Preparation And Mechanical Properties Of Graphene Reinforced Aluminum Matrix Composite By Stirring Casting

A356.2 aluminum alloy is widely used in the production of automobile wheel hub and suspension bracket due to its high specific strength,good corrosion resistance and excellent casting performance.With the increasing requirements of vehicle lightweight and comprehensive mechanical properties of materials,the mechanical properties of A356.2 alloy are difficult to meet the requirements of high standard components because of the coarse eutectic silicon phase.The composite path of the materials fundamentally solves the problems of easy fading and low absorption rate existing in the traditional modification methods of the alloy.Graphene?Gr?is regarded as an ideal reinforcement for composite materials due to its ultra-high strength,ultra-high modulus,excellent electrical and thermal conductivity.In this paper,aiming at the problem of coarse eutectic silicon in A356.2 alloy,the morphology and distribution of silicon phase in the alloy are improved and the comprehensive mechanical properties of the alloy are improved by adding graphene.Graphene/A356.2 composites?graphene:0.1wt.%,0.3wt.%,0.5wt.%,0.7wt.%and1.0wt.%?were prepared by stirring casting method.The influence of graphene addition on the morphology,size and distribution of the silicon phase in the graphene/A356.2 composite matrix was studied by SEM and EDS analysis,and the influence of graphene addition on the morphology and distribution of the silicon phase was obtained.The effects of graphene reinforcement and heat treatment on the phase structure,hardness,static tensile properties,impact properties and corrosion properties of graphene/A356.2 composites were analyzed by X-ray diffraction.The fracture mechanism of graphene/A356.2 composite was studied by SEM.Fe element is easy to form harmful phase with matrix alloy,that is easy to split the matrix and leads to the decrease of mechanical properties.Through the control of raw materials,the selection of casting fixture and the improvement of melt purification process,the introduction of Fe element was reduced and excessive?-Al₅FeSi phase which is harmful to tissues and is readily produced during the preparation of graphene/A356.2 composites was avoided.The graphene with the diameter of 15?m has the best refining effect on the silicon phase compared with the graphene with the diameter of 5?m,15?m and 25?m.As-cast A356.2 alloy for typical?-Al organization and the eutectic silicon phase.The morphology of eutectic silicon is mostly flat and irregular,and the size of the silicon phase is large and the distribution is not uniform.The silicon phase basically presents a short rod-like morphology and is dispersed in the matrix when the addition amount of graphene is 0.5wt.%.The co-crystalline silicon of T6 state A356.2aluminum alloy presents the morphology characteristics of bar and long strip.The co-crystalline silicon has the best morphology and distribution,and the silicon phase is basically spheroidized and dispersed in the matrix of in 0.5wt.%graphene/A356.2composites.The size of the silicon phase in the A356.2 aluminum alloy was about8.07?m,and the size of the silicon phase in the graphene/A356.2 composite material?graphene:0.3wt.%,0.5wt.%and 1.0wt.%?was reduced to 4.93?m,3.59?m and5.22?m,respectively.The hardness values of A356.2 alloy and 0.5wt.%graphene/A356.2 composite at peak aging were 110.4HB and 126.0HB,respectively,when aging at 180?.The hardness value of graphene/A356.2 composite increased by 14.1%,and the time to peak aging was shortened by 1 hour compared with A356.2 aluminum alloy.This is because the addition of graphene increases a large number of phase interface defects,which provide a"fast track"for the diffusion of atoms,thus speeding up the aging hardening process and providing theoretical and practical basis for energy conservation in the subsequent actual production process.The tensile strength and yield strength of the 0.5wt.%graphene/A356.2composite were 383.3MPa and 313.4MPa,respectively,which were 47.4%and 63.9%higher than those of the A356.2 aluminum alloy.The impact toughness and absorption work of 0.5wt.%graphene/A356.2 composites were 2.9J and 3.6J/cm²,respectively,which were 61.1%and 56.5%higher than those of A356.2 aluminum alloy.The typical eutectic region and the spherical Mg2Si phase are shown in the TEM image.The combination of graphene and matrix is well,and there are no holes or defects,and no formation of Al₄C₃ interfacial reactant.Graphene becomes an ideal non-spontaneous nucleation core in aluminum melt and a particle of silicon nucleation,resulting in significant refinement of the silicon phase and improving the mechanical properties of graphene/A356.2 composites due to its unique two-dimensional structure and extremely large specific surface area.The pitting potential increases from-0.907V to-0.734,and the passivation range increases from 0.446V to 0.618V with the amount of graphene is 0.5wt%.The pitting resistance of graphene/A356.2 composite is improved,and it has the best pitting resistance in under aging and the worst pitting resistance in over aging...