Microstructure And Thermal Properties Of Microwave Modified Graphite Film/Aluminum Layered Composites

In this paper,the graphite film was pretreated by microwave modification,and the graphite film/aluminum composite was prepared by spark plasma sintering(SPS)and tape casting + pressure impregnation.The mechanism of microwave modification of graphite film was investigated by characterization of microstructure,structure and thermal conductivity of graphite film.The graphite film distribution,interfacial bonding,element distribution and precipitation phase of the composites were observed.The effects of SPS preparation,microwave modification and graphite film volume fraction on the microstructure and structure of graphite/aluminum composites were investigated.The relationship between microstructure and thermal properties of graphite film/aluminum composites was established,which provided theoretical and experimental basis for the design and preparation of high thermal conductivity graphite film/aluminum layer composites.This topic firstly determined the optimal microwave modification process of graphite film: first acetone treatment for 30 s,microwave treatment for 4s,graphite film XY thermal conductivity increased by 8.1%.After microwave modification,the graphitization degree of graphite film increased from 95.1% to 99.8%,the surface amorphous carbon distribution was more diffuse and fine,and the surface oxygen content of C-O-C functional group decreased from 13.7% to 9.6%.It is proved that microwave modification is a simple and effective pretreatment method to improve the thermal conductivity of graphite film.Secondly,the graphite film/aluminum composite was prepared by SPS method.It was found that the process parameters could be controlled in a small range and the composite layer structure was destroyed.When the graphite film volume fraction is 52%,the thermal conductivity of the composite XY is 624.6W/mK,and the actual thermal conductivity is much lower than the theoretical value.When the graphite film/aluminum composite is prepared by casting molding and pressure infiltration,the volume fraction of the graphite film can be adjusted,and the layered structure of the composite material is complete.When the graphite film volume fraction is 20%,the thermal conductivity of the composite XY can reach 521.9W/mK,and the actual thermal conductivity is close to the theoretical value.Finally,the graphite film was pretreated by microwave modification,and then the graphite film/aluminum composite was prepared by casting and pressure impregnation.The relationship between microstructure and thermal properties of composites was studied.It was analyzed that the thermal conductivity of composites did not reach the theoretical value mainly caused by two kinds of defects,which were the gaps between the internal gap and interface of graphite film.The gap content in the graphite film,22% < 28% < 34% volume fraction composite.The gap content at the interface joint is 28% <34% <22% volume fraction composite.The gap in the graphite film reduces the thermal conductivity of the composite XY,and the interfacial bond gap reduces the thermal conductivity of the composite Z and the interlaminar shear strength.As the volume fraction of graphite film increases,the thermal conductivity of composite XY increases from 494.5W/mK,520.7W/mK to 553.7W/mK,which increases the difference from the theoretical value but improves the high and low temperature impact resistance.The Z-direction thermal conductivity was 13.4W/mK,15.9W/mK,and 11.7W/mK,respectively,and the interlaminar shear strengths were 47.4 MPa,51.3 MPa,and 45.3 MPa,respectively.