and provide the foundation for the subsequent fabrication of the composite powder.2.The rGO is effectively and uniformly dispersed in Al matrix,and the improved powder metallurgy technology route is adopted to realize the preparation of the bulk rGO/Al matrix nanolaminated composite.Firstly,the micro-nano flaky Al powder with high aspect ratio were prepared by wet ball-milling as the matrix module,and the rGO/Al composite powder were prepared by the hybrid process based on the electrostatic adsorption mechanism and the subsequent thermal treatment.The self-assembling and densification of rGO/Al composite powder were conducted by the combined processes of cold pressing,vacuum sintering and hot rolling to prepare densely ordered rGO/Al nanolaminated composites.The microstructure characterization of the composites shows a highly ordered fine nanostructure and the distribution and morphology of rGO at the interface.3.The effect of rGO sheets with different lateral size on the mechanical properties of Al matrix nanocomposites with a bioinspired nanolaminated structure are analyzed.The optimization conditions for the strength-ductility matching of graphene/Al matrix composites with bionanolanimiated was explored.The lateral size of graphene sheets significantly affects the strength and ductility of composites.When the lateral size of graphene is smaller,the strength of the composite increases with the lateral size,but compromises ductility.When the lateral size is large enough,the composite shows a slight decrease in strength but its ductility returns to that of Al matrix.The graphene with largest lateral size was verified to be conducive to realize a good balance of strength and ductility of the nanolaminated composite.This study shows that the lateral size of reinforcement and the architecture design of composites are of great significance for achieving the strengthening and toughening of metal matrix composites.