Research On The Preparation And Properties Of Stir-casting GNPs/2024Al Composites

With its excellent mechanical and physical properties,graphene?GNPs?has attracted more and more attentions as the reinforcement for metal-matrix composites?MMCs?.The problems of uniform dispersion of graphene in metals,interface reaction control and mechanical property optimization still exist in graphene reinforced aluminum-matrix composites.In this article,by taking advantages ball milling graphene and aluminium powders,stirring casting method was applied to prepare Graphene nanosheets/2024Al composites.Hot extrusion and cold drawing was also applied to improve the distribution of graphene in the aluminum matrix.The microstructure of the composites was analyzed bia optical microscope?OM?,scanning electron microscopy?SEM?and transmission electron microscopy?TEM?and Raman spectrum.The mechanical properties and thermal physical properties of the composite were investigated.The morphology of ball-milled powder was observed.It was found that graphene was dispersed into aluminum alloy powders by cold welding of aluminum powder under the conditions of ball-to-material ratio of 10:1,rotation speed of 200rpm and ball-milling time of 10h.The effect of casting temperature on the microstructure of composites was studied under the condition that the semi-solid stirring temperature and stirring time remained unchanged.The optimal casting temperature was determined to be 660?.At this temperature,a large amount of graphene still existed and no obvious interface reaction between graphene and Al occurred.By hot extrusion,GNPs/2024Al composite bar with good surface quality was obtained under the conditions of hot extrusion temperature of 495?with dewelling time of 3h before extrusion and the extrusion speed of 15 mm/s.The grain size of the hot extruded composites was about 14 extruded alloy?m.In addition,the grain size parallel to the extruded direction was elongated,and the density of the composites was increased.GNPs/2024Al composite has obvious aging and hardening effect.The peak aging process is:solid solution at 500?for 96h,aging at 190?for 8h.S'?A1₂CuM g?precipitated phase is dispersed in the matrix alloy after the peak aging.The ultimate tensile strength?UTS?,elastic modulus and elongation of the composites were 465 MPa,81 GPa and 9.78%,respectively.However,when the content of graphene exceeded 2wt.%,the mechanical properties of the composites decreased significantly.As the content of graphene increased,the thermal conductivity of as-cast composites showed a decreasing trend.After hot extrusion,when the mass fraction of graphene was?1wt.%,the thermal conductivity of the composites was about 160W/?m·K?.When the mass fraction reaches 2wt.%,the thermal conductivity decreases sharply.The thermal expansion coefficient of the composites decreases monotonously with the increase of graphene mass fraction.After hot extrusion,the thermal expansion coefficient of the composites with graphene mass fraction of 0.4wt.%,1wt.%and 2wt.%decreases compared with that of the as-cast composites.Cold drawing promoted the homogeneous dispersion of graphene in aluminum alloy matrix.With the increase of cold drawing deformation ratio,the UTS of0.4wt.%GNPs/2024Al composite decreases continuously,but the elongation increases.When the cold drawing ratio reaches 81%,the elongation of the composite is nearly 33%lower than that of the extruded composite.However,compared with the drawn matrix alloy,the elongation of the composite increased by 73%.