Microstructures And Properties Of The Graphite Nano-flakes/6061Al Composites Prepared By Spark Plasma Sintering (SPS)

GF/Al composites have more important potentials as electronic packaging materials,compared with the natural graphite flake/Al composites and the graphene/Al composites,due to their excellent properties such as high thermal conductivity(TC)and low thermal expansion coefficient(CTE),density and cost.Studies on the SPSed GF/6061Al composites are more valuable for providing a technical support in developing new-style and high-property graphite flake/Al composites.In this study,two kinds of the GF with different size were chosen as raw materials.They were blended with the 6061Al alloy powder through ball milling and mechanical agitating,respectively.And then,the powder mixtures were consolidated via the SPS technology.Effects of the mixing style and the GF size on the microstructures and properties of the graphite flake/Al composites were investigated to obtain an optimal composite structure.In terms of the orthogonal experiment,effects of the sintering pressure and the GF content on the microstructures and properties of the composites were also studied to optimize the technical parameters.Finally,a kind of the graphite flake/6061Al composites with excellent comprehensive properties was fabricated.The GF_A/6061Al _Fcomposites were prepared by SPS the mechanically-milled GF_Aand 6061Al alloy powder mixtures at 610°C and 35MPa.The distribution of GF_Ain the GF_A/6061Al _Fcomposites in the X-Y orientation and the property anisotropy of the composites are the largest.The GF_B/6061Al _Scomposites were prepared by SPS the mechanically-agitated GF_Band 6061Al alloy powder mixtures at 610°C and 35MPa.The distribution of GF_Bin the GF_B/6061Al _Scomposites in the X-Y orientation and the property anisotropy of the composites are the lowest.However,the agglomeration of the graphite flakes is the most serious,so,the density of the composites and the GF/Al alloy interface bonding strength are also the lowest.It results in that the strength and thermal conductivity of the GF_B/6061Al _Scomposites are the lowest and the coefficient of thermal expansion is the highest.In contrast,the GF_A/6061Al _Scomposites were prepared by SPS the mechanically-agitated GF_Aand 6061Al alloy powder mixtures under the same SPS process condition.The distribution anisotropy of the GF_Ain the composites is moderate.The thermal conductivity mismatch in the X-Y plane and Z axis directions is small,the coefficient of thermal expansion in the X-Y direction is the lowest,and the flexural strength is higher than 100 MPa,so,the GF_A/6061Al _Scomposites have the highest comprehensive properties.The SPS process of the GF_A/6061Al _Scomposites was further optimized via the orthogonal experiment.The flexural strength,density,thermal conductivity and coefficient of thermal expansion were taken as the evaluation index,respectively,to optimized the SPS process parameters,accordingly.With the increase of the sintering pressure,the orientation degree of the GF increases,the agglomeration of the GF decreases.As a result,the density,the flexural strength and the thermal conductivity of the composites increase,the coefficient of thermal expansion of the composites decreases.The GF content has a significant effect on the thermal conductivity and coefficient of thermal expansion of the composites,as well as on has an apparent effect on the density and flexural strength of the composites.With the increase of the GF content in the composites,the density,flexural strength and coefficient of thermal expansion of the GF_A/6061Al _Scomposites decrease,but the thermal conductivity of the composites increases.