| With the increasingly serious problem of global environmental pollution,reducing the use of fossil energy and reducing greenhouse gas emissions has become an urgent problem.Modern industry puts forward more stringent requirements for the power density,functionality and service conditions of products,among which aluminum matrix composite materials have been widely used in aerospace,automobile manufacturing and other fields due to the advantages of low density,high specific strength,high specific stiffness and good wear resistance.Graphene is a two-dimensional carbon nano material,which is formed by the hybridization of carbon atoms with SP2 orbital.Its physical and chemical properties are excellent,and it is found that graphene is an ideal reinforcement phase.However,the research on graphene reinforced aluminum matrix composite is still in the basic stage.In this paper,flaky powder thixoforming(FPT)combined with the advantages of flaky powder metallurgy and semi-solid thixoforming was proposed,and the hierachical structure reduced graphene oxide(RGO)/2024Al matrix composite is prepared.The effects of ultrasonic power,ultrasonic time,the ratio of anhydrous ethanol and deionized water in GO dispersion and the surface modification of GO on the dispersion of GO were studied.The effects of ultrasonic and agitation,ball milling dispersion and surface acidification of flake aluminum powder assisted by ultrasonic and agitation on the dispersion degree and structure damage of RGO/Al composite powder were analyzed.In addition,the microstructure evolution mechanism of RGO/Al powder briquette during partial remelting was also studied.The thixotropic microstructure,RGO distribution,RGO content,interface structure,mechanical properties,tensile fracture behavior and strengthening mechanism of the hierachical structure RGO/Al composite were analyzed.The main conclusions are as follows:It was found that the concentration of GO was 1 mg/ml according to the volume ratio of anhydrous ethanol and deionized water,and the uniformly dispersed GO solution could be obtained by dispersing it for 60 min under the ultrasonic power of 180 W.With the aid of ultrasonic and stirring,the surface of flake aluminum powder can be acidified to achieve the uniform dispersion of RGO/Al composite powder and retain the structural integrity of RGO to the greatest extent.FPT technology can disperse RGO uniformly in the local area of secondary solidified structures(SSSs)by introducing acidified flake powder as effective carrier,and the dispersion effect of FPT is better than that of ball milling.The UTS,YS and elongation of FPT-0.4wt.%RGO/Al composite are 35.1%,34.9%and 54.5%higher than that of HEM-0.4wt.%RGO/Al composite,respectively.A small amount of Al2O3 and Al4C3 were detected at the interface of RGO/Al composite.At the same time,two mixed interface structures,Al/Al2O3/C and Al/Al4C3/C,were formed in FPT-0.4wt.%RGO/Al composite,which are helpful to improve the mechanical properties of RGO/Al composite.In addition,the influence of different content of RGO on the RGO/Al composite was studied.When the content of RGO is less than 0.4 wt.%,the mechanical properties of the composite will continue to improve with the increase of the content of RGO.The strength of FPT-0.4wt.%RGO/Al(?)composite is the highest,its U TS,YS and elongation are 443 MPa,276 MPa and 8.9%,respectively.It is proved that it is more advantageous for the optimization of composite properties to control the spatial distribution of RGO only by constructing hierarchical structure under the condition of keeping the content of RGO unchanged.However,when the content of RGO is more than 0.4 wt.%,the agglomeration degree of RGO increases,and the properties of the composite will deteriorate.In addition,FPT technology can disperse high content of RGO in aluminum matrix to prepare RGO/Al composite,which is of great significance for the preparation of high-performance RGO/Al composite. |
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