Research On Non-uniform Deformation Behavior Of Graphene Reinforced Aluminum Matrix Composites

Graphene is regarded as an excellent reinforcement due to its excellent properties.Aluminum alloy has the characteristics of light weight and high strength.Therefore,graphene aluminum matrix composite is a new material with potential.However,the current research is mainly the study of homogeneous composite materials.This study proposes a new idea to prepare a non-homogeneous composite material of"skeleton（A）-GNPs-matrix（B）"structure by adjusting the impregnated aluminum alloy,so that the components and performance on both sides of graphene are different,causing inconsistent shear strain on both sides of the graphene during hot extrusion,which promotes the opening of the graphene sheet.In order to verify the"A is harder than B"and"A is softer than B"configuration,three materials with different deformation capabilities are used:pureAl,6061Al,2024Al.Multilayer graphene nanosheets（about 15 layers）was used as a reinforcement.6061Al powder was used as a skeleton,mixed with GNPs to perform high-energy ball milling and pressing into a powder.The non-homogeneous graphene aluminum matrix composites with the content of 0wt.%,0.6wt.%and 1.2wt.%were prepared by infiltration of the pressed powder by pressure infiltration method with 2024Al and pureAl as the matrix,respectively.A homogenous composite material（6061 Al is a matrix material）prepared by the same process was compared.The effects of graphene content,graphene properties,hot extrusion and matrix-matrix system on the microstructure and mechanical properties of the composites were analyzed.In addition,two layers of aluminum-based composites with a content of 0.6wt.%were prepared with a few layers of graphene nanosheets（about 7 layers）as reinforcements:（Gr₂/6061Al）/2024Al and（Gr₂/6061Al）/pureAl（the multilayer graphene used is abbreviated as Gr₁,and the small layer graphene is abbreviated as Gr₂）,and the microstructure and properties of the two graphene composites are analyzed.The microstructure of the composites was studied.It was found that the diffusion of the elements between the internal framework and the matrix of the prepared non-homogeneous graphene-aluminum composites was not obvious,and the distribution of in-plane elements was non-uniform.After hot extrusion,EBSD showed a single peak distribution in the grain size of the homogeneous composite.The grain size in the non-homogeneous composite has a bimodal distribution and the grains are finer.Hot extrusion makes the GNPs and Al matrix in the composites have obvious orientation,and there are two textures of<111>and<100>in the homogeneous composite after extrusion.Non-homogeneous composites have only one texture<111>.Raman analysis showed that the G peak of 1.2 wt.%（Gr₁/6061）/pureAl graphene after hot extrusion moved from 1604.6to 1608.3,while the 1.2 wt.%（Gr₁/6061）/2024Al graphene G peak 1605.8 moved right to 1607.0,indicating that the former is less stratified.Hot extrusion can make the GNPs in the composite less stratified,and the degree of stratification of GNPs is more obvious when the matrix is softer than when the matrix is hard.TEM analysis showed that most of the Al-GNPs interface was better after extrusion,and the graphene was well preserved,but there was a small amount of interfacial reaction.Fine acicular Al₄C₃ was observed at the interface of 0.6 wt%（Gr₁/6061Al）/2024 Al composite,and MgAl₂O₄ was observed at the interface of 0.6 wt%（Gr₁/6061Al）/pure Al.The mechanical properties of the composites were studied.The results show that the hardness,strength and modulus of the composites increase with the increase of graphene content before hot extrusion,which is roughly linear.The flexural strength and plasticity of the Gr₂ composite are lower than that of the Gr₁ composite,but the yield strength and elastic modulus are higher.After hot extrusion,the elastic modulus,bending strength and bending strain of the composite will increase.When annealing is performed after hot extrusion,the performance improvement rate of 1.2wt.%（Gr₁/6061）/pureAl composite is higher than 1.2wt.%（Gr₁/6061）/2024Al due to the less stratification mechanism of graphene.The bending strength is increased by 26.2%compared with that before extrusion,and the bending strain is increased by 115.8%.When solid solution aging（T6）is applied after hot extrusion,due to the strengthening effect of precipitation phase in2024Al,1.2wt.%（Gr₁/6061）/2024Al composite has a performance higher than 1.2 wt.%（Gr₁/6061）/pureAl,and its tensile strength reaches 364.2 MPa,and the yield strength is293 MPa.In order to further improve the performance of the composite material,a softer and heat-treatable alloy than the skeleton（A）should be selected as the matrix（B）,and the strengthening and precipitation phase strengthening of the graphene less layering is obtained.