Heterogeneous-Matrix Design,Fabrication,Microstructure And Properties Of Graphene/Aluminum Composites

Graphene is regarded as an ideal composite reinforcement by researchers due to its superior mechanical properties.Only small additions are required to significantly improve the performance of the matrix material.However,graphene has a very large specific surface area and is very easy to agglomerate.Instead,it will become a crack source,and it is easy to cause premature failure of the composite material when it is loaded.Therefore,how to uniformly disperse graphene in the matrix material has become the key to the development and application of graphene/aluminum composites.In order to solve this problem,based on the graphene/6061Al composite material,this paper designs and prepares a graphene/aluminum composite material with a heterogeneous matrix structure.The purpose is to increase the stress-strain field on both sides of the graphene during the deformation process and promote the agglomeration of graphene to open,in order to achieve uniform dispersion of graphene in the matrix and debonding and less layering,thereby improving the performance of the material.The composite material system was determined by computational simulation design.In the study,first-principles calculations were used to analyze the interface bonding between Al-Mg-Si alloys and graphene:adding Mg and Si elements can increase the interface bonding strength of composite.In addition,through finite element simulation,the changes of stress,strain and stress-strain difference at the interface of the heterogeneous matrix during the deformation process were studied,and the strength ratio of the heterogeneous matrix corresponding to the large stress difference and large strain difference was determined.Based on the calculation and simulation results,pure aluminum or 2024Al and 6061Al were selected to construct a heterogeneous matrix composite.The microstructure of the composite material prepared by the pressure infiltration process was uniform.organization.The effect of deformation treatment on the microstructure and performance of the GNPs/6061Al homogeneous matrix material was investigated.The deformation behavior of 0.6 wt.%GNPs/6061Al composites at different temperatures and strain rates was studied by thermal simulation compression experiments.Based on the experimental results,the flow stress equation was calculated,and the hot working diagram was constructed.The deformation behavior of graphene in the hot extrusion process of graphene/aluminum composites was studied,including interlayer slip,peeling and bending.When hot extruded at 450℃,graphene is well dispersed.At this time,the tensile strength of the composite is the highest and the mechanical propertie reaches 500 MPa.The optimal hot extrusion process window is 420～500℃/0.056～1s^-1.The strengthening mechanism of GNPs/6061Al composites is analyzed.The strengthening effect mainly comes from four aspects.Taking 450℃composite as an example,fine grain strengtheningΔσ_His about 13.3 MPa,thermal mismatch strengtheningΔσ_CETis about 20.9 MPa and orovan is strengthenedΔσ_Oro is about9.6 MPa and load transferΔσ_L.M.is strengthened about 39.1 MPa.It can be seen that load transfer is the main strengthening mechanism.The significance of heterogeneous matrix design is analyzed.After thermal deformation treatment,due to the extra stress field generated by the heterogeneous matrix,the agglomeration of graphene is eliminated to a greater extent,and more graphene with less layers is produced,which effectively improves the strength of the material:the yield strength of the extruded（GNPs/6061Al）/Pure Al composite is increased by 143.1%after annealing and this exceeds the homogeneous composite.Through analysis,it is found that（GNPs/6061Al）/Pure Al heterogeneous matrix composite has a more significant effect on the peeling of GNPs,which makes the load transfer strengthening effect in the composites more obvious.In addition,the effect of hot rolling on the microstructure and properties of the composites was discussed.Through rolling,graphene agglomerates and opens,producing more graphene with few layers,and gradually dispersing and distributing.The characterization method based on Raman spectroscopy and TEM observation was analyzed and determined.The results show that with the progress of thermal deformation treatment,the proportion of less layer graphene in（GNPs/6061Al）/2024Al non-uniform matrix composites is increased by 27%compared with that in as cast condition,and the tensile strength in annealed condition is up to 559 MPa;The yield strength of as-annealed（GNPs/6061Al）/2024Al and（GNPs/6061Al）/Pure Al heterogeneous matrix composite is 89.8%and 119.1%,respectively,which are higher than that of the GNPs/6061Al composites of 80.1%.The strength enhancement of the composites is affected by the evolution of graphene and the microstructure change of the matrix.In addition,in addition to the common bridging effect of graphene sheets in the fracture,the phenomenon of graphene peeling after tensile deformation was also observed in this study.The interface adhesion of GNPs-Al is higher than that between GNPs layers,resulting in graphene delamination.It should be noted that not all graphene is stripped,while this means that there is a certain critical size.The research of this paper enriches the basic theory of microstructure design of aluminum matrix composites,and provides experimental and theoretical basis for composition design,process optimization and performance regulation of graphene/heterogeneous aluminum matrix composites.