| Electronic devices are developing rapidly towards high power,high frequency,miniaturization and integration.The power density of electronic devices are gradually increasing.The hot spot problem caused by thermal accumulation seriously affects the performance and application of electronic devices.The graphite material and the metal matrix are composited to realize the direct packaging of the high thermal conductivity substrate.The thermal management efficiency of electronic devices are improved by eliminating the macro interface thermal resistance.In this paper,a high thermal conductivity composite material is prepared by vacuum hot pressing sintering method,using 6061 aluminum alloy as the matrix material and annealed pyrolytic graphite(APG)as the thermal conductivity component.This new type of carbon material is used as a thermal conductive component for research,and the surface of directional annealed graphite is modified by Ti and Cr by vacuum evaporation coating,so as to control the interface of the composite material and improve the combination between graphite and aluminum alloy.In this case,the interface thermal resistance is reduced,the thermal properties of the directional annealed graphite material are fully utilized,and the mechanical properties of the directional annealed graphite/aluminum composite material are improved.At the same time,the thickness of the aluminum alloy on the surface of the directional annealed graphite was designed,and graphite/aluminum composite materials with different layer thickness ratios were obtained,forming a high thermal conductivity graphite/aluminum composite material system with different performance characteristics.Its main conclusions are as follows:A uniform and complete carbide coating layer is formed on the surface of the directional annealed graphite by the method of vacuum micro-evaporation coating.The corresponding carbides can be formed on the surface of directional annealed graphite after Ti and Cr treatment by vacuum evaporation.The TiC coating is formed on the surface of directional annealed graphite after Ti plating,and APG-TiC-Ti is formed between directional annealed graphite and Ti coating.The interface is combined,and the coating after Cr plating is composed of Cr3C2 and Cr7C3.The APG-Cr3C2/Cr7C3-Cr interface is formed between the directional annealed graphite and the Cr coating.The effect of modification treatment of Ti,Cr and other elements on the surface of directional annealed graphite on the interfacial bonding of composites was explored.The surface-modified directional annealed graphite/aluminum composite was prepared by vacuum hot pressing sintering.Under the conditions of sintering temperature of 590?,holding time of 30 min,and sintering pressure of 40 MPa,clean and complete composites can be prepared in the Graphite/aluminum interface.With the increase of the hot pressing temperature,the bonding state between the interfaces gradually improved,an amorphous transition zone was formed between the carbide-modified directional annealed graphite and the aluminum alloy during the composite process.Among them,the Ti modified layer obtained by vacuum evaporation coating is uniform,complete,dense and good bonding with directional annealed graphite.The prepared composite material has a good interface structure,and an Al-TiC-APG interface is formed with the aluminum alloy.The Cr modified layer obtained by vacuum evaporation coating has good bonding with the directional annealed graphite,but the density needs to be improved.The prepared composite material has the interface bonding of Al-Cr7C3-APG.The carbide modified layer can improve the interfacial bonding between Al-C and inhibit the generation of interfacial detrimental phase Al4C3,convert the weak interfacial bonding between graphite and aluminum alloy into strong metallurgical bonding.The thermal conductivity in the X-Y plane of the directionally annealed graphite/aluminum composites increases with the increase of the graphite/aluminum layer thickness ratio,but the change in the thermal conductivity in the Z direction is not very obvious.The thermal diffusivity of the directional annealed graphite/aluminum composites treated by Ti modification is significantly improved.When the thickness ratio of Al:APG:Al phases increases from 1:2:1 to 1:6:1.The in-plane thermal diffusivity of the Ti modification treatment annealed graphite-aluminum composite was increased from 570 mm2/s to 1056 mm2/s.The graphite surface coating can strengthen the graphite/aluminum composite material and improve the overall mechanical properties.The bending strength of the Ti-modified directional annealed graphite/aluminum composite material is significantly higher than that of the composite material without interfacial modification treatment.When the thickness ratio of Al:APG:Al each phase is 1:3:1,the flexural strength of the composite material reaches 141 MPa,which is 18%higher than that of the composite material without interfacial modification treatment.After the modification treatment,the failure mode of the composite material is mainly concentrated on the interface delamination between graphite and aluminum,and the graphite is extracted and fractured at the fracture.The interface modification layer can absorb the deformation energy.During the failure process,the directional annealed graphite is bent,which offsets part of the stress and improves the mechanical properties of the composite material. |
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