Research On Microstructure Tailoring And Properties Of Graphene/Aluminum Matrix Composites

Graphene reinforced A1 matrix composites have high specific strength,specific stiffness and good wear resistance,which make them have great application prospects in aerospace and automotive industries.However,the improvement of the mechanical properties of the graphene/Al composites is far less than the corresponding excellent properties of graphene,mainly due to the weak interface bonding between the graphene and matrix and the serious agglomeration of graphene in the matrix.Moreover,the strength enhancement of metal matrix composites always accompanies by the obvious decrease in ductility.To overcome these bottleneck problems of improving the performance of graphene/Al matrix composites,the A1 matrix composites with high strength and good ductility based on coupling interface strengthening and hierarchical structure were prepared in this work.Porous reduced graphene oxide(P-RGO)and mixed nano metal oxide particles coated reduced graphene oxide(LDO@RGO)powder were obtained by surface modification of graphene oxide(GO),respectively.The P-RGO/Al and LDO@RGO/Al matrix composites with hierarchical microstructure and A1 matrix composites reinforced by uniformly dispersed GO were prepared by ball milling and discharge plasma sintering(SPS)process,respectively.The main research contents are as follows:(1)P-RGO reinforcement coated by homogeneous distributed nanopores was obtained by chemical etching of the GO surface with H2O2 as the etching agent.P-RGO can be then uniformly dispersed on the surface of flake A1 powder by combining the electrostatic adsorption and ball milling processes and the obtained flake P-RGO/Al composite powder II mixed with spherical A1 alloy powder,preparing composite powder I.The P-RGO/Al composites with alternated spatial distribution of hard regions that were reinforced by homogeneously distributed P-RGO in the Al matrix and relatively soft regions that were free of P-RGO in the A1 matrix were successfully fabricated by SPS.The specific surface area of P-RGO obviously increased due to the formed nanopore defects.The residual oxygen element at the nano-pore defects of P-RGO preferentially reacted with the Al matrix,in-situ forming nano-Al203 interfacial products.Moreover,nano Al12Mg17 phase was simultaneously observed at the P-RGO/Al interface due to the chemical reaction between the segregation of Mg element surrounding this interface and the A1 matrix.This dispersed nano interfacial products effectively act as strong bridge between the A1 matrix and RGO.The ultimate tensile strength(UTS,339.8 MPa),yield strength(YS,296.1 MPa)and elongation(εf,9.1%)of P-RGO/Al matrix composites are increased by 23.1%,78.1%and 9.6%,respectively,compared with GO/Al matrix composites.The main reason for the strengthening is the strong interface bonding between P-RGO and A1 matrix,which significantly improves the load transfer and dislocation strengthening efficiency.In addition,the alternately arranged hard P-RGO-rich and soft P-RGO-free regions make the deformation of the composites more coordinated during the loading process,increasing the crack propagation path through cracks deflect and improving the toughness of the composites.(2)GO substrate surface was uniformly coated by the in-situ formed nanoscale magnesium aluminum double hydroxide(LDH)(LDH@GO).The calcined LDH@GO(LDO@RGO)then mixed with the Al powders and the LDO@RGO/Al matrix hierarchical composite characterized by LDO@RGO-rich zones and LDO@RGO-free zones was fabricated by SPS sintering.The uniformly distributed nano-LDO on the surface of RGO not only increases the dispersion of RGO in A1 matrix but also forms the hybrid interface structure of nano-Al2O3,Al2MgO4,Al12Mg17,a small amount of Al4C3 rods and the RGO/Al2O3 diffusion layer between LDO and A1 matrix.The interfacial mismatch strain between RGO and AI matrix is effectively reduced and the interfacial bonding between RGO and Al matrix is obviously improved.The UTS(398.2 MPa),YS(282.1 MPa),εf(13.6%)and fracture energy(4411 J)of LDO@RGO/Al matrix hierarchical composites are increased by 44.2%,69.6%,63.9%and 140.5%,respectively,compared with GO/Al matrix composites.The theoretical calculation results show that the strength improvement of LDO@RGO/Al matrix hierarchical composite is mainly due to the synergistic strengthening mechanisms of load transfer,Orowan,solid solution,thermal mismatch and geometric necessary dislocation.The cracks can be deflected during the loading process and the crack propagation path increases through spatial distributed "soft/hard phase region",which is benefial for coordinated plastic deformation during tensile testing,improving the toughness of the composite.