Investigation On The Microstructure And Mechanical Properties Of Graphene/Al Composites Processed By Equal Channel Angular Pressing

In this paper,pure Al,1vol.%,3vol.% and 5vol.% graphene/Al composites are prepared by high energy ball milling and hot extrusion.The prepared materials are subjected to equal channel angular pressing.The dispersion of graphene in matrix aluminum is improved by stripping the graphene sheet layer during equal channel angular pressing,and the interface of 1vol.% graphene/Al composite is reinforced.Through the exploration of the ball milling process,the optimum milling parameters of aluminum powder and composite powder are obtained,which are 250rpm×300min and 250rpm×180min,respectively.Under the optimum milling parameters of aluminum powder,the ideal thickness aluminum sheet(~200nm)is prepared.In the optimum milling parameters of the composite powder,the graphene is uniformly dispersed on the surface of the aluminum sheet and the compact tightly.After the isostatic pressing and hot extrusion,the density of the materials is greatly improved.As the graphene volume fraction increases,the density of material decreases gradually with the highest value of 99.2% and lowest value of 98.1%.From the OM images and SEM images of graphene/Al composites,the graphene agglomeration is gradually serious with the increase of the graphene volume fraction.The tensile strength,yield strength and elastic modulus of graphene/Al composites increase first and then decrease when the volume fraction of graphene increases.When the volume fraction of graphene is 3 vol.%,the tensile strength,yield strength and elastic modulus are up to 175.9MPa,95.4MPa and 75.3GPa increasing by 48.4%,78.8% and 11.9% compared to the as-extruded pure aluminum,the elongation gradually decrease with the highest value of 15.5% and the lowest value of 5.2%.By investigating the polished surface microstructure and mechanical properties of 3vol.% graphene/Al composite with equal channel angular pressing 8pass at different temperatures,it is found that graphene in the graphene/Al composite is the most uniform and the mechanical properties is best at 300?.Thereby,determining the optimum equal channel angular pressing temperature is 300?.From the OM images and SEM images of graphene/Al composites,graphene in 1vol.% and 3vol.% graphene /Al composites disperses gradually improve and the mechanical properties of graphene /Al composites increase greatly with the increase of equal channel angular pressing pass.The tensile strength,yield strength,elongation and elastic modulus of 3vol.% graphene/Al composites after equal channel angular pressing 8pass increase by 23.9%,10%,60.6% and 5.3%.compared to as-extruded 3vol.% graphene/Al composite.From the TEM images,the graphene/Al interface is mechanically bonded,with poor adhesion.By exploring the best temperature of heat treatment,3vol.% graphene/Al composites of equal channel angular pressing 8pass are subjected to heat treatment at different temperature and XRD analysis is carried out to determine the best temperature of heat treatment is 650?.And 1vol.% graphene/Al composite is subjected to heat treatment followed by equal channel angular pressing,then it can be seen the graphene is uniform in the graphene/Al composite and interface of graphene/Al is reinforced.The tensile strength,yield strength,elongation and elastic modulus of the composites are 191.6MPa,95.7MPa,18.3% and 76.5GPa,respectively with the increase of 7.8%?13.7%?23.6% and 2.3%,respectively compared with the 1vol.%graphene/Al composite of equal channel angular pressing 8pass without heat treatment.After the heat treatment followed by equal channel angular pressing,it can be seen that graphene is aligned along equal channel angular pressing direction which may make full use of excellent mechanical properties of graphene radial direction,dispersion of graphene in the matrix is improved and the interface of graphene/Al is reinforced.So,graphene on the composite material has played a strengthening role.