| There are no any reports about the liquid method to fabricate graphene reinforced aluminum composites, so we choose graphene of huge specific surface area and pure aluminum powder to fabricate graphene reinforced aluminum composites through ball-milling and liquid pressure infiltration approach. And then we select the appropriate extrusion process to carry out the subsequent extrusion for the composites, so that the orientation of the graphene can be alignment and graphene layers can be reduced. We studied the mechanical and physical properties of the material. Composites are tested after 320 ℃annealing for 2 hours.Through the exploration of the ball-milling process, we get appropriat e ball-milling process of aluminum and composite powders, which is at the ball-to-powder weight ratio of 5: 1, 300 rpm + 1.5h and the ball-to-powder weight ratio of 5: 1, 300 rpm + 3h, respectively. Under the ball-milling process, graphene can disperse on the surface of aluminum particles uniformly without being destroyed.In the extrusion process,we found that the surface quality of the composites was very sensitive to the temperature. In the case of the extrusion ratio of 13:1, the optimum extrusion temperature of the composites was 480 ℃. After the extrusion process, the large grain disappeared, the average grain size reduced to about 10~20 μm. The grains parallel to the extrusion direction were elongated, the density of materials increased 0.98%~1.93%.We carry out mechanical tests on the as-cast composites after annealing, the experiments showed that the addition of graphene can significantly improve the mechanical properties of the material compare to the aluminum matrix. When the mass fraction of graphene is less than 0.21%, the Young’s modulus, tensile strength monotonically increases with the increase of graphene contents, reaching the 75.8GPa and 181.67 MPa, which were 7.21% and 58.28% higher than the matrix respectively. Bending Strength reached the maximum value of 335.96 MPa, which is 68.01% higher than the matrix, when the contents of graphene is 0.54 wt.%. ductility of the composites increased with the contents of graphene decreased, but all were higher than the matrix and the maximum elongation reached 9.08%. It was believed that a small amount addition of graphene can be flattening to relieve stress concentration. When the contents of exceeded 0.21 wt.%, graphene will be agglomerated, which is bad to the strength and ductility of the composites. After hot extrusion process, the strength and ductility of have been greatly improved. When the contents of the graphene is 0.54 wt.%, the maximum value of tensile strength of the composite occurred, reaching to 227.19 MPa, improving 33.75% compared to the composites without extrusion.Conducting performance tests showed that the addition of graphene in right dosage can greatly improve the conductivity. The conductive properties of the composite are higher than the matrix. The electrical conductivity reached 41.05% IACS when the contents of graphene is 0.21 wt.%, representing a 58.57% increase compared to the matrix. After the extrusion process, the conductivity of the composite material is significantly improved, and 0.54 wt.% graphene/aluminum composites’ conductivity increased from 34.01%IACS to 52.25%IACS, improv ing 53.63%.The reasons of the extrusion process improving the mechanical and electrical conductivity of the materials are explained in the following. The first, after the extrusion, the density of the material improved, the porosity reduced. The second, graphene lawyers reduced after the extrusion process. The third, the orientations of graphene became alignment after the extrusion process.In summary, under the experimental conditions, the best contents of the graphene is between 0.21% to 0.54%, in which we could obtain high mechanical properties and electrical conductivity. After thermal extrusion process, the properties described above can be further increased by 30% to 50%. |
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