Preparation,Microstructure And Properties Of Graphene/Al Composites Based On In-situ Graphite Exfoliation

Graphene with excellent mechanical and thermoelectric properties is an ideal reinforcement for metal matrix composites.It has attracted extensive attention in the fields of lightweight precision structural parts with high strength and electronic packaging materials with high thermal conductivity and low expansion coefficient.Based on graphite flakes and pure aluminum as raw materials,graphene/Al composites were prepared by Rotational friction extrusion method,the effects of the technological process and the amount of flake graphite added on the preparation of composites were studied,the structure and properties of composites were also investigated,and the influence mechanism of flake graphite added on the properties of composites was explored.The following main conclusions were obtained:(1)Under the experimental conditions,the optimized process parameters of rotational friction extrusion were:the rotating speed of the mixing tool was 345rpm,the bilateral extrusion speed was 0.28mm/min,the extrusion ratio was 13.44,the pre-heating temperature was 150?.Good macroscopic forming can be obtained with the addition amount of graphite flakes below 2.4wt.%,the densification of the composites exceeds 98.28%,and the reinforcement can be uniformly dispersed.(2)Raman spectroscopy and TEM observations show that the graphite flakes were effectively stripped into graphene and the graphene/Al composites were fabricated successfully.EBSD results show that the grain size of the composite was significantly refined with the increase of the amount of graphite added,and the migration from Low angle grain boundaries to High ones was more obvious.When the graphite flakes were added to 1.86wt.%,the average grain size was only 1.35?m,which was 88%lower than that of the 0wt.%-composites.The interface observation of the composite shows that it presents the interface of diffusion and partial reaction mixing.(3)The mechanical properties test shows that the strength of the composite increases with the increase of the amount of flake graphite.When the amount of graphite is 1.86wt%,the tensile strength and yield strength of the composite are163.2mpa and 76.4mpa,respectively,which is about 71.4%and 91%higher than the matrix processed under the same conditions.The main strengthening mechanism is fine grain strengthening and load transfer,on the one hand,the increase of graphene makes the grains of the composite further refined.On the other hand,the load transmitting effects of the interface between graphene and matrix can be effectively improved by the bridging role of diffusion transition layer and Al₄C_3.(4)Conduction performance results show that in low for the amount of graphite flakes(less than or equal to 0.4wt.%),the electric and thermal conductivity of the composite performance is superior to the matrix processed under the same conditions.Due to the parallel arrangement of some graphene along the extrusion direction during large deformation extrusion,the conductivity of the composite is anisotropic,and the performance along the extrusion direction is better than that in the vertical direction.The thermal stability of the composites increased with the increase of the amount of graphite flakes.The thermal expansion coefficient of the composite with1.86wt%scale graphite is 2.292�10^-5k^-1(mean value of 40?-400?),which is 9%lower than that of the matrix processed under the same conditions.